=pod

=head1 NAME

EVP_PKEY-ML-KEM,
EVP_KEYMGMT-ML-KEM,
EVP_PKEY-ML-KEM-512,
EVP_PKEY-ML-KEM-768,
EVP_PKEY-ML-KEM-1024,
EVP_KEYMGMT-ML-KEM-512,
EVP_KEYMGMT-ML-KEM-768,
EVP_KEYMGMT-ML-KEM-1024
- ML-KEM keytype and algorithm support

=head1 DESCRIPTION

The B<ML-KEM-512>, B<ML-KEM-768>, and B<ML-KEM-1024> keytypes are implemented
in OpenSSL's default and FIPS providers.

=head2 Keygen Parameters

No mandatory parameters are required for generating a key pair.
To set explicit parameters, use EVP_PKEY_CTX_set_params() after calling
EVP_PKEY_keygen_init().

=over 4

=item "seed" (B<OSSL_PKEY_PARAM_ML_KEM_SEED>) <octet string>

Internally, ML-KEM generates keys using a 64-byte random value (seed), which is
the concatenation of the 32-byte I<d> and I<z> parameters described in FIPS 203.
This optional parameter can be used to set a pre-determined seed prior to
keypair generation.

Generated keys default to retaining the seed used.
The seed is also by default retained when keys are loaded from B<PKCS#8> files
in the seed format.
When available, the seed parameter is also used during key export and import,
with keys (by default) regenerated from the seed even when also provided on import.
See L</Provider configuration parameters> below for related controls.

When the seed is retained, it is also available as a B<gettable> parameter,
and private key output to B<PKCS#8> files will by default include the seed.
When the seed was not initially known, or was not retained, B<PKCS#8> private
key files will contain only the private key in FIPS 203 C<dk> format.

=item "properties" (B<OSSL_PKEY_PARAM_PROPERTIES>) <UTF8 string>

Sets properties to be used when fetching algorithm implementations used for
ML-KEM hashing operations.

Use L<EVP_PKEY_CTX_set_params(3)> after calling L<EVP_PKEY_keygen_init(3)>.

=back

=head2 Encoder Parameters

=over 4

=item "output_formats" (B<OSSL_PKEY_PARAM_OUTPUT_FORMATS>) <UTF8 string>

This parameter can be used with L<OSSL_ENCODER_CTX_new_for_pkey(3)>
and L<OSSL_ENCODER_CTX_set_params(3)> to select the preferred B<PKCS#8> output
formats of a private key.
When this parameter is either not specified or empty, the behaviour is
determined by the provider configuration parameters described below.
Otherwise, it has the same syntax and behaviour as the provider configuration
B<ml-kem.output_formats> parameter, except that the B<ml-kem.retain-seed>
parameter is then ignored, i.e. the C<seed-only> and C<seed-priv> formats
remain available so long as the seed was initially known, regardless of any
setting of B<ml-kem.retain-seed>.

=back

=head2 Common parameters

In addition to the common parameters that all keytypes should support (see
L<provider-keymgmt(7)/Common Information Parameters>), B<ML-KEM> keys
support the parameters listed below.
These are gettable using
L<EVP_PKEY_get_octet_string_param(3)> or L<EVP_PKEY_get_params(3)>.
They can be initialised via L<EVP_PKEY_fromdata(3)>, and are returned by
L<EVP_PKEY_todata(3)> given a suitable I<selection>.
Once a public or private key is configured, it can no longer be modified,
nor can another key component be added.

=over 4

=item "pub" (B<OSSL_PKEY_PARAM_PUB_KEY>) <octet string>

The public key value.

This parameter is used when importing or exporting the public key value with
the EVP_PKEY_fromdata() and EVP_PKEY_todata() functions.
The key length and content is that of the FIPS 203 (Algorithm 16:
B<ML-KEM.KeyGen_internal>) B<ek> public key for the given ML-KEM variant.
Initial import aside, this parameter is otherwise only gettable.

=item "priv" (B<OSSL_PKEY_PARAM_PRIV_KEY>) <octet string>

The private key value.

This parameter is used when importing or exporting the private key value with
the EVP_PKEY_fromdata() and EVP_PKEY_todata() functions.
The key length and content is that of the FIPS 203 (Algorithm 16:
B<ML-KEM.KeyGen_internal>) B<dk> private key for the given ML-KEM variant.
Initial import aside, this parameter is otherwise only gettable.

=item "encoded-pub-key" (B<OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY>) <octet string>

Used for getting and setting the encoding of a public key.
The key format is that of B<ek> in FIPS 203, Algorithm 16:
B<ML-KEM.KeyGen_internal>.
Updates of the public and private key components are only allowed on keys that
are empty.
Once a public or private key component is set, no further changes are allowed.
This parameter is gettable and settable (once only).

=back

=head2 Provider configuration parameters

See the description of the B<-provparam> option in L<openssl(1)> to learn
how to set provider configuration parameters in the command line tools.
See L<OSSL_PROVIDER_add_conf_parameter(3)> to learn how to set provider
configuration options programmatically.

=over 4

=item C<ml-kem.import_pct_type> (B<OSSL_PKEY_PARAM_ML_KEM_IMPORT_PCT_TYPE>) <UTF8 string>

When an B<ML-KEM> key is imported as an explicit FIPS 203 B<dk> decapsulation
key, rather than a seed, a pairwise consistency test (PCT) is optionally
performed.
By default, or when this parameter is set explicitly to C<random>, the PCT
is performed with a random entropy value for the encapsulation step.
Setting the parameter to C<fixed>, still runs the test, but the encapsulation
entropy is a fixed 32 byte value.
Specifying any other value of the parameter, e.g. C<none>, skips the test.

=item C<ml-kem.retain_seed> (B<OSSL_PKEY_PARAM_ML_KEM_RETAIN_SEED>) <UTF8 string>

When set to a string representing a false boolean value (see
L<OSSL_PROVIDER_conf_get_bool(3)>), the seed will not be included when
keys are encoded to B<PKCS#8> form, unless the C<output_formats> encoder
parameter is set to a nonempty value, as described above.
The output B<PKCS#8> object will contain only the FIPS 203 C<dk> key.

=item C<ml-kem.prefer_seed> (B<OSSL_PKEY_PARAM_ML_KEM_PREFER_SEED>) <UTF8 string>

When decoding PKCS#8 objects that contain both a seed and the FIPS 203 C<dk>
private key, the seed is by default used to regenerate the key, and the
companion key is ignored.
When this configuration parameter is set to a string representing a false
boolean value (see L<OSSL_PROVIDER_conf_get_bool(3)>), the seed is ignored
(neither used to regenerate the key, nor retained), and the companion key is
used instead.

=item C<ml-kem.input_formats> (B<OSSL_PKEY_PARAM_ML_KEM_INPUT_FORMATS>) <UTF8 string>

List of enabled private key input formats when parsing PKCS#8 objects.
List elements are separated by commas and/or spaces or tabs.
The list of enabled formats can be specified in the configuration file, as seen
in the L</EXAMPLES> section below, or the via the B<-provparam> command-line
option (see also L<OSSL_PROVIDER_add_conf_parameter(3)>).

Values specified on the command-line override any configuration file settings.
By default all the supported formats are enabled.
The supported formats are:

=over 4

=item C<seed-priv>:

This format represents B<PKCS#8> objects in which both the FIPS 203 64-byte
B<(d, z)> seed and the decapsulation key B<dk> are present in the private key
as part of the DER encoding of the ASN.1 sequence:

    ML-KEM-PrivateKey ::= CHOICE {
      seed [0] IMPLICIT OCTET STRING (SIZE (64)),
      expandedKey OCTET STRING (SIZE (1632 | 2400 | 3168)),
      both SEQUENCE {
        seed OCTET STRING (SIZE (64)),
        expandedKey OCTET STRING (SIZE (1632 | 2400 | 3168)) } }

If the C<seed-priv> format is not included in the list, this format will not be
recognised on input.

=item C<seed-only>:

This format represents B<PKCS#8> objects in which only the 64-byte B<(d, z)>
seed is present in the above sequence.
If the C<seed-only> format is not included in the list, this format will not be
recognised on input.

=item C<priv-only>:

This format represents B<PKCS#8> objects in which only the FIPS 203
decapsulation key B<dk> is present in the above sequence.
If the C<priv-only> format is not included in the list, this format will not be
recognised on input.

=item C<oqskeypair>:

This format represents B<PKCS#8> objects in which the private key is a DER
encoding of an octet string containing the concatenaton of the FIPS 203
decapsulation key B<dk> and the encapsulation key B<ek>.
This encoding is used in some builds of the C<oqsprovider>.
If the C<oqskeypair> format is not included in the list, this format will not be
recognised on input.

=item C<bare-seed>:

This format represents B<PKCS#8> objects in which the private key contains
the 64-byte FIPS 203 seed B<(d, z)> without any ASN.1 encapsulation.
If the C<bare-seed> format is not included in the list, this format will not be
recognised on input.

=item C<bare-priv>:

This format represents B<PKCS#8> objects in which the private key contains
the FIPS 203 decapsulation key B<dk> without any ASN.1 encapsulation.
If the C<bare-priv> format is not included in the list, this format will not be
recognised on input.

=back

=item C<ml-kem.output_formats> (B<OSSL_PKEY_PARAM_ML_KEM_OUTPUT_FORMATS>) <UTF8 string>

Ordered list of enabled private key output formats when writing B<PKCS#8> files.
List elements are separated by commas, spaces or tabs.
The list of enabled formats can be specified in the configuration file, as seen
in the L</EXAMPLES> section below, or the via the B<-provparam> command-line
option.

This supports the same set of formats as described under C<ml-kem.input_formats>
above.
The order in which elements are listed is important, the selected format will be
the first one that is possible to output.
If the key seed is known, the first listed format will be selected.
If the key seed is not known, the first format that omits the seed will be selected.
The default order is equivalent to C<seed-priv> first and C<priv-only> second, with
both seed and key output when the seed is available, and just the
key otherwise.
If C<seed-only> is listed first, then the seed will be output without the key
when available, otherwise the output will have just the key.
If C<priv-only> is listed first, then just the key is output regardless of
whether the seed is present.
The legacy C<oqskeypair>, C<bare-seed> and C<bare-priv> formats can also be
output, by listing those first.

=back

=head1 CONFORMING TO

=over 4

=item FIPS 203

=back

=head1 EXAMPLES

An B<EVP_PKEY> context can be obtained by calling:

    EVP_PKEY_CTX *pctx =
        EVP_PKEY_CTX_new_from_name(NULL, "ML-KEM-768", NULL);

An B<ML-KEM-768> key can be generated like this:

    pkey = EVP_PKEY_Q_keygen(NULL, NULL, "ML-KEM-768");

An B<ML-KEM> private key in seed format can be converted to a key in the FIPS
203 B<dk> format by running:

    $ openssl pkey -provparam ml-kem.retain_seed=no \
        -in seed-only.pem -out priv-only.pem

To generate an, e.g., B<ML-KEM-768> key, in FIPS 203 B<dk> format, you can run:

    $ openssl genpkey -provparam ml-kem.retain_seed=no \
        -algorithm ml-kem-768 -out priv-only.pem

If you have a B<PKCS#8> file with both a seed and a key, and prefer to import the
companion key rather than the seed, you can run:

    $ openssl pkey -provparam ml-kem.prefer_seed=no \
        -in seed-priv.pem -out priv-only.pem

In the B<openssl.cnf> file, this looks like:

    openssl_conf = openssl_init

    [openssl_init]
    providers = providers_sect

    # Can be referenced in one or more provider sections
    [ml_kem_sect]
    prefer_seed = yes
    retain_seed = yes
    # OQS legacy formats disabled
    input_formats = seed-priv, seed-only, priv-only
    # Output either the seed alone, or else the key alone
    output_formats = seed-only, priv-only

    [providers_sect]
    default = default_sect
    # Or perhaps just: base = default_sect
    base = base_sect

    [default_sect]
    ml-kem = ml_kem_sect

    [base_sect]
    ml-kem = ml_kem_sect

=head1 SEE ALSO

L<openssl(1)>,
L<openssl-pkey(1)>,
L<openssl-genpkey(1)>,
L<EVP_KEYMGMT(3)>,
L<EVP_PKEY(3)>,
L<EVP_PKEY_get_raw_private_key(3)>,
L<EVP_PKEY_get_raw_public_key(3)>,
L<EVP_PKEY_get1_encoded_public_key(3)>,
L<OSSL_ENCODER_CTX_new_for_pkey(3)>,
L<OSSL_ENCODER_CTX_set_params(3)>,
L<OSSL_PROVIDER_add_conf_parameter(3)>,
L<provider-keymgmt(7)>,
L<EVP_KEM-ML-KEM(7)>

=head1 HISTORY

This functionality was added in OpenSSL 3.5.
The C<output_formats> B<OSSL_ENCODER_CTX> parameter was added in OpenSSL 4.0.

=head1 COPYRIGHT

Copyright 2024-2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.

=cut
