DSA_SIGN(3ossl)

📦
version 15.1 · 3 versions
, in freebsd 15.1

💜 DSA_SIGN — bestie's guide to DSA signatures 💜

okay so this is the DSA_sign(3ossl) page from the OpenSSL manual, and honestly? it's a little bit of a ✨legacy era✨ page. we're talking DSA signatures, and specifically the trio DSA_sign, DSA_sign_setup, and DSA_verify. heads up bestie: all three are deprecated, so this is more of a "for your information, iykyk" situation than a "go use this right now" situation. let's get into it 🫶

🌸 SYNOPSIS 🌸

first things first, you gotta include the header:

#include <openssl/dsa.h>
🚨 important vibe check: the following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value — see openssl_user_macros(7) for the deets.

here are the signatures, exactly as written, no cap:

int DSA_sign(int type, const unsigned char *dgst, int len,
             unsigned char *sigret, unsigned int *siglen, DSA *dsa);

int DSA_sign_setup(DSA *dsa, BN_CTX *ctx, BIGNUM **kinvp, BIGNUM **rp);

int DSA_verify(int type, const unsigned char *dgst, int len,
               unsigned char *sigbuf, int siglen, DSA *dsa);

🦋 DESCRIPTION 🦋

so like, all of the functions described on this page are deprecated. not me being dramatic, that's literally what the page says 😭. applications should instead use EVP_PKEY_sign_init(3), EVP_PKEY_sign(3), EVP_PKEY_verify_init(3) and EVP_PKEY_verify(3). those are the main characters now 👑.

DSA_sign() computes a digital signature on the len byte message digest dgst using the private key dsa, and places its ASN.1 DER encoding at sigret. the length of the signature is places in *siglen (yes, that's how the original words it — i'm keeping it, we don't edit the source material 💅). and listen: sigret must point to DSA_size(dsa) bytes of memory. don't skimp on the buffer, bestie.

DSA_sign_setup() is defined only for backward binary compatibility and should not be used. like, at all. since OpenSSL 1.1.0 the DSA type is opaque and the output of DSA_sign_setup() cannot be used anyway: calling this function will only cause overhead, and does not affect the actual signature (pre-)computation. so it's giving "decorative" 💀. it does nothing useful, it just costs you.

DSA_verify() verifies that the signature sigbuf of size siglen matches a given message digest dgst of size len. dsa is the signer's public key. slay, verification icon 🔥.

the type parameter is ignored. literally ignored. we don't look at it. 🙈

⚠️ also important: the random generator must be seeded when DSA_sign() (or DSA_sign_setup()) is called. if the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to external circumstances (see RAND(7)), the operation will fail. no seed, no signature, periodt.

🎀 RETURN VALUES 🎀

  • DSA_sign() and DSA_sign_setup() — return 1 on success, 0 on error.
  • DSA_verify() — returns 1 for a valid signature, 0 for an incorrect signature and -1 on error.

the error codes can be obtained by ERR_get_error(3). go get 'em 🧚

⭐ CONFORMING TO ⭐

  • US Federal Information Processing Standard FIPS186-4 (Digital Signature Standard, DSS)
  • ANSI X9.30

standards queen behavior honestly 🌈

💖 SEE ALSO 💖

🌸 HISTORY 🌸

all of these functions were deprecated in OpenSSL 3.0. that's the whole history section. short and bittersweet 🥲

copyright 2000-2021 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>.

and that's the whole page bestie 🫶 mwah 💋 — this was 3.5.6, dated 2026-04-07, and the manual page name is DSA_SIGN(3ossl). stay seeded out there ✨💜

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