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[dragonfly.git] / secure / lib / libcrypto / man / PKCS7_sign.3
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138.\" ======================================================================
139.\"
140.IX Title "PKCS7_sign 3"
141.TH PKCS7_sign 3 "0.9.7a" "2003-02-19" "OpenSSL"
142.UC
143.SH "NAME"
144PKCS7_sign \- create a PKCS#7 signedData structure
145.SH "SYNOPSIS"
146.IX Header "SYNOPSIS"
147\&\s-1PKCS7\s0 *PKCS7_sign(X509 *signcert, \s-1EVP_PKEY\s0 *pkey, STACK_OF(X509) *certs, \s-1BIO\s0 *data, int flags);
148.SH "DESCRIPTION"
149.IX Header "DESCRIPTION"
150\&\fIPKCS7_sign()\fR creates and returns a PKCS#7 signedData structure. \fBsigncert\fR
151is the certificate to sign with, \fBpkey\fR is the corresponsding private key.
152\&\fBcerts\fR is an optional additional set of certificates to include in the
153PKCS#7 structure (for example any intermediate CAs in the chain).
154.PP
155The data to be signed is read from \s-1BIO\s0 \fBdata\fR.
156.PP
157\&\fBflags\fR is an optional set of flags.
158.SH "NOTES"
159.IX Header "NOTES"
160Any of the following flags (ored together) can be passed in the \fBflags\fR parameter.
161.PP
162Many S/MIME clients expect the signed content to include valid \s-1MIME\s0 headers. If
163the \fB\s-1PKCS7_TEXT\s0\fR flag is set \s-1MIME\s0 headers for type \fBtext/plain\fR are prepended
164to the data.
165.PP
166If \fB\s-1PKCS7_NOCERTS\s0\fR is set the signer's certificate will not be included in the
167\&\s-1PKCS7\s0 structure, the signer's certificate must still be supplied in the \fBsigncert\fR
168parameter though. This can reduce the size of the signature if the signers certificate
169can be obtained by other means: for example a previously signed message.
170.PP
171The data being signed is included in the \s-1PKCS7\s0 structure, unless \fB\s-1PKCS7_DETACHED\s0\fR
172is set in which case it is omitted. This is used for \s-1PKCS7\s0 detached signatures
173which are used in S/MIME plaintext signed messages for example.
174.PP
175Normally the supplied content is translated into \s-1MIME\s0 canonical format (as required
176by the S/MIME specifications) if \fB\s-1PKCS7_BINARY\s0\fR is set no translation occurs. This
177option should be used if the supplied data is in binary format otherwise the translation
178will corrupt it.
179.PP
180The signedData structure includes several PKCS#7 autenticatedAttributes including
181the signing time, the PKCS#7 content type and the supported list of ciphers in
182an SMIMECapabilities attribute. If \fB\s-1PKCS7_NOATTR\s0\fR is set then no authenticatedAttributes
183will be used. If \fB\s-1PKCS7_NOSMIMECAP\s0\fR is set then just the SMIMECapabilities are
184omitted.
185.PP
186If present the SMIMECapabilities attribute indicates support for the following
187algorithms: 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
188of these algorithms is disabled then it will not be included.
189.SH "BUGS"
190.IX Header "BUGS"
191\&\fIPKCS7_sign()\fR is somewhat limited. It does not support multiple signers, some
192advanced attributes such as counter signatures are not supported.
193.PP
194The \s-1SHA1\s0 digest algorithm is currently always used.
195.PP
196When the signed data is not detached it will be stored in memory within the
197\&\fB\s-1PKCS7\s0\fR structure. This effectively limits the size of messages which can be
198signed due to memory restraints. There should be a way to sign data without
199having to hold it all in memory, this would however require fairly major
200revisions of the OpenSSL \s-1ASN1\s0 code.
201.PP
202Clear text signing does not store the content in memory but the way \fIPKCS7_sign()\fR
203operates means that two passes of the data must typically be made: one to compute
204the signatures and a second to output the data along with the signature. There
205should be a way to process the data with only a single pass.
206.SH "RETURN VALUES"
207.IX Header "RETURN VALUES"
208\&\fIPKCS7_sign()\fR returns either a valid \s-1PKCS7\s0 structure or \s-1NULL\s0 if an error occurred.
209The error can be obtained from \fIERR_get_error\fR\|(3).
210.SH "SEE ALSO"
211.IX Header "SEE ALSO"
212ERR_get_error(3), PKCS7_verify(3)
213.SH "HISTORY"
214.IX Header "HISTORY"
215\&\fIPKCS7_sign()\fR was added to OpenSSL 0.9.5