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104 lines
3.9 KiB
Plaintext
104 lines
3.9 KiB
Plaintext
=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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#include <openssl/pkcs7.h>
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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>
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is the certificate to sign with, B<pkey> is the corresponsding private key.
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B<certs> is an optional additional set of certificates to include in the
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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
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the B<PKCS7_TEXT> flag is set MIME headers for type B<text/plain> are prepended
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to the data.
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If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the
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PKCS7 structure, the signer's certificate must still be supplied in the B<signcert>
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parameter though. This can reduce the size of the signature if the signers certificate
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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>
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is set in which case it is omitted. This is used for PKCS7 detached signatures
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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
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by the S/MIME specifications) if B<PKCS7_BINARY> is set no translation occurs. This
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option should be used if the supplied data is in binary format otherwise the translation
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will corrupt it.
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The signedData structure includes several PKCS#7 autenticatedAttributes including
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the signing time, the PKCS#7 content type and the supported list of ciphers in
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an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no authenticatedAttributes
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will be used. If B<PKCS7_NOSMIMECAP> is set then just the SMIMECapabilities are
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omitted.
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If present the SMIMECapabilities attribute indicates support for the following
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algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any
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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
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is just initialized ready to perform the signing operation. The signing
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is however B<not> performed and the data to be signed is not read from
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the B<data> parameter. Signing is deferred until after the data has been
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written. In this way data can be signed in a single pass. Currently the
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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
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data. If this flag is set the returned B<PKCS7> structure is B<not>
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complete and outputting its contents via a function that does not
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properly finalize the B<PKCS7> structure will give unpredictable
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results.
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At present only the SMIME_write_PKCS7() function properly finalizes the
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structure.
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=head1 BUGS
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PKCS7_sign() is somewhat limited. It does not support multiple signers, some
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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
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B<PKCS7> structure. This effectively limits the size of messages which can be
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signed due to memory restraints. There should be a way to sign data without
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having to hold it all in memory, this would however require fairly major
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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.
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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
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