DSA_SIGN(3)

📦 version 4.4.0, in alpine 3.24, arch rolling

💖 DSA_SIGN(3) — the DSA signatures glow-up 💖

ok so bestie, you're reading the Library Functions Manual page for DSA_sign, DSA_sign_setup, and DSA_verify — three little functions that do that whole digital-signature thing for DSA. let's get into it 🫶

✨ NAME ✨

DSA_sign, DSA_sign_setup, DSA_verify — DSA signatures, literally the whole point of this page 💅

🌸 SYNOPSIS 🌸

       library “libcrypto” #include <openssl/dsa.h>

       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);

like, copy it exactly, no typos, it's giving header-file supremacy 🎀

💜 DESCRIPTION 💜

🦋 DSA_sign() — the main character 🦋

so DSA_sign() computes a digital signature on the len byte message digest dgst using the private key dsa, and it places its ASN.1 DER encoding at sigret. length of the signature goes in *siglen. and here's the ✨iconic✨ little detail: sigret must point to DSA_size(dsa) bytes of memory. no skipping that, it's non-negotiable 🫶

🧚 DSA_sign_setup() — pregame era 🧚

DSA_sign_setup() may be used to precompute part of the signing operation in case signature generation is time-critical. like, bestie is in a rush, we get it ⏱️

it expects dsa to contain DSA parameters. it places the precomputed values in newly allocated BIGNUMs at *kinvp and *rp, after freeing the old ones — unless kinvp and rp are NULL. 👀 these values may be passed to DSA_sign() in dsa->kinv and dsa->r. and ctx is a pre-allocated BN_CTX or NULL.

🌈 DSA_verify() — the vibe check 🌈

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. it's checking IDs at the door, periodt 🔥

and the type parameter? ignored. not even invited to the party. 💀

⭐ RETURN VALUES ⭐

  • DSA_sign() and DSA_sign_setup() — return 1 on success or 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 read that one if you need the tea ☕

🎀 SEE ALSO 🎀

iykyk, go click through them 💅

🌟 STANDARDS 🌟

US Federal Information Processing Standard FIPS 186 (Digital Signature Standard, DSS), ANSI X9.30. very official, very federal, very slay 🎖️

💫 HISTORY 💫

DSA_sign() and DSA_verify() first appeared in SSLeay 0.6.0. DSA_sign_setup() first appeared in SSLeay 0.8.0. all these functions have been available since OpenBSD 2.4. elders of the group chat fr fr 🧓✨

ok that's the whole page, you ate that 🍓

Debian 💖 June 8, 2025 💖 that's the version and the date, mwah, bye bestie 🫶

📦 where this page comes from