Ruby RSA using OpenSSL example

rsa-test.rb

require 'openssl'
require 'base64'
require 'stringio'

plaintext = StringIO.new <<-EOF
  Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
  Also, because I said so.
EOF

target_key = OpenSSL::PKey::RSA.new(640)
# target_key.e = OpenSSL::BN.new('65537') # Note it's a String
# target_key.n = OpenSSL::BN.new(modulus)
block_size = target_key.n.num_bytes
min_padding = 11

puts "#{plaintext.length} byte plaintext, #{target_key.n.to_i.size} byte modulus"
# puts "n=" + target_key.n.to_s
puts

raise "Incorrect exponent" unless target_key.e == 65537

output = ""
while input = plaintext.read(block_size - min_padding) do
  puts "(Encrypting #{input.length.to_s} bytes)"
  output += 
    target_key.public_encrypt(input, OpenSSL::PKey::RSA::PKCS1_PADDING)
end
encoded = [output].pack("m").gsub(/\n/,'')
puts encoded + " (#{encoded.length})"

puts

ciphertext = StringIO.new( Base64.decode64( encoded ) )
output = ""
while input = ciphertext.read(block_size) do
  puts "(Decrypting #{input.length.to_s} bytes)"
  output += 
    target_key.private_decrypt(input, OpenSSL::PKey::RSA::PKCS1_PADDING)
end
puts output