243 lines
7.5 KiB
Groff
243 lines
7.5 KiB
Groff
.\" $OpenBSD: CMS_sign.3,v 1.9 2020/06/24 18:15:00 jmc Exp $
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.\" full merge up to: OpenSSL e9b77246 Jan 20 19:58:49 2017 +0100
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.\"
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.\" This file was written by Dr. Stephen Henson <steve@openssl.org>.
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.\" Copyright (c) 2008 The OpenSSL Project. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\"
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" 3. All advertising materials mentioning features or use of this
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.\" software must display the following acknowledgment:
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.\" "This product includes software developed by the OpenSSL Project
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.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
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.\"
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.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
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.\" endorse or promote products derived from this software without
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.\" prior written permission. For written permission, please contact
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.\" openssl-core@openssl.org.
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.\"
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.\" 5. Products derived from this software may not be called "OpenSSL"
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.\" nor may "OpenSSL" appear in their names without prior written
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.\" permission of the OpenSSL Project.
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.\"
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.\" 6. Redistributions of any form whatsoever must retain the following
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.\" acknowledgment:
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.\" "This product includes software developed by the OpenSSL Project
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.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)"
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
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.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
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.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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.\" OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd $Mdocdate: June 24 2020 $
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.Dt CMS_SIGN 3
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.Os
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.Sh NAME
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.Nm CMS_sign
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.Nd create a CMS SignedData structure
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.Sh SYNOPSIS
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.In openssl/cms.h
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.Ft CMS_ContentInfo *
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.Fo CMS_sign
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.Fa "X509 *signcert"
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.Fa "EVP_PKEY *pkey"
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.Fa "STACK_OF(X509) *certs"
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.Fa "BIO *data"
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.Fa "unsigned int flags"
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.Fc
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.Sh DESCRIPTION
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.Fn CMS_sign
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creates and returns a CMS
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.Vt SignedData
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structure.
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.Fa signcert
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is the certificate to sign with,
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.Fa pkey
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is the corresponding private key.
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.Fa certs
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is an optional additional set of certificates to include in the CMS
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structure (for example any intermediate CAs in the chain).
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Any or all of these parameters can be
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.Dv NULL .
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.Pp
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The data to be signed is read from
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.Fa data .
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.Pp
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Any of the following flags (OR'ed together) can be passed in the
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.Fa flags
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argument:
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.Bl -tag -width Ds
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.It Dv CMS_TEXT
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Prepend MIME headers for the type text/plain to the data.
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Many S/MIME clients expect the signed content to include valid MIME
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headers.
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.It Dv CMS_NOCERTS
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Do not include the signer's certificate in the
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.Vt CMS_ContentInfo
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structure.
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The signer's certificate must still be supplied in the
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.Fa signcert
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parameter though.
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This can reduce the size of the signature if the signer's certificate can
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be obtained by other means, for example from a previously signed message.
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.It Dv CMS_DETACHED
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Omit the data being signed from the
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.Vt CMS_ContentInfo
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structure.
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This is used for
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.Vt CMS_ContentInfo
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detached signatures which are used in S/MIME plaintext signed messages
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for example.
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.It Dv CMS_BINARY
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Do not translate the supplied content into MIME canonical format
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even though that is required by the S/MIME specifications.
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This option should be used if the supplied data is in binary format.
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Otherwise the translation will corrupt it.
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.It Dv CMS_NOATTR
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Do not add any
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.Vt SignedAttributes .
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By default, the
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.Fa signerInfos
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field includes several CMS
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.Vt SignedAttributes
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including the signing time, the CMS content type,
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and the supported list of ciphers in an
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.Vt SMIMECapabilities
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attribute.
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.It Dv CMS_NOSMIMECAP
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Omit just the
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.Vt SMIMECapabilities .
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If present, the SMIMECapabilities attribute indicates support for the
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following algorithms in preference order: 256-bit AES, Gost R3411-94,
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Gost 28147-89, 192-bit AES, 128-bit AES, triple DES, 128-bit RC2, 64-bit
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RC2, DES and 40-bit RC2.
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If any of these algorithms is not available, then it will not be
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included.
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.It Dv CMS_USE_KEYID
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Use the subject key identifier value to identify signing certificates.
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An error occurs if the signing certificate does not have a subject key
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identifier extension.
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By default, issuer name and serial number are used instead.
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.It Dv CMS_STREAM
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Only initialize the returned
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.Vt CMS_ContentInfo
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structure to prepare it for performing the signing operation.
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The signing is however
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.Em not
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performed and the data to be signed is not read from the
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.Fa data
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parameter.
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Signing is deferred until after the data has been written.
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In this way, data can be signed in a single pass.
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The returned
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.Vt CMS_ContentInfo
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structure is
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.Em not
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complete and outputting its contents via a function that does not
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properly finalize the
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.Vt CMS_ContentInfo
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structure will give unpredictable results.
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Several functions including
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.Xr SMIME_write_CMS 3 ,
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.Xr i2d_CMS_bio_stream 3 ,
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or
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.Xr PEM_write_bio_CMS_stream 3
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finalize the structure.
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Alternatively, finalization can be performed by obtaining the streaming
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ASN1
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.Vt BIO
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directly using
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.Xr BIO_new_CMS 3 .
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.It Dv CMS_PARTIAL
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Output a partial
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.Vt CMS_ContentInfo
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structure to which additional signers and capabilities can be
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added before finalization.
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.El
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.Pp
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If a signer is specified, it will use the default digest for the signing
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algorithm.
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This is SHA1 for both RSA and DSA keys.
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.Pp
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If
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.Fa signcert
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and
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.Fa pkey
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are
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.Dv NULL ,
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then a certificates only CMS structure is output.
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.Pp
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The function
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.Fn CMS_sign
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is a basic CMS signing function whose output will be suitable for many
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purposes.
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For finer control of the output format the
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.Fa certs ,
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.Fa signcert
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and
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.Fa pkey
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parameters can all be
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.Dv NULL
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and the
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.Dv CMS_PARTIAL
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flag set.
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Then one or more signers can be added using the function
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.Xr CMS_add1_signer 3 ,
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non default digests can be used and custom attributes added.
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.Xr CMS_final 3
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must then be called to finalize the structure if streaming is not
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enabled.
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.Sh RETURN VALUES
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.Fn CMS_sign
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returns either a valid
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.Vt CMS_ContentInfo
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structure or
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.Dv NULL
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if an error occurred.
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The error can be obtained from
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.Xr ERR_get_error 3 .
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.Sh SEE ALSO
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.Xr CMS_add0_cert 3 ,
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.Xr CMS_add1_signer 3 ,
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.Xr CMS_ContentInfo_new 3 ,
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.Xr CMS_final 3 ,
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.Xr CMS_sign_receipt 3 ,
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.Xr CMS_verify 3
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.Sh STANDARDS
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RFC 5652: Cryptographic Message Syntax (CMS)
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.Bl -dash -compact -offset indent
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.It
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section 5.1: SignedData Type
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.It
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section 5.3: SignerInfo Type
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.El
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.Pp
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RFC 8551: Secure/Multipurpose Internet Mail Extensions (S/MIME)
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Version\ 4.0 Message Specification,
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section 2.5.2: SMIMECapabilities Attribute
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.Sh HISTORY
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.Fn CMS_sign
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first appeared in OpenSSL 0.9.8h
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and has been available since
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.Ox 6.7 .
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.Sh BUGS
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Some attributes such as counter signatures are not supported.
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