Merge pull request #165 from datta-agni/master

RSA cryptographic algorithm implemented in Ruby.

ciphers/rsa.rb

@@ -0,0 +1,94 @@
+require "prime"
+
+def initialize(keys = {})
+  @e ||= keys[:e]
+  @n ||= keys[:n]
+end
+
+def cipher(message)
+  message.bytes.map do |byte|
+    cbyte = ((byte.to_i ** e) % n).to_s
+    missing_chars = n.to_s.size - cbyte.size
+    "0" * missing_chars + cbyte
+  end.join
+end
+
+def decipher(ciphed_message)
+  ciphed_message.chars.each_slice(n.to_s.size).map do |arr|
+    (arr.join.to_i ** d) % n
+  end.pack("c*")
+end
+
+def public_keys
+  { n: n, e: e }
+end
+
+private
+
+def p
+  @p ||= random_prime_number
+end
+
+def q
+  @q ||= random_prime_number
+end
+
+def n
+  @n ||= p * q
+end
+
+def totient
+  @totient ||= (p - 1) * (q - 1)
+end
+
+def e
+  @e ||= totient.downto(2).find do |i|
+    Prime.prime?(i) && totient % i != 0
+  end
+end
+
+def d
+  @d ||= invmod(e, totient)
+end
+
+def extended_gcd(a, b)
+  last_remainder, remainder = a.abs, b.abs
+  x, last_x, y, last_y = 0, 1, 1, 0
+  while remainder != 0
+    last_remainder, (quotient, remainder) = remainder, last_remainder.divmod(remainder)
+    x, last_x = last_x - quotient * x, x
+    y, last_y = last_y - quotient * y, y
+  end
+
+  return last_remainder, last_x * (a < 0 ? -1 : 1)
+end
+
+def invmod(e, et)
+  g, x = extended_gcd(e, et)
+  raise "The maths are broken!" if g != 1
+  x % et
+end
+
+def random_prime_number
+  number = Random.rand(1..1000)
+  until Prime.prime?(number) || number == p || number == q
+    number = Random.rand(1..1000)
+  end
+  number
+end
+
+def main()
+  puts "Enter the message you want to encrypt and decrypt with RSA algorithm: "
+  message = gets.chomp().to_s
+  puts "Encoded Text:"
+  puts cipher(message)
+  puts "Decoded Text:"
+  puts decipher(cipher(message))
+  puts "p: #{p()}"
+  puts "q: #{q()}"
+  puts "e: #{e()}"
+  puts "d: #{d()}"
+  puts "totient: #{totient()}"
+end
+
+main()