Class: Tem::Keys::Symmetric

Inherits:
Tem::Key show all
Defined in:
lib/tem/keys/symmetric.rb

Overview

Wraps a TEM symmetric key, e.g. an AES key.

Constant Summary collapse

@@cipher_mode = 
'EDE-CBC'
@@signature_mode = 
'CBC'

Instance Attribute Summary

Attributes inherited from Tem::Key

#ssl_key

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Tem::Key

new_from_ssl_key, #to_tem_key

Constructor Details

#initialize(ssl_key, raw_key = nil) ⇒ Symmetric

Creates a new symmetric key based on an OpenSSL Cipher instance, augmented with a key accessor.

Args:

ssl_key:: the OpenSSL key, or a string containing the raw key
raw_key:: if the OpenSSL key does not support calls to +key+, the raw key



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# File 'lib/tem/keys/symmetric.rb', line 29

def initialize(ssl_key, raw_key = nil)
  if ssl_key.kind_of? OpenSSL::Cipher
    @key = raw_key || ssl_key.key
    @cipher_class = ssl_key.class
  else
    @key = ssl_key
    @cipher_class = OpenSSL::Cipher::DES
  end
  
  # Create an OpenSSL wrapper for the key we received.
  cipher = @cipher_class.new @@cipher_mode
  class <<cipher
    def key=(new_key)
      super
      @_key = new_key
    end
    def key
      @_key
    end
  end
  cipher.key = @key
  cipher.iv = "\0" * 16

  super cipher
end

Class Method Details

.generate ⇒ Object

Generates a new symmetric key.



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# File 'lib/tem/keys/symmetric.rb', line 17

def self.generate
  cipher = OpenSSL::Cipher::DES.new @@cipher_mode
  key = cipher.random_key
  self.new key
end

.new_from_array(array) ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 121

def self.new_from_array(array)    
  cipher_class = array[0].split('::').inject(Kernel) do |scope, name|
    scope.const_get name
  end
  
  # Cipher instance used solely to point to the right class.
  cipher = cipher_class.new @@cipher_mode
  self.new cipher, array[1]      
end

.new_from_yaml_str(yaml_str) ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 131

def self.new_from_yaml_str(yaml_str)
  array = YAML.load yaml_str
  new_from_array array
end

Instance Method Details

#decrypt(data) ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 91

def decrypt(data)
  encrypt_or_decrypt data, false
end

#encrypt(data) ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 87

def encrypt(data)
  encrypt_or_decrypt data, true
end

#encrypt_or_decrypt(data, do_encrypt) ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 56

def encrypt_or_decrypt(data, do_encrypt)
  cipher = @cipher_class.new @@cipher_mode
  do_encrypt ? cipher.encrypt : cipher.decrypt
  cipher.key = @key
  cipher.iv = "\0" * 16
  cipher.padding = 0

  pdata = data.respond_to?(:pack) ? data.pack('C*') : data
  if do_encrypt
    pdata << "\x80"
    if pdata.length % cipher.block_size != 0
      pdata << "\0" * (cipher.block_size - pdata.length % cipher.block_size)
    end
  end
  
  result = cipher.update pdata
  result += cipher.final
  
  unless do_encrypt
    result_length = result.length
    loop do
      result_length -= 1
      next if result[result_length].ord == 0
      raise "Invalid padding" unless result[result_length].ord == 0x80
      break
    end
    result = result[0, result_length]
  end        
  data.respond_to?(:pack) ? result.unpack('C*') : result
end

#sign(data) ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 95

def sign(data)    
  cipher = @cipher_class.new @@cipher_mode
  cipher.encrypt
  cipher.key = @key
  cipher.iv = "\0" * 16
  cipher.padding = 0
  
  pdata = data.respond_to?(:pack) ? data.pack('C*') : data
  pdata << "\x80"
  if pdata.length % cipher.block_size != 0
    pdata << "\0" * (cipher.block_size - pdata.length % cipher.block_size)
  end
  
  result = cipher.update pdata
  result += cipher.final
  result = result[-cipher.block_size, cipher.block_size]
  data.respond_to?(:pack) ? result.unpack('C*') : result
end

#to_array ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 136

def to_array
  [@cipher_class.name, @key]
end

#to_yaml_str ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 140

def to_yaml_str
  self.to_array.to_yaml.to_s
end

#verify(data, signature) ⇒ Object 



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# File 'lib/tem/keys/symmetric.rb', line 114

def verify(data, signature)
  hmac = sign(data)
  hmac = hmac.pack('C*') if hmac.respond_to?(:pack)
  signature = signature.pack('C*') if signature.respond_to?(:pack)
  hmac == signature
end