Module: JWA::Algorithms::ContentEncryption::AesCbcHs

Included in:
A128CbcHs256, A192CbcHs384, A256CbcHs512
Defined in:
lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb

Overview

Abstract AES in CBC mode, with SHA2 signature for different key sizes.

Defined Under Namespace

Modules: ClassMethods

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#iv ⇒ Object (readonly)

Returns the value of attribute iv.



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 8

def iv
  @iv
end

#key ⇒ Object (readonly)

Returns the value of attribute key.



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 8

def key
  @key
end

Class Method Details

.included(base) ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 70

def self.included(base)
  base.extend(ClassMethods)
end

Instance Method Details

#cipher ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 66

def cipher
  @cipher ||= Cipher.for(self.class.cipher_name)
end

#cipher_round(direction, data) ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 41

def cipher_round(direction, data)
  cipher.send(direction)
  cipher.key = enc_key
  cipher.iv = @iv

  cipher.update(data) + cipher.final
end

#decrypt(ciphertext, authenticated_data, tag) ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 30

def decrypt(ciphertext, authenticated_data, tag)
  signature = generate_tag(authenticated_data, ciphertext)
  if signature != tag
    raise JWA::BadDecrypt, 'Signature check failed. The AAD may have been tampered.'
  end

  cipher_round(:decrypt, ciphertext)
rescue OpenSSL::Cipher::CipherError
  raise JWA::BadDecrypt, 'Invalid ciphertext or authentication tag.'
end

#enc_key ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 62

def enc_key
  @key[self.class.key_length / 2..-1]
end

#encrypt(plaintext, authenticated_data) ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 23

def encrypt(plaintext, authenticated_data)
  ciphertext = cipher_round(:encrypt, plaintext)
  signature = generate_tag(authenticated_data, ciphertext)

  [ciphertext, signature]
end

#generate_tag(authenticated_data, ciphertext) ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 49

def generate_tag(authenticated_data, ciphertext)
  length = [authenticated_data.length * 8].pack('Q>') # 64bit big endian

  to_sign = authenticated_data + @iv + ciphertext + length
  signature = OpenSSL::HMAC.digest(self.class.hash, mac_key, to_sign)

  signature[0...mac_key.length]
end

#initialize(key, iv = nil) ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 10

def initialize(key, iv = nil)
  @key = key
  @iv = iv || SecureRandom.random_bytes(16)

  if @key.length != self.class.key_length
    raise ArgumentError, "Invalid Key. Expected length: #{self.class.key_length}. Actual: #{@key.length}."
  end

  if @iv.length != 16
    raise ArgumentError, "Invalid IV. Expected length: 16. Actual: #{@iv.length}."
  end
end

#mac_key ⇒ Object 



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# File 'lib/jwa/algorithms/content_encryption/aes_cbc_hs.rb', line 58

def mac_key
  @key[0...self.class.key_length / 2]
end