init

1 files changed, 67 insertions, 0 deletions

diff --git a/algorithms/letter_substitution_cipher.rb b/algorithms/letter_substitution_cipher.rb
new file mode 100755
index 0000000..01bde9b
--- /dev/null
+++ b/algorithms/letter_substitution_cipher.rb
@@ -0,0 +1,67 @@
+#!/usr/bin/env ruby
+
+
+ALPHABET = ('a'..'z').to_a
+ALPHABET << ' '
+puts ALPHABET.to_s
+
+def mklettersubstitioncipher
+  cipher = {}
+  ALPHABET.each { |i|
+    while true
+      c = ALPHABET[ Random.rand(ALPHABET.size) ]
+      if not cipher.values.include? c
+        cipher[i] = c
+        break
+      end
+    end
+  }
+  return cipher
+end
+
+def encrypt(key, plaintext)
+  s = ''
+  plaintext.each_char { |i| s += key[i] }
+  return s
+end
+
+def decrypt(key, ciphertext)
+  s = ''
+  ciphertext.each_char { |i|
+    key.each_pair { |p|
+      if p[1] == i
+        s += p[0]
+      end
+    }
+  }
+  return s
+end
+
+def randomcipherstring(cipher)
+  length = Random.rand(49)+1
+  s = ''
+  length.times {
+    s += cipher[ ALPHABET[Random.rand(ALPHABET.size)] ]
+  }
+  return s
+end
+
+def sample(n, cipher)
+  a = []
+  n.times {
+    a << randomcipherstring(cipher)
+  }
+  puts a.to_s
+end
+
+def test
+  cipher = mklettersubstitioncipher
+  s = "das ist das haus vom nikolaus"
+  s_enc = encrypt(cipher, s)
+  s_dec = decrypt(cipher, s_enc)
+  puts "#{s}\n#{s_enc}\n#{s_dec}"
+end
+
+
+test
+