From ce246cb722f7f61b3a1ba7223857627f1bed4f4c Mon Sep 17 00:00:00 2001
From: Azul <azul@riseup.net>
Date: Fri, 5 Oct 2012 12:44:22 +0200
Subject: made m and m2 calculation srp 6A compatible

Also added session_test that tests agains values calculated with py_srp
---
 lib/srp/session.rb   | 16 +++++++++-------
 test/session_test.rb | 28 ++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 7 deletions(-)
 create mode 100644 test/session_test.rb

diff --git a/lib/srp/session.rb b/lib/srp/session.rb
index a1153e0..db8d428 100644
--- a/lib/srp/session.rb
+++ b/lib/srp/session.rb
@@ -27,15 +27,16 @@ module SRP
 
     def authenticate(m)
       if(m == calculate_m(server_secret))
-        return calculate_m2(m, server_secret)
+        return calculate_m2
       end
     end
 
     protected
 
-    def initialize_server(aa)
+    # only seed b for testing purposes.
+    def initialize_server(aa, b = nil)
       @aa = aa
-      @b = bigrand(32).hex
+      @b =  b || bigrand(32).hex
       # B = g^b + k v (mod N)
       @bb = (modpow(GENERATOR, @b) + multiplier * @user.verifier) % BIG_PRIME_N
       @u = calculate_u
@@ -66,13 +67,14 @@ module SRP
     # this is outdated - SRP 6a uses
     # M = H(H(N) xor H(g), H(I), s, A, B, K)
     def calculate_m(secret)
-      n_xor_g_hash = sha256_str(hn_xor_hg).hex
+      @k = sha256_int(secret).hex
+      n_xor_g_long = hn_xor_hg.bytes.map{|b| "%02x" % b.ord}.join.hex
       username_hash = sha256_str(@user.username).hex
-      sha256_int(n_xor_g_hash, username_hash, @user.salt, @aa, @bb, secret).hex
+      @m = sha256_int(n_xor_g_long, username_hash, @user.salt, @aa, @bb, @k).hex
     end
 
-    def calculate_m2(m, secret)
-      sha256_int(@aa, m, secret).hex
+    def calculate_m2
+      sha256_int(@aa, @m, @k).hex
     end
 
     def calculate_u
diff --git a/test/session_test.rb b/test/session_test.rb
new file mode 100644
index 0000000..f41b34b
--- /dev/null
+++ b/test/session_test.rb
@@ -0,0 +1,28 @@
+require File.expand_path(File.dirname(__FILE__) + '/test_helper')
+
+class SessionTest < Test::Unit::TestCase
+
+  attr_accessor :salt, :verifier, :username
+
+  def setup
+    @username = "testuser"
+    @password = "password"
+    @salt = '4c78c3f8'.hex
+    @client = SRP::Client.new(@username, @password, @salt)
+    @verifier = @client.verifier
+  end
+
+  def test_equivalance_to_py_srp
+    aa = '9ff9d176b37d9100ad4d788b94ef887df6c88786f5fa2419c9a964001e1c1fa5cd22ea39dcf27682dac6cd8861d9de88184653451fd47f5654845ed24e828d531f95c44377c9bc3f5dd83a669716257c7b975a3a032d4d8adb605553cf4d45c483d7aceb7e6a23c5bd4b0aeeb2ef138b7fc75b27d9d706851c3ab9c721710272'.hex
+    b = 'ce414b3b52d13a1f67416b7e00cdefb07c874291aed395efeab9435ec1ad6ac3'.hex
+    bb = 'b2e852fe7af02d7931186f4958844b829d2976dd58c7bc7928ba3102ff269a9029c707112ab0b7cafdaf86a760f7b50ddd9c847e0c97f564d53cfd52daf61982f06582d49bbb3ea4ad6be55d513028eaf400a6d5a9d26b47689d3438a552716d65680d1b6ee77df3c9b3b6ba61023985562f2be4a6f1723282a2013160594565'.hex
+    m = 'a0c066844117ffe7a7999f84356f3a7c8dce38e4e936eca2b6979ab0fce6ff6d'.hex
+    m2 = '1f4a5ba9c5280b5b752465670f351bb1e61ff9ca06e02ad43c4418affeb3a1ef'.hex
+    session = SRP::Session.new(self, aa)
+    session.send(:initialize_server, aa, b) # seeding b to compare to py_srp
+    assert_equal bb.to_s(16), session.bb.to_s(16)
+    assert_equal m2, session.authenticate(m)
+  end
+
+
+end
-- 
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