101 lines
3.9 KiB
Text
101 lines
3.9 KiB
Text
=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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