Ubuntu Manpage: PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure

Provided by: libssl-doc_3.0.13-0ubuntu3_all

NAME

       PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure

SYNOPSIS

        #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);

DESCRIPTION

       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().

VERIFY PROCESS

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.

NOTES

       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).

RETURN VALUES

       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).

BUGS

       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.

COPYRIGHT

       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>.