1=pod
2
3=head1 NAME
4
5PKCS7_sign_add_signer - add a signer PKCS7 signed data structure.
6
7=head1 SYNOPSIS
8
9 #include <openssl/pkcs7.h>
10
11 PKCS7_SIGNER_INFO *PKCS7_sign_add_signer(PKCS7 *p7, X509 *signcert, EVP_PKEY *pkey, const EVP_MD *md, int flags);
12
13
14=head1 DESCRIPTION
15
16PKCS7_sign_add_signer() adds a signer with certificate B<signcert> and private
17key B<pkey> using message digest B<md> to a PKCS7 signed data structure
18B<p7>.
19
20The PKCS7 structure should be obtained from an initial call to PKCS7_sign()
21with the flag B<PKCS7_PARTIAL> set or in the case or re-signing a valid PKCS7
22signed data structure.
23
24If the B<md> parameter is B<NULL> then the default digest for the public
25key algorithm will be used.
26
27Unless the B<PKCS7_REUSE_DIGEST> flag is set the returned PKCS7 structure
28is not complete and must be finalized either by streaming (if applicable) or
29a call to PKCS7_final().
30
31
32=head1 NOTES
33
34The main purpose of this function is to provide finer control over a PKCS#7
35signed data structure where the simpler PKCS7_sign() function defaults are
36not appropriate. For example if multiple signers or non default digest
37algorithms are needed.
38
39Any of the following flags (ored together) can be passed in the B<flags>
40parameter.
41
42If B<PKCS7_REUSE_DIGEST> is set then an attempt is made to copy the content
43digest value from the PKCS7 struture: to add a signer to an existing structure.
44An error occurs if a matching digest value cannot be found to copy. The
45returned PKCS7 structure will be valid and finalized when this flag is set.
46
47If B<PKCS7_PARTIAL> is set in addition to B<PKCS7_REUSE_DIGEST> then the
48B<PKCS7_SIGNER_INO> structure will not be finalized so additional attributes
49can be added. In this case an explicit call to PKCS7_SIGNER_INFO_sign() is
50needed to finalize it.
51
52If B<PKCS7_NOCERTS> is set the signer's certificate will not be included in the
53PKCS7 structure, the signer's certificate must still be supplied in the
54B<signcert> parameter though. This can reduce the size of the signature if the
55signers certificate can be obtained by other means: for example a previously
56signed message.
57
58The signedData structure includes several PKCS#7 autenticatedAttributes
59including the signing time, the PKCS#7 content type and the supported list of
60ciphers in an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no
61authenticatedAttributes will be used. If B<PKCS7_NOSMIMECAP> is set then just
62the SMIMECapabilities are omitted.
63
64If present the SMIMECapabilities attribute indicates support for the following
65algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any of
66these algorithms is disabled then it will not be included.
67
68
69PKCS7_sign_add_signers() returns an internal pointer to the PKCS7_SIGNER_INFO
70structure just added, this can be used to set additional attributes
71before it is finalized.
72
73=head1 RETURN VALUES
74
75PKCS7_sign_add_signers() returns an internal pointer to the PKCS7_SIGNER_INFO
76structure just added or NULL if an error occurs.
77
78=head1 SEE ALSO
79
80L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_sign(3)|PKCS7_sign(3)>,
81L<PKCS7_final(3)|PKCS7_final(3)>,
82
83=head1 HISTORY
84
85PPKCS7_sign_add_signer() was added to OpenSSL 1.0.0
86
87=cut
88