cryptify.rb in cryptify-0.0.2

- old
+ new
@@ -1,15 +1,129 @@
 require "cryptify/version"
+require 'prime'
 
 module Cryptify
 
 	#
 	# RSA implementation class.
 	#
 	class Rsa
-		def self.debug
-			puts 'Dummy output from Rsa::debug'
+
+		#
+		# Attributes used.
+		#
+		# 	@p, @q
+		# 		Random prime numbers.
+		#
+		# 	@e
+		# 		Public exponent
+		#
+		# 	@n
+		# 		@p and @q computation
+		#
+		#   @d
+		#   	Inverse multiplicative
+		#
+
+
+		#
+		# Construtor.
+		#
+		def initialize
+
+			prime_list = Prime.take(100)
+
+			# Generate p and q
+			@p = prime_list.sample
+			prime_list.delete(@p)
+			@q = prime_list.sample
+
+			# Compute n.
+			@n = @p * @q
+
+			# 1.3 Calculate `z`.
+			@z = (@p - 1) * (@q - 1)
+
+			# 1.4 Calculate coprime.
+			@z.downto(0) do |i|
+				if self.is_coprime(i, @z)
+					@e = i; break;
+				end
+			end
+
+			# 1.5 Modular inverse
+			@d = modinv(@e, @z)
+
 		end
-	end
 
+
+		#
+		# Encrypt a message.
+		#
+		def encrypt(message)
+
+			# Represent the message as a positive integer.
+			# message = 29
+
+			# Compute the ciphertext c to b.
+			(message ** @e) % @n
+		end
+
+
+		#
+		# Decrypt message.
+		#
+		def decrypt(encrypted_message)
+
+			# Uses his private key (n, d) to compute:
+			(encrypted_message ** @d) % @n
+
+		end
+
+
+		#
+		# Checks whether `a` and `b` are coprime.
+		#
+		def is_coprime(a, b)
+
+			# Cycle from 2 until the smaller number of a and b.
+			2.upto([a, b].min) do |i|
+
+				# If both modulus with `i` are equal to `0`
+				# then, the numbers are no coprime.
+				if a % i == b % i && a % i == 0
+					return false
+				end
+			end
+
+			return true
+		end
+
+
+		#
+		# Returns a triple (g, x, y), such that ax + by = g = gcd(a, b).
+		# Assumes a, b >= 0, and that at least one of them is > 0.
+		# Bounds on output values: |x|, |y| < [a, b].max
+		#
+		def egcd(a, b)
+
+			if a == 0
+				return [b, 0, 1]
+			else
+				g, y, x = egcd(b % a, a)
+				return [g, x - (b / a) * y, y]
+			end
+
+		end
+
+		#
+		# Modular inverse.
+		#
+		def modinv(a, m)
+			g, x, y = self.egcd(a, m)
+			return g != 1 ? nil : x % m
+		end
+
+
+	end
 end
 