Updated: 2021/Apr/14

PKCS7_verify(3)                     OpenSSL                    PKCS7_verify(3)

       PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure

       libcrypto, -lcrypto

        #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);

       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 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.  If the content is not
       detached and indata is not NULL, then the structure has both embedded
       and external content. To treat this as an error, use the flag
       PKCS7_NO_DUAL_CONTENT.  The default behavior allows this, for
       compatibility with older versions of OpenSSL.

       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
       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().

       ERR_get_error(3), PKCS7_sign(3)

       Copyright 2002-2020 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at

1.1.1i                            2020-12-10                   PKCS7_verify(3)