1=pod 2 3=head1 NAME 4 5 CMS_add1_signer, CMS_SignerInfo_sign - add a signer to a CMS_ContentInfo signed data structure. 6 7=head1 SYNOPSIS 8 9 #include <openssl/cms.h> 10 11 CMS_SignerInfo *CMS_add1_signer(CMS_ContentInfo *cms, X509 *signcert, EVP_PKEY *pkey, const EVP_MD *md, unsigned int flags); 12 13 int CMS_SignerInfo_sign(CMS_SignerInfo *si); 14 15 16=head1 DESCRIPTION 17 18CMS_add1_signer() adds a signer with certificate B<signcert> and private 19key B<pkey> using message digest B<md> to CMS_ContentInfo SignedData 20structure B<cms>. 21 22The CMS_ContentInfo structure should be obtained from an initial call to 23CMS_sign() with the flag B<CMS_PARTIAL> set or in the case or re-signing a 24valid CMS_ContentInfo SignedData structure. 25 26If the B<md> parameter is B<NULL> then the default digest for the public 27key algorithm will be used. 28 29Unless the B<CMS_REUSE_DIGEST> flag is set the returned CMS_ContentInfo 30structure is not complete and must be finalized either by streaming (if 31applicable) or a call to CMS_final(). 32 33The CMS_SignerInfo_sign() function will explicitly sign a CMS_SignerInfo 34structure, its main use is when B<CMS_REUSE_DIGEST> and B<CMS_PARTIAL> flags 35are both set. 36 37=head1 NOTES 38 39The main purpose of CMS_add1_signer() is to provide finer control 40over a CMS signed data structure where the simpler CMS_sign() function defaults 41are not appropriate. For example if multiple signers or non default digest 42algorithms are needed. New attributes can also be added using the returned 43CMS_SignerInfo structure and the CMS attribute utility functions or the 44CMS signed receipt request functions. 45 46Any of the following flags (ored together) can be passed in the B<flags> 47parameter. 48 49If B<CMS_REUSE_DIGEST> is set then an attempt is made to copy the content 50digest value from the CMS_ContentInfo structure: to add a signer to an existing 51structure. An error occurs if a matching digest value cannot be found to copy. 52The returned CMS_ContentInfo structure will be valid and finalized when this 53flag is set. 54 55If B<CMS_PARTIAL> is set in addition to B<CMS_REUSE_DIGEST> then the 56CMS_SignerInfo structure will not be finalized so additional attributes 57can be added. In this case an explicit call to CMS_SignerInfo_sign() is 58needed to finalize it. 59 60If B<CMS_NOCERTS> is set the signer's certificate will not be included in the 61CMS_ContentInfo structure, the signer's certificate must still be supplied in 62the B<signcert> parameter though. This can reduce the size of the signature if 63the signers certificate can be obtained by other means: for example a 64previously signed message. 65 66The SignedData structure includes several CMS signedAttributes including the 67signing time, the CMS content type and the supported list of ciphers in an 68SMIMECapabilities attribute. If B<CMS_NOATTR> is set then no signedAttributes 69will be used. If B<CMS_NOSMIMECAP> is set then just the SMIMECapabilities are 70omitted. 71 72OpenSSL will by default identify signing certificates using issuer name 73and serial number. If B<CMS_USE_KEYID> is set it will use the subject key 74identifier value instead. An error occurs if the signing certificate does not 75have a subject key identifier extension. 76 77If present the SMIMECapabilities attribute indicates support for the following 78algorithms in preference order: 256 bit AES, Gost R3411-94, Gost 28147-89, 192 79bit AES, 128 bit AES, triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. 80If 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 81not loaded. 82 83CMS_add1_signer() returns an internal pointer to the CMS_SignerInfo 84structure just added, this can be used to set additional attributes 85before it is finalized. 86 87=head1 RETURN VALUES 88 89CMS_add1_signer() returns an internal pointer to the CMS_SignerInfo 90structure just added or NULL if an error occurs. 91 92=head1 SEE ALSO 93 94L<ERR_get_error(3)|ERR_get_error(3)>, L<CMS_sign(3)|CMS_sign(3)>, 95L<CMS_final(3)|CMS_final(3)>, 96 97=head1 HISTORY 98 99CMS_add1_signer() was added to OpenSSL 0.9.8 100 101=cut 102