decrypt-archive.rb

require "openssl"

ARCHIVE_MAGIC = "D*ARCHIVE"

if ARGV[0].nil?
  puts "Usage: #{__FILE__} <encrypted archive>"
  exit 1
end

File.open(ARGV[0], "rb") do |f|
  if f.read(9) != ARCHIVE_MAGIC
    puts "Bad magic"
    exit 2
  end

  STDERR.puts "Enter password:"
  password = STDIN.readline.rstrip

  salt = f.read(16)
  iv = f.read(16)
  key = OpenSSL::PKCS5.pbkdf2_hmac_sha1(password, salt, 20000, 32)

  cipher = OpenSSL::Cipher::AES256.new(:CBC).decrypt
  cipher.key = key
  cipher.iv = iv
  File.open("/tmp/out.json.gz", "wb") do |o|
   o.write(cipher.update(f.read) + cipher.final)
  end
end