.\" $OpenBSD: PKCS7_verify.3,v 1.11 2022/03/31 17:27:17 naddy Exp $ .\" OpenSSL a528d4f0 Oct 27 13:40:11 2015 -0400 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2002, 2006, 2013, 2014, 2015 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. 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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: March 31 2022 $ .Dt PKCS7_VERIFY 3 .Os .Sh NAME .Nm PKCS7_verify , .Nm PKCS7_get0_signers .Nd verify a PKCS#7 signedData structure .Sh SYNOPSIS .In openssl/pkcs7.h .Ft int .Fo PKCS7_verify .Fa "PKCS7 *p7" .Fa "STACK_OF(X509) *certs" .Fa "X509_STORE *store" .Fa "BIO *indata" .Fa "BIO *out" .Fa "int flags" .Fc .Ft STACK_OF(X509) * .Fo PKCS7_get0_signers .Fa "PKCS7 *p7" .Fa "STACK_OF(X509) *certs" .Fa "int flags" .Fc .Sh DESCRIPTION .Fn PKCS7_verify verifies a PKCS#7 signedData structure. .Fa p7 is the .Vt PKCS7 structure to verify. .Fa certs is a set of certificates in which to search for the signer's certificate. .Fa store is a trusted certificate store (used for chain verification). .Fa indata is the signed data if the content is not present in .Fa p7 , that is if it is detached. The content is written to .Fa out if it is not .Dv NULL . .Pp .Fa flags is an optional set of flags, which can be used to modify the verify operation. .Pp .Fn PKCS7_get0_signers retrieves the signer's certificates from .Fa p7 . The signers must be freed with .Fn sk_X509_free . It does .Sy not check their validity or whether any signatures are valid. The .Fa certs and .Fa flags parameters have the same meanings as in .Fn PKCS7_verify . .Pp Normally the verify process proceeds as follows. .Pp Initially some sanity checks are performed on .Fa p7 . The type of .Fa p7 must be signedData. There must be at least one signature on the data and if the content is detached, .Fa indata cannot be .Dv NULL . .Pp An attempt is made to locate all the signer's certificates, first looking in the .Fa certs parameter (if it is not .Dv NULL ) and then looking in any certificates contained in the .Fa p7 structure itself. If any signer's certificates cannot be located, the operation fails. .Pp Each signer's certificate is chain verified using the .Sy smimesign purpose and the supplied trusted certificate store. Any internal certificates in the message are used as untrusted CAs. 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's checked. .Pp If all signature's verify correctly then the function is successful. .Pp Any of the following flags (OR'ed together) can be passed in the .Fa flags parameter to change the default verify behaviour. Only the flag .Dv PKCS7_NOINTERN is meaningful to .Fn PKCS7_get0_signers . .Pp If .Dv PKCS7_NOINTERN is set, the certificates in the message itself are not searched when locating the signer's certificate. This means that all the signer's certificates must be in the .Fa certs parameter. .Pp If the .Dv PKCS7_TEXT flag is set, MIME headers for type .Sy text/plain are deleted from the content. If the content is not of type .Sy text/plain , then an error is returned. .Pp If .Dv PKCS7_NOVERIFY is set, the signer's certificates are not chain verified. .Pp If .Dv PKCS7_NOCHAIN is set, then the certificates contained in the message are not used as untrusted CAs. This means that the whole verify chain (apart from the signer's certificate) must be contained in the trusted store. .Pp If .Dv PKCS7_NOSIGS is set, then the signatures on the data are not checked. .Pp One application of .Dv PKCS7_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 Care should be taken when modifying the default verify behaviour, for example setting .Dv PKCS7_NOVERIFY | PKCS7_NOSIGS will totally disable all verification and any signed message 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 PKCS7_verify returns 1 for a successful verification and 0 or a negative value if an error occurs. .Pp .Fn PKCS7_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 PKCS7_decrypt 3 , .Xr PKCS7_new 3 , .Xr PKCS7_sign 3 , .Xr X509_STORE_new 3 .Sh HISTORY .Fn PKCS7_verify and .Fn PKCS7_get0_signers first appeared in OpenSSL 0.9.5 and have been available since .Ox 2.7 . .Sh BUGS The trusted certificate store is not searched for the signer's certificate. This is primarily due to the inadequacies of the current .Vt X509_STORE functionality. .Pp The lack of single pass processing and the need to hold all data in memory as mentioned in .Xr PKCS7_sign 3 also applies to .Fn PKCS7_verify .