CMS_SIGN(3ossl) OpenSSL CMS_SIGN(3ossl)
NAME
CMS_sign, CMS_sign_ex - create a CMS SignedData structure
SYNOPSIS
#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);
DESCRIPTION
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(3) is similar to CMS_sign_ex() but uses default values of NULL
for the library context libctx and the property query propq.
NOTES
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(3) 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.
BUGS
Some attributes such as counter signatures are not supported.
RETURN VALUES
CMS_sign(3) return either a valid CMS_ContentInfo
structure or NULL if an error occurred. The error can be obtained from
ERR_get_error(3).
SEE ALSO
ERR_get_error(3), CMS_verify(3)
HISTORY
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.
Since OpenSSL 3.2, CMS_sign(3) ignore any duplicate
certificates in their certs argument and no longer throw an error for
them.
COPYRIGHT
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>.
3.3.2 2024-09-04 CMS_SIGN(3ossl)
openssl 3.3.2 - Generated Sat Sep 7 14:18:14 CDT 2024