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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" EVP_SIGNATURE\-SLH\-DSA, EVP_SIGNATURE\-SLH\-DSA\-SHA2\-128s, EVP_SIGNATURE\-SLH\-DSA\-SHA2\-128f, EVP_SIGNATURE\-SLH\-DSA\-SHA2\-192s, EVP_SIGNATURE\-SLH\-DSA\-SHA2\-192f, EVP_SIGNATURE\-SLH\-DSA\-SHA2\-256s, EVP_SIGNATURE\-SLH\-DSA\-SHA2\-256f, EVP_SIGNATURE\-SLH\-DSA\-SHAKE\-128s, EVP_SIGNATURE\-SLH\-DSA\-SHAKE\-128f, EVP_SIGNATURE\-SLH\-DSA\-SHAKE\-192s, EVP_SIGNATURE\-SLH\-DSA\-SHAKE\-192f, EVP_SIGNATURE\-SLH\-DSA\-SHAKE\-256s, EVP_SIGNATURE\-SLH\-DSA\-SHAKE\-256f \&\- EVP_PKEY SLH\-DSA support .SH "DESCRIPTION" .IX Header "DESCRIPTION" The \fBSLH\-DSA\-SHA2\-128s\fR, \fBEVP_PKEY\-SLH\-DSA\-SHA2\-128f\fR, \&\fBSLH\-DSA\-SHA2\-192s\fR, \fBEVP_PKEY\-SLH\-DSA\-SHA2\-192f\fR, \&\fBSLH\-DSA\-SHA2\-256s\fR, \fBEVP_PKEY\-SLH\-DSA\-SHA2\-256f\fR, \&\fBSLH\-DSA\-SHAKE\-128s\fR, \fBEVP_PKEY\-SLH\-DSA\-SHAKE\-128f\fR, \&\fBSLH\-DSA\-SHAKE\-192s\fR, \fBEVP_PKEY\-SLH\-DSA\-SHAKE\-192f\fR, \&\fBSLH\-DSA\-SHAKE\-256s\fR and \fBEVP_PKEY\-SLH\-DSA\-SHAKE\-256f\fR \s-1EVP_PKEY\s0 implementations supports key generation, one-shot sign and verify using the SLH-DSA signature schemes described in \s-1FIPS 205.\s0 .PP The different algorithms names correspond to the parameter sets defined in \&\s-1FIPS 205\s0 Section 11 Table 2. \&\f(CW\*(C`s\*(C'\fR types have smaller signature sizes, and the \f(CW\*(C`f\*(C'\fR variants are faster, (The signatures range from ~8K to ~50K depending on the type chosen). There are 3 different security categories also depending on the type. .PP \&\fIEVP_SIGNATURE_fetch\fR\|(3) can be used to explicitely fetch one of the 12 algorithms which can then be used with \fIEVP_PKEY_sign_message_init\fR\|(3), \&\fIEVP_PKEY_sign\fR\|(3), \fIEVP_PKEY_verify_message_init\fR\|(3), and \&\fIEVP_PKEY_verify\fR\|(3) to perform one-shot message signing or verification. .PP The normal signing process (called Pure SLH-DSA Signature Generation) encodes the message internally as 0x00 || len(ctx) || ctx || message. where \fBctx\fR is some optional value of size 0x00..0xFF. OpenSSL also allows the message to not be encoded which is required for testing. OpenSSL does not support Pre Hash SLH-DSA Signature Generation, but this may be done by the user by doing Pre hash encoding externally and then chosing the option to not encode the message. .SS "SLH-DSA Signature Parameters" .IX Subsection "SLH-DSA Signature Parameters" The \f(CW\*(C`context\-string\*(C'\fR parameter, described below, can be used for both signing and verification. It may be set by passing an \s-1OSSL_PARAM\s0 array to \fIEVP_PKEY_sign_init_ex2\fR\|(3) or \&\fIEVP_PKEY_verify_init_ex2\fR\|(3) .ie n .IP """context-string"" (\fB\s-1OSSL_SIGNATURE_PARAM_CONTEXT_STRING\s0\fR) " 4 .el .IP "``context-string'' (\fB\s-1OSSL_SIGNATURE_PARAM_CONTEXT_STRING\s0\fR) " 4 .IX Item "context-string (OSSL_SIGNATURE_PARAM_CONTEXT_STRING) " A string of octets with length at most 255. By default it is the empty string. .PP The following parameters can be used when signing: They can be set by passing an \s-1OSSL_PARAM\s0 array to \fIEVP_PKEY_sign_init_ex2\fR\|(3). .ie n .IP """message-encoding"" (\fB\s-1OSSL_SIGNATURE_PARAM_MESSAGE_ENCODING\s0\fR) " 4 .el .IP "``message-encoding'' (\fB\s-1OSSL_SIGNATURE_PARAM_MESSAGE_ENCODING\s0\fR) " 4 .IX Item "message-encoding (OSSL_SIGNATURE_PARAM_MESSAGE_ENCODING) " The default value of 1 uses 'Pure SLH-DSA Signature Generation' as described above. Setting it to 0 does not encode the message, which is used for testing, but can also be used for 'Pre Hash SLH-DSA Signature Generation'. .ie n .IP """test-entropy"" (\fB\s-1OSSL_SIGNATURE_PARAM_TEST_ENTROPY\s0 " 4 .el .IP "``deterministic'' (\fB\s-1OSSL_SIGNATURE_PARAM_DETERMINISTIC\s0\fR) " 4 .IX Item "deterministic (OSSL_SIGNATURE_PARAM_DETERMINISTIC) " The default value of 0 generates a random value (using a \s-1DRBG\s0) this is used when processing the message. Setting this to 1 causes the private key seed to be used instead. This value is ignored if \*(L"test-entropy\*(R" is set. .PP See \s-1\fIEVP_PKEY\-SLH\-DSA\s0\fR\|(7) for information related to \fBSLH-DSA\fR keys. .SH "NOTES" .IX Header "NOTES" For backwards compatibility reasons \fIEVP_DigestSignInit_ex()\fR, \fIEVP_DigestSign()\fR, \&\fIEVP_DigestVerifyInit_ex()\fR and \fIEVP_DigestVerify()\fR may also be used, but the digest passed in \fImdname\fR must be \s-1NULL.\s0 .SH "EXAMPLES" .IX Header "EXAMPLES" To sign a message using an SLH-DSA \s-1EVP_PKEY\s0 structure: .PP .Vb 10 \& void do_sign(EVP_PKEY *key, unsigned char *msg, size_t msg_len) \& { \& size_t sig_len; \& unsigned char *sig = NULL; \& const OSSL_PARAM params[] = { \& OSSL_PARAM_octet_string("context\-string", (unsigned char *)"A context string", 33), \& OSSL_PARAM_END \& }; \& EVP_PKEY_CTX *sctx = EVP_PKEY_CTX_new_from_pkey(NULL, pkey, NULL); \& EVP_SIGNATURE *sig_alg = EVP_SIGNATURE_fetch(NULL, "SLH\-DSA\-SHA2\-128s", NULL); \& \& EVP_PKEY_sign_message_init(sctx, sig_alg, params); \& /* Calculate the required size for the signature by passing a NULL buffer. */ \& EVP_PKEY_sign(sctx, NULL, &sig_len, msg, msg_len); \& sig = OPENSSL_zalloc(sig_len); \& EVP_PKEY_sign(sctx, sig, &sig_len, msg, msg_len); \& ... \& OPENSSL_free(sig); \& EVP_SIGNATURE(sig_alg); \& EVP_PKEY_CTX_free(sctx); \& } .Ve .SH "SEE ALSO" .IX Header "SEE ALSO" \&\s-1\fIEVP_PKEY\-SLH\-DSA\s0\fR\|(7) \&\fIprovider\-signature\fR\|(7), \&\fIEVP_PKEY_sign\fR\|(3), \&\fIEVP_PKEY_verify\fR\|(3), .SH "HISTORY" .IX Header "HISTORY" This functionality was added in OpenSSL 3.5. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2024\-2025 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at .