1.\" $OpenBSD: CMS_verify.3,v 1.9 2023/06/05 17:17:23 job Exp $ 2.\" full merge up to: OpenSSL 35fd9953 May 28 14:49:38 2019 +0200 3.\" 4.\" This file was written by Dr. Stephen Henson <steve@openssl.org>. 5.\" Copyright (c) 2008 The OpenSSL Project. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in 16.\" the documentation and/or other materials provided with the 17.\" distribution. 18.\" 19.\" 3. All advertising materials mentioning features or use of this 20.\" software must display the following acknowledgment: 21.\" "This product includes software developed by the OpenSSL Project 22.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 23.\" 24.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 25.\" endorse or promote products derived from this software without 26.\" prior written permission. For written permission, please contact 27.\" openssl-core@openssl.org. 28.\" 29.\" 5. Products derived from this software may not be called "OpenSSL" 30.\" nor may "OpenSSL" appear in their names without prior written 31.\" permission of the OpenSSL Project. 32.\" 33.\" 6. Redistributions of any form whatsoever must retain the following 34.\" acknowledgment: 35.\" "This product includes software developed by the OpenSSL Project 36.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 37.\" 38.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 39.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 40.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 41.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 42.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 43.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 44.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 45.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 46.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 47.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 48.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 49.\" OF THE POSSIBILITY OF SUCH DAMAGE. 50.\" 51.Dd $Mdocdate: June 5 2023 $ 52.Dt CMS_VERIFY 3 53.Os 54.Sh NAME 55.Nm CMS_verify , 56.Nm CMS_get0_signers 57.Nd verify a CMS SignedData structure 58.Sh SYNOPSIS 59.In openssl/cms.h 60.Ft int 61.Fo CMS_verify 62.Fa "CMS_ContentInfo *cms" 63.Fa "STACK_OF(X509) *certs" 64.Fa "X509_STORE *store" 65.Fa "BIO *indata" 66.Fa "BIO *out" 67.Fa "unsigned int flags" 68.Fc 69.Ft STACK_OF(X509) * 70.Fo CMS_get0_signers 71.Fa "CMS_ContentInfo *cms" 72.Fc 73.Sh DESCRIPTION 74.Fn CMS_verify 75verifies the CMS 76.Vt SignedData 77structure 78.Fa cms . 79.Fa certs 80is a set of certificates in which to search for the signing 81certificate(s). 82.Fa store 83is a trusted certificate store used for chain verification. 84.Fa indata 85is the detached content if the content is not present in 86.Fa cms . 87The content is written to 88.Fa out 89if it is not 90.Dv NULL . 91.Pp 92.Fn CMS_get0_signers 93retrieves the signing certificate(s) from 94.Fa cms . 95It may only be called after a successful 96.Fn CMS_verify 97operation. 98The signers must be freed with 99.Fn sk_X509_free . 100.Pp 101Normally the verify process proceeds as follows. 102.Pp 103Initially some sanity checks are performed on 104.Fa cms . 105There must be at least one signature on the data. 106If the content is detached, 107.Fa indata 108cannot be 109.Dv NULL . 110.Pp 111An attempt is made to locate all the signing certificate(s), first 112looking in the 113.Fa certs 114parameter (if it is not 115.Dv NULL ) 116and then looking in any certificates contained in the 117.Fa cms 118structure itself. 119If any signing certificate cannot be located, the operation fails. 120.Pp 121Each signing certificate is chain verified using the 122.Sy smimesign 123purpose and the supplied trusted certificate 124.Fa store . 125Any internal certificates in the message are used as untrusted CAs. 126If CRL checking is enabled in 127.Fa store , 128any internal CRLs are used in addition to attempting to look them up in 129.Fa store . 130If any chain verify fails, an error code is returned. 131.Pp 132Finally the signed content is read (and written to 133.Fa out 134if it is not 135.Dv NULL ) 136and the signature is checked. 137.Pp 138If all signatures verify correctly, then the function is successful. 139.Pp 140Any of the following 141.Fa flags 142(OR'ed together) can be passed to change the default verify behaviour: 143.Bl -tag -width Ds 144.It Dv CMS_NOINTERN 145Do not use the certificates in the message itself when 146locating the signing certificate(s). 147This means that all the signing certificates must be in the 148.Fa certs 149parameter. 150.It Dv CMS_NOCRL 151If CRL checking is enabled in 152.Fa store , 153then any CRLs in the message itself are ignored. 154.It Dv CMS_TEXT 155MIME headers for type text/plain are deleted from the content. 156If the content is not of type text/plain, an error is returned. 157.It Dv CMS_NO_SIGNER_CERT_VERIFY 158Do not verify signing certificates. 159.It Dv CMS_NO_ATTR_VERIFY 160Do not check the signed attributes signature. 161.It Dv CMS_NO_CONTENT_VERIFY 162Do not check the content digest. 163.El 164.Pp 165One application of 166.Dv CMS_NOINTERN 167is to only accept messages signed by a small number of certificates. 168The acceptable certificates would be passed in the 169.Fa certs 170parameter. 171In this case, if the signer is not one of the certificates supplied in 172.Fa certs , 173then the verify will fail because the signer cannot be found. 174.Pp 175In some cases the standard techniques for looking up and validating 176certificates are not appropriate: for example an application may wish to 177lookup certificates in a database or perform customised verification. 178This can be achieved by setting and verifying the signers certificates 179manually using the signed data utility functions. 180.Pp 181Care should be taken when modifying the default verify behaviour, for 182example setting 183.Dv CMS_NO_CONTENT_VERIFY 184will totally disable all content verification and any modified content 185will be considered valid. 186This combination is however useful if one merely wishes to write the 187content to 188.Fa out 189and its validity is not considered important. 190.Pp 191Chain verification should arguably be performed using the signing time 192rather than the current time. 193However since the signing time is supplied by the signer it cannot be 194trusted without additional evidence (such as a trusted timestamp). 195.Sh RETURN VALUES 196.Fn CMS_verify 197returns 1 for a successful verification or 0 if an error occurred. 198.Pp 199.Fn CMS_get0_signers 200returns all signers or 201.Dv NULL 202if an error occurred. 203The signers must be freed with 204.Fn sk_X509_free . 205.Pp 206The error can be obtained from 207.Xr ERR_get_error 3 . 208.Sh SEE ALSO 209.Xr CMS_ContentInfo_new 3 , 210.Xr CMS_get0_SignerInfos 3 , 211.Xr CMS_sign 3 , 212.Xr CMS_verify_receipt 3 213.Sh STANDARDS 214RFC 5652: Cryptographic Message Syntax (CMS), 215section 5.1: SignedData Type 216.Sh HISTORY 217These functions first appeared in OpenSSL 0.9.8h 218and have been available since 219.Ox 6.7 . 220.Sh BUGS 221The trusted certificate store is not searched for the signing certificate. 222This is primarily due to the inadequacies of the current 223.Vt X509_STORE 224functionality. 225.Pp 226The lack of single pass processing means that the signed content must 227all be held in memory if it is not detached. 228