=pod

=head1 NAME

EVP_SIGNATURE-LMS
- The EVP_PKEY B<LMS> signature implementation

=head1 DESCRIPTION

The B<LMS> EVP_PKEY implementation supports Leighton-Micali Signatures (LMS)
described in [RFC 8554](https://datatracker.ietf.org/doc/html/rfc8854)
and [SP 800-208](https://csrc.nist.gov/pubs/sp/800/208/final).
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.

EVP_PKEY_verify_message_init() and EVP_PKEY_verify() are the only supported
functions used for LMS signatures. Streaming is not currently supported,
and since the signature data contains data related to the digest used, functions
that specify the digest name are not necessary.

=head1 NOTES

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

For backwards compatibility reasons EVP_DigestVerifyInit_ex() and
EVP_DigestVerify() may also be used, but the digest passed in I<mdname> must be NULL.

LMS should only be used for older deployments.
New deployments should use either L<EVP_SIGNATURE-ML-DSA(7)>
or <L/EVP_SIGNATURE-SLH-DSA(7)>.

=head1 EXAMPLES

Error checking has been omitted from the following examples

=head2 LMS signature verification

 /* See L<EVP_PKEY-LMS(7)/EXAMPLES for an example of loading a LMS |pub| key */
 ctx = EVP_PKEY_CTX_new_from_pkey(libctx, pub, propq);
 sig = EVP_SIGNATURE_fetch(libctx, "LMS", propq);
 EVP_PKEY_verify_message_init(ctx, sig, NULL);
 /*
  * EVP_PKEY_verify_message_update() and EVP_PKEY_verify_message_final()
  * are not supported
  */
 ret = EVP_PKEY_verify(ctx, sigdata, sigdata_len, msg, msglen);
 /*
  * ret == 1 indicates success, 0 verify failure and < 0 for some
  * other error.
  */

=head1 SEE ALSO

L<EVP_PKEY-LMS(7)>,
L<provider-signature(7)>,

=head1 HISTORY

This functionality was added in OpenSSL 3.6.
Support for EVP_DigestVerifyInit_ex() and  EVP_DigestVerify() 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
