=pod =head1 NAME PKCS7_sign - create a PKCS#7 signedData structure =head1 SYNOPSIS 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. =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. Clear text signing does not store the content in memory but the way PKCS7_sign() 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. =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 =cut