X509_SIGN(3)

NAME
X509_sign, X509_sign_ctx, X509_REQ_sign, X509_REQ_sign_ctx, X509_ACERT_sign, X509_ACERT_sign_ctx, X509_CRL_sign, X509_CRL_sign_ctx - sign certificate, certificate request, or CRL signature

SYNOPSIS
 #include <openssl/x509.h>

 int X509_sign(X509 *x, EVP_PKEY *pkey, const EVP_MD *md);
 int X509_sign_ctx(X509 *x, EVP_MD_CTX *ctx);

 int X509_REQ_sign(X509_REQ *x, EVP_PKEY *pkey, const EVP_MD *md);
 int X509_REQ_sign_ctx(X509_REQ *x, EVP_MD_CTX *ctx);

 int X509_CRL_sign(X509_CRL *x, EVP_PKEY *pkey, const EVP_MD *md);
 int X509_CRL_sign_ctx(X509_CRL *x, EVP_MD_CTX *ctx);

 #include <openssl/x509_acert.h>

 int X509_ACERT_sign(X509_ACERT *x, EVP_PKEY *pkey, const EVP_MD *md);
 int X509_ACERT_sign_ctx(X509_ACERT *x, EVP_MD_CTX *ctx);

DESCRIPTION
X509_sign() signs certificate x using private key pkey and message digest md and sets the signature in x. X509_sign_ctx() also signs certificate x but uses the parameters contained in digest context ctx. If the certificate information includes X.509 extensions, these two functions make sure that the certificate bears X.509 version 3.

X509_REQ_sign(), X509_REQ_sign_ctx(), X509_ACERT_sign(), X509_ACERT_sign_ctx(), X509_CRL_sign(), and X509_CRL_sign_ctx() sign certificate requests and CRLs, respectively.

NOTES
X509_sign_ctx() is used where the default parameters for the corresponding public key and digest are not suitable. It can be used to sign keys using RSA-PSS for example.

For efficiency reasons and to work around ASN.1 encoding issues the encoding of the signed portion of a certificate, certificate request and CRL is cached internally. If the signed portion of the structure is modified the encoding is not always updated meaning a stale version is sometimes used. This is not normally a problem because modifying the signed portion will invalidate the signature and signing will always update the encoding.

When signing X509 certificates and certificate requests, any empty subjectKeyIdentifier (empty string) or authorityKeyIdentifier (empty sequence) extensions are flagged as an error and the signature operation fails.

RETURN VALUES
All functions return the size of the signature in bytes for success and zero for failure.

SEE ALSO
ERR_get_error(3), X509_NAME_add_entry_by_txt(3), X509_new(3), X509_verify_cert(3), X509_verify(3), X509_REQ_verify_ex(3), X509_REQ_verify(3), X509_CRL_verify(3)

HISTORY
The X509_sign(), X509_REQ_sign() and X509_CRL_sign() functions are available in all versions of OpenSSL.

The X509_sign_ctx(), X509_REQ_sign_ctx() and X509_CRL_sign_ctx() functions were added in OpenSSL 1.0.1.

The X509_ACERT_sign() and X509_ACERT_sign_ctx() functions were added in OpenSSL 3.4.

COPYRIGHT
Copyright 2015-2026 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>.