PKCS#7: Implement a parser [RFC 2315]

Implement a parser for a PKCS#7 signed-data message as described in part of
RFC 2315.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 03a6eb9..a7cec9d 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -37,4 +37,13 @@
 	  data and provides the ability to instantiate a crypto key from a
 	  public key packet found inside the certificate.
 
+config PKCS7_MESSAGE_PARSER
+	tristate "PKCS#7 message parser"
+	depends on X509_CERTIFICATE_PARSER
+	select ASN1
+	select OID_REGISTRY
+	help
+	  This option provides support for parsing PKCS#7 format messages for
+	  signature data and provides the ability to verify the signature.
+
 endif # ASYMMETRIC_KEY_TYPE