[crypto] Add an abstraction of an elliptic curve

Define an abstraction of an elliptic curve with a fixed generator and
one supported operation (scalar multiplication of a curve point).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/crypto.h

@@ -195,6 +195,23 @@ struct pubkey_algorithm {
 			  const void *public_key, size_t public_key_len );
 };
 
+/** An elliptic curve */
+struct elliptic_curve {
+	/** Curve name */
+	const char *name;
+	/** Key size */
+	size_t keysize;
+	/** Multiply scalar by curve point
+	 *
+	 * @v base		Base point (or NULL to use generator)
+	 * @v scalar		Scalar multiple
+	 * @v result		Result point to fill in
+	 * @ret rc		Return status code
+	 */
+	int ( * multiply ) ( const void *base, const void *scalar,
+			     void *result );
+};
+
 static inline void digest_init ( struct digest_algorithm *digest,
 				 void *ctx ) {
 	digest->init ( ctx );
@@ -302,6 +319,12 @@ static inline int pubkey_match ( struct pubkey_algorithm *pubkey,
 			       public_key_len );
 }
 
+static inline int elliptic_multiply ( struct elliptic_curve *curve,
+				      const void *base, const void *scalar,
+				      void *result ) {
+	return curve->multiply ( base, scalar, result );
+}
+
 extern void digest_null_init ( void *ctx );
 extern void digest_null_update ( void *ctx, const void *src, size_t len );
 extern void digest_null_final ( void *ctx, void *out );

src/include/ipxe/x25519.h

@@ -11,6 +11,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <stdint.h>
 #include <ipxe/bigint.h>
+#include <ipxe/crypto.h>
 
 /** X25519 unsigned big integer size
  *
@@ -88,4 +89,6 @@ extern int x25519_key ( const struct x25519_value *base,
 			const struct x25519_value *scalar,
 			struct x25519_value *result );
 
+extern struct elliptic_curve x25519_curve;
+
 #endif /* _IPXE_X25519_H */