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PKCS7_verify(3) OpenSSL PKCS7_verify(3)
PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure
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);
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
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 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
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
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 one for a successful verification and zero if an
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
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
1.0.2h 2016-05-03 PKCS7_verify(3)