From dbb5f2d6a3d34c0fa899fd26313873cc69dbad9d Mon Sep 17 00:00:00 2001
From: Shen Noether <Shen.Noether@gmx.com>
Date: Sat, 9 Jul 2016 20:04:23 +0100
Subject: [PATCH] ringct: optimization/cleanup of hash functions

---
 src/ringct/rctOps.cpp  | 25 +++++++++++++++++++++++++
 src/ringct/rctOps.h    |  3 +++
 src/ringct/rctSigs.cpp | 39 +++++++++++++++++----------------------
 3 files changed, 45 insertions(+), 22 deletions(-)

diff --git a/src/ringct/rctOps.cpp b/src/ringct/rctOps.cpp
index 3fa870fd..c18ee6f2 100644
--- a/src/ringct/rctOps.cpp
+++ b/src/ringct/rctOps.cpp
@@ -423,6 +423,31 @@ namespace rct {
         return rv;
     }
     
+   //cn_fast_hash for a key-vector of arbitrary length
+   //this is useful since you take a number of keys
+   //put them in the key vector and it concatenates them
+   //and then hashes them
+   key cn_fast_hash(const keyV &keys) {
+       size_t l = keys.size();
+       vector<unsigned char> m(l * 32);
+       size_t i, j;
+       for (i = 0 ; i < l ; i++) {
+           for (j = 0 ; j < 32 ; j++) {
+               m[i * 32 + j] = keys[i][j];
+           }
+       }
+       key rv;
+       cn_fast_hash(rv, &m[0], 32 * l);
+       //dp(rv);
+       return rv;
+   }
+   
+   key hash_to_scalar(const keyV &keys) {
+       key rv = cn_fast_hash(keys);
+       sc_reduce32(rv.bytes);
+       return rv;
+   }
+
     key hashToPointSimple(const key & hh) {
         key pointk;
         ge_p1p1 point2;
diff --git a/src/ringct/rctOps.h b/src/ringct/rctOps.h
index ad6c520d..6438a1f0 100644
--- a/src/ringct/rctOps.h
+++ b/src/ringct/rctOps.h
@@ -151,6 +151,9 @@ namespace rct {
     key hash_to_scalar128(const void * in);
     key cn_fast_hash(ctkeyV PC);
     key hash_to_scalar(ctkeyV PC);
+    //for mg sigs 
+    key cn_fast_hash(const keyV &keys);
+    key hash_to_scalar(const keyV &keys);
 
     //returns hashToPoint as described in https://github.com/ShenNoether/ge_fromfe_writeup 
     key hashToPointSimple(const key &in);
diff --git a/src/ringct/rctSigs.cpp b/src/ringct/rctSigs.cpp
index c9e34ddb..7fcb8e15 100644
--- a/src/ringct/rctSigs.cpp
+++ b/src/ringct/rctSigs.cpp
@@ -169,22 +169,21 @@ namespace rct {
         keyV alpha(rows);
         keyV aG(rows);
         keyV aHP(rows);
-        key m2hash;
-        unsigned char m2[128]; 
-        memcpy(m2, message.bytes, 32);
+        keyV toHash(1 + 3 * rows);
+        toHash[0] = message;
         DP("here1");
         for (i = 0; i < rows; i++) {
             skpkGen(alpha[i], aG[i]); //need to save alphas for later..
             Hi = hashToPoint(pk[index][i]);
             aHP[i] = scalarmultKey(Hi, alpha[i]);
-            memcpy(m2+32, pk[index][i].bytes, 32);
-            memcpy(m2 + 64, aG[i].bytes, 32);
-            memcpy(m2 + 96, aHP[i].bytes, 32);
+            toHash[3 * i + 1] = pk[index][i];
+            toHash[3 * i + 2] = aG[i];
+            toHash[3 * i + 3] = aHP[i];
             rv.II[i] = scalarmultKey(Hi, xx[i]);
             precomp(Ip[i].k, rv.II[i]);
-            m2hash = hash_to_scalar128(m2);
-            sc_add(c_old.bytes, c_old.bytes, m2hash.bytes);
         }
+        c_old = hash_to_scalar(toHash);
+
         
         i = (index + 1) % cols;
         if (i == 0) {
@@ -198,12 +197,11 @@ namespace rct {
                 addKeys2(L, rv.ss[i][j], c_old, pk[i][j]);
                 hashToPoint(Hi, pk[i][j]);
                 addKeys3(R, rv.ss[i][j], Hi, c_old, Ip[j].k);
-                memcpy(m2+32, pk[i][j].bytes, 32);
-                memcpy(m2 + 64, L.bytes, 32);
-                memcpy(m2 + 96, R.bytes, 32);      
-                m2hash = hash_to_scalar128(m2);
-                sc_add(c.bytes, c.bytes, m2hash.bytes);
+                toHash[3 * j + 1] = pk[i][j];
+                toHash[3 * j + 2] = L; 
+                toHash[3 * j + 3] = R;
             }
+            c = hash_to_scalar(toHash);
             copy(c_old, c);
             i = (i + 1) % cols;
             
@@ -248,10 +246,8 @@ namespace rct {
         for (i= 0 ; i< rows ; i++) {
             precomp(Ip[i].k, II[i]);
         }
-        unsigned char m2[128]; 
-        memcpy(m2, message.bytes, 32);
-        
-        key m2hash;
+        keyV toHash(1 + 3 * rows);
+        toHash[0] = message;
         i = 0;
         while (i < cols) {
             sc_0(c.bytes);
@@ -259,12 +255,11 @@ namespace rct {
                 addKeys2(L, rv.ss[i][j], c_old, pk[i][j]);
                 hashToPoint(Hi, pk[i][j]);
                 addKeys3(R, rv.ss[i][j], Hi, c_old, Ip[j].k);
-                memcpy(m2 + 32, pk[i][j].bytes, 32);
-                memcpy(m2 + 64, L.bytes, 32);
-                memcpy(m2 + 96, R.bytes, 32);      
-                m2hash = hash_to_scalar128(m2);
-                sc_add(c.bytes, c.bytes, m2hash.bytes);
+                toHash[3 * j + 1] = pk[i][j];
+                toHash[3 * j + 2] = L; 
+                toHash[3 * j + 3] = R;
             }
+            c = hash_to_scalar(toHash);
             copy(c_old, c);
             i = (i + 1);
         }