Class: Sandal::Enc::AGCM

Inherits:
Object
  • Object
show all
Defined in:
lib/sandal/enc/agcm.rb

Overview

Base implementation of the AES/GCM family of encryption algorithms.

Direct Known Subclasses

A128GCM, A256GCM

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(aes_size, alg) ⇒ AGCM

Returns a new instance of AGCM.



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# File 'lib/sandal/enc/agcm.rb', line 16

def initialize(aes_size, alg)
  @aes_size = aes_size
  @name = "A#{aes_size}GCM"
  @cipher_name = "aes-#{aes_size}-gcm"
  @alg = alg
end

Instance Attribute Details

#alg ⇒ Object (readonly)

The JWA algorithm used to encrypt the content master key.



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# File 'lib/sandal/enc/agcm.rb', line 14

def alg
  @alg
end

#name ⇒ Object (readonly)

The JWA name of the encryption.



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# File 'lib/sandal/enc/agcm.rb', line 11

def name
  @name
end

Instance Method Details

#decrypt(parts, decoded_parts) ⇒ Object 



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# File 'lib/sandal/enc/agcm.rb', line 40

def decrypt(parts, decoded_parts)
  cipher = OpenSSL::Cipher.new(@cipher_name).decrypt
  cipher.key = @alg.decrypt_cmk(decoded_parts[1])
  cipher.iv = decoded_parts[2]
  cipher.auth_tag = decoded_parts[4]
  cipher.auth_data = parts.take(3).join('.')
  cipher.update(decoded_parts[3]) + cipher.final
end

#encrypt(header, payload) ⇒ Object 



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# File 'lib/sandal/enc/agcm.rb', line 23

def encrypt(header, payload)
  cipher = OpenSSL::Cipher.new(@cipher_name).encrypt
  content_master_key = @alg.respond_to?(:cmk) ? @alg.cmk : cipher.random_key
  encrypted_key = @alg.encrypt_cmk(content_master_key)

  cipher.key = content_master_key
  iv = cipher.random_iv

  auth_parts = [MultiJson.dump(header), encrypted_key, iv]
  auth_data = auth_parts.map { |part| Sandal::Util.base64_encode(part) }.join('.')
  cipher.auth_data  = auth_data

  ciphertext = cipher.update(payload) + cipher.final
  remainder = [ciphertext, cipher.auth_tag].map { |part| Sandal::Util.base64_encode(part) }.join('.')
  [auth_data, remainder].join('.')
end