Factor away Verifier#generate_B method which is not needed for the pu…

…blic API.

lib/sirp/client.rb

@@ -61,7 +61,7 @@ def process_challenge(username, password, xsalt, xbb)
     # @return [true,false] returns true if the server and client agree on the
     #   H_AMK value, false if not
     def verify(server_HAMK)
-      return false unless @H_AMK
+      return false unless @H_AMK && server_HAMK
       # Secure constant time comparison, hash the params to ensure
       # that both strings being compared are equal length 32 Byte strings.
       secure_compare(Digest::SHA256.hexdigest(@H_AMK), Digest::SHA256.hexdigest(server_HAMK))

lib/sirp/verifier.rb

@@ -39,7 +39,10 @@ def get_challenge_and_proof(username, xverifier, xsalt, xaa)
       # SRP-6a safety check
       return false if (xaa.to_i(16) % @N).zero?
 
-      generate_B(xverifier)
+      # Generate b and B
+      v = xverifier.to_i(16)
+      @b ||= SecureRandom.hex(32).hex
+      @B = num_to_hex(calc_B(@b, k, v, @N, @g))
 
       {
         challenge: { B: @B, salt: xsalt },
@@ -88,13 +91,5 @@ def verify_session(proof, client_M)
         false
       end
     end
-
-    # @param xverifier [String] the server stored verifier for the username in hex
-    # @return [String] the B value in hex
-    def generate_B(xverifier)
-      v = xverifier.to_i(16)
-      @b ||= SecureRandom.hex(32).hex
-      @B = num_to_hex(calc_B(@b, k, v, @N, @g))
-    end
   end
 end

spec/authentication.rb → spec/authentication_spec.rb

@@ -31,14 +31,14 @@
       # phaase 1 (server)
       v = @auth[:verifier]
       salt = @auth[:salt]
-      bb = verifier.generate_B(v)
-      b = format('%x' % verifier.b)
+
+      cp = verifier.get_challenge_and_proof(@username, v, salt, aa)
 
       # phase 2 (client)
-      client_M = client.process_challenge(@username, 'icnivad', salt, bb)
+      client_M = client.process_challenge(@username, 'icnivad', salt, cp[:proof][:B])
 
       # phase 2 (server)
-      proof = { A: aa, B: bb, b: b, I: @username, s: salt, v: v }
+      proof = { A: aa, B: cp[:proof][:B], b: cp[:proof][:b], I: @username, s: salt, v: v }
       server_H_AMK = verifier.verify_session(proof, client_M)
       expect(server_H_AMK).to be_truthy
 
@@ -56,14 +56,13 @@
       # phaase 1 (server)
       v = @auth[:verifier]
       salt = @auth[:salt]
-      bb = verifier.generate_B(v)
-      b = format('%x' % verifier.b)
+      cp = verifier.get_challenge_and_proof(@username, v, salt, aa)
 
       # phase 2 (client)
-      client_M = client.process_challenge(@username, 'BAD PASSWORD', salt, bb)
+      client_M = client.process_challenge(@username, 'BAD PASSWORD', salt, cp[:proof][:B])
 
       # phase 2 (server)
-      proof = { A: aa, B: bb, b: b, I: @username, s: salt, v: v }
+      proof = { A: aa, B: cp[:proof][:B], b: cp[:proof][:b], I: @username, s: salt, v: v }
       server_H_AMK = verifier.verify_session(proof, client_M)
       expect(server_H_AMK).to be false
 

spec/verifier_spec.rb

@@ -71,6 +71,17 @@
       expect(cp[:proof].key?(:s)).to be true
       expect(cp[:proof].key?(:v)).to be true
     end
+
+    it 'should generate expected B with predefined b' do
+      v = '321307d87ca3462f5b0cb5df295bea04498563794e5401899b2f32dd5cab5b7de9da78e7d62ea235e6d7f43a4ea09fea7c0dafdee6e79a1d12e2e374048deeaf5ba7c68e2ad952a3f5dc084400a7f1599a31d6d9d50269a9208db88f84090e8aa3c7b019f39529dcc19baa985a8d7ffb2d7628071d2313c9eaabc504d3333688'
+      verifier = SIRP::Verifier.new(1024)
+      @auth = verifier.generate_userauth('foo', 'bar')
+      verifier.set_b(@b.to_i(16))
+      cp = verifier.get_challenge_and_proof(@username, v, @auth[:salt], @auth[:verifier])
+      expect(('%b' % cp[:proof][:b].to_i(16)).length).to be > 200
+      expect(('%b' % cp[:challenge][:B].to_i(16)).length).to be >= 1000
+      expect(cp[:challenge][:B]).to eq '56777d24af1121bd6af6aeb84238ff8d250122fe75ed251db0f47c289642ae7adb9ef319ce3ab23b6ecc97e5904749fc42f12bb016ecf39691db541f066667b8399bfa685c82b03ad8f92f75975ed086dbe0d470d4dd907ce11b19ee41b74aee72bd8445cde6b58c01f678e39ed9cd6b93c79382637df90777a96c10a768c510'
+    end
   end
 
   context 'verify_session' do
@@ -108,21 +119,4 @@
       expect(verifier.H_AMK).to eq 'a93d906ef5c0a15a8e525da6a271692d2e553c72'
     end
   end
-
-  context 'generate_B' do
-    it 'should generate B with predefined b' do
-      v = '321307d87ca3462f5b0cb5df295bea04498563794e5401899b2f32dd5cab5b7de9da78e7d62ea235e6d7f43a4ea09fea7c0dafdee6e79a1d12e2e374048deeaf5ba7c68e2ad952a3f5dc084400a7f1599a31d6d9d50269a9208db88f84090e8aa3c7b019f39529dcc19baa985a8d7ffb2d7628071d2313c9eaabc504d3333688'
-      verifier = SIRP::Verifier.new(1024)
-      verifier.set_b(@b.to_i(16))
-      bb = verifier.generate_B(v)
-      expect(bb).to eq '56777d24af1121bd6af6aeb84238ff8d250122fe75ed251db0f47c289642ae7adb9ef319ce3ab23b6ecc97e5904749fc42f12bb016ecf39691db541f066667b8399bfa685c82b03ad8f92f75975ed086dbe0d470d4dd907ce11b19ee41b74aee72bd8445cde6b58c01f678e39ed9cd6b93c79382637df90777a96c10a768c510'
-    end
-
-    it 'should generate B' do
-      verifier = SIRP::Verifier.new(1024)
-      bb = verifier.generate_B('0')
-      expect(('%b' % bb.to_i(16)).length).to be >= 1000
-      expect(('%b' % verifier.b).length).to be > 200
-    end
-  end
 end