| =pod |
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| =head1 NAME |
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| PKCS7_sign - create a PKCS#7 signedData structure |
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| =head1 SYNOPSIS |
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| PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs, BIO *data, int flags); |
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| =head1 DESCRIPTION |
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| 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). |
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| The data to be signed is read from BIO B<data>. |
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| B<flags> is an optional set of flags. |
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| =head1 NOTES |
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| Any of the following flags (ored together) can be passed in the B<flags> parameter. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| =head1 NOTES |
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| 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. |
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| At present only the SMIME_write_PKCS7() function properly finalizes the |
| structure. |
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| =head1 BUGS |
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| PKCS7_sign() is somewhat limited. It does not support multiple signers, some |
| advanced attributes such as counter signatures are not supported. |
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| The SHA1 digest algorithm is currently always used. |
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| 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. |
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| =head1 RETURN VALUES |
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| PKCS7_sign() returns either a valid PKCS7 structure or NULL if an error occurred. |
| The error can be obtained from ERR_get_error(3). |
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| =head1 SEE ALSO |
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| L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_verify(3)|PKCS7_verify(3)> |
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| =head1 HISTORY |
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| PKCS7_sign() was added to OpenSSL 0.9.5 |
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| The B<PKCS7_PARTSIGN> flag was added in OpenSSL 0.9.8 |
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| =cut |