Document signature accessors.

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=head1 NAME

X509_get0_signature, X509_get_signature_nid, X509_REQ_get0_signature,

X509_REQ_get_signature_nid, X509_CRL_get0_signature,

X509_CRL_get_signature_nid - signature information.

=head1 SYNOPSIS

 #include <openssl/x509.h>

 void X509_get0_signature(ASN1_BIT_STRING **psig, X509_ALGOR **palg,

                          const X509 *x);

 int X509_get_signature_nid(const X509 *x);

 void X509_REQ_get0_signature(ASN1_BIT_STRING **psig, X509_ALGOR **palg,

                              const X509_REQ *crl);

 int X509_REQ_get_signature_nid(const X509_REQ *crl);

 void X509_CRL_get0_signature(ASN1_BIT_STRING **psig, X509_ALGOR **palg,

                              const X509_CRL *crl);

 int X509_CRL_get_signature_nid(const X509_CRL *crl);

=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_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.

=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).

=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.

=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.

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