EVP_SIGNATURE-RSA(7ossl)

📦
version 3.5.9 · 8 versions
, in alpine 3.23, alpine 3.24

💖 EVP_SIGNATURE-RSA 💖

okay so this is the OpenSSL manual page EVP_SIGNATURE-RSA from the 7ossl section — it's giving "the RSA signature glow-up in EVP_PKEY" and honestly? iconic. sit down bestie, we're learning 💅

✨ NAME ✨

EVP_SIGNATURE-RSA — the EVP_PKEY RSA signature implementation. yes, the whole implementation. main character energy fr fr 🌟

🦋 DESCRIPTION 🦋

So basically this is all the support for computing RSA signatures. if you wanna know about RSA keys themselves (like, the actual key situation), that's a different page, go look at EVP_PKEY-RSA(7) 🫶

🌸 Algorithm Names 🌸

okay so in this list, names are grouped together to signify that they're the same algorithm having multiple names. that also includes the OID in canonical decimal form — which lowkey means they're possible to fetch if the caller has a mere OID that came out in this form after a call to OBJ_obj2txt(3) 👑

  • "RSA", "rsaEncryption", "1.2.840.113549.1.1.1" — the base signature algorithm. supported explicitly fetched with EVP_PKEY_sign_init_ex2(3), and implicitly fetched (through RSA keys) with EVP_DigestSignInit(3) and EVP_DigestVerifyInit(3). it can't be used with EVP_PKEY_sign_message_init(3) — nope, not happening, not today 💀
  • "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"

^ all the ones in that big group are PKCS#1 v1.5 RSA signature schemes with diverse message digest algorithms 🧚 they're all supported explicitly fetched with EVP_PKEY_sign_init_ex2(3) and EVP_PKEY_sign_message_init(3). they're all pre-set to use the pad mode "pkcs1". and this cannot be changed — periodt, no take-backs 🙅‍♀️

🎀 Signature Parameters 🎀

okay so these following signature parameters can be set using EVP_PKEY_CTX_set_params(). you can call that after EVP_PKEY_sign_init() or EVP_PKEY_verify_init(), and before calling EVP_PKEY_sign() or EVP_PKEY_verify(). they may also be set using EVP_PKEY_sign_init_ex() or EVP_PKEY_verify_init_ex() ✨

  • "digest" (OSSL_SIGNATURE_PARAM_DIGEST) <UTF8 string>
  • "properties" (OSSL_SIGNATURE_PARAM_PROPERTIES) <UTF8 string>

so these two are not supported with the RSA signature schemes that already include a message digest algorithm — see "Algorithm Names" above 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 the following:
    • "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 — rules are 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 the following 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:

  • "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.
⚠️ ngl this one's serious: this option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0. like, actually breaks it. 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) 🌈

  • "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, obviously 💅

🔥 SEE ALSO 🔥

EVP_PKEY_CTX_set_params(3), EVP_PKEY_sign(3), EVP_PKEY_verify(3), provider-signature(7) 🦋

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>.

aaand that's the page bestie 🎀 version 3.5.9, dated 2026-09-29 — from the EVP_SIGNATURE-RSA(7ossl) era of OpenSSL. go forth and sign responsibly, i'm obsessed with you fr fr 💖✨

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