Data commit

Task/RSA-code/Ruby/rsa-code.rb

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+#!/usr/bin/ruby
+
+require 'openssl' # for mod_exp only
+require 'prime'
+
+def rsa_encode blocks, e, n
+  blocks.map{|b| b.to_bn.mod_exp(e, n).to_i}
+end
+
+def rsa_decode ciphers, d, n
+  rsa_encode ciphers, d, n
+end
+
+# all numbers in blocks have to be < modulus, or information is lost
+# for secure encryption only use big modulus and blocksizes
+def text_to_blocks text, blocksize=64 # 1 hex = 4 bit => default is 256bit
+  text.each_byte.reduce(""){|acc,b| acc << b.to_s(16).rjust(2, "0")} # convert text to hex (preserving leading 0 chars)
+      .each_char.each_slice(blocksize).to_a                          # slice hexnumbers in pieces of blocksize
+      .map{|a| a.join("").to_i(16)}                                  # convert each slice into internal number
+end
+
+def blocks_to_text blocks
+  blocks.map{|d| d.to_s(16)}.join("")                                # join all blocks into one hex-string
+        .each_char.each_slice(2).to_a                                # group into pairs
+	.map{|s| s.join("").to_i(16)}                                # number from 2 hexdigits is byte
+	.flatten.pack("C*")                                          # pack bytes into ruby-string
+	.force_encoding(Encoding::default_external)                  # reset encoding
+end
+
+def generate_keys p1, p2
+  n = p1 * p2
+  t = (p1 - 1) * (p2 - 1)
+  e = 2.step.each do |i|
+    break i if i.gcd(t) == 1
+  end
+  d = 1.step.each do |i|
+    break i if (i * e) % t == 1
+  end
+  return e, d, n
+end
+
+p1, p2 = Prime.take(100).last(2)
+public_key, private_key, modulus =
+  generate_keys p1, p2
+
+print "Message: "
+message = gets
+blocks = text_to_blocks message, 4 # very small primes
+print "Numbers: "; p blocks
+encoded = rsa_encode(blocks, public_key, modulus)
+print "Encrypted as: "; p encoded
+decoded = rsa_decode(encoded, private_key, modulus)
+print "Decrypted to: "; p decoded
+final = blocks_to_text(decoded)
+print "Decrypted Message: "; puts final