PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure
#include <openssl/pkcs7.h>
int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs, X509_STORE *store,
BIO *indata, BIO *out, int flags);
STACK_OF(X509) *PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags);
PKCS7_verify() is very similar to
CMS_verify(3). It verifies a
PKCS#7 signedData structure given in
p7. The optional
certs
parameter refers to a set of certificates in which to search for signer's
certificates.
p7 may contain extra untrusted CA certificates that may
be used for chain building as well as CRLs that may be used for certificate
validation.
store may be NULL or point to the trusted certificate store
to use for chain verification.
indata refers to the signed data if the
content is detached from
p7. Otherwise
indata should be NULL,
and then the signed data must be in
p7. The content is written to the
BIO
out unless it is NULL.
flags is an optional set of flags,
which can be used to modify the operation.
PKCS7_get0_signers() retrieves the signer's certificates from
p7,
it does
not check their validity or whether any signatures are valid.
The
certs and
flags parameters have the same meanings as in
PKCS7_verify().
Normally the verify process proceeds as follows.
Initially some sanity checks are performed on
p7. The type of
p7
must be SignedData. There must be at least one signature on the data and if
the content is detached
indata cannot be NULL. If the content is not
detached and
indata is not NULL then the structure has both embedded
and external content. To treat this as an error, use the flag
PKCS7_NO_DUAL_CONTENT. The default behavior allows this, for
compatibility with older versions of OpenSSL.
An attempt is made to locate all the signer's certificates, first looking in the
certs parameter (if it is not NULL). Then they are looked up in any
certificates contained in the
p7 structure unless
PKCS7_NOINTERN
is set. If any signer's certificates cannot be located the operation fails.
Each signer's certificate is chain verified using the
smimesign purpose
and using the trusted certificate store
store if supplied. Any internal
certificates in the message, which may have been added using
PKCS7_add_certificate(3), are used as untrusted CAs unless
PKCS7_NOCHAIN is set. If CRL checking is enabled in
store and
PKCS7_NOCRL is not set, any internal CRLs, which may have been added
using
PKCS7_add_crl(3), are used in addition to attempting to look them
up in
store. If
store is not NULL and any chain verify fails an
error code is returned.
Finally the signed content is read (and written to
out unless it is NULL)
and the signature is checked.
If all signatures verify correctly then the function is successful.
Any of the following flags (ored together) can be passed in the
flags
parameter to change the default verify behaviour. Only the flag
PKCS7_NOINTERN is meaningful to
PKCS7_get0_signers().
If
PKCS7_NOINTERN is set the certificates in the message itself are not
searched when locating the signer's certificates. This means that all the
signer's certificates must be in the
certs parameter.
If
PKCS7_NOCRL is set and CRL checking is enabled in
store then
any CRLs in the message itself are ignored.
If the
PKCS7_TEXT flag is set MIME headers for type
"text/plain" are deleted from the content. If the content is not of
type "text/plain" then an error is returned.
If
PKCS7_NOVERIFY is set the signer's certificates are not chain
verified.
If
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 certificates) must be contained in the trusted store.
If
PKCS7_NOSIGS is set then the signatures on the data are not checked.
One application of
PKCS7_NOINTERN is to only accept messages signed by a
small number of certificates. The acceptable certificates would be passed in
the
certs parameter. In this case if the signer's certificate is not
one of the certificates supplied in
certs then the verify will fail
because the signer cannot be found.
Care should be taken when modifying the default verify behaviour, for example
setting "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
out and
its validity is not considered important.
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).
PKCS7_verify() returns 1 for a successful verification and 0 if an error
occurs.
PKCS7_get0_signers() returns all signers or NULL if an error occurred.
The error can be obtained from
ERR_get_error(3).
The trusted certificate store is not searched for the signer's certificates.
This is primarily due to the inadequacies of the current
X509_STORE
functionality.
The lack of single pass processing means that the signed content must all be
held in memory if it is not detached.
CMS_verify(3),
PKCS7_add_certificate(3),
PKCS7_add_crl(3),
ERR_get_error(3),
PKCS7_sign(3)
Copyright 2002-2022 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy in the
file LICENSE in the source distribution or at
<
https://www.openssl.org/source/license.html>.