1 files changed, 48 insertions, 0 deletions
diff --git a/lib/srp/client.rb b/lib/srp/client.rb
new file mode 100644
index 0000000..f4662e6
--- /dev/null
+++ b/lib/srp/client.rb
@@ -0,0 +1,48 @@
+require File.expand_path(File.dirname(__FILE__) + '/util')
+
+module SRP
+  class Client
+
+    include Util
+
+    attr_reader :salt, :verifier
+
+    def initialize(username, password)
+      @username = username
+      @password = password
+      @salt = bigrand(10).hex
+      @multiplier = multiplier # let's cache it
+      calculate_verifier
+    end
+
+    def authenticate(server, username, password)
+      x = calculate_x(username, password, salt)
+      a = bigrand(32).hex
+      aa = modpow(GENERATOR, a, PRIME_N) # A = g^a (mod N)
+      bb, u = server.initialize_auth(aa)
+      client_s = calculate_client_s(x, a, bb, u)
+      server.authenticate(aa, client_s)
+    end
+
+    protected
+    def calculate_verifier
+      x = calculate_x(@username, @password, @salt)
+      @verifier = modpow(GENERATOR, x, PRIME_N)
+    end
+
+    def calculate_x(username, password, salt)
+      shex = '%x' % [salt]
+      spad = if shex.length.odd? then '0' else '' end
+      sha1_hex(spad + shex + sha1_str([username, password].join(':'))).hex
+    end
+
+    def calculate_client_s(x, a, bb, u)
+      base = bb
+      base += PRIME_N * @multiplier
+      base -= modpow(GENERATOR, x, PRIME_N) * @multiplier
+      base = base % PRIME_N
+      modpow(base, x * u + a, PRIME_N)
+    end
+  end
+end
+