/xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
0.9.7e/doc/crypto
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PKCS7_verify(3) 9/Oct/2002 (0.9.7e) PKCS7_verify(3)
NAME
PKCS7_verify - verify a PKCS#7 signedData structure
SYNOPSIS
int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs,
X509_STORE *store, BIO *indata, BIO *out, int flags);
int 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.
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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 1 for a successful verification and
zero or a negative value if an error occurs.
PKCS7_get0_signers() returns all signers or NULL if an error
occurred.
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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
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