Provides symmetric encryption from abc.txt to abc.encrypted and abc.encrypted to abc.txt.

symmetric.rb

# See http://ruby-doc.org/stdlib-1.9.2/libdoc/digest/rdoc/Digest/Class.html#method-c-digest
# See http://ruby-doc.org/stdlib-1.9.2/libdoc/openssl/rdoc/OpenSSL/Cipher.html
# See http://ruby.about.com/od/rubyfeatures/a/argv.htm

require 'openssl'

# Use this section to encrypt a file

input_file = 'abc.txt'
output_file = 'abc.encrypted'
encryption_key = 'secret password'
encryption_key = Digest::SHA256.digest(encryption_key) # Hash the password to make a 256 bit key

# Set up AES
cipher = OpenSSL::Cipher::Cipher.new('aes-256-cbc')
cipher.encrypt
cipher.key = encryption_key
cipher.iv = iv = cipher.random_iv # Save the IV so that we can store it in the file

# Open the encryption output file
File.open output_file, 'w' do |output|
  output << iv # Store the IV
  # Open the input file
  File.open input_file do |input|
    while text = input.read(256)
      output << cipher.update(text) # Output the block of encrypted data
    end
  end
  output << cipher.final # Output the end of encrypted data
end

# Use this section to decrypt a file

input_file = 'abc.encrypted'
output_file = 'abc.txt'
encryption_key = 'secret password'
encryption_key = Digest::SHA256.digest(encryption_key) # Hash the password to make a 256 bit key

# Set up AES
cipher = OpenSSL::Cipher::Cipher.new('aes-256-cbc')
cipher.decrypt
cipher.key = encryption_key

# Open the output file
File.open output_file, 'w' do |output|
  # Open the encrypted input file
  File.open input_file do |input|
    cipher.iv = input.read(cipher.iv_len) # Load the IV from the file
    while text = input.read(256)
      output << cipher.update(text) # Output the block of decrypted data
    end
    output << cipher.final # Output the end of decrypted data
  end
end