Class: RbNaCl::SimpleBox

Inherits:
Object
  • Object
show all
Extended by:
Forwardable
Defined in:
lib/rbnacl/simple_box.rb

Overview

The simplest nonce strategy that could possibly work

This class implements the simplest possible nonce generation strategy to wrap a RbNaCl::Box or RbNaCl::SecretBox. A 24-byte random nonce is used for the encryption and is prepended to the message. When it is time to open the box, the message is split into nonce and ciphertext, and then the box is decrypted.

Thanks to the size of the nonce, the chance of a collision is negligible. For example, after encrypting 2^64 messages, the odds of their having been repeated nonce is approximately 2^-64. As an additional convenience, the ciphertexts may be encoded or decoded by any of the encoders implemented in the library.

The resulting ciphertexts are 40 bytes longer than the plain text (24 byte nonce plus a 16 byte authenticator). This might be annoying if you're encrypting tweets, but for files represents a fairly small overhead.

Some caveats:

  • If your random source is broken, so is the security of the messages. You have bigger problems than just this library at that point, but it's worth saying.
  • The confidentiality of your messages is assured with this strategy, but there is no protection against messages being reordered and replayed by an active adversary.

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(box) ⇒ RandomNonceBox

Create a new RandomNonceBox



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# File 'lib/rbnacl/simple_box.rb', line 39

def initialize(box)
  @box = box
end

Class Method Details

.from_keypair(public_key, private_key) ⇒ RandomNonceBox

Use a pair of keys to create a RandomNonceBox

This is a convenience method. It takes a pair of keys and instantiates a Box under the hood, then returns the new RandomNonceBox.



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# File 'lib/rbnacl/simple_box.rb', line 64

def self.from_keypair(public_key, private_key)
  new(Box.new(public_key, private_key))
end

.from_secret_key(secret_key) ⇒ RandomNonceBox

Use a secret key to create a RandomNonceBox

This is a convenience method. It takes a secret key and instantiates a SecretBox under the hood, then returns the new RandomNonceBox.



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# File 'lib/rbnacl/simple_box.rb', line 51

def self.from_secret_key(secret_key)
  new(SecretBox.new(secret_key))
end

Instance Method Details

#box(message) ⇒ String Also known as: encrypt

Encrypts the message with a random nonce

Encrypts the message with a random nonce, then returns the ciphertext with the nonce prepended. Optionally encodes the message using an encoder.



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# File 'lib/rbnacl/simple_box.rb', line 76

def box(message)
  nonce = generate_nonce
  cipher_text = @box.box(nonce, message)
  nonce + cipher_text
end

#open(enciphered_message) ⇒ String Also known as: decrypt

Decrypts the ciphertext with a random nonce

Takes a ciphertext, optionally decodes it, then splits the nonce off the front and uses this to decrypt. Returns the message.

Raises:

  • (CryptoError)

    If the message has been tampered with.



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# File 'lib/rbnacl/simple_box.rb', line 93

def open(enciphered_message)
  nonce, ciphertext = extract_nonce(enciphered_message.to_s)
  @box.open(nonce, ciphertext)
end