1.\" $OpenBSD: CMS_verify.3,v 1.7 2019/11/02 15:39:46 schwarze 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: November 2 2019 $ 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 must be called after a successful 96.Fn CMS_verify 97operation. 98.Pp 99Normally the verify process proceeds as follows. 100.Pp 101Initially some sanity checks are performed on 102.Fa cms . 103There must be at least one signature on the data. 104If the content is detached, 105.Fa indata 106cannot be 107.Dv NULL . 108.Pp 109An attempt is made to locate all the signing certificate(s), first 110looking in the 111.Fa certs 112parameter (if it is not 113.Dv NULL ) 114and then looking in any certificates contained in the 115.Fa cms 116structure itself. 117If any signing certificate cannot be located, the operation fails. 118.Pp 119Each signing certificate is chain verified using the 120.Sy smimesign 121purpose and the supplied trusted certificate 122.Fa store . 123Any internal certificates in the message are used as untrusted CAs. 124If CRL checking is enabled in 125.Fa store , 126any internal CRLs are used in addition to attempting to look them up in 127.Fa store . 128If any chain verify fails, an error code is returned. 129.Pp 130Finally the signed content is read (and written to 131.Fa out 132if it is not 133.Dv NULL ) 134and the signature is checked. 135.Pp 136If all signatures verify correctly, then the function is successful. 137.Pp 138Any of the following 139.Fa flags 140(OR'ed together) can be passed to change the default verify behaviour: 141.Bl -tag -width Ds 142.It Dv CMS_NOINTERN 143Do not use the certificates in the message itself when 144locating the signing certificate(s). 145This means that all the signing certificates must be in the 146.Fa certs 147parameter. 148.It Dv CMS_NOCRL 149If CRL checking is enabled in 150.Fa store , 151then any CRLs in the message itself are ignored. 152.It Dv CMS_TEXT 153MIME headers for type text/plain are deleted from the content. 154If the content is not of type text/plain, an error is returned. 155.It Dv CMS_NO_SIGNER_CERT_VERIFY 156Do not verify signing certificates. 157.It Dv CMS_NO_ATTR_VERIFY 158Do not check the signed attributes signature. 159.It Dv CMS_NO_CONTENT_VERIFY 160Do not check the content digest. 161.El 162.Pp 163One application of 164.Dv CMS_NOINTERN 165is to only accept messages signed by a small number of certificates. 166The acceptable certificates would be passed in the 167.Fa certs 168parameter. 169In this case, if the signer is not one of the certificates supplied in 170.Fa certs , 171then the verify will fail because the signer cannot be found. 172.Pp 173In some cases the standard techniques for looking up and validating 174certificates are not appropriate: for example an application may wish to 175lookup certificates in a database or perform customised verification. 176This can be achieved by setting and verifying the signers certificates 177manually using the signed data utility functions. 178.Pp 179Care should be taken when modifying the default verify behaviour, for 180example setting 181.Dv CMS_NO_CONTENT_VERIFY 182will totally disable all content verification and any modified content 183will be considered valid. 184This combination is however useful if one merely wishes to write the 185content to 186.Fa out 187and its validity is not considered important. 188.Pp 189Chain verification should arguably be performed using the signing time 190rather than the current time. 191However since the signing time is supplied by the signer it cannot be 192trusted without additional evidence (such as a trusted timestamp). 193.Sh RETURN VALUES 194.Fn CMS_verify 195returns 1 for a successful verification or 0 if an error occurred. 196.Pp 197.Fn CMS_get0_signers 198returns all signers or 199.Dv NULL 200if an error occurred. 201.Pp 202The error can be obtained from 203.Xr ERR_get_error 3 . 204.Sh SEE ALSO 205.Xr CMS_ContentInfo_new 3 , 206.Xr CMS_get0_SignerInfos 3 , 207.Xr CMS_sign 3 , 208.Xr CMS_verify_receipt 3 209.Sh STANDARDS 210RFC 5652: Cryptographic Message Syntax (CMS), 211section 5.1: SignedData Type 212.Sh HISTORY 213These functions first appeared in OpenSSL 0.9.8h 214and have been available since 215.Ox 6.7 . 216.Sh BUGS 217The trusted certificate store is not searched for the signing certificate. 218This is primarily due to the inadequacies of the current 219.Vt X509_STORE 220functionality. 221.Pp 222The lack of single pass processing means that the signed content must 223all be held in memory if it is not detached. 224