=pod

=head1 NAME

EVP_PKEY-LMS, EVP_KEYMGMT-LMS, LMS
- EVP_PKEY Leighton-Micali Signature (LMS) keytype and algorithm support

=head1 DESCRIPTION

The B<LMS> keytype is implemented in OpenSSL's default and FIPS providers.
The OpenSSL providers only support LMS signature verification, as this is a
[SP 800-208](https://csrc.nist.gov/pubs/sp/800/208/final) requirement for
FIPS software modules.

=head2 Common LMS parameters

LMS public keys are encoded in XDR format (i.e. not ASN1 format).
The following parameters are used by EVP_PKEY_fromdata() and by the
LMS keymanager for import and export.

=over 4

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

Used for getting and setting the encoding of an LMS public key. The public key
is expected to be in XDR format.

=back

The following parameters is gettable using EVP_PKEY_get_utf8_string_param().

=over 4

=item "mandatory-digest" (B<OSSL_PKEY_PARAM_MANDATORY_DIGEST>) <UTF8 string>

The empty string, signifying that no digest may be specified.

=back

=head1 CONFORMING TO

=over 4

=item RFC 8554

Leighton-Micali Hash-Based Signatures

=item NIST SP800-208

Recommendation for Stateful Hash-Based Signature Schemes

=item CNSA 2.0

Commercial National Security Algorithm Suite

=back

=head1 NOTES

LMS support is disabled by default at compile-time.
To enable it, specify the B<enable-lms> build configuration option.

=head1 EXAMPLES

NOTE error checking has been omitted in these examples

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

    EVP_PKEY_CTX *ctx = EVP_PKEY_CTX_new_from_name(libctx, "LMS", propq);

An B<LMS> public key can be loaded simply like this:

     EVP_PKEY *pkey = NULL;
     OSSL_DECODER_CTX *dctx = NULL;
     int selection = OSSL_KEYMGMT_SELECT_PUBLIC_KEY;

     dctx = OSSL_DECODER_CTX_new_for_pkey(&pkey, "XDR", NULL,
                                          "LMS", selection, libctx, propq);
     ret = OSSL_DECODER_from_bio(dctx, bio);
     OSSL_DECODER_CTX_free(dctx);

To load a LMS key from XDR encoded "data" of size "datalen":

    EVP_PKEY *key = NULL;
    OSSL_PARAM params[2];

    params[0] =
        OSSL_PARAM_construct_octet_string(OSSL_PKEY_PARAM_ENCODED_PUBLIC_KEY,
                                          (unsigned char *)data, datalen);
    params[1] = OSSL_PARAM_construct_end();
    ret = EVP_PKEY_fromdata_init(ctx)
    ret = EVP_PKEY_fromdata(ctx, &key, EVP_PKEY_PUBLIC_KEY, params);

=head1 SEE ALSO

L<EVP_KEYMGMT(3)>,
L<EVP_PKEY(3)>,
L<EVP_SIGNATURE-LMS(7)>,
L<provider-keymgmt(7)>

=head1 HISTORY

This functionality was added in OpenSSL 3.6.
The gettable "mandatory-digest" and support for loading LMS public keys in
SubjectPublicKeyInfo format was added in OpenSSL 4.0.

=head1 COPYRIGHT

Copyright 2025-2026 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
