DSA_DO_SIGN(3) | Library Functions Manual | DSA_DO_SIGN(3)

# NAME

`DSA_do_sign`, `DSA_do_verify` — raw DSA signature operations

# SYNOPSIS

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

DSA_SIG *
`DSA_do_sign`(const unsigned char *dgst, int dlen, DSA *dsa);

int
`DSA_do_verify`(const unsigned char *dgst, int dgst_len, DSA_SIG *sig, DSA *dsa);

# DESCRIPTION

`DSA_do_sign`() computes a digital signature on the dlen byte message digest dgst using the private key dsa and returns it in a newly allocated DSA_SIG structure.

DSA_sign_setup(3) may be used to precompute part of the signing operation in case signature generation is time-critical.

`DSA_do_verify`() verifies that the signature sig matches a given message digest dgst of size dgst_len. dsa is the signer's public key.

# RETURN VALUES

`DSA_do_sign`() returns the signature or `NULL` on error. `DSA_do_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_get0_key(3), DSA_meth_set_sign(3), DSA_new(3), DSA_SIG_new(3), DSA_sign(3)

# HISTORY

`DSA_do_sign`() and `DSA_do_verify`() first appeared in OpenSSL 0.9.3 and have been available since OpenBSD 2.6.

June 8, 2025 | Debian