From 933567499fa4c46e42d45de6066064559cfded09 Mon Sep 17 00:00:00 2001
From: Azul <azul@riseup.net>
Date: Fri, 12 Jul 2013 11:50:45 +0200
Subject: also prefix our own toString(16) hex values

---
 spec/calculate_spec.js |  4 ++++
 spec/session_spec.js   |  2 +-
 src/srp_calculate.js   | 19 +++++++++++++++----
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/spec/calculate_spec.js b/spec/calculate_spec.js
index f60c343..be916c1 100644
--- a/spec/calculate_spec.js
+++ b/spec/calculate_spec.js
@@ -22,6 +22,10 @@ describe("Calculate", function() {
     expect(calculate.A(compare.a)).toBe(compare.aa);
   });
   
+  it("prefixes A with 0 if needed", function() {
+    expect(calculate.A("3971782b")[0]).toBe("0");
+  });
+  
   it("calculates the right x", function() {
     x = calculate.X("testuser","password","7686acb8")
     expect(x).toBe('84d6bb567ddf584b1d8c8728289644d45dbfbb02deedd05c0f64db96740f0398');
diff --git a/spec/session_spec.js b/spec/session_spec.js
index 8f19c71..e4e75b6 100644
--- a/spec/session_spec.js
+++ b/spec/session_spec.js
@@ -21,7 +21,7 @@ describe("Session", function() {
     aa: "4decb8543891f5a744b1e9b5bc375a474bfe3c5417e1db176cefcc7ba915338a14f309f8e0a4c7641bc9c9b9bd2e91c4d1beda1772c30d0350c9ba44f7c5911dfe6bb593ac2a2b30f1f6e5ec8a656cb4947c1907cf62f8d7283cbe32eb44b02158b51091ae130afa6063bb28cdea9ae159d4f222571e146f8715bfa31af09868",
     a: "d498c3d024ec17689b5320e33fc349a3f3f91320384155b3043fa410c90eab71",
     bb: "dee64fd54daafc18b338c5783ade3ff4275dfee8c97008e2d9fb445880a2e1d452c822a35e8e3f012bc6facaa28022f8de3fb1d632667d635abde0afc0ca4ed06c9197ea88f379042b10bc7b7f816a1ec14fefe6e9adef4ab904315b3a3f36749f3f6d1083b0eb0029173770f8e9342b098298389ba49a88d4ea6b78a7f576a4",
-    s: "50973f6e8134f95bd04f54f522e6e57d957d0640f91f0a989ff775712b81d5856ae3bdd2aa9c5eda8019e9db18065519c99c33a62c7f12f98e7aed60b153feee9ab73ba1272b4d76aa002da8cd47c6da733c88a0e70d4c3d6752fd366d66efe40870d26fd5d1755883b9489721e1881376628bf6ef89902f35e5e7e31227e2f",
+    s: "050973f6e8134f95bd04f54f522e6e57d957d0640f91f0a989ff775712b81d5856ae3bdd2aa9c5eda8019e9db18065519c99c33a62c7f12f98e7aed60b153feee9ab73ba1272b4d76aa002da8cd47c6da733c88a0e70d4c3d6752fd366d66efe40870d26fd5d1755883b9489721e1881376628bf6ef89902f35e5e7e31227e2f",
     k: "dd93e648abfe2ac6c6d46e062ded60b31ec043e55ceca1946ec29508f4c68461",
     m: "0ccf0c492f715484dc8343e22cd5967c2c5d01de743c5f0a9c5cfd017db1804c"
   };
diff --git a/src/srp_calculate.js b/src/srp_calculate.js
index 93a4568..9196e0c 100644
--- a/src/srp_calculate.js
+++ b/src/srp_calculate.js
@@ -9,7 +9,7 @@ srp.Calculate = function() {
 
   this.A = function(_a) { 
     a = new BigInteger(_a, 16);
-    return g.modPow(a, N).toString(16);
+    return zeroPrefix(g.modPow(a, N).toString(16));
   };
 
   // Calculates the X value
@@ -36,7 +36,7 @@ srp.Calculate = function() {
     var kgx = k.multiply(g.modPow(x, N));  
     var aux = a.add(u.multiply(x)); 
     
-    return B.subtract(kgx).modPow(aux, N).toString(16); 
+    return zeroPrefix(B.subtract(kgx).modPow(aux, N).toString(16)); 
   }
 
   this.K = function(_S) {
@@ -68,12 +68,13 @@ srp.Calculate = function() {
     {
       a = new BigInteger(32, rng);
     }
-    return a.toString(16);
+    return zeroPrefix(a.toString(16));
   };
   
   // some 16 byte random number
   this.randomSalt = function() {
-    return new BigInteger(64, rng).toString(16);
+    salt = new BigInteger(64, rng);
+    return zeroPrefix(salt.toString(16));
   }
 
   function hex2a(hex) {
@@ -86,6 +87,16 @@ srp.Calculate = function() {
     return str;
   }
 
+
+  function zeroPrefix(hex) {
+    if (hex.length % 2) {
+      return "0" + hex;
+    } else {
+      return hex;
+    }
+  }
+    
+
   function removeLeading0(hex) {
     if (hex[0] == "0") {
       return hex.substr(1);
-- 
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