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 certficate
store (used for chain verification).
indata is the signed data if the
content is not present in
p7 (that is 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().
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.
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 is 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 (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 certificate. This means that all the
signers 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.
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 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 one for a successful verification and zero 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 signers certificate, this
is primarily due to the inadequacies of the current
X509_STORE
functionality.
The lack of single pass processing and need to hold all data in memory as
mentioned in
PKCS7_sign() also applies to
PKCS7_verify().
SEE ALSO¶
ERR_get_error(3),
PKCS7_sign(3)
HISTORY¶
PKCS7_verify() was added to OpenSSL 0.9.5