YANG Data Types and Groupings for Cryptography
RFC 9640
Kent Watsen
Watsen Networks
kent+ietf@watsen.net
October 2024
OPS
netconf
This document presents a YANG 1.1 (RFC 7950) module defining identities, typedefs, and groupings useful to cryptographic applications.
Introduction
This document presents a YANG 1.1 [RFC7950] module defining identities, typedefs, and groupings useful to cryptographic applications.
Relation to Other RFCs
This document presents a YANG module [RFC7950] that is part of a collection of RFCs that work together to, ultimately, support the configuration of both the clients and servers of both the Network Configuration Protocol (NETCONF) [RFC6241] and RESTCONF [RFC8040].
The dependency relationship between the primary YANG groupings defined in the various RFCs is presented in the below diagram. In some cases, a document may define secondary groupings that introduce dependencies not illustrated in the diagram. The labels in the diagram are shorthand names for the defining RFCs. The citation references for the shorthand names are provided below the diagram.
Please note that the arrows in the diagram point from referencer to referenced. For example, the "crypto-types" RFC does not have any dependencies, whilst the "keystore" RFC depends on the "crypto-types" RFC.

                               crypto-types
                                 ^      ^
                                /        \
                               /          \
                      truststore         keystore
                       ^     ^             ^  ^
                       |     +---------+   |  |
                       |               |   |  |
                       |      +------------+  |
tcp-client-server      |     /         |      |
   ^    ^        ssh-client-server     |      |
   |    |           ^            tls-client-server
   |    |           |              ^     ^        http-client-server
   |    |           |              |     |                 ^
   |    |           |        +-----+     +---------+       |
   |    |           |        |                     |       |
   |    +-----------|--------|--------------+      |       |
   |                |        |              |      |       |
   +-----------+    |        |              |      |       |
               |    |        |              |      |       |
               |    |        |              |      |       |
            netconf-client-server       restconf-client-server

Labels in Diagram to RFC Mapping
Label in Diagram | Reference
crypto-types | RFC 9640
truststore | [RFC9641]
keystore | [RFC9642]
tcp-client-server | [RFC9643]
ssh-client-server | [RFC9644]
tls-client-server | [RFC9645]
http-client-server | [I-D.ietf-netconf-http-client-server]
netconf-client-server | [I-D.ietf-netconf-netconf-client-server]
restconf-client-server | [I-D.ietf-netconf-restconf-client-server]
Specification Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
Adherence to the NMDA
This document is compliant with the Network Management Datastore Architecture (NMDA) [RFC8342]. It does not define any protocol-accessible nodes that are "config false".
Conventions
Various examples in this document use "BASE64VALUE=" as a placeholder value for binary data that has been base64 encoded (per Section 9.8 of [RFC7950]). This placeholder value is used because real base64-encoded structures are often many lines long and hence distracting to the example being presented.
Various examples in this document use the XML [W3C.REC-xml-20081126] encoding. Other encodings, such as JSON [RFC8259], could alternatively be used.
Various examples in this document contain long lines that may be folded, as described in [RFC8792].
The "ietf-crypto-types" Module
This section defines a YANG 1.1 [RFC7950] module called "ietf-crypto-types". A high-level overview of the module is provided in Section 2.1. Examples illustrating the module's use are provided in Section 2.2. The YANG module itself is defined in Section 2.3.
Data Model Overview
This section provides an overview of the "ietf-crypto-types" module in terms of its features, identities, typedefs, and groupings.
Features
The following diagram lists all the "feature" statements defined in the "ietf-crypto-types" module:

Features:
  +-- one-symmetric-key-format
  +-- one-asymmetric-key-format
  +-- symmetrically-encrypted-value-format
  +-- asymmetrically-encrypted-value-format
  +-- cms-enveloped-data-format
  +-- cms-encrypted-data-format
  +-- p10-csr-format
  +-- csr-generation
  +-- certificate-expiration-notification
  +-- cleartext-passwords
  +-- encrypted-passwords
  +-- cleartext-symmetric-keys
  +-- hidden-symmetric-keys
  +-- encrypted-symmetric-keys
  +-- cleartext-private-keys
  +-- hidden-private-keys
  +-- encrypted-private-keys

The diagram above uses syntax that is similar to but not the same as that in [RFC8340].
Identities
The following diagram illustrates the hierarchical relationship amongst the "identity" statements defined in the "ietf-crypto-types" module:

Identities:
  +-- public-key-format
  |  +-- subject-public-key-info-format
  |  +-- ssh-public-key-format
  +-- private-key-format
  |  +-- rsa-private-key-format
  |  +-- ec-private-key-format
  |  +-- one-asymmetric-key-format
  |            {one-asymmetric-key-format}?
  +-- symmetric-key-format
  |  +-- octet-string-key-format
  |  +-- one-symmetric-key-format
  |            {one-symmetric-key-format}?
  +-- encrypted-value-format
  |  +-- symmetrically-encrypted-value-format
  |  |  |      {symmetrically-encrypted-value-format}?
  |  |  +-- cms-encrypted-data-format
  |  |         {cms-encrypted-data-format}?
  |  +-- asymmetrically-encrypted-value-format
  |     |      {asymmetrically-encrypted-value-format}?
  |     +-- cms-enveloped-data-format
  |            {cms-enveloped-data-format}?
  +-- csr-format
        +-- p10-csr-format {p10-csr-format?}

The diagram above uses syntax that is similar to but not the same as that in [RFC8340].
Comments:
- The diagram shows that there are five base identities. The first three identities are used to indicate the format for the key data, while the fourth identity is used to indicate the format for encrypted values. The fifth identity is used to indicate the format for a certificate signing request (CSR). The base identities are "abstract", in the object oriented programming sense, in that they only define a "class" of formats, rather than a specific format.
- The various terminal identities define specific encoding formats. The derived identities defined in this document are sufficient for the effort described in Section 1.1, but by nature of them being identities, additional derived identities MAY be defined by future efforts.
- Identities used to specify uncommon formats are enabled by "feature" statements, allowing applications to support them when needed.
Typedefs
The following diagram illustrates the relationship amongst the "typedef" statements defined in the "ietf-crypto-types" module:

Typedefs:
  binary
    +-- csr-info
    +-- csr
    +-- x509
    |  +-- trust-anchor-cert-x509
    |  +-- end-entity-cert-x509
    +-- crl
    +-- ocsp-request
    +-- ocsp-response
    +-- cms
       +-- data-content-cms
       +-- signed-data-cms
       |  +-- trust-anchor-cert-cms
       |  +-- end-entity-cert-cms
       +-- enveloped-data-cms
       +-- digested-data-cms
       +-- encrypted-data-cms
       +-- authenticated-data-cms

The diagram above uses syntax that is similar to but not the same as that in [RFC8340].
Comments:
- All the typedefs defined in the "ietf-crypto-types" module extend the "binary" type defined in [RFC7950].
- Additionally, all the typedefs define a type for encoding an ASN.1 [ITU.X680.2021] structure using DER [ITU.X690.2021].
- The "trust-anchor-*" and "end-entity-*" typedefs are syntactically identical to their base typedefs and only distinguish themselves by the expected nature of their content. These typedefs are defined to facilitate common modeling needs.
Groupings
The "ietf-crypto-types" module defines the following "grouping" statements:
- encrypted-value-grouping
- password-grouping
- symmetric-key-grouping
- public-key-grouping
- private-key-grouping
- asymmetric-key-pair-grouping
- certificate-expiration-grouping
- trust-anchor-cert-grouping
- end-entity-cert-grouping
- generate-csr-grouping
- asymmetric-key-pair-with-cert-grouping
- asymmetric-key-pair-with-certs-grouping
Each of these groupings are presented in the following subsections.
The "encrypted-value-grouping" Grouping
The following tree diagram [RFC8340] illustrates the "encrypted-value-grouping" grouping:

  grouping encrypted-value-grouping:
    +-- encrypted-by
    +-- encrypted-value-format    identityref
    +-- encrypted-value           binary

Comments:
- The "encrypted-by" node is an empty container (difficult to see in the diagram) that a consuming module MUST augment key references into. The "ietf-crypto-types" module is unable to populate this container as the module only defines groupings. Section 2.2.1 presents an example illustrating a consuming module populating the "encrypted-by" container.
- The "encrypted-value" node is the value encrypted by the key referenced by the "encrypted-by" node and encoded in the format appropriate for the kind of key it was encrypted by.
  - If the value is encrypted by a symmetric key, then the encrypted value is encoded using the format associated with the "symmetrically-encrypted-value-format" identity.
  - If the value is encrypted by an asymmetric key, then the encrypted value is encoded using the format associated with the "asymmetrically-encrypted-value-format" identity.
See Section 2.1.2 for information about the "format" identities.
The "password-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "password-grouping" grouping. This tree diagram does not expand the internally used "grouping" statement(s):

  grouping password-grouping:
    +-- (password-type)
       +--:(cleartext-password) {cleartext-passwords}?
       |  +-- cleartext-password?   string
       +--:(encrypted-password) {encrypted-passwords}?
          +-- encrypted-password
             +---u encrypted-value-grouping

Comments:
- The "password-grouping" enables the configuration of credentials needed to authenticate to a remote system. The "ianach:crypt-hash" typedef from [RFC7317] should be used instead when needing to configure a password to authenticate a local account.
- For the referenced "grouping" statement(s):
  - The "encrypted-value-grouping" grouping is discussed in Section 2.1.4.1.
- The "choice" statement enables the password data to be cleartext or encrypted, as follows:
  - The "cleartext-password" node can encode any cleartext value.
  - The "encrypted-password" node is an instance of the "encrypted-value-grouping" discussed in Section 2.1.4.1.
The "symmetric-key-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "symmetric-key-grouping" grouping. This tree diagram does not expand the internally used "grouping" statement(s):

  grouping symmetric-key-grouping:
    +-- key-format?                      identityref
    +-- (key-type)
       +--:(cleartext-symmetric-key)
       |  +-- cleartext-symmetric-key?   binary
       |          {cleartext-symmetric-keys}?
       +--:(hidden-symmetric-key) {hidden-symmetric-keys}?
       |  +-- hidden-symmetric-key?      empty
       +--:(encrypted-symmetric-key) {encrypted-symmetric-keys}?
          +-- encrypted-symmetric-key
             +---u encrypted-value-grouping

Comments:
- For the referenced "grouping" statement(s):
  - The "encrypted-value-grouping" grouping is discussed in Section 2.1.4.1.
- The "key-format" node is an identity-reference to the "symmetric-key-format" abstract base identity discussed in Section 2.1.2, enabling the symmetric key to be encoded using any of the formats defined by the derived identities.
- The "choice" statement enables the private key data to be cleartext, encrypted, or hidden, as follows:
  - The "cleartext-symmetric-key" node can encode any cleartext key value.
  - The "hidden-symmetric-key" node is of type "empty" as the real value cannot be presented via the management interface.
  - The "encrypted-symmetric-key" node's structure is discussed in Section 2.1.4.1.
The "public-key-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "public-key-grouping" grouping. This tree diagram does not expand any internally used "grouping" statement(s):

  grouping public-key-grouping:
    +-- public-key-format    identityref
    +-- public-key           binary

Comments:
- The "public-key-format" node is an identity-reference to the "public-key-format" abstract base identity discussed in Section 2.1.2, enabling the public key to be encoded using any of the formats defined by the derived identities.
- The "public-key" node is the public key data in the selected format. No "choice" statement is used to hide or encrypt the public key data because it is unnecessary to do so for public keys.
The "private-key-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "private-key-grouping" grouping. This tree diagram does not expand the internally used "grouping" statement(s):

  grouping private-key-grouping:
    +-- private-key-format?            identityref
    +-- (private-key-type)
       +--:(cleartext-private-key) {cleartext-private-keys}?
       |  +-- cleartext-private-key?   binary
       +--:(hidden-private-key) {hidden-private-keys}?
       |  +-- hidden-private-key?      empty
       +--:(encrypted-private-key) {encrypted-private-keys}?
          +-- encrypted-private-key
             +---u encrypted-value-grouping

Comments:
- For the referenced "grouping" statement(s):
  - The "encrypted-value-grouping" grouping is discussed in Section 2.1.4.1.
- The "private-key-format" node is an identity-reference to the "private-key-format" abstract base identity discussed in Section 2.1.2, enabling the private key to be encoded using any of the formats defined by the derived identities.
- The "choice" statement enables the private key data to be cleartext, encrypted, or hidden, as follows:
  - The "cleartext-private-key" node can encode any cleartext key value.
  - The "hidden-private-key" node is of type "empty" as the real value cannot be presented via the management interface.
  - The "encrypted-private-key" node's structure is discussed in Section 2.1.4.1.
The "asymmetric-key-pair-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "asymmetric-key-pair-grouping" grouping. This tree diagram does not expand the internally used "grouping" statement(s):

  grouping asymmetric-key-pair-grouping:
    +---u public-key-grouping
    +---u private-key-grouping

Comments:
- For the referenced "grouping" statement(s):
  - The "public-key-grouping" grouping is discussed in Section 2.1.4.4.
  - The "private-key-grouping" grouping is discussed in Section 2.1.4.5.
The "certificate-expiration-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "certificate-expiration-grouping" grouping:

  grouping certificate-expiration-grouping:
    +---n certificate-expiration
            {certificate-expiration-notification}?
       +-- expiration-date    yang:date-and-time

Comments:
- This grouping's only purpose is to define the "certificate-expiration" notification statement, used by the groupings defined in Sections 2.1.4.8 and 2.1.4.9.
- The "certificate-expiration" notification enables servers to notify clients when certificates are nearing expiration.
- The "expiration-date" node indicates when the designated certificate will (or did) expire.
- Identification of the certificate that is expiring is built into the notification itself. For an example, please see Section 2.2.3.
The "trust-anchor-cert-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "trust-anchor-cert-grouping" grouping. This tree diagram does not expand the internally used "grouping" statement(s):

  grouping trust-anchor-cert-grouping:
    +-- cert-data?                         trust-anchor-cert-cms
    +---u certificate-expiration-grouping

Comments:
- For the referenced "grouping" statement(s):
  - The "certificate-expiration-grouping" grouping is discussed in Section 2.1.4.7.
- The "cert-data" node contains a chain of one or more certificates containing at most one self-signed certificate (the "root" certificate), encoded using a "signed-data-cms" typedef discussed in Section 2.1.3.
The "end-entity-cert-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "end-entity-cert-grouping" grouping. This tree diagram does not expand the internally used "grouping" statement(s):

  grouping end-entity-cert-grouping:
    +-- cert-data?                         end-entity-cert-cms
    +---u certificate-expiration-grouping

Comments:
- For the referenced "grouping" statement(s):
  - The "certificate-expiration-grouping" grouping is discussed in Section 2.1.4.7.
- The "cert-data" node contains a chain of one or more certificates containing at most one certificate that is not self-signed and does not have Basic constraint "CA true" (where "CA" means Certification Authority), encoded using a "signed-data-cms" typedef discussed in Section 2.1.3.
The "generate-csr-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "generate-csr-grouping" grouping:

  grouping generate-csr-grouping:
    +---x generate-csr {csr-generation}?
       +---w input
       |  +---w csr-format    identityref
       |  +---w csr-info      csr-info
       +--ro output
          +--ro (csr-type)
             +--:(p10-csr)
                +--ro p10-csr?   p10-csr

Comments:
- This grouping's only purpose is to define the "generate-csr" action statement, used by the groupings defined in Sections 2.1.4.11 and 2.1.4.12.
- This action takes two input parameters: a "csr-info" parameter, for what content should be in the certificate, and a "csr-format" parameter, for what CSR format to return. The action returns the CSR in the specified format. Both the "csr-info" and "csr" types are discussed in Section 2.1.3.
- For an example, please see Section 2.2.2.
The "asymmetric-key-pair-with-cert-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "asymmetric-key-pair-with-cert-grouping" grouping. This tree diagram does not expand the internally used "grouping" statement(s):

  grouping asymmetric-key-pair-with-cert-grouping:
    +---u asymmetric-key-pair-grouping
    +---u end-entity-cert-grouping
    +---u generate-csr-grouping

Comments:
- This grouping defines an asymmetric key with at most one associated certificate, a commonly needed combination in protocol models.
- For the referenced "grouping" statement(s):
  - The "asymmetric-key-pair-grouping" grouping is discussed in Section 2.1.4.6.
  - The "end-entity-cert-grouping" grouping is discussed in Section 2.1.4.9.
  - The "generate-csr-grouping" grouping is discussed in Section 2.1.4.10.
The "asymmetric-key-pair-with-certs-grouping" Grouping
This section presents a tree diagram [RFC8340] illustrating the "asymmetric-key-pair-with-certs-grouping" grouping. This tree diagram does not expand the internally used "grouping" statement(s):

  grouping asymmetric-key-pair-with-certs-grouping:
    +---u asymmetric-key-pair-grouping
    +-- certificates
    |  +-- certificate* [name]
    |     +-- name                       string
    |     +---u end-entity-cert-grouping
    +---u generate-csr-grouping

Comments:
- This grouping defines an asymmetric key with one or more associated certificates, a commonly needed combination in configuration models.
- For the referenced "grouping" statement(s):
  - The "asymmetric-key-pair-grouping" grouping is discussed in Section 2.1.4.6.
  - The "end-entity-cert-grouping" grouping is discussed in Section 2.1.4.9.
  - The "generate-csr-grouping" grouping is discussed in Section 2.1.4.10.
Protocol-Accessible Nodes
The "ietf-crypto-types" module does not contain any protocol-accessible nodes, but the module needs to be "implemented", as described in Section 5.6.5 of [RFC7950], in order for the identities in Section 2.1.2 to be defined.
Example Usage
The "symmetric-key-grouping", "asymmetric-key-pair-with-certs-grouping", and "password-grouping" Groupings
The following non-normative module is constructed in order to illustrate the use of the "symmetric-key-grouping" (Section 2.1.4.3), the "asymmetric-key-pair-with-certs-grouping" (Section 2.1.4.12), and the "password-grouping" (Section 2.1.4.2) "grouping" statements.
Notably, this example module and associated configuration data illustrates that a hidden private key (ex-hidden-asymmetric-key) has been used to encrypt a symmetric key (ex-encrypted-one-symmetric-based-symmetric-key) that has been used to encrypt another private key (ex-encrypted-rsa-based-asymmetric-key). Additionally, the symmetric key is also used to encrypt a password (ex-encrypted-password).
Example Module

module ex-crypto-types-usage {
  yang-version 1.1;
  namespace "https://example.com/ns/example-crypto-types-usage";
  prefix ectu;

  import ietf-crypto-types {
    prefix ct;
    reference
      "RFC 9640: YANG Data Types and Groupings for Cryptography";
  }

  organization
    "Example Corporation";
  contact
    "YANG Designer <mailto:yang.designer@example.com>";

  description
    "This example module illustrates the 'symmetric-key-grouping'
     and 'asymmetric-key-grouping' groupings defined in the
    'ietf-crypto-types' module defined in RFC 9640.";

  revision 2024-10-10 {
    description
      "Initial version.";
    reference
      "RFC 9640: YANG Data Types and Groupings for Cryptography";
  }

  container symmetric-keys {
    description
      "A container of symmetric keys.";
    list symmetric-key {
      key "name";
      description
        "A symmetric key.";
      leaf name {
        type string;
        description
          "An arbitrary name for this key.";
      }
      uses ct:symmetric-key-grouping {
        augment "key-type/encrypted-symmetric-key/"
              + "encrypted-symmetric-key/encrypted-by" {
          description
            "Augments in a 'choice' statement enabling the
             encrypting key to be any other symmetric or
             asymmetric key.";
          uses encrypted-by-grouping;
        }
      }
    }
  }
  container asymmetric-keys {
    description
      "A container of asymmetric keys.";
    list asymmetric-key {
      key "name";
      leaf name {
        type string;
        description
          "An arbitrary name for this key.";
      }
      uses ct:asymmetric-key-pair-with-certs-grouping {
        augment "private-key-type/encrypted-private-key/"
              + "encrypted-private-key/encrypted-by" {
          description
            "Augments in a 'choice' statement enabling the
             encrypting key to be any other symmetric or
             asymmetric key.";
          uses encrypted-by-grouping;
        }
      }
      description
        "An asymmetric key pair with associated certificates.";
    }
  }
  container passwords {
    description
      "A container of passwords.";
    list password {
      key "name";
      leaf name {
        type string;
        description
          "An arbitrary name for this password.";
      }
      uses ct:password-grouping {
        augment "password-type/encrypted-password/"
              + "encrypted-password/encrypted-by" {
          description
            "Augments in a 'choice' statement enabling the
             encrypting key to be any symmetric or
             asymmetric key.";
          uses encrypted-by-grouping;
        }
      }
      description
        "A password.";
    }
  }

  grouping encrypted-by-grouping {
    description
      "A grouping that defines a choice enabling references
       to other keys.";
    choice encrypted-by {
      mandatory true;
      description
        "A choice amongst other symmetric or asymmetric keys.";
      case symmetric-key-ref {
        leaf symmetric-key-ref {
          type leafref {
            path "/ectu:symmetric-keys/ectu:symmetric-key/"
               + "ectu:name";
          }
          description
            "Identifies the symmetric key that encrypts this key.";
        }
      }
      case asymmetric-key-ref {
        leaf asymmetric-key-ref {
          type leafref {
            path "/ectu:asymmetric-keys/ectu:asymmetric-key/"
               + "ectu:name";
          }
          description
            "Identifies the asymmetric key that encrypts this key.";
        }
      }
    }
  }
}

Tree Diagram for the Example Module
The tree diagram [RFC8340] for this example module is as follows:

module: ex-crypto-types-usage
  +--rw symmetric-keys
  |  +--rw symmetric-key* [name]
  |     +--rw name                             string
  |     +--rw key-format?                      identityref
  |     +--rw (key-type)
  |        +--:(cleartext-symmetric-key)
  |        |  +--rw cleartext-symmetric-key?   binary
  |        |          {cleartext-symmetric-keys}?
  |        +--:(hidden-symmetric-key) {hidden-symmetric-keys}?
  |        |  +--rw hidden-symmetric-key?      empty
  |        +--:(encrypted-symmetric-key) {encrypted-symmetric-keys}?
  |           +--rw encrypted-symmetric-key
  |              +--rw encrypted-by
  |              |  +--rw (encrypted-by)
  |              |     +--:(symmetric-key-ref)
  |              |     |  +--rw symmetric-key-ref?    leafref
  |              |     +--:(asymmetric-key-ref)
  |              |        +--rw asymmetric-key-ref?   leafref
  |              +--rw encrypted-value-format    identityref
  |              +--rw encrypted-value           binary
  +--rw asymmetric-keys
  |  +--rw asymmetric-key* [name]
  |     +--rw name                           string
  |     +--rw public-key-format?             identityref
  |     +--rw public-key?                    binary
  |     +--rw private-key-format?            identityref
  |     +--rw (private-key-type)
  |     |  +--:(cleartext-private-key) {cleartext-private-keys}?
  |     |  |  +--rw cleartext-private-key?   binary
  |     |  +--:(hidden-private-key) {hidden-private-keys}?
  |     |  |  +--rw hidden-private-key?      empty
  |     |  +--:(encrypted-private-key) {encrypted-private-keys}?
  |     |     +--rw encrypted-private-key
  |     |        +--rw encrypted-by
  |     |        |  +--rw (encrypted-by)
  |     |        |     +--:(symmetric-key-ref)
  |     |        |     |  +--rw symmetric-key-ref?    leafref
  |     |        |     +--:(asymmetric-key-ref)
  |     |        |        +--rw asymmetric-key-ref?   leafref
  |     |        +--rw encrypted-value-format    identityref
  |     |        +--rw encrypted-value           binary
  |     +--rw certificates
  |     |  +--rw certificate* [name]
  |     |     +--rw name                      string
  |     |     +--rw cert-data                 end-entity-cert-cms
  |     |     +---n certificate-expiration
  |     |             {certificate-expiration-notification}?
  |     |        +-- expiration-date    yang:date-and-time
  |     +---x generate-csr {csr-generation}?
  |        +---w input
  |        |  +---w csr-format    identityref
  |        |  +---w csr-info      csr-info
  |        +--ro output
  |           +--ro (csr-type)
  |              +--:(p10-csr)
  |                 +--ro p10-csr?   p10-csr
  +--rw passwords
     +--rw password* [name]
        +--rw name                        string
        +--rw (password-type)
           +--:(cleartext-password) {cleartext-passwords}?
           |  +--rw cleartext-password?   string
           +--:(encrypted-password) {encrypted-passwords}?
              +--rw encrypted-password
                 +--rw encrypted-by
                 |  +--rw (encrypted-by)
                 |     +--:(symmetric-key-ref)
                 |     |  +--rw symmetric-key-ref?    leafref
                 |     +--:(asymmetric-key-ref)
                 |        +--rw asymmetric-key-ref?   leafref
                 +--rw encrypted-value-format    identityref
                 +--rw encrypted-value           binary

Usage Example for the Example Module
Finally, the following example illustrates various symmetric and asymmetric keys as they might appear in configuration.

=============== NOTE: '\' line wrapping per RFC 8792 ================

<symmetric-keys
  xmlns="https://example.com/ns/example-crypto-types-usage"
  xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
  <symmetric-key>
    <name>ex-hidden-symmetric-key</name>
    <hidden-symmetric-key/>
  </symmetric-key>
  <symmetric-key>
    <name>ex-octet-string-based-symmetric-key</name>
    <key-format>ct:octet-string-key-format</key-format>
    <cleartext-symmetric-key>BASE64VALUE=</cleartext-symmetric-key>
  </symmetric-key>
  <symmetric-key>
    <name>ex-one-symmetric-based-symmetric-key</name>
    <key-format>ct:one-symmetric-key-format</key-format>
    <cleartext-symmetric-key>BASE64VALUE=</cleartext-symmetric-key>
  </symmetric-key>
  <symmetric-key>
    <name>ex-encrypted-one-symmetric-based-symmetric-key</name>
    <key-format>ct:one-symmetric-key-format</key-format>
    <encrypted-symmetric-key>
      <encrypted-by>
        <asymmetric-key-ref>ex-hidden-asymmetric-key</asymmetric-key\
-ref>
      </encrypted-by>
      <encrypted-value-format>ct:cms-enveloped-data-format</encrypte\
d-value-format>
      <encrypted-value>BASE64VALUE=</encrypted-value>
    </encrypted-symmetric-key>
  </symmetric-key>
</symmetric-keys>

<asymmetric-keys
  xmlns="https://example.com/ns/example-crypto-types-usage"
  xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
  <asymmetric-key>
    <name>ex-hidden-asymmetric-key</name>
    <public-key-format>ct:subject-public-key-info-format</public-key\
-format>
    <public-key>BASE64VALUE=</public-key>
    <hidden-private-key/>
    <certificates>
      <certificate>
        <name>ex-hidden-asymmetric-key-cert</name>
        <cert-data>BASE64VALUE=</cert-data>
      </certificate>
    </certificates>
  </asymmetric-key>
  <asymmetric-key>
    <name>ex-rsa-based-asymmetric-key</name>
    <public-key-format>ct:subject-public-key-info-format</public-key\
-format>
    <public-key>BASE64VALUE=</public-key>
    <private-key-format>ct:rsa-private-key-format</private-key-forma\
t>
    <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
    <certificates>
      <certificate>
        <name>ex-cert</name>
        <cert-data>BASE64VALUE=</cert-data>
      </certificate>
    </certificates>
  </asymmetric-key>
  <asymmetric-key>
    <name>ex-one-asymmetric-based-asymmetric-key</name>
    <public-key-format>ct:subject-public-key-info-format</public-key\
-format>
    <public-key>BASE64VALUE=</public-key>
    <private-key-format>ct:one-asymmetric-key-format</private-key-fo\
rmat>
    <cleartext-private-key>BASE64VALUE=</cleartext-private-key>
  </asymmetric-key>
  <asymmetric-key>
    <name>ex-encrypted-rsa-based-asymmetric-key</name>
    <public-key-format>ct:subject-public-key-info-format</public-key\
-format>
    <public-key>BASE64VALUE=</public-key>
    <private-key-format>ct:rsa-private-key-format</private-key-forma\
t>
    <encrypted-private-key>
      <encrypted-by>
        <symmetric-key-ref>ex-encrypted-one-symmetric-based-symmetri\
c-key</symmetric-key-ref>
      </encrypted-by>
      <encrypted-value-format>ct:cms-encrypted-data-format</encrypte\
d-value-format>
      <encrypted-value>BASE64VALUE=</encrypted-value>
    </encrypted-private-key>
  </asymmetric-key>
</asymmetric-keys>

<passwords
  xmlns="https://example.com/ns/example-crypto-types-usage"
  xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
  <password>
    <name>ex-cleartext-password</name>
    <cleartext-password>super-secret</cleartext-password>
  </password>
  <password>
    <name>ex-encrypted-password</name>
    <encrypted-password>
      <encrypted-by>
        <symmetric-key-ref>ex-encrypted-one-symmetric-based-symmetri\
c-key</symmetric-key-ref>
      </encrypted-by>
      <encrypted-value-format>ct:cms-encrypted-data-format</encrypte\
d-value-format>
      <encrypted-value>BASE64VALUE=</encrypted-value>
    </encrypted-password>
  </password>
</passwords>

The "generate-csr" Action
The following example illustrates the "generate-csr" action, discussed in Section 2.1.4.10, with the NETCONF protocol.
REQUEST

<rpc message-id="101"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0"
  xmlns:ct="urn:ietf:params:xml:ns:yang:ietf-crypto-types">
  <action xmlns="urn:ietf:params:xml:ns:yang:1">
    <asymmetric-keys
      xmlns="https://example.com/ns/example-crypto-types-usage">
      <asymmetric-key>
        <name>ex-hidden-asymmetric-key</name>
        <generate-csr>
          <csr-format>ct:p10-csr-format</csr-format>
          <csr-info>BASE64VALUE=</csr-info>
        </generate-csr>
      </asymmetric-key>
    </asymmetric-keys>
  </action>
</rpc>

RESPONSE

=============== NOTE: '\' line wrapping per RFC 8792 ================

<rpc-reply message-id="101"
  xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <p10-csr xmlns="https://example.com/ns/example-crypto-types-usage"\
>BASE64VALUE=</p10-csr>
</rpc-reply>

The "certificate-expiration" Notification
The following example illustrates the "certificate-expiration" notification, discussed in Section 2.1.4.7, with the NETCONF protocol.

=============== NOTE: '\' line wrapping per RFC 8792 ================

<notification
  xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
  <eventTime>2018-05-25T00:01:00Z</eventTime>
  <asymmetric-keys xmlns="https://example.com/ns/example-crypto-type\
s-usage">
    <asymmetric-key>
      <name>ex-hidden-asymmetric-key</name>
      <certificates>
        <certificate>
          <name>ex-hidden-asymmetric-key-cert</name>
          <certificate-expiration>
            <expiration-date>2018-08-05T14:18:53-05:00</expiration-d\
ate>
          </certificate-expiration>
        </certificate>
      </certificates>
    </asymmetric-key>
  </asymmetric-keys>
</notification>

YANG Module
This module has normative references to [RFC2119], [RFC2986], [RFC4253], [RFC5280], [RFC5652], [RFC5915], [RFC5958], [RFC6031], [RFC6960], [RFC6991], [RFC7093], [RFC8017], [RFC8174], [RFC8341], and [ITU.X690.2021].

module ietf-crypto-types {
  yang-version 1.1;
  namespace "urn:ietf:params:xml:ns:yang:ietf-crypto-types";
  prefix ct;

  import ietf-yang-types {
    prefix yang;
    reference
      "RFC 6991: Common YANG Data Types";
  }

  import ietf-netconf-acm {
    prefix nacm;
    reference
      "RFC 8341: Network Configuration Access Control Model";
  }

  organization
    "IETF NETCONF (Network Configuration) Working Group";

  contact
    "WG Web:   https://datatracker.ietf.org/wg/netconf
     WG List:  NETCONF WG list <mailto:netconf@ietf.org>
     Author:   Kent Watsen <mailto:kent+ietf@watsen.net>";

  description
    "This module defines common YANG types for cryptographic
     applications.

     The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
     'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
     'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
     are to be interpreted as described in BCP 14 (RFC 2119)
     (RFC 8174) when, and only when, they appear in all
     capitals, as shown here.

     Copyright (c) 2024 IETF Trust and the persons identified
     as authors of the code.  All rights reserved.

     Redistribution and use in source and binary forms, with
     or without modification, is permitted pursuant to, and
     subject to the license terms contained in, the Revised
     BSD License set forth in Section 4.c of the IETF Trust's
     Legal Provisions Relating to IETF Documents
     (https://trustee.ietf.org/license-info).

     This version of this YANG module is part of RFC 9640
     (https://www.rfc-editor.org/info/rfc9640); see the RFC
     itself for full legal notices.";

  revision 2024-10-10 {
    description
      "Initial version.";
    reference
      "RFC 9640: YANG Data Types and Groupings for Cryptography";
  }

  /****************/
  /*   Features   */
  /****************/

  feature one-symmetric-key-format {
    description
      "Indicates that the server supports the
       'one-symmetric-key-format' identity.";
  }

  feature one-asymmetric-key-format {
    description
      "Indicates that the server supports the
       'one-asymmetric-key-format' identity.";
  }

  feature symmetrically-encrypted-value-format {
    description
      "Indicates that the server supports the
       'symmetrically-encrypted-value-format' identity.";
  }

  feature asymmetrically-encrypted-value-format {
    description
      "Indicates that the server supports the
       'asymmetrically-encrypted-value-format' identity.";
  }

  feature cms-enveloped-data-format {
    description
      "Indicates that the server supports the
       'cms-enveloped-data-format' identity.";
  }

  feature cms-encrypted-data-format {
    description
      "Indicates that the server supports the
       'cms-encrypted-data-format' identity.";
  }

  feature p10-csr-format {
    description
      "Indicates that the server implements support
       for generating P10-based CSRs, as defined
       in RFC 2986.";
    reference
      "RFC 2986: PKCS #10: Certification Request Syntax
                 Specification Version 1.7";
  }

  feature csr-generation {
    description
      "Indicates that the server implements the
       'generate-csr' action.";
  }

  feature certificate-expiration-notification {
    description
      "Indicates that the server implements the
       'certificate-expiration' notification.";
  }

  feature cleartext-passwords {
    description
      "Indicates that the server supports cleartext
       passwords.";
  }

  feature encrypted-passwords {
    description
      "Indicates that the server supports password
       encryption.";
  }

  feature cleartext-symmetric-keys {
    description
      "Indicates that the server supports cleartext
       symmetric keys.";
  }

  feature hidden-symmetric-keys {
    description
      "Indicates that the server supports hidden keys.";
  }

  feature encrypted-symmetric-keys {
    description
      "Indicates that the server supports encryption
       of symmetric keys.";
  }

  feature cleartext-private-keys {
    description
      "Indicates that the server supports cleartext
       private keys.";
  }

  feature hidden-private-keys {
    description
      "Indicates that the server supports hidden keys.";
  }

  feature encrypted-private-keys {
    description
      "Indicates that the server supports encryption
       of private keys.";
  }

  /*************************************************/
  /*   Base Identities for Key Format Structures   */
  /*************************************************/

  identity symmetric-key-format {
    description
      "Base key-format identity for symmetric keys.";
  }

  identity public-key-format {
    description
      "Base key-format identity for public keys.";
  }

  identity private-key-format {
    description
      "Base key-format identity for private keys.";
  }

  /****************************************************/
  /*   Identities for Private Key Format Structures   */
  /****************************************************/

  identity rsa-private-key-format {
    base private-key-format;
    description
      "Indicates that the private key value is encoded as
       an RSAPrivateKey (from RFC 8017), encoded using ASN.1
       distinguished encoding rules (DER), as specified in
       ITU-T X.690.";
    reference
      "RFC 8017:
         PKCS #1: RSA Cryptography Specifications Version 2.2
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  identity ec-private-key-format {
    base private-key-format;
    description
      "Indicates that the private key value is encoded as
       an ECPrivateKey (from RFC 5915), encoded using ASN.1
       distinguished encoding rules (DER), as specified in
       ITU-T X.690.";
    reference
      "RFC 5915:
         Elliptic Curve Private Key Structure
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  identity one-asymmetric-key-format {
    if-feature "one-asymmetric-key-format";
    base private-key-format;
    description
      "Indicates that the private key value is a
       Cryptographic Message Syntax (CMS) OneAsymmetricKey
       structure, as defined in RFC 5958, encoded using
       ASN.1 distinguished encoding rules (DER), as
       specified in ITU-T X.690.";
    reference
      "RFC 5958:
         Asymmetric Key Packages
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  /***************************************************/
  /*   Identities for Public Key Format Structures   */
  /***************************************************/

  identity ssh-public-key-format {
    base public-key-format;
    description
      "Indicates that the public key value is a Secure Shell (SSH)
       public key, as specified in RFC 4253, Section 6.6, i.e.:

         string    certificate or public key format
                   identifier
         byte[n]   key/certificate data.";
    reference
      "RFC 4253: The Secure Shell (SSH) Transport Layer Protocol";
  }

  identity subject-public-key-info-format {
    base public-key-format;
    description
      "Indicates that the public key value is a SubjectPublicKeyInfo
       structure, as described in RFC 5280, encoded using ASN.1
       distinguished encoding rules (DER), as specified in
       ITU-T X.690.";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  /******************************************************/
  /*   Identities for Symmetric Key Format Structures   */
  /******************************************************/

  identity octet-string-key-format {
    base symmetric-key-format;
    description
      "Indicates that the key is encoded as a raw octet string.
       The length of the octet string MUST be appropriate for
       the associated algorithm's block size.

       The identity of the associated algorithm is outside the
       scope of this specification.  This is also true when
       the octet string has been encrypted.";
  }

  identity one-symmetric-key-format {
    if-feature "one-symmetric-key-format";
    base symmetric-key-format;
    description
      "Indicates that the private key value is a CMS
       OneSymmetricKey structure, as defined in RFC 6031,
       encoded using ASN.1 distinguished encoding rules
       (DER), as specified in ITU-T X.690.";
    reference
      "RFC 6031:
         Cryptographic Message Syntax (CMS)
         Symmetric Key Package Content Type
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  /*************************************************/
  /*   Identities for Encrypted Value Structures   */
  /*************************************************/

  identity encrypted-value-format {
    description
      "Base format identity for encrypted values.";
  }

  identity symmetrically-encrypted-value-format {
    if-feature "symmetrically-encrypted-value-format";
    base encrypted-value-format;
    description
      "Base format identity for symmetrically encrypted
       values.";
  }

  identity asymmetrically-encrypted-value-format {
    if-feature "asymmetrically-encrypted-value-format";
    base encrypted-value-format;
    description
      "Base format identity for asymmetrically encrypted
       values.";
  }

  identity cms-encrypted-data-format {
    if-feature "cms-encrypted-data-format";
    base symmetrically-encrypted-value-format;
    description
      "Indicates that the encrypted value conforms to
       the 'encrypted-data-cms' type with the constraint
       that the 'unprotectedAttrs' value is not set.";
    reference
      "RFC 5652:
         Cryptographic Message Syntax (CMS)
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  identity cms-enveloped-data-format {
    if-feature "cms-enveloped-data-format";
    base asymmetrically-encrypted-value-format;
    description
      "Indicates that the encrypted value conforms to the
       'enveloped-data-cms' type with the following constraints:

       The EnvelopedData structure MUST have exactly one
       'RecipientInfo'.

       If the asymmetric key supports public key cryptography
       (e.g., RSA), then the 'RecipientInfo' must be a
       'KeyTransRecipientInfo' with the 'RecipientIdentifier'
       using a 'subjectKeyIdentifier' with the value set using
       'method 1' in RFC 7093 over the recipient's public key.

       Otherwise, if the asymmetric key supports key agreement
       (e.g., Elliptic Curve Cryptography (ECC)), then the
       'RecipientInfo' must be a 'KeyAgreeRecipientInfo'.  The
       'OriginatorIdentifierOrKey' value must use the
       'OriginatorPublicKey' alternative.  The
       'UserKeyingMaterial' value must not be present.  There
       must be exactly one 'RecipientEncryptedKeys' value
       having the 'KeyAgreeRecipientIdentifier' set to 'rKeyId'
       with the value set using 'method 1' in RFC 7093 over the
       recipient's public key.";
    reference
      "RFC 5652:
         Cryptographic Message Syntax (CMS)
       RFC 7093:
         Additional Methods for Generating Key
         Identifiers Values
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  /*********************************************************/
  /*   Identities for Certificate Signing Request Formats  */
  /*********************************************************/

  identity csr-format {
    description
      "A base identity for the certificate signing request
       formats.  Additional derived identities MAY be defined
       by future efforts.";
  }

  identity p10-csr-format {
    if-feature "p10-csr-format";
    base csr-format;
    description
      "Indicates the CertificationRequest structure
       defined in RFC 2986.";
    reference
      "RFC 2986: PKCS #10: Certification Request Syntax
                 Specification Version 1.7";
  }

  /***************************************************/
  /*   Typedefs for ASN.1 structures from RFC 2986   */
  /***************************************************/

  typedef csr-info {
    type binary;
    description
      "A CertificationRequestInfo structure, as defined in
       RFC 2986, encoded using ASN.1 distinguished encoding
       rules (DER), as specified in ITU-T X.690.";
    reference
      "RFC 2986:
         PKCS #10: Certification Request Syntax
         Specification Version 1.7
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  typedef p10-csr {
    type binary;
    description
      "A CertificationRequest structure, as specified in
       RFC 2986, encoded using ASN.1 distinguished encoding
       rules (DER), as specified in ITU-T X.690.";
    reference
      "RFC 2986:
         PKCS #10: Certification Request Syntax Specification
         Version 1.7
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  /***************************************************/
  /*   Typedefs for ASN.1 structures from RFC 5280   */
  /***************************************************/

  typedef x509 {
    type binary;
    description
      "A Certificate structure, as specified in RFC 5280,
       encoded using ASN.1 distinguished encoding rules (DER),
       as specified in ITU-T X.690.";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  typedef crl {
    type binary;
    description
      "A CertificateList structure, as specified in RFC 5280,
       encoded using ASN.1 distinguished encoding rules (DER),
       as specified in ITU-T X.690.";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  /***************************************************/
  /*   Typedefs for ASN.1 structures from RFC 6960   */
  /***************************************************/

  typedef oscp-request {
    type binary;
    description
      "A OCSPRequest structure, as specified in RFC 6960,
       encoded using ASN.1 distinguished encoding rules
       (DER), as specified in ITU-T X.690.";
    reference
      "RFC 6960:
         X.509 Internet Public Key Infrastructure Online
         Certificate Status Protocol - OCSP
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  typedef oscp-response {
    type binary;
    description
      "A OCSPResponse structure, as specified in RFC 6960,
       encoded using ASN.1 distinguished encoding rules
       (DER), as specified in ITU-T X.690.";
    reference
      "RFC 6960:
         X.509 Internet Public Key Infrastructure Online
         Certificate Status Protocol - OCSP
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  /***********************************************/
  /*   Typedefs for ASN.1 structures from 5652   */
  /***********************************************/

  typedef cms {
    type binary;
    description
      "A ContentInfo structure, as specified in RFC 5652,
       encoded using ASN.1 distinguished encoding rules (DER),
       as specified in ITU-T X.690.";
    reference
      "RFC 5652:
         Cryptographic Message Syntax (CMS)
       ITU-T X.690:
         Information technology - ASN.1 encoding rules:
         Specification of Basic Encoding Rules (BER),
         Canonical Encoding Rules (CER) and Distinguished
         Encoding Rules (DER) 02/2021";
  }

  typedef data-content-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       data content type, as described in Section 4 of RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef signed-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       signed-data content type, as described in Section 5 of
       RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef enveloped-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       enveloped-data content type, as described in Section 6
       of RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef digested-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       digested-data content type, as described in Section 7
       of RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef encrypted-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       encrypted-data content type, as described in Section 8
       of RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  typedef authenticated-data-cms {
    type cms;
    description
      "A CMS structure whose top-most content type MUST be the
       authenticated-data content type, as described in Section 9
       of RFC 5652.";
    reference
      "RFC 5652: Cryptographic Message Syntax (CMS)";
  }

  /*********************************************************/
  /*   Typedefs for ASN.1 structures related to RFC 5280   */
  /*********************************************************/

  typedef trust-anchor-cert-x509 {
    type x509;
    description
      "A Certificate structure that MUST encode a self-signed
       root certificate.";
  }

  typedef end-entity-cert-x509 {
    type x509;
    description
      "A Certificate structure that MUST encode a certificate
       that is neither self-signed nor has Basic constraint
       CA true.";
  }

  /*********************************************************/
  /*   Typedefs for ASN.1 structures related to RFC 5652   */
  /*********************************************************/

  typedef trust-anchor-cert-cms {
    type signed-data-cms;
    description
      "A CMS SignedData structure that MUST contain the chain of
       X.509 certificates needed to authenticate the certificate
       presented by a client or end entity.

       The CMS MUST contain only a single chain of certificates.
       The client or end-entity certificate MUST only authenticate
       to the last intermediate CA certificate listed in the chain.

       In all cases, the chain MUST include a self-signed root
       certificate.  In the case where the root certificate is
       itself the issuer of the client or end-entity certificate,
       only one certificate is present.

       This CMS structure MAY (as applicable where this type is
       used) also contain suitably fresh (as defined by local
       policy) revocation objects with which the device can
       verify the revocation status of the certificates.

       This CMS encodes the degenerate form of the SignedData
       structure (RFC 5652, Section 5.2) that is commonly used
       to disseminate X.509 certificates and revocation objects
       (RFC 5280).";
    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile
       RFC 5652:
         Cryptographic Message Syntax (CMS)";
  }

  typedef end-entity-cert-cms {
    type signed-data-cms;
    description
      "A CMS SignedData structure that MUST contain the end-entity
       certificate itself and MAY contain any number
       of intermediate certificates leading up to a trust
       anchor certificate.  The trust anchor certificate
       MAY be included as well.

       The CMS MUST contain a single end-entity certificate.
       The CMS MUST NOT contain any spurious certificates.

       This CMS structure MAY (as applicable where this type is
       used) also contain suitably fresh (as defined by local
       policy) revocation objects with which the device can
       verify the revocation status of the certificates.

       This CMS encodes the degenerate form of the SignedData
       structure (RFC 5652, Section 5.2) that is commonly
       used to disseminate X.509 certificates and revocation
       objects (RFC 5280).";

    reference
      "RFC 5280:
         Internet X.509 Public Key Infrastructure Certificate
         and Certificate Revocation List (CRL) Profile
       RFC 5652:
         Cryptographic Message Syntax (CMS)";
  }

  /*****************/
  /*   Groupings   */
  /*****************/

  grouping encrypted-value-grouping {
    description
      "A reusable grouping for a value that has been encrypted by
       a referenced symmetric or asymmetric key.";
    container encrypted-by {
      nacm:default-deny-write;
      description
        "An empty container enabling a reference to the key that
         encrypted the value to be augmented in.  The referenced
         key MUST be a symmetric key or an asymmetric key.

         A symmetric key MUST be referenced via a leaf node called
         'symmetric-key-ref'.  An asymmetric key MUST be referenced
         via a leaf node called 'asymmetric-key-ref'.

         The leaf nodes MUST be direct descendants in the data tree
         and MAY be direct descendants in the schema tree (e.g.,
         'choice'/'case' statements are allowed but not a
         container).";
    }
    leaf encrypted-value-format {
      type identityref {
        base encrypted-value-format;
      }
      mandatory true;
      description
        "Identifies the format of the 'encrypted-value' leaf.

         If 'encrypted-by' points to a symmetric key, then an
         identity based on 'symmetrically-encrypted-value-format'
         MUST be set (e.g., 'cms-encrypted-data-format').

         If 'encrypted-by' points to an asymmetric key, then an
         identity based on 'asymmetrically-encrypted-value-format'
         MUST be set (e.g., 'cms-enveloped-data-format').";
    }
    leaf encrypted-value {
      nacm:default-deny-write;
      type binary;
      must '../encrypted-by';
      mandatory true;
      description
        "The value, encrypted using the referenced symmetric
         or asymmetric key.  The value MUST be encoded using
         the format associated with the 'encrypted-value-format'
         leaf.";
    }
  }

  grouping password-grouping {
    description
      "A password used for authenticating to a remote system.

       The 'ianach:crypt-hash' typedef from RFC 7317 should be
       used instead when needing a password to authenticate a
       local account.";
    choice password-type {
      nacm:default-deny-write;
      mandatory true;
      description
        "Choice between password types.";
      case cleartext-password {
        if-feature "cleartext-passwords";
        leaf cleartext-password {
          nacm:default-deny-all;
          type string;
          description
            "The cleartext value of the password.";
        }
      }
      case encrypted-password {
        if-feature "encrypted-passwords";
        container encrypted-password {
          description
            "A container for the encrypted password value.";
          uses encrypted-value-grouping;
        }
      }
    }
  }

  grouping symmetric-key-grouping {
    description
      "A symmetric key.";
    leaf key-format {
      nacm:default-deny-write;
      type identityref {
        base symmetric-key-format;
      }
      description
        "Identifies the symmetric key's format.  Implementations
         SHOULD ensure that the incoming symmetric key value is
         encoded in the specified format.

         For encrypted keys, the value is the decrypted key's
         format (i.e., the 'encrypted-value-format' conveys the
         encrypted key's format).";
    }
    choice key-type {
      nacm:default-deny-write;
      mandatory true;
      description
        "Choice between key types.";
      case cleartext-symmetric-key {
        leaf cleartext-symmetric-key {
          if-feature "cleartext-symmetric-keys";
          nacm:default-deny-all;
          type binary;
          must '../key-format';
          description
            "The binary value of the key.  The interpretation of
             the value is defined by the 'key-format' field.";
        }
      }
      case hidden-symmetric-key {
        if-feature "hidden-symmetric-keys";
        leaf hidden-symmetric-key {
          type empty;
          must 'not(../key-format)';
          description
            "A hidden key is not exportable and not extractable;
             therefore, it is of type 'empty' as its value is
             inaccessible via management interfaces.  Though hidden
             to users, such keys are not hidden to the server and
             may be referenced by configuration to indicate which
             key a server should use for a cryptographic operation.
             How such keys are created is outside the scope of this
             module.";
        }
      }
      case encrypted-symmetric-key {
        if-feature "encrypted-symmetric-keys";
        container encrypted-symmetric-key {
          must '../key-format';
          description
            "A container for the encrypted symmetric key value.
             The interpretation of the 'encrypted-value' node
             is via the 'key-format' node";
          uses encrypted-value-grouping;
        }
      }
    }
  }

  grouping public-key-grouping {
    description
      "A public key.";
    leaf public-key-format {
      nacm:default-deny-write;
      type identityref {
        base public-key-format;
      }
      mandatory true;
      description
        "Identifies the public key's format.  Implementations SHOULD
         ensure that the incoming public key value is encoded in the
         specified format.";
    }
    leaf public-key {
      nacm:default-deny-write;
      type binary;
      mandatory true;
      description
        "The binary value of the public key.  The interpretation
         of the value is defined by the 'public-key-format' field.";
    }
  }

  grouping private-key-grouping {
    description
      "A private key.";
    leaf private-key-format {
      nacm:default-deny-write;
      type identityref {
        base private-key-format;
      }
      description
        "Identifies the private key's format.  Implementations SHOULD
         ensure that the incoming private key value is encoded in the
         specified format.

         For encrypted keys, the value is the decrypted key's
         format (i.e., the 'encrypted-value-format' conveys the
         encrypted key's format).";
    }
    choice private-key-type {
      nacm:default-deny-write;
      mandatory true;
      description
        "Choice between key types.";
      case cleartext-private-key {
        if-feature "cleartext-private-keys";
        leaf cleartext-private-key {
          nacm:default-deny-all;
          type binary;
          must '../private-key-format';
          description
            "The value of the binary key.  The key's value is
             interpreted by the 'private-key-format' field.";
        }
      }
      case hidden-private-key {
        if-feature "hidden-private-keys";
        leaf hidden-private-key {
          type empty;
          must 'not(../private-key-format)';
          description
            "A hidden key.  It is of type 'empty' as its value is
             inaccessible via management interfaces.  Though hidden
             to users, such keys are not hidden to the server and
             may be referenced by configuration to indicate which
             key a server should use for a cryptographic operation.
             How such keys are created is outside the scope of this
             module.";
        }
      }
      case encrypted-private-key {
        if-feature "encrypted-private-keys";
        container encrypted-private-key {
          must '../private-key-format';
          description
            "A container for the encrypted asymmetric private key
             value.  The interpretation of the 'encrypted-value'
             node is via the 'private-key-format' node";
          uses encrypted-value-grouping;
        }
      }
    }
  }

  grouping asymmetric-key-pair-grouping {
    description
      "A private key and, optionally, its associated public key.
       Implementations MUST ensure that the two keys, when both
       are specified, are a matching pair.";
    uses public-key-grouping {
      refine "public-key-format" {
        mandatory false;
      }
      refine "public-key" {
        mandatory false;
      }
    }
    uses private-key-grouping;
  }

  grouping certificate-expiration-grouping {
    description
      "A notification for when a certificate is about to expire or
       has already expired.";
    notification certificate-expiration {
      if-feature "certificate-expiration-notification";
      description
        "A notification indicating that the configured certificate
         is either about to expire or has already expired.  When to
         send notifications is an implementation-specific decision,
         but it is RECOMMENDED that a notification be sent once a
         month for 3 months, then once a week for four weeks, and
         then once a day thereafter until the issue is resolved.

         If the certificate's issuer maintains a Certificate
         Revocation List (CRL), the expiration notification MAY
         be sent if the CRL is about to expire.";
      leaf expiration-date {
        type yang:date-and-time;
        mandatory true;
        description
          "Identifies the expiration date on the certificate.";
      }
    }
  }

  grouping trust-anchor-cert-grouping {
    description
      "A trust anchor certificate and a notification for when
       it is about to expire or has already expired.";
    leaf cert-data {
      nacm:default-deny-all;
      type trust-anchor-cert-cms;
      description
        "The binary certificate data for this certificate.";
    }
    uses certificate-expiration-grouping;
  }

  grouping end-entity-cert-grouping {
    description
      "An end-entity certificate and a notification for when
       it is about to expire or has already expired.  Implementations
       SHOULD assert that, where used, the end-entity certificate
       contains the expected public key.";
    leaf cert-data {
      nacm:default-deny-all;
      type end-entity-cert-cms;
      description
        "The binary certificate data for this certificate.";
    }
    uses certificate-expiration-grouping;
  }

  grouping generate-csr-grouping {
    description
      "Defines the 'generate-csr' action.";
    action generate-csr {
      if-feature "csr-generation";
      nacm:default-deny-all;
      description
        "Generates a certificate signing request structure for
         the associated asymmetric key using the passed subject
         and attribute values.

         This 'action' statement is only available when the
         associated 'public-key-format' node's value is
         'subject-public-key-info-format'.";
      input {
        leaf csr-format {
          type identityref {
            base csr-format;
          }
          mandatory true;
          description
            "Specifies the format for the returned certificate.";
        }
        leaf csr-info {
          type csr-info;
          mandatory true;
          description
            "A CertificationRequestInfo structure, as defined in
             RFC 2986.

             Enables the client to provide a fully populated
             CertificationRequestInfo structure that the server
             only needs to sign in order to generate the complete
             CertificationRequest structure to return in the
             'output'.

             The 'AlgorithmIdentifier' field contained inside
             the 'SubjectPublicKeyInfo' field MUST be one known
             to be supported by the device.";
          reference
            "RFC 2986:
               PKCS #10: Certification Request Syntax Specification
             RFC 9640:
               YANG Data Types and Groupings for Cryptography";
        }
      }
      output {
        choice csr-type {
          mandatory true;
          description
            "A choice amongst certificate signing request formats.
             Additional formats MAY be augmented into this 'choice'
             statement by future efforts.";
          case p10-csr {
            leaf p10-csr {
              type p10-csr;
              description
                "A CertificationRequest, as defined in RFC 2986.";
            }
            description
              "A CertificationRequest, as defined in RFC 2986.";
            reference
              "RFC 2986:
                 PKCS #10: Certification Request Syntax Specification
               RFC 9640:
                 YANG Data Types and Groupings for Cryptography";
          }
        }
      }
    }
  } // generate-csr-grouping

  grouping asymmetric-key-pair-with-cert-grouping {
    description
      "A private/public key pair and an associated certificate.
       Implementations MUST assert that the certificate contains
       the matching public key.";
    uses asymmetric-key-pair-grouping;
    uses end-entity-cert-grouping;
    uses generate-csr-grouping;
  } // asymmetric-key-pair-with-cert-grouping

  grouping asymmetric-key-pair-with-certs-grouping {
    description
      "A private/public key pair and a list of associated
       certificates.  Implementations MUST assert that
       certificates contain the matching public key.";
    uses asymmetric-key-pair-grouping;
    container certificates {
      nacm:default-deny-write;
      description
        "Certificates associated with this asymmetric key.";
      list certificate {
        key "name";
        description
          "A certificate for this asymmetric key.";
        leaf name {
          type string;
          description
            "An arbitrary name for the certificate.";
        }
        uses end-entity-cert-grouping {
          refine "cert-data" {
            mandatory true;
          }
        }
      }
    }
    uses generate-csr-grouping;
  } // asymmetric-key-pair-with-certs-grouping

}

Security Considerations
No Support for CRMF
This document uses PKCS #10 [RFC2986] for the "generate-csr" action. The use of Certificate Request Message Format (CRMF) [RFC4211] was considered, but it was unclear if there was market demand for it. If it is desired to support CRMF in the future, a backwards compatible solution can be defined at that time.
No Support for Key Generation
Early revisions of this document included "rpc" statements for generating symmetric and asymmetric keys. These statements were removed due to an inability to obtain consensus for how to generically identify the key algorithm to use. Hence, the solution presented in this document only supports keys to be configured via an external client.
Separate protocol-specific modules can present protocol-specific key-generating RPCs (e.g., the "generate-asymmetric-key-pair" RPC in [RFC9644] and [RFC9645]).
Unconstrained Public Key Usage
This module defines the "public-key-grouping" grouping, which enables the configuration of public keys without constraints on their usage, e.g., what operations the key is allowed to be used for (e.g., encryption, verification, or both).
The "asymmetric-key-pair-grouping" grouping uses the aforementioned "public-key-grouping" grouping and carries the same traits.
The "asymmetric-key-pair-with-cert-grouping" grouping uses the aforementioned "asymmetric-key-pair-grouping" grouping, whereby associated certificates MUST constrain the usage of the public key according to local policy.
Unconstrained Private Key Usage
This module defines the "asymmetric-key-pair-grouping" grouping, which enables the configuration of private keys without constraints on their usage, e.g., what operations the key is allowed to be used for (e.g., signature, decryption, or both).
The "asymmetric-key-pair-with-cert-grouping" grouping uses the aforementioned "asymmetric-key-pair-grouping" grouping, whereby configured certificates (e.g., identity certificates) may constrain the use of the public key according to local policy.
Cleartext Passwords and Keys
The module contained within this document enables, only when specific "feature" statements are enabled, for the cleartext value of passwords and keys to be stored in the configuration database. Storing cleartext values for passwords and keys is NOT RECOMMENDED.
Encrypting Passwords and Keys
The module contained within this document enables cleartext passwords and keys to be encrypted via another key, either symmetric or asymmetric. Both formats use a CMS structure (EncryptedData and EnvelopedData, respectively), which allows any encryption algorithm to be used.
To securely encrypt a password or key with a symmetric key, a proper block cipher mode, such as an Authenticated Encryption with Associated Data (AEAD) or Cipher Block Chaining (CBC), MUST be used.
This ensures that a random Initialization Vector (IV) is part of the input, which guarantees that the output for encrypting the same password or key still produces a different unpredictable ciphertext. This avoids leaking that some encrypted keys or passwords are the same and makes it much harder to pre-generate rainbow tables to brute-force attack weak passwords. The Electronic Codebook (ECB) block cipher mode MUST NOT be used.
Deletion of Cleartext Key Values
This module defines storage for cleartext key values that SHOULD be zeroized when deleted so as to prevent the remnants of their persisted storage locations from being analyzed in any meaningful way.
The cleartext key values are the "cleartext-symmetric-key" node defined in the "symmetric-key-grouping" grouping (Section 2.1.4.3) and the "cleartext-private-key" node defined in the "asymmetric-key-pair-grouping" grouping (Section 2.1.4.6).
Considerations for the "ietf-crypto-types" YANG Module
This section is modeled after the template defined in Section 3.7.1 of [RFC8407].
The "ietf-crypto-types" YANG module defines "grouping" statements that are designed to be accessed via YANG-based management protocols, such as NETCONF [RFC6241] and RESTCONF [RFC8040]. Both of these protocols have mandatory-to-implement secure transport layers (e.g., Secure Shell (SSH) [RFC4252], TLS [RFC8446], and QUIC [RFC9000]) and mandatory-to-implement mutual authentication.
The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular users to a preconfigured subset of all available protocol operations and content.
Since the module in this document only defines groupings, these considerations are primarily for the designers of other modules that use these groupings.
Some of the readable data nodes defined in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control read access (e.g., via get, get-config, or notification) to these data nodes. The following subtrees and data nodes have particular sensitivity/vulnerability:
- The "cleartext-password" node:
  - The "cleartext-password" node defined in the "password-grouping" grouping is additionally sensitive to read operations such that, in normal use cases, it should never be returned to a client. For this reason, the NACM extension "default-deny-all" has been applied to it.
- The "cleartext-symmetric-key" node:
  - The "cleartext-symmetric-key" node defined in the "symmetric-key-grouping" grouping is additionally sensitive to read operations such that, in normal use cases, it should never be returned to a client. For this reason, the NACM extension "default-deny-all" has been applied to it.
- The "cleartext-private-key" node:
  - The "cleartext-private-key" node defined in the "asymmetric-key-pair-grouping" grouping is additionally sensitive to read operations such that, in normal use cases, it should never be returned to a client. For this reason, the NACM extension "default-deny-all" has been applied to it.
- The "cert-data" node:
  - The "cert-data" node defined in both the "trust-anchor-cert-grouping" and "end-entity-cert-grouping" groupings is additionally sensitive to read operations, as certificates may provide insight into which other resources/applications/servers this particular server communicates with, as well as potentially divulge personally identifying information (e.g., end-entity certificates). For this reason, the NACM extension "default-deny-all" has been applied to it.
All the writable data nodes defined by all the groupings defined in this module may be considered sensitive or vulnerable in some network environments. For instance, even the modification of a public key or a certificate can dramatically alter the implemented security policy. For this reason, the NACM extension "default-deny-write" has been applied to all the data nodes defined in the module.
Some of the operations in this YANG module may be considered sensitive or vulnerable in some network environments. It is thus important to control access to these operations. These are the operations and their sensitivity/vulnerability:
- generate-csr:
  - This "action" statement SHOULD only be executed by authorized users. For this reason, the NACM extension "default-deny-all" has been applied. Note that NACM uses "default-deny-all" to protect "rpc" and "action" statements; it does not define, e.g., an extension called "default-deny-execute".
  - For this action, it is RECOMMENDED that implementations assert channel binding [RFC5056] so as to ensure that the application layer that sent the request is the same as the device authenticated when the secure transport layer was established.
IANA Considerations
The IETF XML Registry
IANA has registered the following URI in the "ns" registry of the "IETF XML Registry" [RFC3688].
URI:
urn:ietf:params:xml:ns:yang:ietf-crypto-types
Registrant Contact:
The IESG
XML:
N/A; the requested URI is an XML namespace.
The YANG Module Names Registry
IANA has registered the following YANG module in the "YANG Module Names" registry [RFC6020].
Name:
ietf-crypto-types
Namespace:
urn:ietf:params:xml:ns:yang:ietf-crypto-types
Prefix:
ct
Reference:
RFC 9640
References
Normative References
[ITU.X680.2021]

Information technology - Abstract Syntax Notation One (ASN.1): Specification of basic notation
ITU-T
February 2021
ITU-T Recommendation X.680
ISO/IEC 8824-1:2021
[ITU.X690.2021]

Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)
ITU-T
February 2021
ITU-T Recommendation X.690
ISO/IEC 8825-1:2021
Informative References
[RFC9641]

A YANG Data Model for a Truststore
Kent Watsen
Watsen Networks
October 2024
RFC 9641
DOI 10.17487/RFC9641
[RFC9642]

A YANG Data Model for a Keystore
Kent Watsen
Watsen Networks
October 2024
RFC 9642
DOI 10.17487/RFC9642
[RFC9643]

YANG Groupings for TCP Clients and TCP Servers
Kent Watsen
Watsen Networks
Michael Scharf
Hochschule Esslingen - University of Applied Sciences
October 2024
RFC 9643
DOI 10.17487/RFC9643
[RFC9644]

YANG Groupings for SSH Clients and SSH Servers
Kent Watsen
Watsen Networks
October 2024
RFC 9644
DOI 10.17487/RFC9644
[RFC9645]

YANG Groupings for TLS Clients and TLS Servers
Kent Watsen
Watsen Networks
October 2024
RFC 9645
DOI 10.17487/RFC9645
[W3C.REC-xml-20081126]

Extensible Markup Language (XML) 1.0 (Fifth Edition)
Tim Bray
Jean Paoli
C. M. Sperberg-McQueen
Eve Maler
François Yergeau
November 2008
World Wide Web Consortium Recommendation REC-xml-20081126
[RFC7950]
[RFC6241]
[RFC8040]
[I-D.ietf-netconf-http-client-server]
[I-D.ietf-netconf-netconf-client-server]
[I-D.ietf-netconf-restconf-client-server]
[RFC2119]
[RFC8174]
[RFC8342]
[RFC8259]
[RFC8792]
[RFC8340]
[RFC7317]
[RFC2986]
[RFC4253]
[RFC5280]
[RFC5652]
[RFC5915]
[RFC5958]
[RFC6031]
[RFC6960]
[RFC6991]
[RFC7093]
[RFC8017]
[RFC8341]
[RFC4211]
[RFC8407]
[RFC4252]
[RFC8446]
[RFC9000]
[RFC5056]
[RFC3688]
[RFC6020]
Acknowledgements
The authors would like to thank the following for lively discussions on list and in the halls (ordered by first name): Balázs Kovács, Carsten Bormann, Dale Worley, Eric Voit, Éric Vyncke, Francesca Palombini, Jürgen Schönwälder, Lars Eggert, Liang Xia, Mahesh Jethanandani, Martin Björklund, Murray Kucherawy, Nick Hancock, Orie Steele, Paul Wouters, Rich Salz, Rifaat Shekh-Yusef, Rob Wilton, Roman Danyliw, Russ Housley, Sandra Murphy, Tom Petch, Valery Smyslov, Wang Haiguang, Warren Kumari, and Zaheduzzaman Sarker.