xts

README

XTS -- Tweaked

Big N decided to flip the endianness of their implementation of the sector tweak for XTS This is the golang xts from go 1.17, tweaked to compensate.

Documentation

Overview

Package xts implements the XTS cipher mode as specified in IEEE P1619/D16.

XTS mode is typically used for disk encryption, which presents a number of novel problems that make more common modes inapplicable. The disk is conceptually an array of sectors and we must be able to encrypt and decrypt a sector in isolation. However, an attacker must not be able to transpose two sectors of plaintext by transposing their ciphertext.

XTS wraps a block cipher with Rogaway's XEX mode in order to build a tweakable block cipher. This allows each sector to have a unique tweak and effectively create a unique key for each sector.

XTS does not provide any authentication. An attacker can manipulate the ciphertext and randomise a block (16 bytes) of the plaintext. This package does not implement ciphertext-stealing so sectors must be a multiple of 16 bytes.

Note that XTS is usually not appropriate for any use besides disk encryption. Most users should use an AEAD mode like GCM (from crypto/cipher.NewGCM) instead.

Index

• type Cipher
  • func NewCipher(cipherFunc func([]byte) (cipher.Block, error), key []byte) (c *Cipher, err error)
  • func (c *Cipher) Decrypt(plaintext, ciphertext []byte, sectorNum uint64)
  • func (c *Cipher) Encrypt(ciphertext, plaintext []byte, sectorNum uint64)

Types

type Cipher

type Cipher struct {
	// contains filtered or unexported fields
}

Cipher contains an expanded key structure. It is safe for concurrent use if the underlying block cipher is safe for concurrent use.

func NewCipher

func NewCipher(cipherFunc func([]byte) (cipher.Block, error), key []byte) (c *Cipher, err error)

NewCipher creates a Cipher given a function for creating the underlying block cipher (which must have a block size of 16 bytes). The key must be twice the length of the underlying cipher's key.

func (*Cipher) Decrypt

func (c *Cipher) Decrypt(plaintext, ciphertext []byte, sectorNum uint64)

Decrypt decrypts a sector of ciphertext and puts the result into plaintext. Plaintext and ciphertext must overlap entirely or not at all. Sectors must be a multiple of 16 bytes and less than 2²⁴ bytes.

func (*Cipher) Encrypt

func (c *Cipher) Encrypt(ciphertext, plaintext []byte, sectorNum uint64)

Encrypt encrypts a sector of plaintext and puts the result into ciphertext. Plaintext and ciphertext must overlap entirely or not at all. Sectors must be a multiple of 16 bytes and less than 2²⁴ bytes.