142 lines
5.8 KiB
Plaintext
142 lines
5.8 KiB
Plaintext
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=pod
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=head1 NAME
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PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure
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=head1 SYNOPSIS
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#include <openssl/pkcs7.h>
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int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs, X509_STORE *store,
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BIO *indata, BIO *out, int flags);
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STACK_OF(X509) *PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags);
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=head1 DESCRIPTION
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PKCS7_verify() is very similar to L<CMS_verify(3)>.
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It verifies a PKCS#7 signedData structure given in I<p7>.
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The optional I<certs> parameter refers to a set of certificates
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in which to search for signer's certificates.
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I<p7> may contain extra untrusted CA certificates that may be used for
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chain building as well as CRLs that may be used for certificate validation.
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I<store> may be NULL or point to
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the trusted certificate store to use for chain verification.
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I<indata> refers to the signed data if the content is detached from I<p7>.
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Otherwise I<indata> should be NULL, and then the signed data must be in I<p7>.
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The content is written to the BIO I<out> unless it is NULL.
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I<flags> is an optional set of flags, which can be used to modify the operation.
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PKCS7_get0_signers() retrieves the signer's certificates from I<p7>, it does
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B<not> check their validity or whether any signatures are valid. The I<certs>
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and I<flags> parameters have the same meanings as in PKCS7_verify().
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=head1 VERIFY PROCESS
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Normally the verify process proceeds as follows.
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Initially some sanity checks are performed on I<p7>. The type of I<p7> must
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be SignedData. There must be at least one signature on the data and if
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the content is detached I<indata> cannot be NULL. If the content is
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not detached and I<indata> is not NULL then the structure has both
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embedded and external content. To treat this as an error, use the flag
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B<PKCS7_NO_DUAL_CONTENT>.
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The default behavior allows this, for compatibility with older
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versions of OpenSSL.
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An attempt is made to locate all the signer's certificates, first looking in
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the I<certs> parameter (if it is not NULL). Then they are looked up in any
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certificates contained in the I<p7> structure unless B<PKCS7_NOINTERN> is set.
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If any signer's certificates cannot be located the operation fails.
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Each signer's certificate is chain verified using the B<smimesign> purpose and
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using the trusted certificate store I<store> if supplied.
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Any internal certificates in the message, which may have been added using
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L<PKCS7_add_certificate(3)>, are used as untrusted CAs unless B<PKCS7_NOCHAIN>
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is set.
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If CRL checking is enabled in I<store> and B<PKCS7_NOCRL> is not set,
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any internal CRLs, which may have been added using L<PKCS7_add_crl(3)>,
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are used in addition to attempting to look them up in I<store>.
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If I<store> is not NULL and any chain verify fails an error code is returned.
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Finally the signed content is read (and written to I<out> unless it is NULL)
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and the signature is checked.
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If all signatures verify correctly then the function is successful.
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Any of the following flags (ored together) can be passed in the I<flags>
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parameter to change the default verify behaviour.
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Only the flag B<PKCS7_NOINTERN> is meaningful to PKCS7_get0_signers().
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If B<PKCS7_NOINTERN> is set the certificates in the message itself are not
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searched when locating the signer's certificates.
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This means that all the signer's certificates must be in the I<certs> parameter.
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If B<PKCS7_NOCRL> is set and CRL checking is enabled in I<store> then any
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CRLs in the message itself are ignored.
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If the B<PKCS7_TEXT> flag is set MIME headers for type C<text/plain> are deleted
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from the content. If the content is not of type C<text/plain> then an error is
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returned.
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If B<PKCS7_NOVERIFY> is set the signer's certificates are not chain verified.
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If B<PKCS7_NOCHAIN> is set then the certificates contained in the message are
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not used as untrusted CAs. This means that the whole verify chain (apart from
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the signer's certificates) must be contained in the trusted store.
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If B<PKCS7_NOSIGS> is set then the signatures on the data are not checked.
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=head1 NOTES
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One application of B<PKCS7_NOINTERN> is to only accept messages signed by
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a small number of certificates. The acceptable certificates would be passed
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in the I<certs> parameter. In this case if the signer's certificate is not one
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of the certificates supplied in I<certs> then the verify will fail because the
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signer cannot be found.
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Care should be taken when modifying the default verify behaviour, for example
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setting B<PKCS7_NOVERIFY|PKCS7_NOSIGS> will totally disable all verification
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and any signed message will be considered valid. This combination is however
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useful if one merely wishes to write the content to I<out> and its validity
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is not considered important.
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Chain verification should arguably be performed using the signing time rather
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than the current time. However, since the signing time is supplied by the
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signer it cannot be trusted without additional evidence (such as a trusted
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timestamp).
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=head1 RETURN VALUES
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PKCS7_verify() returns 1 for a successful verification and 0 if an error occurs.
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PKCS7_get0_signers() returns all signers or NULL if an error occurred.
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The error can be obtained from L<ERR_get_error(3)>.
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=head1 BUGS
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The trusted certificate store is not searched for the signer's certificates.
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This is primarily due to the inadequacies of the current B<X509_STORE>
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functionality.
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The lack of single pass processing means that the signed content must all
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be held in memory if it is not detached.
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=head1 SEE ALSO
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L<CMS_verify(3)>, L<PKCS7_add_certificate(3)>, L<PKCS7_add_crl(3)>,
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L<ERR_get_error(3)>, L<PKCS7_sign(3)>
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=head1 COPYRIGHT
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Copyright 2002-2022 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the OpenSSL license (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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