PKCS7_verify — verify a PKCS#7 signedData structure
int PKCS7_verify(PKCS7 *p7, STACK_OF(X509)
*certs, X509_STORE *store, BIO *indata, BIO *out, int flags);
PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags);
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().
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
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
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.
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).
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.
The error can be obtained from ERR_get_error(3)
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().
PKCS7_verify() was added to OpenSSL 0.9.5