1 files changed, 25 insertions, 22 deletions
diff --git a/lib/srp/util.rb b/lib/srp/util.rb
index bf4c248..1e4beac 100644
--- a/lib/srp/util.rb
+++ b/lib/srp/util.rb
@@ -10,7 +10,7 @@ module SRP
 115b8b692e0e045692cf280b436735c77a5a9e8a9e7ed56c965f87db5b2a2ece3
     EOS
 
-    BIG_PRIME_N = <<-EOS # 1024 bits modulus (N)
+    BIG_PRIME_N = <<-EOS.split.join.hex # 1024 bits modulus (N)
 eeaf0ab9adb38dd69c33f80afa8fc5e86072618775ff3c0b9ea2314c9c25657
 6d674df7496ea81d3383b4813d692c6e0e0d5d8e250b98be48e495c1d6089da
 d15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e5
@@ -19,8 +19,12 @@ d15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e5
     EOS
     GENERATOR = 2 # g
 
+    def hn_xor_hg
+      byte_xor_hex(sha256_int(BIG_PRIME_N), sha256_int(GENERATOR))
+    end
+
     # a^n (mod m)
-    def modpow(a, n, m)
+    def modpow(a, n, m = BIG_PRIME_N)
       r = 1
       while true
         r = r * a % m if n[0] == 1
@@ -30,8 +34,15 @@ d15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e5
       end
     end
 
-    def sha256_hex(h)
-      Digest::SHA2.hexdigest([h].pack('H*'))
+    #  Hashes the (long) int args
+    def sha256_int(*args)
+      sha256_hex(*args.map{|a| "%02x" % a})
+    end
+
+    #  Hashes the hex args
+    def sha256_hex(*args)
+      h = args.join('')
+      sha256_str([h].pack('H*'))
     end
 
     def sha256_str(s)
@@ -43,34 +54,26 @@ d15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e5
     end
 
     def multiplier
-      return "c46d46600d87fef149bd79b81119842f3c20241fda67d06ef412d8f6d9479c58".hex % PRIME_N
       @k ||= calculate_multiplier
     end
 
     protected
 
     def calculate_multiplier
-      n = PRIME_N
-      g = GENERATOR
-      nhex = '%x' % [n]
-      nlen = nhex.length + (nhex.length.odd? ? 1 : 0 )
-      ghex = '%x' % [g]
-      hashin = '0' * (nlen - nhex.length) + nhex \
-        + '0' * (nlen - ghex.length) + ghex
-      sha256_hex(hashin).hex % n
+      sha256_int(BIG_PRIME_N, GENERATOR).hex
     end
 
-    def calculate_m(aa, bb, s)
-      hashin = '%x%x%x' % [aa, bb, s]
-      sha256_str(hashin).hex
+    # turn two hex strings into byte arrays and xor them
+    #
+    # returns byte array
+    def byte_xor_hex(a, b)
+      a = [a].pack('H*')
+      b = [b].pack('H*')
+      a.bytes.each_with_index.map do |a_byte, i|
+        (a_byte ^ (b[i] || 0)).chr
+      end.join
     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
-    end
   end
 
 end