From b889ef34d4fff0d156901ae2aebfcee02339ce77 Mon Sep 17 00:00:00 2001
From: Azul <azul@riseup.net>
Date: Thu, 4 Oct 2012 10:22:46 +0200
Subject: some cleanup, sha functions now concat multiple args

also u does not depend on n
---
 lib/srp/authentication.rb |  2 +-
 lib/srp/client.rb         |  4 ++--
 lib/srp/util.rb           | 29 +++++++++++++++--------------
 3 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/lib/srp/authentication.rb b/lib/srp/authentication.rb
index 0505a58..0fd275c 100644
--- a/lib/srp/authentication.rb
+++ b/lib/srp/authentication.rb
@@ -17,7 +17,7 @@ module SRP
       end
 
       def u
-        calculate_u(aa, bb, BIG_PRIME_N)
+        calculate_u(aa, bb)
       end
 
       # do not cache this - it's secret and someone might store the
diff --git a/lib/srp/client.rb b/lib/srp/client.rb
index 947bd7b..65052f5 100644
--- a/lib/srp/client.rb
+++ b/lib/srp/client.rb
@@ -20,7 +20,7 @@ module SRP
       a = bigrand(32).hex
       aa = modpow(GENERATOR, a, BIG_PRIME_N) # A = g^a (mod N)
       bb = server.handshake(username, aa)
-      u = calculate_u(aa, bb, BIG_PRIME_N)
+      u = calculate_u(aa, bb)
       client_s = calculate_client_s(x, a, bb, u)
       server.validate(calculate_m(aa, bb, client_s))
     end
@@ -35,7 +35,7 @@ module SRP
     def calculate_x(username = @username, password = @password)
       shex = '%x' % [@salt]
       inner = sha256_str([username, password].join(':'))
-      sha256_str([shex].pack('H*') + [inner].pack('H*')).hex
+      sha256_hex(shex, inner).hex
     end
 
     def calculate_client_s(x, a, bb, u)
diff --git a/lib/srp/util.rb b/lib/srp/util.rb
index cafa5f4..fcbab31 100644
--- a/lib/srp/util.rb
+++ b/lib/srp/util.rb
@@ -30,8 +30,15 @@ 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| a.to_s(16)})
+    end
+
+    #  Hashes the hex args
+    def sha256_hex(*args)
+      h = args.join('')
+      sha256_str([h].pack('H*'))
     end
 
     def sha256_str(s)
@@ -49,23 +56,17 @@ d15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e5
     protected
 
     def calculate_multiplier
-      n = BIG_PRIME_N
-      g = GENERATOR
-      nhex = '%x' % n
-      ghex = '0%x' % g
-      hashin = [nhex].pack('H*') + [ghex].pack('H*')
-      sha256_str(hashin).hex
+      # GENERATOR hex needs to be prefixed with 0 so it's not "2" -> 32
+      ghex = '0%x' % GENERATOR
+      sha256_hex(BIG_PRIME_N.to_s(16), ghex).hex
     end
 
     def calculate_m(aa, bb, s)
-      hashin = '%x%x%x' % [aa, bb, s]
-      sha256_hex(hashin).hex
+      sha256_int(aa, bb, s).hex
     end
 
-    def calculate_u(aa, bb, n)
-      aahex = '%x' % [aa]
-      bbhex = '%x' % [bb]
-      return sha256_hex("%x%x" % [aa, bb]).hex
+    def calculate_u(aa, bb)
+      sha256_int(aa, bb).hex
     end
   end
 
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