.\" $OpenBSD: CMS_verify.3,v 1.8 2022/01/19 20:28:06 tb Exp $ .\" full merge up to: OpenSSL 35fd9953 May 28 14:49:38 2019 +0200 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2008 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. All advertising materials mentioning features or use of this .\" software must display the following acknowledgment: .\" "This product includes software developed by the OpenSSL Project .\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)" .\" .\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to .\" endorse or promote products derived from this software without .\" prior written permission. For written permission, please contact .\" openssl-core@openssl.org. .\" .\" 5. Products derived from this software may not be called "OpenSSL" .\" nor may "OpenSSL" appear in their names without prior written .\" permission of the OpenSSL Project. .\" .\" 6. Redistributions of any form whatsoever must retain the following .\" acknowledgment: .\" "This product includes software developed by the OpenSSL Project .\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" .\" .\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY .\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: January 19 2022 $ .Dt CMS_VERIFY 3 .Os .Sh NAME .Nm CMS_verify , .Nm CMS_get0_signers .Nd verify a CMS SignedData structure .Sh SYNOPSIS .In openssl/cms.h .Ft int .Fo CMS_verify .Fa "CMS_ContentInfo *cms" .Fa "STACK_OF(X509) *certs" .Fa "X509_STORE *store" .Fa "BIO *indata" .Fa "BIO *out" .Fa "unsigned int flags" .Fc .Ft STACK_OF(X509) * .Fo CMS_get0_signers .Fa "CMS_ContentInfo *cms" .Fc .Sh DESCRIPTION .Fn CMS_verify verifies the CMS .Vt SignedData structure .Fa cms . .Fa certs is a set of certificates in which to search for the signing certificate(s). .Fa store is a trusted certificate store used for chain verification. .Fa indata is the detached content if the content is not present in .Fa cms . The content is written to .Fa out if it is not .Dv NULL . .Pp .Fn CMS_get0_signers retrieves the signing certificate(s) from .Fa cms . It must be called after a successful .Fn CMS_verify operation. The signers must be freed with .Fn sk_X509_free . .Pp Normally the verify process proceeds as follows. .Pp Initially some sanity checks are performed on .Fa cms . There must be at least one signature on the data. If the content is detached, .Fa indata cannot be .Dv NULL . .Pp An attempt is made to locate all the signing certificate(s), first looking in the .Fa certs parameter (if it is not .Dv NULL ) and then looking in any certificates contained in the .Fa cms structure itself. If any signing certificate cannot be located, the operation fails. .Pp Each signing certificate is chain verified using the .Sy smimesign purpose and the supplied trusted certificate .Fa store . Any internal certificates in the message are used as untrusted CAs. If CRL checking is enabled in .Fa store , any internal CRLs are used in addition to attempting to look them up in .Fa store . If any chain verify fails, an error code is returned. .Pp Finally the signed content is read (and written to .Fa out if it is not .Dv NULL ) and the signature is checked. .Pp If all signatures verify correctly, then the function is successful. .Pp Any of the following .Fa flags (OR'ed together) can be passed to change the default verify behaviour: .Bl -tag -width Ds .It Dv CMS_NOINTERN Do not use the certificates in the message itself when locating the signing certificate(s). This means that all the signing certificates must be in the .Fa certs parameter. .It Dv CMS_NOCRL If CRL checking is enabled in .Fa store , then any CRLs in the message itself are ignored. .It Dv CMS_TEXT MIME headers for type text/plain are deleted from the content. If the content is not of type text/plain, an error is returned. .It Dv CMS_NO_SIGNER_CERT_VERIFY Do not verify signing certificates. .It Dv CMS_NO_ATTR_VERIFY Do not check the signed attributes signature. .It Dv CMS_NO_CONTENT_VERIFY Do not check the content digest. .El .Pp One application of .Dv CMS_NOINTERN is to only accept messages signed by a small number of certificates. The acceptable certificates would be passed in the .Fa certs parameter. In this case, if the signer is not one of the certificates supplied in .Fa certs , then the verify will fail because the signer cannot be found. .Pp In some cases the standard techniques for looking up and validating certificates are not appropriate: for example an application may wish to lookup certificates in a database or perform customised verification. This can be achieved by setting and verifying the signers certificates manually using the signed data utility functions. .Pp Care should be taken when modifying the default verify behaviour, for example setting .Dv CMS_NO_CONTENT_VERIFY will totally disable all content verification and any modified content will be considered valid. This combination is however useful if one merely wishes to write the content to .Fa out and its validity is not considered important. .Pp Chain verification should arguably be performed using the signing time rather than the current time. However since the signing time is supplied by the signer it cannot be trusted without additional evidence (such as a trusted timestamp). .Sh RETURN VALUES .Fn CMS_verify returns 1 for a successful verification or 0 if an error occurred. .Pp .Fn CMS_get0_signers returns all signers or .Dv NULL if an error occurred. The signers must be freed with .Fn sk_X509_free . .Pp The error can be obtained from .Xr ERR_get_error 3 . .Sh SEE ALSO .Xr CMS_ContentInfo_new 3 , .Xr CMS_get0_SignerInfos 3 , .Xr CMS_sign 3 , .Xr CMS_verify_receipt 3 .Sh STANDARDS RFC 5652: Cryptographic Message Syntax (CMS), section 5.1: SignedData Type .Sh HISTORY These functions first appeared in OpenSSL 0.9.8h and have been available since .Ox 6.7 . .Sh BUGS The trusted certificate store is not searched for the signing certificate. This is primarily due to the inadequacies of the current .Vt X509_STORE functionality. .Pp The lack of single pass processing means that the signed content must all be held in memory if it is not detached.