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- =pod
- =head1 NAME
- PKCS7_sign - create a PKCS#7 signedData structure
- =head1 SYNOPSIS
- #include <openssl/pkcs7.h>
- PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags);
- =head1 DESCRIPTION
- PKCS7_sign() creates and returns a PKCS#7 signedData structure. B<signcert>
- is the certificate to sign with, B<pkey> is the corresponsding private key.
- B<certs> is an optional additional set of certificates to include in the
- PKCS#7 structure (for example any intermediate CAs in the chain).
- The data to be signed is read from BIO B<data>.
- B<flags> is an optional set of flags.
- =head1 NOTES
- Any of the following flags (ored together) can be passed in the B<flags> parameter.
- Many S/MIME clients expect the signed content to include valid MIME headers. If
- the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are prepended
- to the data.
- If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the
- PKCS7 structure, the signer's certificate must still be supplied in the B<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 data being signed is included in the PKCS7 structure, unless B<PKCS7_DETACHED>
- is set in which case it is omitted. This is used for PKCS7 detached signatures
- which are used in S/MIME plaintext signed messages for example.
- Normally the supplied content is translated into MIME canonical format (as required
- by the S/MIME specifications) if B<PKCS7_BINARY> is set no translation occurs. This
- option should be used if the supplied data is in binary format otherwise the translation
- will corrupt it.
- 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 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.
- If the flags B<PKCS7_PARTSIGN> is set then the returned B<PKCS7> structure
- is just initialized ready to perform the signing operation. The signing
- is however B<not> performed and the data to be signed is not read from
- the B<data> parameter. Signing is deferred until after the data has been
- written. In this way data can be signed in a single pass. Currently the
- flag B<PKCS7_DETACHED> B<must> also be set.
- =head1 NOTES
- Currently the flag B<PKCS7_PARTSIGN> is only supported for detached
- data. If this flag is set the returned B<PKCS7> structure is B<not>
- complete and outputting its contents via a function that does not
- properly finalize the B<PKCS7> structure will give unpredictable
- results.
- At present only the SMIME_write_PKCS7() function properly finalizes the
- structure.
- =head1 BUGS
- PKCS7_sign() is somewhat limited. It does not support multiple signers, some
- advanced attributes such as counter signatures are not supported.
- The SHA1 digest algorithm is currently always used.
- When the signed data is not detached it will be stored in memory within the
- B<PKCS7> 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 ASN1 code.
- =head1 RETURN VALUES
- PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error occurred.
- The error can be obtained from ERR_get_error(3).
- =head1 SEE ALSO
- L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_verify(3)|PKCS7_verify(3)>
- =head1 HISTORY
- PKCS7_sign() was added to OpenSSL 0.9.5
- The B<PKCS7_PARTSIGN> flag was added in OpenSSL 0.9.8
- =cut
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