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101 lines
3.9 KiB
101 lines
3.9 KiB
=pod |
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=head1 NAME |
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CMS_add1_signer, CMS_SignerInfo_sign - add a signer to a CMS_ContentInfo signed data structure. |
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=head1 SYNOPSIS |
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#include <openssl/cms.h> |
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CMS_SignerInfo *CMS_add1_signer(CMS_ContentInfo *cms, X509 *signcert, EVP_PKEY *pkey, const EVP_MD *md, unsigned int flags); |
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int CMS_SignerInfo_sign(CMS_SignerInfo *si); |
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=head1 DESCRIPTION |
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CMS_add1_signer() adds a signer with certificate B<signcert> and private |
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key B<pkey> using message digest B<md> to CMS_ContentInfo SignedData |
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structure B<cms>. |
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The CMS_ContentInfo structure should be obtained from an initial call to |
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CMS_sign() with the flag B<CMS_PARTIAL> set or in the case or re-signing a |
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valid CMS_ContentInfo SignedData structure. |
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If the B<md> parameter is B<NULL> then the default digest for the public |
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key algorithm will be used. |
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Unless the B<CMS_REUSE_DIGEST> flag is set the returned CMS_ContentInfo |
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structure is not complete and must be finalized either by streaming (if |
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applicable) or a call to CMS_final(). |
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The CMS_SignerInfo_sign() function will explicitly sign a CMS_SignerInfo |
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structure, its main use is when B<CMS_REUSE_DIGEST> and B<CMS_PARTIAL> flags |
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are both set. |
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=head1 NOTES |
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The main purpose of CMS_add1_signer() is to provide finer control |
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over a CMS signed data structure where the simpler CMS_sign() function defaults |
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are not appropriate. For example if multiple signers or non default digest |
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algorithms are needed. New attributes can also be added using the returned |
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CMS_SignerInfo structure and the CMS attribute utility functions or the |
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CMS signed receipt request functions. |
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Any of the following flags (ored together) can be passed in the B<flags> |
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parameter. |
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If B<CMS_REUSE_DIGEST> is set then an attempt is made to copy the content |
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digest value from the CMS_ContentInfo structure: to add a signer to an existing |
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structure. An error occurs if a matching digest value cannot be found to copy. |
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The returned CMS_ContentInfo structure will be valid and finalized when this |
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flag is set. |
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If B<CMS_PARTIAL> is set in addition to B<CMS_REUSE_DIGEST> then the |
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CMS_SignerInfo structure will not be finalized so additional attributes |
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can be added. In this case an explicit call to CMS_SignerInfo_sign() is |
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needed to finalize it. |
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If B<CMS_NOCERTS> is set the signer's certificate will not be included in the |
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CMS_ContentInfo structure, the signer's certificate must still be supplied in |
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the B<signcert> parameter though. This can reduce the size of the signature if |
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the signers certificate can be obtained by other means: for example a |
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previously signed message. |
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The SignedData structure includes several CMS signedAttributes including the |
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signing time, the CMS content type and the supported list of ciphers in an |
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SMIMECapabilities attribute. If B<CMS_NOATTR> is set then no signedAttributes |
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will be used. If B<CMS_NOSMIMECAP> is set then just the SMIMECapabilities are |
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omitted. |
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OpenSSL will by default identify signing certificates using issuer name |
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and serial number. If B<CMS_USE_KEYID> is set it will use the subject key |
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identifier value instead. An error occurs if the signing certificate does not |
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have a subject key identifier extension. |
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If present the SMIMECapabilities attribute indicates support for the following |
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algorithms in preference order: 256 bit AES, Gost R3411-94, Gost 28147-89, 192 |
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bit AES, 128 bit AES, triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. |
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If any of these algorithms is not available then it will not be included: for example the GOST algorithms will not be included if the GOST ENGINE is |
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not loaded. |
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CMS_add1_signer() returns an internal pointer to the CMS_SignerInfo |
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structure just added, this can be used to set additional attributes |
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before it is finalized. |
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=head1 RETURN VALUES |
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CMS_add1_signer() returns an internal pointer to the CMS_SignerInfo |
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structure just added or NULL if an error occurs. |
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=head1 SEE ALSO |
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L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_sign(3)|CMS_sign(3)>, |
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L<CMS_final(3)|CMS_final(3)>, |
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=head1 HISTORY |
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CMS_add1_signer() was added to OpenSSL 0.9.8 |
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=cut
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