5 CMS_sign - create a CMS SignedData structure
9 #include <openssl/cms.h>
11 CMS_ContentInfo *CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs,
12 BIO *data, unsigned int flags);
16 CMS_sign() creates and returns a CMS SignedData structure. B<signcert> is
17 the certificate to sign with, B<pkey> is the corresponding private key.
18 B<certs> is an optional additional set of certificates to include in the CMS
19 structure (for example any intermediate CAs in the chain). Any or all of
20 these parameters can be B<NULL>, see B<NOTES> below.
22 The data to be signed is read from BIO B<data>.
24 B<flags> is an optional set of flags.
28 Any of the following flags (ored together) can be passed in the B<flags>
31 Many S/MIME clients expect the signed content to include valid MIME headers. If
32 the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are prepended
35 If B<CMS_NOCERTS> is set the signer's certificate will not be included in the
36 CMS_ContentInfo structure, the signer's certificate must still be supplied in
37 the B<signcert> parameter though. This can reduce the size of the signature if
38 the signers certificate can be obtained by other means: for example a
39 previously signed message.
41 The data being signed is included in the CMS_ContentInfo structure, unless
42 B<CMS_DETACHED> is set in which case it is omitted. This is used for
43 CMS_ContentInfo detached signatures which are used in S/MIME plaintext signed
46 Normally the supplied content is translated into MIME canonical format (as
47 required by the S/MIME specifications) if B<CMS_BINARY> is set no translation
48 occurs. This option should be used if the supplied data is in binary format
49 otherwise the translation will corrupt it.
51 The SignedData structure includes several CMS signedAttributes including the
52 signing time, the CMS content type and the supported list of ciphers in an
53 SMIMECapabilities attribute. If B<CMS_NOATTR> is set then no signedAttributes
54 will be used. If B<CMS_NOSMIMECAP> is set then just the SMIMECapabilities are
57 If present the SMIMECapabilities attribute indicates support for the following
58 algorithms in preference order: 256 bit AES, Gost R3411-94, Gost 28147-89, 192
59 bit AES, 128 bit AES, triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2.
60 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
63 OpenSSL will by default identify signing certificates using issuer name
64 and serial number. If B<CMS_USE_KEYID> is set it will use the subject key
65 identifier value instead. An error occurs if the signing certificate does not
66 have a subject key identifier extension.
68 If the flags B<CMS_STREAM> is set then the returned B<CMS_ContentInfo>
69 structure is just initialized ready to perform the signing operation. The
70 signing is however B<not> performed and the data to be signed is not read from
71 the B<data> parameter. Signing is deferred until after the data has been
72 written. In this way data can be signed in a single pass.
74 If the B<CMS_PARTIAL> flag is set a partial B<CMS_ContentInfo> structure is
75 output to which additional signers and capabilities can be added before
78 If the flag B<CMS_STREAM> is set the returned B<CMS_ContentInfo> structure is
79 B<not> complete and outputting its contents via a function that does not
80 properly finalize the B<CMS_ContentInfo> structure will give unpredictable
83 Several functions including SMIME_write_CMS(), i2d_CMS_bio_stream(),
84 PEM_write_bio_CMS_stream() finalize the structure. Alternatively finalization
85 can be performed by obtaining the streaming ASN1 B<BIO> directly using
88 If a signer is specified it will use the default digest for the signing
89 algorithm. This is B<SHA1> for both RSA and DSA keys.
91 If B<signcert> and B<pkey> are NULL then a certificates only CMS structure is
94 The function CMS_sign() is a basic CMS signing function whose output will be
95 suitable for many purposes. For finer control of the output format the
96 B<certs>, B<signcert> and B<pkey> parameters can all be B<NULL> and the
97 B<CMS_PARTIAL> flag set. Then one or more signers can be added using the
98 function CMS_sign_add1_signer(), non default digests can be used and custom
99 attributes added. CMS_final() must then be called to finalize the
100 structure if streaming is not enabled.
104 Some attributes such as counter signatures are not supported.
108 CMS_sign() returns either a valid CMS_ContentInfo structure or NULL if an error
109 occurred. The error can be obtained from ERR_get_error(3).
113 L<ERR_get_error(3)>, L<CMS_verify(3)>
117 The B<CMS_STREAM> flag is only supported for detached data in OpenSSL 0.9.8,
118 it is supported for embedded data in OpenSSL 1.0.0 and later.
122 Copyright 2008-2016 The OpenSSL Project Authors. All Rights Reserved.
124 Licensed under the OpenSSL license (the "License"). You may not use
125 this file except in compliance with the License. You can obtain a copy
126 in the file LICENSE in the source distribution or at
127 L<https://www.openssl.org/source/license.html>.