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=head1 NAME

X509_sign, X509_sign_ctx, X509_verify, X509_REQ_sign, X509_REQ_sign_ctx,
X509_REQ_verify, X509_CRL_sign, X509_CRL_sign_ctx, X509_CRL_verify -
sign or verify 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_verify(X509 *a, EVP_PKEY *r);

 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_REQ_verify(X509_REQ *a, EVP_PKEY *r);

 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);
 int X509_CRL_verify(X509_CRL *a, EVP_PKEY *r);

=head1 DESCRIPTION

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

X509_verify() verifies the signature of certificate B<x> using public key
B<pkey>. Only the signature is checked: no other checks (such as certificate
chain validity) are perfored.

X509_REQ_sign(), X509_REQ_sign_ctx(), X509_REQ_verify(),
X509_CRL_sign(), X509_CRL_sign_ctx() and X509_CRL_verify() sign and verify
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.

=head1 RETURN VALUES

X509_sign(), X509_sign_ctx(), X509_REQ_sign(), X509_REQ_sign_ctx(),
X509_CRL_sign() and X509_CRL_sign_ctx() return the size of the signature
in bytes for success and zero for failure.

X509_verify(), X509_REQ_verify() and X509_CRL_verify() return 1 if the
signature is valid and 0 if the signature check fails. If the signature
could not be checked at all because it was invalid or some other error
occurred then -1 is returned.

=head1 SEE ALSO

L<d2i_X509(3)>,
L<ERR_get_error(3)>,
L<X509_CRL_get0_by_serial(3)>,
L<X509_get0_signature(3)>,
L<X509_get_ext_d2i(3)>,
L<X509_get_extension_flags(3)>,
L<X509_get_pubkey(3)>,
L<X509_get_subject_name(3)>,
L<X509_get_version(3)>,
L<X509_NAME_add_entry_by_txt(3)>,
L<X509_NAME_ENTRY_get_object(3)>,
L<X509_NAME_get_index_by_NID(3)>,
L<X509_NAME_print_ex(3)>,
L<X509_new(3)>,
L<X509V3_get_d2i(3)>,
L<X509_verify_cert(3)>

=head1 HISTORY

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

X509_sign_ctx(), X509_REQ_sign_ctx() and X509_CRL_sign_ctx() were first added
to OpenSSL 1.0.1.

=head1 COPYRIGHT

Copyright 2015-2016 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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>.

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