NetBSD/lib/libcrypto/man/PKCS7_sign.3

.\"	$NetBSD: PKCS7_sign.3,v 1.3 2005/03/26 03:26:46 christos Exp $
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.\" ========================================================================
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.IX Title "PKCS7_sign 3"
.TH PKCS7_sign 3 "2003-07-24" "0.9.7f" "OpenSSL"
.SH "NAME"
PKCS7_sign \- create a PKCS#7 signedData structure
.SH "LIBRARY"
libcrypto, -lcrypto
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
\&\s-1PKCS7\s0 *PKCS7_sign(X509 *signcert, \s-1EVP_PKEY\s0 *pkey, \s-1STACK_OF\s0(X509) *certs, \s-1BIO\s0 *data, int flags);
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fIPKCS7_sign()\fR creates and returns a PKCS#7 signedData structure. \fBsigncert\fR
is the certificate to sign with, \fBpkey\fR is the corresponsding private key.
\&\fBcerts\fR is an optional additional set of certificates to include in the
PKCS#7 structure (for example any intermediate CAs in the chain). 
.PP
The data to be signed is read from \s-1BIO\s0 \fBdata\fR.
.PP
\&\fBflags\fR is an optional set of flags.
.SH "NOTES"
.IX Header "NOTES"
Any of the following flags (ored together) can be passed in the \fBflags\fR parameter.
.PP
Many S/MIME clients expect the signed content to include valid \s-1MIME\s0 headers. If
the \fB\s-1PKCS7_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are prepended
to the data.
.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 data being signed is included in the \s-1PKCS7\s0 structure, unless \fB\s-1PKCS7_DETACHED\s0\fR 
is set in which case it is omitted. This is used for \s-1PKCS7\s0 detached signatures
which are used in S/MIME plaintext signed messages for example.
.PP
Normally the supplied content is translated into \s-1MIME\s0 canonical format (as required
by the S/MIME specifications) if \fB\s-1PKCS7_BINARY\s0\fR is set no translation occurs. This
option should be used if the supplied data is in binary format otherwise the translation
will corrupt it.
.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.
.SH "BUGS"
.IX Header "BUGS"
\&\fIPKCS7_sign()\fR is somewhat limited. It does not support multiple signers, some
advanced attributes such as counter signatures are not supported.
.PP
The \s-1SHA1\s0 digest algorithm is currently always used.
.PP
When the signed data is not detached it will be stored in memory within the
\&\fB\s-1PKCS7\s0\fR structure. This effectively limits the size of messages which can be
signed due to memory restraints. There should be a way to sign data without
having to hold it all in memory, this would however require fairly major
revisions of the OpenSSL \s-1ASN1\s0 code.
.PP
Clear text signing does not store the content in memory but the way \fIPKCS7_sign()\fR
operates means that two passes of the data must typically be made: one to compute
the signatures and a second to output the data along with the signature. There
should be a way to process the data with only a single pass.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fIPKCS7_sign()\fR returns either a valid \s-1PKCS7\s0 structure or \s-1NULL\s0 if an error occurred.
The error can be obtained from \fIERR_get_error\fR\|(3).
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIERR_get_error\fR\|(3), \fIPKCS7_verify\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
\&\fIPKCS7_sign()\fR was added to OpenSSL 0.9.5