From 693b6d1e36828fa17915a9297595f65c739b611a Mon Sep 17 00:00:00 2001
From: Azul <azul@riseup.net>
Date: Thu, 4 Oct 2012 09:54:47 +0200
Subject: using BIG_PRIME_N and hashing the byte array - tests pass

We still calculate M differently than in SRP 6a
---
 lib/srp/authentication.rb |  8 ++++----
 lib/srp/client.rb         | 20 ++++++++++----------
 lib/srp/util.rb           |  5 ++---
 test/auth_test.rb         |  2 +-
 4 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/lib/srp/authentication.rb b/lib/srp/authentication.rb
index 4afe20b..0505a58 100644
--- a/lib/srp/authentication.rb
+++ b/lib/srp/authentication.rb
@@ -13,18 +13,18 @@ module SRP
         @aa = aa
         @b = bigrand(32).hex
         # B = g^b + k v (mod N)
-        @bb = (modpow(GENERATOR, @b, PRIME_N) + multiplier * verifier) % PRIME_N
+        @bb = (modpow(GENERATOR, @b, BIG_PRIME_N) + multiplier * verifier) % BIG_PRIME_N
       end
 
       def u
-        calculate_u(aa, bb, PRIME_N)
+        calculate_u(aa, bb, BIG_PRIME_N)
       end
 
       # do not cache this - it's secret and someone might store the
       # session in a CookieStore
       def secret(verifier)
-        base = (modpow(verifier, u, PRIME_N) * aa) % PRIME_N
-        modpow(base, @b, PRIME_N)
+        base = (modpow(verifier, u, BIG_PRIME_N) * aa) % BIG_PRIME_N
+        modpow(base, @b, BIG_PRIME_N)
       end
 
       def m1(verifier)
diff --git a/lib/srp/client.rb b/lib/srp/client.rb
index 37f37d7..947bd7b 100644
--- a/lib/srp/client.rb
+++ b/lib/srp/client.rb
@@ -10,17 +10,17 @@ module SRP
     def initialize(username, password, salt = nil)
       @username = username
       @password = password
-      @salt = salt.hex || bigrand(4).hex
+      @salt = (salt || bigrand(4)).hex
       @multiplier = multiplier # let's cache it
       calculate_verifier
     end
 
     def authenticate(server, username, password)
-      x = calculate_x(username, password, salt)
+      x = calculate_x(username, password)
       a = bigrand(32).hex
-      aa = modpow(GENERATOR, a, PRIME_N) # A = g^a (mod N)
+      aa = modpow(GENERATOR, a, BIG_PRIME_N) # A = g^a (mod N)
       bb = server.handshake(username, aa)
-      u = calculate_u(aa, bb, PRIME_N)
+      u = calculate_u(aa, bb, BIG_PRIME_N)
       client_s = calculate_client_s(x, a, bb, u)
       server.validate(calculate_m(aa, bb, client_s))
     end
@@ -32,18 +32,18 @@ module SRP
       @verifier
     end
 
-    def calculate_x
+    def calculate_x(username = @username, password = @password)
       shex = '%x' % [@salt]
-      inner = sha256_str([@username, @password].join(':'))
+      inner = sha256_str([username, password].join(':'))
       sha256_str([shex].pack('H*') + [inner].pack('H*')).hex
     end
 
     def calculate_client_s(x, a, bb, u)
       base = bb
-      base += PRIME_N * @multiplier
-      base -= modpow(GENERATOR, x, PRIME_N) * @multiplier
-      base = base % PRIME_N
-      modpow(base, x * u + a, PRIME_N)
+      base += BIG_PRIME_N * @multiplier
+      base -= modpow(GENERATOR, x, BIG_PRIME_N) * @multiplier
+      base = base % BIG_PRIME_N
+      modpow(base, x * u + a, BIG_PRIME_N)
     end
   end
 end
diff --git a/lib/srp/util.rb b/lib/srp/util.rb
index 66bd9e7..cafa5f4 100644
--- a/lib/srp/util.rb
+++ b/lib/srp/util.rb
@@ -59,14 +59,13 @@ d15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e5
 
     def calculate_m(aa, bb, s)
       hashin = '%x%x%x' % [aa, bb, s]
-      sha256_str(hashin).hex
+      sha256_hex(hashin).hex
     end
 
     def calculate_u(aa, bb, n)
-      nlen = 2 * ((('%x' % [n]).length * 4 + 7) >> 3)
       aahex = '%x' % [aa]
       bbhex = '%x' % [bb]
-      return sha256_str("%x%x" % [aa, bb]).hex
+      return sha256_hex("%x%x" % [aa, bb]).hex
     end
   end
 
diff --git a/test/auth_test.rb b/test/auth_test.rb
index 4311683..559403a 100644
--- a/test/auth_test.rb
+++ b/test/auth_test.rb
@@ -35,7 +35,7 @@ class AuthTest < Test::Unit::TestCase
     assert @client.authenticate(@server, @username, @password)
   end
 
-  def test_wrong_password
+  def test_a_wrong_password
     assert !@client.authenticate(@server, @username, "wrong password")
   end
 
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