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.\" ========================================================================
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.IX Title "PKCS7_sign_add_signer 3"
.TH PKCS7_sign_add_signer 3 "2019-12-20" "1.0.2u" "OpenSSL"
.SH "NAME"
PKCS7_sign_add_signer \- add a signer PKCS7 signed data structure.
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/pkcs7.h>
.Ve
.PP
.Vb 1
\& PKCS7_SIGNER_INFO *PKCS7_sign_add_signer(PKCS7 *p7, X509 *signcert, EVP_PKEY *pkey, const EVP_MD *md, int flags);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIPKCS7_sign_add_signer()\fR adds a signer with certificate \fBsigncert\fR and private
key \fBpkey\fR using message digest \fBmd\fR to a \s-1PKCS7\s0 signed data structure
\&\fBp7\fR.
.PP
The \s-1PKCS7\s0 structure should be obtained from an initial call to \fIPKCS7_sign()\fR
with the flag \fB\s-1PKCS7_PARTIAL\s0\fR set or in the case or re-signing a valid \s-1PKCS7\s0
signed data structure.
.PP
If the \fBmd\fR parameter is \fB\s-1NULL\s0\fR then the default digest for the public
key algorithm will be used.
.PP
Unless the \fB\s-1PKCS7_REUSE_DIGEST\s0\fR flag is set the returned \s-1PKCS7\s0 structure
is not complete and must be finalized either by streaming (if applicable) or
a call to \fIPKCS7_final()\fR.
.SH "NOTES"
.IX Header "NOTES"
The main purpose of this function is to provide finer control over a PKCS#7
signed data structure where the simpler \fIPKCS7_sign()\fR function defaults are
not appropriate. For example if multiple signers or non default digest
algorithms are needed.
.PP
Any of the following flags (ored together) can be passed in the \fBflags\fR
parameter.
.PP
If \fB\s-1PKCS7_REUSE_DIGEST\s0\fR is set then an attempt is made to copy the content
digest value from the \s-1PKCS7\s0 struture: to add a signer to an existing structure.
An error occurs if a matching digest value cannot be found to copy. The
returned \s-1PKCS7\s0 structure will be valid and finalized when this flag is set.
.PP
If \fB\s-1PKCS7_PARTIAL\s0\fR is set in addition to \fB\s-1PKCS7_REUSE_DIGEST\s0\fR then the 
\&\fB\s-1PKCS7_SIGNER_INO\s0\fR structure will not be finalized so additional attributes
can be added. In this case an explicit call to \fIPKCS7_SIGNER_INFO_sign()\fR is
needed to finalize it.
.PP
If \fB\s-1PKCS7_NOCERTS\s0\fR is set the signer's certificate will not be included in the
\&\s-1PKCS7\s0 structure, the signer's certificate must still be supplied in the
\&\fBsigncert\fR 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.
.PP
The signedData structure includes several PKCS#7 autenticatedAttributes
including the signing time, the PKCS#7 content type and the supported list of
ciphers in an SMIMECapabilities attribute. If \fB\s-1PKCS7_NOATTR\s0\fR is set then no
authenticatedAttributes will be used. If \fB\s-1PKCS7_NOSMIMECAP\s0\fR is set then just
the SMIMECapabilities are omitted.
.PP
If present the SMIMECapabilities attribute indicates support for the following
algorithms: triple \s-1DES\s0, 128 bit \s-1RC2\s0, 64 bit \s-1RC2\s0, \s-1DES\s0 and 40 bit \s-1RC2\s0. If any of
these algorithms is disabled then it will not be included.
.PP
\&\fIPKCS7_sign_add_signers()\fR returns an internal pointer to the \s-1PKCS7_SIGNER_INFO\s0
structure just added, this can be used to set additional attributes 
before it is finalized.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIPKCS7_sign_add_signers()\fR returns an internal pointer to the \s-1PKCS7_SIGNER_INFO\s0
structure just added or \s-1NULL\s0 if an error occurs.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIERR_get_error\fR\|(3), \fIPKCS7_sign\fR\|(3),
\&\fIPKCS7_final\fR\|(3),
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIPPKCS7_sign_add_signer()\fR was added to OpenSSL 1.0.0