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CMS_SIGN(3)			    OpenSSL			   CMS_SIGN(3)

       CMS_sign	- create a CMS SignedData structure

	#include <openssl/cms.h>

	CMS_ContentInfo	*CMS_sign(X509 *signcert, EVP_PKEY *pkey, STACK_OF(X509) *certs,
				  BIO *data, unsigned int flags);

       CMS_sign() 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). 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.

       Any of the following flags (ored	together) can be passed	in the flags

       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

       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

       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

       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_sign_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() returns 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.

       Copyright 2008-2016 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (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

1.1.1k				  2021-03-25			   CMS_SIGN(3)


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