RSA: Implement signature verification algorithm [PKCS#1 / RFC3447]

Implement RSA public key cryptography [PKCS#1 / RFC3447].  At this time, only
the signature verification algorithm is supported.  This uses the asymmetric
public key subtype to hold its key data.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index bbfccaa..561759d 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -18,4 +18,11 @@
 	  appropriate hash algorithms (such as SHA-1) must be available.
 	  ENOPKG will be reported if the requisite algorithm is unavailable.
 
+config PUBLIC_KEY_ALGO_RSA
+	tristate "RSA public-key algorithm"
+	depends on ASYMMETRIC_PUBLIC_KEY_SUBTYPE
+	select MPILIB_EXTRA
+	help
+	  This option enables support for the RSA algorithm (PKCS#1, RFC3447).
+
 endif # ASYMMETRIC_KEY_TYPE