Class: Keystores::Jks::KeyProtector

Inherits:
Object
  • Object
show all
Defined in:
lib/keystores/jks/key_protector.rb

Constant Summary collapse

SALT_LEN = 
20
DIGEST_LEN = 
20
KEY_PROTECTOR_OID = 
'1.3.6.1.4.1.42.2.17.1.1'

Instance Method Summary collapse

Constructor Details

#initialize(password) ⇒ KeyProtector

Returns a new instance of KeyProtector.



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# File 'lib/keystores/jks/key_protector.rb', line 60

def initialize(password)
  @password = password
  @passwd_bytes = []
  password.unpack('c*').each do |byte|
    @passwd_bytes << (byte >> 8)
    @passwd_bytes << byte
  end
  @message_digest = OpenSSL::Digest::SHA1.new
end

Instance Method Details

#protect(key) ⇒ Object 



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# File 'lib/keystores/jks/key_protector.rb', line 70

def protect(key)
  if key.nil?
    raise ArgumentError.new("plaintext key can't be null")
  end

  plain_key = key.to_pkcs8_der.unpack('c*')

  # Determine the number of digest rounds
  num_rounds = plain_key.length / DIGEST_LEN
  num_rounds += 1 if (plain_key.length % DIGEST_LEN) != 0

  salt = SecureRandom.random_bytes(SALT_LEN)
  xor_key = Array.new(plain_key.length, 0)

  xor_offset = 0
  digest = salt

  # Compute the digests, and store them in xor_key
  for i in 1..num_rounds
    @message_digest.update(@passwd_bytes.pack('c*'))
    @message_digest.update(digest)
    digest = @message_digest.digest
    @message_digest.reset

    if i < num_rounds
      xor_key[xor_offset..(digest.length + xor_offset -1)] = digest.bytes
    else
      xor_key[xor_offset..-1] = digest[0..(xor_key.length - xor_offset - 1)].bytes
    end
    xor_offset += DIGEST_LEN
  end

  # XOR plain_key with xor_key, and store the result in tmpKey
  tmp_key = []
  for i in 0..(plain_key.length - 1)
    tmp_key[i] = plain_key[i] ^ xor_key[i]
  end

  # Store salt and tmp_key in encr_key
  encr_key = salt.unpack('c*') + tmp_key

  # Append digest(password, plain_key) as an integrity check to encr_key
  @message_digest << @passwd_bytes.pack('c*')
  @passwd_bytes.fill(0)
  @passwd_bytes = nil
  @message_digest << plain_key.pack('c*')
  digest = @message_digest.digest
  @message_digest.reset

  encr_key += digest.unpack('c*')
  Keystores::Jks::EncryptedPrivateKeyInfo.new(:algorithm => KEY_PROTECTOR_OID,
                                              :encrypted_data => encr_key.pack('c*')).encoded
end

#recover(encrypted_private_key_info) ⇒ Object 



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# File 'lib/keystores/jks/key_protector.rb', line 124

def recover(encrypted_private_key_info)
  unless encrypted_private_key_info.algorithm == KEY_PROTECTOR_OID
    raise IOError.new("Unsupported key protection algorithm: #{encrypted_private_key_info.algorithm}")
  end

  protected_key = encrypted_private_key_info.encrypted_data

  # Get the salt associated with this key (the first SALT_LEN bytes of protected_key)
  salt = protected_key.slice(0..(SALT_LEN - 1))

  # Determine the number of digest rounds
  encr_key_len = protected_key.length - SALT_LEN - DIGEST_LEN
  num_rounds = encr_key_len / DIGEST_LEN
  num_rounds += 1 if (encr_key_len % DIGEST_LEN) != 0

  # Get the encrypted key portion
  encr_key = protected_key.slice(SALT_LEN..(encr_key_len + SALT_LEN - 1))

  xor_key = Array.new(encr_key.size, 0)
  xor_offset = 0

  digest = salt
  # Compute the digests, and store them in xor_key
  for i in 1..num_rounds
    @message_digest.update(@passwd_bytes.pack('c*'))
    @message_digest.update(digest)
    digest = @message_digest.digest
    @message_digest.reset

    if i < num_rounds
      xor_key[xor_offset..(digest.length + xor_offset -1)] = digest.bytes
    else
      xor_key[xor_offset..-1] = digest[0..(xor_key.length - xor_offset - 1)].bytes
    end
    xor_offset += DIGEST_LEN
  end

  # XOR encr_key with xor_key, and store the result in plain_key
  plain_key = []
  encr_key_unpacked = encr_key.bytes

  for i in 0..(encr_key.size - 1)
    plain_key[i] = encr_key_unpacked[i] ^ xor_key[i]
  end

  # Check the integrity of the recovered key by concatenating it with
  # the password, digesting the concatenation, and comparing the
  # result of the digest operation with the digest provided at the end
  # of protected_key. If the two digest values are
  # * different, raise an error.
  @message_digest << @passwd_bytes.pack('c*')
  @passwd_bytes.fill(0)
  @passwd_bytes = nil
  @message_digest << plain_key.pack('c*')
  digest = @message_digest.digest
  @message_digest.reset

  for i in 0..(digest.length - 1)
    if digest[i] != protected_key[SALT_LEN + encr_key_len + i]
      raise IOError.new('Cannot recover key')
    end
  end
  OpenSSL::PKey.pkcs8_parse(plain_key.pack('c*'))
end