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()
verifies a PKCS#7 signedData structure. p7 is the
PKCS7 structure to verify. certs
is a set of certificates in which to search for the signer's certificate.
store is a trusted certificate store (used for chain
verification). indata is the signed data if the
content is not present in p7, that is if it is
detached. The content is written to out if it is not
NULL.
flags is an optional set of flags, which can be used to modify the verify 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.
An attempt is made to locate all the signer's certificates, first
looking in the certs parameter (if it is not
NULL) and then looking in any certificates contained
in the p7 structure itself. If any signer's
certificates cannot be located the operation fails.
Each signer's certificate is chain verified using the 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.
Finally, the signed content is read (and written to
out if it is not NULL) and the
signature's checked.
If all signature's verify correctly then the function is successful.
Any of the following flags (OR'ed
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
certificate. This means that all the signer's certificates must be in the
certs parameter.
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 certificate) 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 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 or a negative value 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).
SEE ALSO
ERR_get_error(3), PKCS7_new(3), PKCS7_sign(3), X509_STORE_new(3)
HISTORY
PKCS7_verify() and
PKCS7_get0_signers() first appeared in OpenSSL 0.9.5
and have been available since OpenBSD 2.7.
BUGS
The trusted certificate store is not searched for the signer's certificate. This is primarily due to the inadequacies of the current X509_STORE functionality.
The lack of single pass processing and the need to hold all data
in memory as mentioned in
PKCS7_sign(3) also applies to
PKCS7_verify().