DSA_SIGN(3) | Library Functions Manual | DSA_SIGN(3)

# NAME

`DSA_sign`, `DSA_sign_setup`, `DSA_verify` — DSA signatures

# 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);

# DESCRIPTION

`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 placed in *siglen. sigret must point to `DSA_size`(dsa) bytes of memory.

`DSA_sign_setup`() may be used to precompute part of the signing operation in case signature generation is time-critical. 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. ctx is a pre-allocated BN_CTX or `NULL`.

`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.

The type parameter is ignored.

# 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).

# SEE ALSO

DSA_do_sign(3), DSA_get0_key(3), DSA_new(3)

# STANDARDS

US Federal Information Processing Standard FIPS 186 (Digital Signature Standard, DSS), ANSI X9.30

# 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.

June 8, 2025 | Debian