DSA_sign(3) | OpenSSL | DSA_sign(3)

# NAME

DSA_sign, DSA_sign_setup, DSA_verify - DSA signatures

# SYNOPSIS

     #include <openssl/dsa.h>

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):

     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

All of the functions described on this page are deprecated. Applications should instead use EVP_PKEY_sign_init(3), EVP_PKEY_sign(3), EVP_PKEY_verify_init(3) and EVP_PKEY_verify(3).

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. sigret must point to DSA_size(dsa) bytes of memory.

DSA_sign_setup() is defined only for backward binary compatibility and should not be used. 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.

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.

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.

# 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).

# CONFORMING TO

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

# SEE ALSO

DSA_new(3), ERR_get_error(3), RAND_bytes(3), DSA_do_sign(3), RAND(7)

# HISTORY

All of these functions were deprecated in OpenSSL 3.0.

# COPYRIGHT

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>.

2026-06-09 | 3.5.7