1 files changed, 53 insertions, 0 deletions
diff --git a/lib/srp/util.rb b/lib/srp/util.rb
new file mode 100644
index 0000000..6792105
--- /dev/null
+++ b/lib/srp/util.rb
@@ -0,0 +1,53 @@
+require 'digest'
+require 'openssl'
+
+module SRP
+  module Util
+
+    # constants both sides know
+    PRIME_N = <<-EOS.split.join.hex # 1024 bits modulus (N)
+eeaf0ab9adb38dd69c33f80afa8fc5e86072618775ff3c0b9ea2314c9c25657
+6d674df7496ea81d3383b4813d692c6e0e0d5d8e250b98be48e495c1d6089da
+d15dc7d7b46154d6b6ce8ef4ad69b15d4982559b297bcf1885c529f566660e5
+7ec68edbc3c05726cc02fd4cbf4976eaa9afd5138fe8376435b9fc61d2fc0eb
+06e3
+    EOS
+    GENERATOR = 2 # g
+
+    # a^n (mod m)
+    def modpow(a, n, m)
+      r = 1
+      while true
+        r = r * a % m if n[0] == 1
+        n >>= 1
+        return r if n == 0
+        a = a * a % m
+      end
+    end
+
+    def sha1_hex(h)
+      Digest::SHA1.hexdigest([h].pack('H*'))
+    end
+
+    def sha1_str(s)
+      Digest::SHA1.hexdigest(s)
+    end
+
+    def bigrand(bytes)
+      OpenSSL::Random.random_bytes(bytes).unpack("H*")[0]
+    end
+
+    def 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
+      sha1_hex(hashin).hex % n
+    end
+  end
+
+end
+