xref: /openssl/doc/man3/PKCS7_sign.pod (revision da1c088f)
1=pod
2
3=head1 NAME
4
5PKCS7_sign_ex, PKCS7_sign
6- create a PKCS#7 signedData structure
7
8=head1 SYNOPSIS
9
10 #include <openssl/pkcs7.h>
11
12 PKCS7 *PKCS7_sign_ex(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs,
13                      BIO *data, int flags, OSSL_LIB_CTX *libctx,
14                      const char *propq);
15 PKCS7 *PKCS7_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs,
16                   BIO *data, int flags);
17
18=head1 DESCRIPTION
19
20PKCS7_sign_ex() creates and returns a PKCS#7 signedData structure.
21I<signcert> is the certificate to sign with, I<pkey> is the corresponding
22private key. I<certs> is an optional set of extra certificates to include
23in the PKCS#7 structure (for example any intermediate CAs in the chain).
24The library context I<libctx> and property query I<propq> are used when
25retrieving algorithms from providers.
26
27The data to be signed is read from BIO I<data>.
28
29I<flags> is an optional set of flags.
30
31Any of the following flags (ored together) can be passed in the I<flags>
32parameter.
33
34Many S/MIME clients expect the signed content to include valid MIME headers. If
35the B<PKCS7_TEXT> flag is set MIME headers for type C<text/plain> are prepended
36to the data.
37
38If B<PKCS7_NOCERTS> is set the signer's certificate and the extra I<certs>
39will not be included in the PKCS7 structure.
40The signer's certificate must still be supplied in the I<signcert> parameter
41though. This can reduce the size of the signatures if the signer's certificates
42can be obtained by other means: for example a previously signed message.
43
44The data being signed is included in the PKCS7 structure, unless
45B<PKCS7_DETACHED> is set in which case it is omitted. This is used for PKCS7
46detached signatures which are used in S/MIME plaintext signed messages for
47example.
48
49Normally the supplied content is translated into MIME canonical format (as
50required by the S/MIME specifications) if B<PKCS7_BINARY> is set no translation
51occurs. This option should be used if the supplied data is in binary format
52otherwise the translation will corrupt it.
53
54The signedData structure includes several PKCS#7 authenticatedAttributes
55including the signing time, the PKCS#7 content type and the supported list of
56ciphers in an SMIMECapabilities attribute. If B<PKCS7_NOATTR> is set then no
57authenticatedAttributes will be used. If B<PKCS7_NOSMIMECAP> is set then just
58the SMIMECapabilities are omitted.
59
60If present the SMIMECapabilities attribute indicates support for the following
61algorithms: triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2. If any of
62these algorithms is disabled then it will not be included.
63
64If the flags B<PKCS7_STREAM> is set then the returned B<PKCS7> structure is
65just initialized ready to perform the signing operation. The signing is however
66B<not> performed and the data to be signed is not read from the I<data>
67parameter. Signing is deferred until after the data has been written. In this
68way data can be signed in a single pass.
69
70If the B<PKCS7_PARTIAL> flag is set a partial B<PKCS7> structure is output to
71which additional signers and capabilities can be added before finalization.
72
73If the flag B<PKCS7_STREAM> is set the returned B<PKCS7> structure is B<not>
74complete and outputting its contents via a function that does not properly
75finalize the B<PKCS7> structure will give unpredictable results.
76
77Several functions including SMIME_write_PKCS7(), i2d_PKCS7_bio_stream(),
78PEM_write_bio_PKCS7_stream() finalize the structure. Alternatively finalization
79can be performed by obtaining the streaming ASN1 B<BIO> directly using
80BIO_new_PKCS7().
81
82If a signer is specified it will use the default digest for the signing
83algorithm. This is B<SHA1> for both RSA and DSA keys.
84
85The I<certs>, I<signcert> and I<pkey> parameters can all be
86NULL if the B<PKCS7_PARTIAL> flag is set. One or more signers can be added
87using the function PKCS7_sign_add_signer(). PKCS7_final() must also be
88called to finalize the structure if streaming is not enabled. Alternative
89signing digests can also be specified using this method.
90
91If I<signcert> and I<pkey> are NULL then a certificates only
92PKCS#7 structure is output.
93
94In versions of OpenSSL before 1.0.0 the I<signcert> and I<pkey> parameters must
95not be NULL.
96
97PKCS7_sign() is like PKCS7_sign_ex() except that it uses default values of
98NULL for the library context I<libctx> and the property query I<propq>.
99This is retained for API backward compatibility.
100
101=head1 BUGS
102
103Some advanced attributes such as counter signatures are not supported.
104
105=head1 RETURN VALUES
106
107PKCS7_sign_ex() and PKCS7_sign() return either a valid PKCS7 structure
108or NULL if an error occurred.  The error can be obtained from ERR_get_error(3).
109
110=head1 SEE ALSO
111
112L<ERR_get_error(3)>, L<PKCS7_verify(3)>
113
114=head1 HISTORY
115
116The function PKCS7_sign_ex() was added in OpenSSL 3.0.
117
118The B<PKCS7_PARTIAL> flag, and the ability for I<certs>, I<signcert>,
119and I<pkey> parameters to be NULL were added in OpenSSL 1.0.0.
120
121The B<PKCS7_STREAM> flag was added in OpenSSL 1.0.0.
122
123=head1 COPYRIGHT
124
125Copyright 2002-2023 The OpenSSL Project Authors. All Rights Reserved.
126
127Licensed under the Apache License 2.0 (the "License").  You may not use
128this file except in compliance with the License.  You can obtain a copy
129in the file LICENSE in the source distribution or at
130L<https://www.openssl.org/source/license.html>.
131
132=cut
133