encryption.rb

require 'openssl'
require 'base64'

module Cipher
  extend self

  def encrypt(plaintext)
    encode(aes(plaintext))
  end

  def decrypt(encoded_encrypted)
    aes_decrypt(decode(encoded_encrypted))
  end

  private

  KEY = "vVLkVzo15UDK12ULC8oVldnHQqDUEdUjJ0bWvNxBMs0="
  IV_LENGTH = 16

  def encryption_cipher
    Thread.current[:encryption_cipher] ||= begin
      cipher = OpenSSL::Cipher::Cipher.new("aes-256-cbc")
      cipher.encrypt
      cipher.key = key
      cipher
    end
  end

  def decryption_cipher
    Thread.current[:decryption_cipher] ||= begin
      cipher = OpenSSL::Cipher::Cipher.new("aes-256-cbc")
      cipher.decrypt
      cipher.key = key
      cipher
    end
  end

  def aes(plaintext)
    encryption_cipher.iv = iv = encryption_cipher.random_iv
    raise "IV length != #{IV_LENGTH} (#{iv.length})" unless iv.length == IV_LENGTH
    cipher_text = encryption_cipher.update(plaintext) + encryption_cipher.final

    iv + cipher_text
  end

  def aes_decrypt(unencoded_encrypted)
    iv = unencoded_encrypted.slice!(0, IV_LENGTH)
    decryption_cipher.iv = iv

    decryption_cipher.update(unencoded_encrypted) + decryption_cipher.final
  end

  def encode(str)
    Base64.strict_encode64(str).gsub(/\s/, '')
  end

  def decode(encoded_str)
    Base64.strict_decode64(encoded_str)
  end

  def key
    decode(KEY)
  end
end

test.md

plain = "We were sitting on the front porch\nWith the weather rolling in\nLaughing louder than the big south wind\nYou ran out to roll your window\nLight rain falling on your hair\nYour tan legs checkered from a folding chair\nThere's country music in the kitchen\nI hear it singing through the screen\nWeather warnings in between\nGlad you got out of the city\nThere's no telling what's in store\nAlong the 35 Corridor\nKerosene to feed the flame\nYour effect is quite the same\nShadows dancing on the wall and\nWaiting for the sky to fall\nCouldn't ask for better weather\nYou were sayin with a grin\nUntil the sound of hailstone hitting tin\nIt's loud enough you gotta yell now\nThe whole thing hits me like a song\nA pretty one that won't last long\nKerosene to feed the flame\nYour effect is quite the same\nShadows dancing on the wall and\nWaiting for the sky to fall and\nWaiting for the sky to fall\nYeah in the broken morning light\nThat simple shade of blue\nThe kind that always follow you\nKerosene to feed the flame\nYour effect is quite the same\nShadows dancing on the wall and\nWaitingWaitingWaitingWaitingand\nWaiWaiWaiWaiWaiWaiWaiWaiall"
str = Cipher.encrypt(plain)
p str
p Cipher.decrypt str

"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"
"We were sitting on the front porch\nWith the weather rolling in\nLaughing louder than the big south wind\nYou ran out to roll your window\nLight rain falling on your hair\nYour tan legs checkered from a folding chair\nThere's country music in the kitchen\nI hear it singing through the screen\nWeather warnings in between\nGlad you got out of the city\nThere's no telling what's in store\nAlong the 35 Corridor\nKerosene to feed the flame\nYour effect is quite the same\nShadows dancing on the wall and\nWaiting for the sky to fall\nCouldn't ask for better weather\nYou were sayin with a grin\nUntil the sound of hailstone hitting tin\nIt's loud enough you gotta yell now\nThe whole thing hits me like a song\nA pretty one that won't last long\nKerosene to feed the flame\nYour effect is quite the same\nShadows dancing on the wall and\nWaiting for the sky to fall and\nWaiting for the sky to fall\nYeah in the broken morning light\nThat simple shade of blue\nThe kind that always follow you\nKerosene to feed the flame\nYour effect is quite the same\nShadows dancing on the wall and\nWaitingWaitingWaitingWaitingand\nWaiWaiWaiWaiWaiWaiWaiWaiall"