1 files changed, 87 insertions, 0 deletions
diff --git a/lib/srp/session.rb b/lib/srp/session.rb
new file mode 100644
index 0000000..b61058b
--- /dev/null
+++ b/lib/srp/session.rb
@@ -0,0 +1,87 @@
+require File.expand_path(File.dirname(__FILE__) + '/util')
+
+module SRP
+  class Session
+    include Util
+    attr_accessor :user, :aa, :bb
+
+    def initialize(user, aa=nil)
+      @user = user
+      aa ? initialize_server(aa) : initialize_client
+    end
+
+    # client -> server: I, A = g^a
+    def handshake(server)
+      @bb = server.handshake(user.username, aa)
+      @u = calculate_u
+    end
+
+    # client -> server: M = H(H(N) xor H(g), H(I), s, A, B, K)
+    def validate(server)
+      server.validate(calculate_m(client_secret))
+    end
+
+    def authenticate!(m)
+      authenticate(m) || raise(SRP::WrongPassword)
+    end
+
+    def authenticate(m)
+      if(m == calculate_m(server_secret))
+        return m2
+      end
+    end
+
+    protected
+
+    def initialize_server(aa)
+      @aa = aa
+      @b = bigrand(32).hex
+      # B = g^b + k v (mod N)
+      @bb = (modpow(GENERATOR, @b) + multiplier * @user.verifier) % BIG_PRIME_N
+      @u = calculate_u
+    end
+
+    def initialize_client
+      @a = bigrand(32).hex
+      @aa = modpow(GENERATOR, @a) # A = g^a (mod N)
+    end
+
+    # client: K = H( (B - kg^x) ^ (a + ux) )
+    def client_secret
+      base = @bb
+      # base += BIG_PRIME_N * @multiplier
+      base -= modpow(GENERATOR, @user.private_key) * multiplier
+      base = base % BIG_PRIME_N
+      modpow(base, @user.private_key * @u + @a)
+    end
+
+    # server: K = H( (Av^u) ^ b )
+    # do not cache this - it's secret and someone might store the
+    # session in a CookieStore
+    def server_secret
+      base = (modpow(@user.verifier, @u) * @aa) % BIG_PRIME_N
+      modpow(base, @b)
+    end
+
+    def m1
+      calculate_m(server_secret)
+    end
+
+    def m2
+      sha256_int(@aa, m1, server_secret).hex
+    end
+
+    # this is outdated - SRP 6a uses
+    # M = H(H(N) xor H(g), H(I), s, A, B, K)
+    def calculate_m(s)
+      sha256_int(@aa, @bb, s).hex
+    end
+
+    def calculate_u
+      sha256_int(@aa, @bb).hex
+    end
+  end
+end
+
+
+