1=pod 2 3=head1 NAME 4 5PKCS7_sign - create a PKCS#7 signedData structure 6 7=head1 SYNOPSIS 8 9PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags); 10 11=head1 DESCRIPTION 12 13PKCS7_sign() creates and returns a PKCS#7 signedData structure. B<signcert> 14is the certificate to sign with, B<pkey> is the corresponsding private key. 15B<certs> is an optional additional set of certificates to include in the 16PKCS#7 structure (for example any intermediate CAs in the chain). 17 18The data to be signed is read from BIO B<data>. 19 20B<flags> is an optional set of flags. 21 22=head1 NOTES 23 24Any of the following flags (ored together) can be passed in the B<flags> parameter. 25 26Many S/MIME clients expect the signed content to include valid MIME headers. If 27the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are prepended 28to the data. 29 30If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the 31PKCS7 structure, the signer's certificate must still be supplied in the B<signcert> 32parameter though. This can reduce the size of the signature if the signers certificate 33can be obtained by other means: for example a previously signed message. 34 35The data being signed is included in the PKCS7 structure, unless B<PKCS7_DETACHED> 36is set in which case it is omitted. This is used for PKCS7 detached signatures 37which are used in S/MIME plaintext signed messages for example. 38 39Normally the supplied content is translated into MIME canonical format (as required 40by the S/MIME specifications) if B<PKCS7_BINARY> is set no translation occurs. This 41option should be used if the supplied data is in binary format otherwise the translation 42will corrupt it. 43 44The signedData structure includes several PKCS#7 autenticatedAttributes including 45the signing time, the PKCS#7 content type and the supported list of ciphers in 46an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no authenticatedAttributes 47will be used. If B<PKCS7_NOSMIMECAP> is set then just the SMIMECapabilities are 48omitted. 49 50If present the SMIMECapabilities attribute indicates support for the following 51algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any 52of these algorithms is disabled then it will not be included. 53 54If the flags B<PKCS7_PARTSIGN> is set then the returned B<PKCS7> structure 55is just initialized ready to perform the signing operation. The signing 56is however B<not> performed and the data to be signed is not read from 57the B<data> parameter. Signing is deferred until after the data has been 58written. In this way data can be signed in a single pass. Currently the 59flag B<PKCS7_DETACHED> B<must> also be set. 60 61=head1 NOTES 62 63Currently the flag B<PKCS7_PARTSIGN> is only supported for detached 64data. If this flag is set the returned B<PKCS7> structure is B<not> 65complete and outputting its contents via a function that does not 66properly finalize the B<PKCS7> structure will give unpredictable 67results. 68 69At present only the SMIME_write_PKCS7() function properly finalizes the 70structure. 71 72=head1 BUGS 73 74PKCS7_sign() is somewhat limited. It does not support multiple signers, some 75advanced attributes such as counter signatures are not supported. 76 77The SHA1 digest algorithm is currently always used. 78 79When the signed data is not detached it will be stored in memory within the 80B<PKCS7> structure. This effectively limits the size of messages which can be 81signed due to memory restraints. There should be a way to sign data without 82having to hold it all in memory, this would however require fairly major 83revisions of the OpenSSL ASN1 code. 84 85 86=head1 RETURN VALUES 87 88PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error occurred. 89The error can be obtained from ERR_get_error(3). 90 91=head1 SEE ALSO 92 93L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_verify(3)|PKCS7_verify(3)> 94 95=head1 HISTORY 96 97PKCS7_sign() was added to OpenSSL 0.9.5 98 99The B<PKCS7_PARTSIGN> flag was added in OpenSSL 0.9.8 100 101=cut 102