use latest rabin

docs/rabin.rst

@@ -2,35 +2,25 @@
 Rabin Signature
 ===============
 
-`Rabin signature <https://nchain.com/app/uploads/2018/09/Rabin-Signatures-in-Bitcoin-Cash.pdf>`_ is an alternative form of digital signature to ECDSA used in Bitcoin.
+`Rabin signature <https://medium.com/@xiaohuiliu/access-external-data-from-bitcoin-smart-contracts-2ecdc7448c43>`_ is an alternative form of digital signature to ECDSA used in Bitcoin.
 
 .. code-block:: solidity
 
     contract RabinSignature {
-        Ripemd160 nHash;    // nHash = b"88d9931ea73d60eaf7e5671efc0552b912911f2a"
-
-        function hash3072(bytes x) returns (bytes) {
-            Sha256 y = sha256(x);
-
-            int i = 0;
-            // start with empty
-            bytes ret = b"";
-            // divide into 3072 / 256 = 12 slices
-            loop (12) {
-                // 256 bits is 32 bytes
-                bytes slice = y[32 * i : 32 * (i + 1)];
-                ret = ret ++ sha256(slice);
-                i = i + 1;
-            }
-
-            // 3072 bit hash
-            return ret;
+        public function verifySig(int sig, bytes msg, bytes padding, int n) {
+            int h = this.fromLEUnsigned(this.hash(msg ++ padding));
+            require((sig * sig) % n == h % n);
         }
 
-        public function verifySig(int S, bytes U, bytes m, int lambda, bytes n) {
-            require(hash160(n) == this.nHash);
+        function hash(bytes x) returns (bytes) {
+            // expand into 512 bit hash
+            bytes hx = sha256(x);
+            int idx = length(hx) / 2;
+            return sha256(hx[:idx]) ++ sha256(hx[idx:]);
+        }
 
-            int h = unpack(this.hash3072(m ++ U));
-            require(S * S == h + lambda * unpack(n));
+        function fromLEUnsigned(bytes b) returns (int) {
+            // append positive sign byte. This does not hurt even when sign bit is already positive
+            return unpack(b ++ b"00");
         }
     }