X509_GET0_SIGNATURE(3) | Library Functions Manual | X509_GET0_SIGNATURE(3)

# NAME

`X509_get0_signature`, `X509_REQ_get0_signature`, `X509_CRL_get0_signature`, `X509_get0_tbs_sigalg`, `X509_CRL_get0_tbs_sigalg`, `X509_get_signature_type`, `X509_get_signature_nid`, `X509_REQ_get_signature_nid`, `X509_CRL_get_signature_nid`, `X509_get_signature_info` — signature information

# SYNOPSIS

library “libcrypto”
`#include <openssl/x509.h>`

void
`X509_get0_signature`(const ASN1_BIT_STRING **psig, const X509_ALGOR **palg, const X509 *x);

void
`X509_REQ_get0_signature`(const X509_REQ *req, const ASN1_BIT_STRING **psig, const X509_ALGOR **palg);

void
`X509_CRL_get0_signature`(const X509_CRL *crl, const ASN1_BIT_STRING **psig, const X509_ALGOR **palg);

const X509_ALGOR *
`X509_get0_tbs_sigalg`(const X509 *x);

const X509_ALGOR *
`X509_CRL_get0_tbs_sigalg`(const X509_CRL *crl);

int
`X509_get_signature_type`(const X509 *x);

int
`X509_get_signature_nid`(const X509 *x);

int
`X509_REQ_get_signature_nid`(const X509_REQ *req);

int
`X509_CRL_get_signature_nid`(const X509_CRL *crl);

int
`X509_get_signature_info`(X509 *x, int *md_nid, int *pkey_nid, int *security_bits, uint32_t *flags);

# DESCRIPTION

`X509_get0_signature`(), `X509_REQ_get0_signature`(), and `X509_CRL_get0_signature`() set *psig to the signature and *palg to the signature algorithm of x, req, or crl, respectively. `X509_get0_tbs_sigalg`() and `X509_CRL_get0_tbs_sigalg`() return the signature algorithm in the signed portion of x or crl, respectively. The values returned are internal pointers that must not be freed by the caller.

`X509_get_signature_type`() returns the base NID corresponding to the signature algorithm of x just like EVP_PKEY_base_id(3) does.

`X509_get_signature_nid`(), `X509_REQ_get_signature_nid`(), and `X509_CRL_get_signature_nid`() return the NID corresponding to the signature algorithm of x, req, or crl, respectively, just like EVP_PKEY_id(3) does.

`X509_get_signature_info`() retrieves information about the signature of certificate x. The NID of the digest algorithm is written to *md_nid, the public key algorithm to *pkey_nid, the effective security bits to *security_bits, and flag details to *flags. Any of the output parameters can be set to `NULL` if the information is not required. If flags is not a `NULL` pointer, *flags is set to the bitwise OR of:

`X509_SIG_INFO_VALID`
  No error occurred. This flag is set if `X509_get_signature_info`() returns 1.
`X509_SIG_INFO_TLS`
  The signature algorithm is appropriate for use in TLS. For a supported EdDSA algorithm (in LibreSSL this is Ed25519) this flag is always set. For an RSASSA-PSS PSS algorithm this flag is set if the parameters are DER encoded, the digest algorithm is one of SHA-256, SHA-384, or SHA-512, the same digest algorithm is used in the mask generation function, and the salt length is equal to the digest algorithm's output length. For all other signature algorithms this flag is set if the digest algorithm is one of SHA-1, SHA-256, SHA-384, or SHA-512.

`X509_get_signature_info`() returns 1 on success and 0 on failure. Failure conditions include unsupported signature algorithms, certificate parsing errors and memory allocation failure.

These functions provide lower level access to the signature for cases where an application wishes to analyse or generate a signature in a form where X509_sign(3) is not appropriate, for example in a non-standard or unsupported format.

# SEE ALSO

EVP_PKEY_base_id(3), OBJ_obj2nid(3), X509_ALGOR_new(3), X509_CRL_get0_by_serial(3), X509_CRL_new(3), X509_get_pubkey(3), X509_get_subject_name(3), X509_get_version(3), X509_new(3), X509_REQ_new(3), X509_sign(3), X509_signature_dump(3), X509_verify_cert(3)

# HISTORY

`X509_get_signature_type`() first appeared in SSLeay 0.8.0 and has been available since OpenBSD 2.4.

`X509_get0_signature`() and `X509_get_signature_nid`() first appeared in OpenSSL 1.0.2. `X509_REQ_get0_signature`(), `X509_CRL_get0_signature`(), `X509_get0_tbs_sigalg`(), `X509_REQ_get_signature_nid`(), and `X509_CRL_get_signature_nid`() first appeared in OpenSSL 1.1.0. All these functions have been available since OpenBSD 6.3.

`X509_CRL_get0_tbs_sigalg`() first appeared in LibreSSL 3.7.1 and has been available since OpenBSD 7.3.

`X509_get_signature_info`() first appeared in OpenSSL 1.1.1 and has been available since OpenBSD 7.6.

# CAVEATS

The security bits returned by `X509_get_signature_info`() refer to the information available from the certificate signature (such as the signing digest). In some cases the actual security of the signature is smaller because the signing key is less secure. For example in a certificate signed using SHA-512 and a 1024-bit RSA key.

# BUGS

The signatures of `X509_get0_signature`(), `X509_REQ_get0_signature`(), and `X509_CRL_get0_signature`() are inconsistent.

July 6, 2025 | Debian