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=head1 NAME

PKCS7_sign_add_signer,
PKCS7_add_certificate, PKCS7_add_crl - add information to PKCS7 structure

=head1 SYNOPSIS

 #include <openssl/pkcs7.h>

 PKCS7_SIGNER_INFO *PKCS7_sign_add_signer(PKCS7 *p7, X509 *signcert,
                                          EVP_PKEY *pkey, const EVP_MD *md, int flags);
 int PKCS7_add_certificate(PKCS7 *p7, X509 *cert);
 int PKCS7_add_crl(PKCS7 *p7, X509_CRL *crl);

=head1 DESCRIPTION

PKCS7_sign_add_signer() adds a signer with certificate I<signcert> and private
key I<pkey> using message digest I<md> to a PKCS7 signed data structure I<p7>.

The B<PKCS7> structure should be obtained from an initial call to PKCS7_sign()
with the flag B<PKCS7_PARTIAL> set or in the case or re-signing a valid PKCS#7
signed data structure.

If the I<md> parameter is NULL then the default digest for the public
key algorithm will be used.

Unless the B<PKCS7_REUSE_DIGEST> flag is set the returned B<PKCS7> structure
is not complete and must be finalized either by streaming (if applicable) or
a call to PKCS7_final().


=head1 NOTES

The main purpose of this function is to provide finer control over a PKCS#7
signed data structure where the simpler PKCS7_sign() function defaults are
not appropriate. For example if multiple signers or non default digest
algorithms are needed.

Any of the following flags (ored together) can be passed in the I<flags>
parameter.

If B<PKCS7_REUSE_DIGEST> is set then an attempt is made to copy the content
digest value from the B<PKCS7> structure: to add a signer to an existing structure.
An error occurs if a matching digest value cannot be found to copy. The
returned B<PKCS7> structure will be valid and finalized when this flag is set.

If B<PKCS7_PARTIAL> is set in addition to B<PKCS7_REUSE_DIGEST> then the
B<PKCS7_SIGNER_INO> structure will not be finalized so additional attributes
can be added. In this case an explicit call to PKCS7_SIGNER_INFO_sign() is
needed to finalize it.

If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the
B<PKCS7> structure, the signer's certificate must still be supplied in the
I<signcert> parameter though. This can reduce the size of the signature if the
signers certificate can be obtained by other means: for example a previously
signed message.

The signedData structure includes several PKCS#7 authenticatedAttributes
including the signing time, the PKCS#7 content type and the supported list of
ciphers in an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no
authenticatedAttributes will be used. If B<PKCS7_NOSMIMECAP> is set then just
the SMIMECapabilities are omitted.

If present the SMIMECapabilities attribute indicates support for the following
algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any of
these algorithms is disabled then it will not be included.

PKCS7_sign_add_signers() returns an internal pointer to the B<PKCS7_SIGNER_INFO>
structure just added, which can be used to set additional attributes
before it is finalized.

PKCS7_add_certificate() adds to the B<PKCS7> structure I<p7> the certificate
I<cert>, which may be an end-entity (signer) certificate
or a CA certificate useful for chain building.
This is done internally by L<PKCS7_sign_ex(3)> and similar signing functions.
It may have to be used before calling L<PKCS7_verify(3)>
in order to provide any missing certificate(s) needed for verification.

PKCS7_add_crl() adds the CRL I<crl> to the B<PKCS7> structure I<p7>.
This may be called to provide certificate status information
to be included when signing or to use when verifying the B<PKCS7> structure.

=head1 RETURN VALUES

PKCS7_sign_add_signers() returns an internal pointer to the B<PKCS7_SIGNER_INFO>
structure just added or NULL if an error occurs.

PKCS7_add_certificate() and PKCS7_add_crl() return 1 on success, 0 on error.

=head1 SEE ALSO

L<ERR_get_error(3)>, L<PKCS7_sign_ex(3)>,
L<PKCS7_final(3)>, L<PKCS7_verify(3)>

=head1 HISTORY

The PPKCS7_sign_add_signer() function was added in OpenSSL 1.0.0.

=head1 COPYRIGHT

Copyright 2007-2022 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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