227 lines
7.3 KiB
Groff
227 lines
7.3 KiB
Groff
.\" $OpenBSD: CMS_verify.3,v 1.9 2023/06/05 17:17:23 job Exp $
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.\" full merge up to: OpenSSL 35fd9953 May 28 14:49:38 2019 +0200
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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 5 2023 $
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.Dt CMS_VERIFY 3
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.Os
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.Sh NAME
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.Nm CMS_verify ,
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.Nm CMS_get0_signers
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.Nd verify a CMS SignedData structure
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.Sh SYNOPSIS
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.In openssl/cms.h
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.Ft int
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.Fo CMS_verify
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.Fa "CMS_ContentInfo *cms"
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.Fa "STACK_OF(X509) *certs"
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.Fa "X509_STORE *store"
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.Fa "BIO *indata"
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.Fa "BIO *out"
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.Fa "unsigned int flags"
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.Fc
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.Ft STACK_OF(X509) *
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.Fo CMS_get0_signers
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.Fa "CMS_ContentInfo *cms"
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.Fc
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.Sh DESCRIPTION
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.Fn CMS_verify
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verifies the CMS
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.Vt SignedData
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structure
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.Fa cms .
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.Fa certs
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is a set of certificates in which to search for the signing
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certificate(s).
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.Fa store
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is a trusted certificate store used for chain verification.
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.Fa indata
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is the detached content if the content is not present in
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.Fa cms .
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The content is written to
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.Fa out
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if it is not
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.Dv NULL .
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.Pp
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.Fn CMS_get0_signers
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retrieves the signing certificate(s) from
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.Fa cms .
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It may only be called after a successful
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.Fn CMS_verify
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operation.
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The signers must be freed with
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.Fn sk_X509_free .
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.Pp
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Normally the verify process proceeds as follows.
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.Pp
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Initially some sanity checks are performed on
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.Fa cms .
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There must be at least one signature on the data.
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If the content is detached,
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.Fa indata
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cannot be
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.Dv NULL .
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.Pp
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An attempt is made to locate all the signing certificate(s), first
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looking in the
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.Fa certs
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parameter (if it is not
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.Dv NULL )
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and then looking in any certificates contained in the
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.Fa cms
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structure itself.
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If any signing certificate cannot be located, the operation fails.
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.Pp
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Each signing certificate is chain verified using the
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.Sy smimesign
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purpose and the supplied trusted certificate
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.Fa store .
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Any internal certificates in the message are used as untrusted CAs.
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If CRL checking is enabled in
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.Fa store ,
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any internal CRLs are used in addition to attempting to look them up in
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.Fa store .
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If any chain verify fails, an error code is returned.
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.Pp
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Finally the signed content is read (and written to
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.Fa out
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if it is not
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.Dv NULL )
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and the signature is checked.
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.Pp
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If all signatures verify correctly, then the function is successful.
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.Pp
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Any of the following
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.Fa flags
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(OR'ed together) can be passed to change the default verify behaviour:
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.Bl -tag -width Ds
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.It Dv CMS_NOINTERN
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Do not use the certificates in the message itself when
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locating the signing certificate(s).
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This means that all the signing certificates must be in the
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.Fa certs
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parameter.
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.It Dv CMS_NOCRL
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If CRL checking is enabled in
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.Fa store ,
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then any CRLs in the message itself are ignored.
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.It Dv CMS_TEXT
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MIME headers for type text/plain are deleted from the content.
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If the content is not of type text/plain, an error is returned.
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.It Dv CMS_NO_SIGNER_CERT_VERIFY
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Do not verify signing certificates.
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.It Dv CMS_NO_ATTR_VERIFY
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Do not check the signed attributes signature.
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.It Dv CMS_NO_CONTENT_VERIFY
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Do not check the content digest.
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.El
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.Pp
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One application of
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.Dv CMS_NOINTERN
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is to only accept messages signed by a small number of certificates.
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The acceptable certificates would be passed in the
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.Fa certs
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parameter.
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In this case, if the signer is not one of the certificates supplied in
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.Fa certs ,
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then the verify will fail because the signer cannot be found.
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.Pp
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In some cases the standard techniques for looking up and validating
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certificates are not appropriate: for example an application may wish to
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lookup certificates in a database or perform customised verification.
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This can be achieved by setting and verifying the signers certificates
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manually using the signed data utility functions.
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.Pp
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Care should be taken when modifying the default verify behaviour, for
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example setting
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.Dv CMS_NO_CONTENT_VERIFY
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will totally disable all content verification and any modified content
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will be considered valid.
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This combination is however useful if one merely wishes to write the
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content to
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.Fa out
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and its validity is not considered important.
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.Pp
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Chain verification should arguably be performed using the signing time
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rather than the current time.
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However since the signing time is supplied by the signer it cannot be
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trusted without additional evidence (such as a trusted timestamp).
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.Sh RETURN VALUES
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.Fn CMS_verify
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returns 1 for a successful verification or 0 if an error occurred.
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.Pp
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.Fn CMS_get0_signers
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returns all signers or
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.Dv NULL
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if an error occurred.
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The signers must be freed with
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.Fn sk_X509_free .
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.Pp
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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_ContentInfo_new 3 ,
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.Xr CMS_get0_SignerInfos 3 ,
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.Xr CMS_sign 3 ,
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.Xr CMS_verify_receipt 3
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.Sh STANDARDS
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RFC 5652: Cryptographic Message Syntax (CMS),
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section 5.1: SignedData Type
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.Sh HISTORY
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These functions first appeared in OpenSSL 0.9.8h
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and have been available since
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.Ox 6.7 .
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.Sh BUGS
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The trusted certificate store is not searched for the signing certificate.
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This is primarily due to the inadequacies of the current
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.Vt X509_STORE
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functionality.
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.Pp
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The lack of single pass processing means that the signed content must
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all be held in memory if it is not detached.
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