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=head1 NAME

X509_get0_signature, X509_get_signature_nid, X509_get0_tbs_sigalg,
X509_REQ_get0_signature, X509_REQ_get_signature_nid, X509_CRL_get0_signature,
X509_CRL_get_signature_nid, X509_get_signature_info, X509_SIG_INFO_get,
X509_SIG_INFO_set - signature information

=head1 SYNOPSIS

 #include <openssl/x509.h>

 void X509_get0_signature(const ASN1_BIT_STRING **psig,
                          const X509_ALGOR **palg,
                          const X509 *x);
 int X509_get_signature_nid(const X509 *x);
 const X509_ALGOR *X509_get0_tbs_sigalg(const X509 *x);

 void X509_REQ_get0_signature(const X509_REQ *crl,
                              const ASN1_BIT_STRING **psig,
                              const X509_ALGOR **palg);
 int X509_REQ_get_signature_nid(const X509_REQ *crl);

 void X509_CRL_get0_signature(const X509_CRL *crl,
                              const ASN1_BIT_STRING **psig,
                              const X509_ALGOR **palg);
 int X509_CRL_get_signature_nid(const X509_CRL *crl);

 int X509_get_signature_info(X509 *x, int *mdnid, int *pknid, int *secbits,
                             uint32_t *flags);

 int X509_SIG_INFO_get(const X509_SIG_INFO *siginf, int *mdnid, int *pknid,
                      int *secbits, uint32_t *flags);
 void X509_SIG_INFO_set(X509_SIG_INFO *siginf, int mdnid, int pknid,
                        int secbits, uint32_t flags);

=head1 DESCRIPTION

X509_get0_signature() sets B<*psig> to the signature of B<x> and B<*palg>
to the signature algorithm of B<x>. The values returned are internal
pointers which B<MUST NOT> be freed up after the call.

X509_get0_tbs_sigalg() returns the signature algorithm in the signed
portion of B<x>.

X509_get_signature_nid() returns the NID corresponding to the signature
algorithm of B<x>.

X509_REQ_get0_signature(), X509_REQ_get_signature_nid()
X509_CRL_get0_signature() and X509_CRL_get_signature_nid() perform the
same function for certificate requests and CRLs.

X509_get_signature_info() retrieves information about the signature of
certificate B<x>. The NID of the signing digest is written to B<*mdnid>,
the public key algorithm to B<*pknid>, the effective security bits to
B<*secbits> and flag details to B<*flags>. Any of the parameters can
be set to B<NULL> if the information is not required.

X509_SIG_INFO_get() and X509_SIG_INFO_set() get and set information
about a signature in an B<X509_SIG_INFO> structure. They are only
used by implementations of algorithms which need to set custom
signature information: most applications will never need to call
them.

=head1 NOTES

These functions provide lower level access to signatures in certificates
where an application wishes to analyse or generate a signature in a form
where X509_sign() et al is not appropriate (for example a non standard
or unsupported format).

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

=head1 RETURN VALUES

X509_get_signature_nid(), X509_REQ_get_signature_nid() and
X509_CRL_get_signature_nid() return a NID.

X509_get0_signature(), X509_REQ_get0_signature() and
X509_CRL_get0_signature() do not return values.

X509_get_signature_info() returns 1 if the signature information
returned is valid or 0 if the information is not available (e.g.
unknown algorithms or malformed parameters).

=head1 SEE ALSO

L<d2i_X509(3)>,
L<ERR_get_error(3)>,
L<X509_CRL_get0_by_serial(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<X509_sign(3)>,
L<X509V3_get_d2i(3)>,
L<X509_verify_cert(3)>

=head1 HISTORY

X509_get0_signature() and X509_get_signature_nid() were first added to
OpenSSL 1.0.2.

X509_REQ_get0_signature(), X509_REQ_get_signature_nid(),
X509_CRL_get0_signature() and X509_CRL_get_signature_nid() were first added
to OpenSSL 1.1.0.

=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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