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
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.