CMS_sign, CMS_sign_ex - create a CMS SignedData structure
#include <openssl/cms.h>
CMS_ContentInfo *CMS_sign_ex(X509 *signcert, EVP_PKEY *pkey,
STACK_OF(X509) *certs, BIO *data,
unsigned int flags, OSSL_LIB_CTX *ctx,
const char *propq);
CMS_ContentInfo *CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs,
BIO *data, unsigned int flags);
CMS_sign_ex() creates and returns a CMS SignedData structure.
signcert is the certificate to sign with,
pkey is the
corresponding private key.
certs is an optional additional set of
certificates to include in the CMS structure (for example any intermediate CAs
in the chain). The library context
libctx and the property query
propq are used when retrieving algorithms from providers. Any or all of
these parameters can be
NULL, see
NOTES below.
The data to be signed is read from BIO
data.
flags is an optional set of flags.
CMS_sign() is similar to
CMS_sign_ex() but uses default values of
NULL for the library context
libctx and the property query
propq.
Any of the following flags (ored together) can be passed in the
flags
parameter.
Many S/MIME clients expect the signed content to include valid MIME headers. If
the
CMS_TEXT flag is set MIME headers for type
text/plain are
prepended to the data.
If
CMS_NOCERTS is set the signer's certificate will not be included in
the CMS_ContentInfo structure, the signer's certificate must still be supplied
in the
signcert parameter though. This can reduce the size of the
signature if the signers certificate can be obtained by other means: for
example a previously signed message.
The data being signed is included in the CMS_ContentInfo structure, unless
CMS_DETACHED is set in which case it is omitted. This is used for
CMS_ContentInfo detached signatures which are used in S/MIME plaintext signed
messages for example.
Normally the supplied content is translated into MIME canonical format (as
required by the S/MIME specifications) if
CMS_BINARY is set no
translation occurs. This option should be used if the supplied data is in
binary format otherwise the translation will corrupt it.
The SignedData structure includes several CMS signedAttributes including the
signing time, the CMS content type and the supported list of ciphers in an
SMIMECapabilities attribute. If
CMS_NOATTR is set then no
signedAttributes will be used. If
CMS_NOSMIMECAP is set then just the
SMIMECapabilities are omitted.
If present the SMIMECapabilities attribute indicates support for the following
algorithms in preference order: 256 bit AES, Gost R3411-94, Gost 28147-89, 192
bit AES, 128 bit AES, triple DES, 128 bit RC2, 64 bit RC2, DES and 40 bit RC2.
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 not
loaded.
OpenSSL will by default identify signing certificates using issuer name and
serial number. If
CMS_USE_KEYID is set it will use the subject key
identifier value instead. An error occurs if the signing certificate does not
have a subject key identifier extension.
If the flags
CMS_STREAM is set then the returned
CMS_ContentInfo
structure is just initialized ready to perform the signing operation. The
signing is however
not performed and the data to be signed is not read
from the
data parameter. Signing is deferred until after the data has
been written. In this way data can be signed in a single pass.
If the
CMS_PARTIAL flag is set a partial
CMS_ContentInfo structure
is output to which additional signers and capabilities can be added before
finalization.
If the flag
CMS_STREAM is set the returned
CMS_ContentInfo
structure is
not complete and outputting its contents via a function
that does not properly finalize the
CMS_ContentInfo structure will give
unpredictable results.
Several functions including
SMIME_write_CMS(),
i2d_CMS_bio_stream(),
PEM_write_bio_CMS_stream() finalize the
structure. Alternatively finalization can be performed by obtaining the
streaming ASN1
BIO directly using
BIO_new_CMS().
If a signer is specified it will use the default digest for the signing
algorithm. This is
SHA1 for both RSA and DSA keys.
If
signcert and
pkey are NULL then a certificates only CMS
structure is output.
The function
CMS_sign() is a basic CMS signing function whose output will
be suitable for many purposes. For finer control of the output format the
certs,
signcert and
pkey parameters can all be
NULL and the
CMS_PARTIAL flag set. Then one or more signers can
be added using the function
CMS_add1_signer(), non default digests can
be used and custom attributes added.
CMS_final() must then be called to
finalize the structure if streaming is not enabled.
Some attributes such as counter signatures are not supported.
CMS_sign_ex() and
CMS_sign() return either a valid CMS_ContentInfo
structure or NULL if an error occurred. The error can be obtained from
ERR_get_error(3).
ERR_get_error(3),
CMS_verify(3)
The
CMS_STREAM flag is only supported for detached data in OpenSSL 0.9.8,
it is supported for embedded data in OpenSSL 1.0.0 and later.
The
CMS_sign_ex() method was added in OpenSSL 3.0.
Copyright 2008-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy in the
file LICENSE in the source distribution or at
<
https://www.openssl.org/source/license.html>.