add RandomCode

lib/random_code.rb

+require 'securerandom'
+#
+#
+# Generates a random code in which there are no ambiguous characters.
+# This way, no one has to puzzle if that is an 'l' or a '1'.
+#
+# With only lowercase and no ambiguous characters, the entropy of strings
+# generated with RandomCode is lower than a string with capital letters
+# and confusing characters. To compensate, you should pick a longer string.
+#
+# Entropy is:
+#
+#   possible_chars = 32
+#   Math.log(length**possible_chars, 2)
+#
+# length 8  => 96 bits
+# length 9  => 101 bits
+# length 10 => 106 bits
+# length 11 => 110 bits
+# length 12 => 114 bits
+# length 13 => 118 bits
+# length 14 => 121 bits
+# length 15 => 125 bits
+# length 16 => 128 bits
+# length 17 => 130 bits
+# length 18 => 133 bits
+# length 19 => 135 bits
+# length 20 => 138 bits
+#
+module RandomCode
+  POSSIBLE = %w[a b c d e f g h i j k m n p q r s t u v w x y z 2 3 4 5 6 7 8 9]
+
+  def self.entropy(length)
+    Math.log(length ** POSSIBLE.length, 2).truncate
+  end
+
+  def self.create(length, split=nil)
+    possible = POSSIBLE.shuffle
+    str = SecureRandom.random_bytes(length).each_byte.map {|byte|
+      possible[byte % possible.length]
+    }.join
+    if split
+      return str.scan(/.{#{split}}/).join('-')
+    else
+      return str
+    end
+  end
+
+end