CMS_add1_signer.pod revision 273399 
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