EVP_SIGNATURE-RSA(7ossl)

📦
version 15.1 · 3 versions
, in freebsd 15.1

💖 NAME 💖

okay so bestie, this page is EVP_SIGNATURE-RSA — the EVP_PKEY RSA signature implementation. that's it, that's the whole name. it lives in the OpenSSL 7ossl manual section and it's literally the glow-up guide for how RSA signing works under the hood. 🎀

✨ DESCRIPTION ✨

it's support for computing RSA signatures. periodt. 💅

if you need the tea on RSA keys themselves (like, the actual key objects, not the signing bit), that's a different page — go read EVP_PKEY-RSA(7). 🦋

🌈 Algorithm Names

okay so in this list, the names are grouped together to signify that they're the same algorithm just with multiple names. no cap. and yes — that grouping also includes the OID in canonical decimal form, which (fun fact) means you can totally fetch them if all your caller has is a bare OID that came out in this form after a call to OBJ_obj2txt(3). iykyk. 👑

⚠️ heads up bestie — it can't be used with EVP_PKEY_sign_message_init(3). don't try it. 💀
  • "RSA-RIPEMD160", "ripemd160WithRSA", "1.3.36.3.3.1.2"
  • "RSA-SHA2-256", "RSA-SHA256", "sha256WithRSAEncryption", "1.2.840.113549.1.1.11"
  • "RSA-SHA2-384", "RSA-SHA384", "sha384WithRSAEncryption", "1.2.840.113549.1.1.12"
  • "RSA-SHA2-512", "RSA-SHA512", "sha512WithRSAEncryption", "1.2.840.113549.1.1.13"
  • "RSA-SHA2-224", "RSA-SHA224", "sha224WithRSAEncryption", "1.2.840.113549.1.1.14"
  • "RSA-SHA2-512/224", "RSA-SHA512-224", "sha512-224WithRSAEncryption", "1.2.840.113549.1.1.15"
  • "RSA-SHA2-512/256", "RSA-SHA512-256", "sha512-256WithRSAEncryption", "1.2.840.113549.1.1.16"
  • "RSA-SHA3-224", "id-rsassa-pkcs1-v1_5-with-sha3-224", "2.16.840.1.101.3.4.3.13"
  • "RSA-SHA3-256", "id-rsassa-pkcs1-v1_5-with-sha3-256", "2.16.840.1.101.3.4.3.14"
  • "RSA-SHA3-384", "id-rsassa-pkcs1-v1_5-with-sha3-384", "2.16.840.1.101.3.4.3.15"
  • "RSA-SHA3-512", "id-rsassa-pkcs1-v1_5-with-sha3-512", "2.16.840.1.101.3.4.3.16"
  • "RSA-SM3", "sm3WithRSAEncryption", "1.2.156.10197.1.504"

so those last batch — from "RSA-RIPEMD160" all the way down to "RSA-SM3" — are the PKCS#1 v1.5 RSA signature schemes with a whole diverse squad of message digest algorithms. 🫶 they are all supported explicitly fetched with EVP_PKEY_sign_init_ex2(3) and EVP_PKEY_sign_message_init(3). and they are all pre-set to use the pad mode "pkcs1".

💀 and that pad mode cannot be changed. it's giving "no notes, this is the final answer". don't come for it, it's not switching up for you. periodt.

🧚 Signature Parameters

the following signature parameters can be set using EVP_PKEY_CTX_set_params(). 🌸

you can call this after EVP_PKEY_sign_init() or EVP_PKEY_verify_init(), and before calling EVP_PKEY_sign() or EVP_PKEY_verify(). you can also set them using EVP_PKEY_sign_init_ex() or EVP_PKEY_verify_init_ex(). so many doors, same room, love that for us. 💜

  • "digest" (OSSL_SIGNATURE_PARAM_DIGEST) <UTF8 string>
  • "properties" (OSSL_SIGNATURE_PARAM_PROPERTIES) <UTF8 string>
btw these two are not supported with the RSA signature schemes that already include a message digest algorithm — go look back up at "Algorithm Names", bestie, it's right there. 👀

these common parameters are described in provider-signature(7).

  • "pad-mode" (OSSL_SIGNATURE_PARAM_PAD_MODE) <UTF8 string> — the type of padding to be used. its value can be one of these:
    • "none" (OSSL_PKEY_RSA_PAD_MODE_NONE)
    • "pkcs1" (OSSL_PKEY_RSA_PAD_MODE_PKCSV15)
    • "x931" (OSSL_PKEY_RSA_PAD_MODE_X931)
      • ⚠️ this padding mode is no longer supported by the FIPS provider for signature generation, but it may be used for signature verification for legacy use cases. (this is a FIPS 140-3 requirement — not us being dramatic, it's literally the rules.) 😭
    • "pss" (OSSL_PKEY_RSA_PAD_MODE_PSS)
  • "mgf1-digest" (OSSL_SIGNATURE_PARAM_MGF1_DIGEST) <UTF8 string> — the digest algorithm name to use for the maskGenAlgorithm used by "pss" mode. 🌟
  • "mgf1-properties" (OSSL_SIGNATURE_PARAM_MGF1_PROPERTIES) <UTF8 string> — sets the name of the property query associated with the "mgf1-digest" algorithm. NULL is used if this optional value is not set. 🦋
  • "saltlen" (OSSL_SIGNATURE_PARAM_PSS_SALTLEN) <integer> or <UTF8 string> — the "pss" mode minimum salt length. the value can either be an integer, a string value representing a number, or one of these iconic string values:
    • "digest" (OSSL_PKEY_RSA_PSS_SALT_LEN_DIGEST) — use the same length as the digest size. 🎀
    • "max" (OSSL_PKEY_RSA_PSS_SALT_LEN_MAX) — use the maximum salt length. 🔥
    • "auto" (OSSL_PKEY_RSA_PSS_SALT_LEN_AUTO) — auto detect the salt length. ✨
    • "auto-digestmax" (OSSL_PKEY_RSA_PSS_SALT_LEN_AUTO_DIGEST_MAX) — auto detect the salt length when verifying. maximize the salt length up to the digest size when signing, to comply with FIPS 186-4 section 5.5. 📋

the OpenSSL FIPS provider also supports the following parameters, bestie, keep up:

  • "key-check" (OSSL_SIGNATURE_PARAM_FIPS_KEY_CHECK) <integer>
  • "digest-check" (OSSL_SIGNATURE_PARAM_FIPS_DIGEST_CHECK) <integer>
  • "sign-x931-pad-check" (OSSL_SIGNATURE_PARAM_FIPS_SIGN_X931_PAD_CHECK) <integer>

these parameters are described in provider-signature(7). 🫶

  • "rsa-pss-saltlen-check" (OSSL_SIGNATURE_PARAM_FIPS_RSA_PSS_SALTLEN_CHECK) <integer> — the default value of 1 causes an error during signature generation or verification if salt length (OSSL_SIGNATURE_PARAM_PSS_SALTLEN) is not between zero and the output block size of the digest function (inclusive). setting this to zero will ignore the error and set the approved "fips-indicator" to 0.
🚨 and listen — this option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0. like, actually. not a vibe. be careful. 🙈

the following signature parameters can be retrieved using EVP_PKEY_CTX_get_params(). 👑

  • "algorithm-id" (OSSL_SIGNATURE_PARAM_ALGORITHM_ID) <octet string>
  • "fips-indicator" (OSSL_SIGNATURE_PARAM_FIPS_APPROVED_INDICATOR) <integer>
  • "verify-message" (OSSL_SIGNATURE_PARAM_FIPS_VERIFY_MESSAGE <integer>

these common parameter are described in provider-signature(7). (yes, the original says "parameter" singular, we're leaving it, it's camp 💅)

  • "digest" (OSSL_SIGNATURE_PARAM_DIGEST) <UTF8 string>
  • "pad-mode" (OSSL_SIGNATURE_PARAM_PAD_MODE) <UTF8 string>
  • "mgf1-digest" (OSSL_SIGNATURE_PARAM_MGF1_DIGEST) <UTF8 string>
  • "saltlen" (OSSL_SIGNATURE_PARAM_PSS_SALTLEN) <integer> or <UTF8 string>

these parameters are as described above. ⬆️ scroll up bestie, they're the same ones, we're just reading them back now. 🍓

🌸 SEE ALSO 🌸

go read these next, they're all linked in the group chat:

Copyright 2020-2026 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 <https://www.openssl.org/source/license.html>. 🌈

okay that's the whole page, you ate that. this was OpenSSL 3.5.6, dated 2026-04-07 — mwah, go sign something. 💅✨🎀

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