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=head1 NAME

CMS_get0_SignerInfos, CMS_SignerInfo_get0_signer_id, CMS_SignerInfo_get0_signature, CMS_SignerInfo_cert_cmp, CMS_set1_signer_cert - CMS signedData signer functions.

=head1 SYNOPSIS

 #include <openssl/cms.h>

 STACK_OF(CMS_SignerInfo) *CMS_get0_SignerInfos(CMS_ContentInfo *cms);

 int CMS_SignerInfo_get0_signer_id(CMS_SignerInfo *si, ASN1_OCTET_STRING **keyid, X509_NAME **issuer, ASN1_INTEGER **sno);
 ASN1_OCTET_STRING *CMS_SignerInfo_get0_signature(CMS_SignerInfo *si);
 int CMS_SignerInfo_cert_cmp(CMS_SignerInfo *si, X509 *cert);
 void CMS_SignerInfo_set1_signer_cert(CMS_SignerInfo *si, X509 *signer);

=head1 DESCRIPTION

The function CMS_get0_SignerInfos() returns all the CMS_SignerInfo structures
associated with a CMS signedData structure.

CMS_SignerInfo_get0_signer_id() retrieves the certificate signer identifier
associated with a specific CMS_SignerInfo structure B<si>. Either the
keyidentifier will be set in B<keyid> or B<both> issuer name and serial number
in B<issuer> and B<sno>.

CMS_SignerInfo_get0_signature() retrieves the signature associated with 
B<si> in a pointer to an ASN1_OCTET_STRING structure. This pointer returned
corresponds to the internal signature value if B<si> so it may be read or
modified.

CMS_SignerInfo_cert_cmp() compares the certificate B<cert> against the signer
identifier B<si>. It returns zero if the comparison is successful and non zero
if not.

CMS_SignerInfo_set1_signer_cert() sets the signers certificate of B<si> to
B<signer>.

=head1 NOTES

The main purpose of these functions is to enable an application to lookup
signers certificates using any appropriate technique when the simpler method
of CMS_verify() is not appropriate.

In typical usage and application will retrieve all CMS_SignerInfo structures
using CMS_get0_SignerInfo() and retrieve the identifier information using
CMS. It will then obtain the signer certificate by some unspecified means
(or return and error if it cannot be found) and set it using
CMS_SignerInfo_set1_signer_cert().

Once all signer certificates have been set CMS_verify() can be used.

Although CMS_get0_SignerInfos() can return NULL is an error occur B<or> if
there are no signers this is not a problem in practice because the only
error which can occur is if the B<cms> structure is not of type signedData
due to application error.

=head1 RETURN VALUES

CMS_get0_SignerInfos() returns all CMS_SignerInfo structures, or NULL there
are no signers or an error occurs.

CMS_SignerInfo_get0_signer_id() returns 1 for success and 0 for failure.

CMS_SignerInfo_cert_cmp() returns 0 for a successful comparison and non
zero otherwise.

CMS_SignerInfo_set1_signer_cert() does not return a value.

Any error can be obtained from L<ERR_get_error(3)>

=head1 SEE ALSO

L<ERR_get_error(3)>, L<CMS_verify(3)>

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