=pod

=head1 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

=head1 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);

=head1 DESCRIPTION

X509_sign() signs certificate I<x> using private key I<pkey> and message
digest I<md> and sets the signature in I<x>. X509_sign_ctx() also signs
certificate I<x> but uses the parameters contained in digest context I<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.

=head1 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 B<empty>
subjectKeyIdentifier (empty string) or authorityKeyIdentifier (empty sequence)
extensions are flagged as an error and the signature operation fails.

=head1 RETURN VALUES

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

=head1 SEE ALSO

L<ERR_get_error(3)>,
L<X509_NAME_add_entry_by_txt(3)>,
L<X509_new(3)>,
L<X509_verify_cert(3)>,
L<X509_verify(3)>,
L<X509_REQ_verify_ex(3)>, L<X509_REQ_verify(3)>,
L<X509_CRL_verify(3)>

=head1 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.

=head1 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
L<https://www.openssl.org/source/license.html>.

=cut
