cipher

Documentation

Overview

Package cipher implements standard block cipher modes that can be wrapped around low-level block cipher implementations. See http://csrc.nist.gov/groups/ST/toolkit/BCM/current_modes.html and NIST Special Publication 800-38A.

Index

• type AEAD
  • func NewGCM(cipher Block) (AEAD, error)
• type Block
• type BlockMode
  • func NewCBCDecrypter(b Block, iv []byte) BlockMode
  • func NewCBCEncrypter(b Block, iv []byte) BlockMode
• type Stream
  • func NewCFBDecrypter(block Block, iv []byte) Stream
  • func NewCFBEncrypter(block Block, iv []byte) Stream
  • func NewCTR(block Block, iv []byte) Stream
  • func NewOFB(b Block, iv []byte) Stream
• type StreamReader
  • func (r StreamReader) Read(dst []byte) (n int, err error)
• type StreamWriter
  • func (w StreamWriter) Close() error
  • func (w StreamWriter) Write(src []byte) (n int, err error)

Types

type AEAD

type AEAD interface {
	// NonceSize returns the size of the nonce that must be passed to Seal
	// and Open.
	NonceSize() int

	// Overhead returns the maximum difference between the lengths of a
	// plaintext and ciphertext.
	Overhead() int

	// Seal encrypts and authenticates plaintext, authenticates the
	// additional data and appends the result to dst, returning the updated
	// slice. The nonce must be NonceSize() bytes long and unique for all
	// time, for a given key.
	//
	// The plaintext and dst may alias exactly or not at all.
	Seal(dst, nonce, plaintext, data []byte) []byte

	// Open decrypts and authenticates ciphertext, authenticates the
	// additional data and, if successful, appends the resulting plaintext
	// to dst, returning the updated slice. The nonce must be NonceSize()
	// bytes long and both it and the additional data must match the
	// value passed to Seal.
	//
	// The ciphertext and dst may alias exactly or not at all.
	Open(dst, nonce, ciphertext, data []byte) ([]byte, error)
}

AEAD is a cipher mode providing authenticated encryption with associated data.

func NewGCM

func NewGCM(cipher Block) (AEAD, error)

NewGCM returns the given 128-bit, block cipher wrapped in Galois Counter Mode.

type Block

type Block interface {
	// BlockSize returns the cipher's block size.
	BlockSize() int

	// Encrypt encrypts the first block in src into dst.
	// Dst and src may point at the same memory.
	Encrypt(dst, src []byte)

	// Decrypt decrypts the first block in src into dst.
	// Dst and src may point at the same memory.
	Decrypt(dst, src []byte)
}

A Block represents an implementation of block cipher using a given key. It provides the capability to encrypt or decrypt individual blocks. The mode implementations extend that capability to streams of blocks.

type BlockMode

type BlockMode interface {
	// BlockSize returns the mode's block size.
	BlockSize() int

	// CryptBlocks encrypts or decrypts a number of blocks. The length of
	// src must be a multiple of the block size. Dst and src may point to
	// the same memory.
	CryptBlocks(dst, src []byte)
}

A BlockMode represents a block cipher running in a block-based mode (CBC, ECB etc).

func NewCBCDecrypter

func NewCBCDecrypter(b Block, iv []byte) BlockMode

NewCBCDecrypter returns a BlockMode which decrypts in cipher block chaining mode, using the given Block. The length of iv must be the same as the Block's block size and must match the iv used to encrypt the data.

func NewCBCEncrypter

func NewCBCEncrypter(b Block, iv []byte) BlockMode

NewCBCEncrypter returns a BlockMode which encrypts in cipher block chaining mode, using the given Block. The length of iv must be the same as the Block's block size.

type Stream

type Stream interface {
	// XORKeyStream XORs each byte in the given slice with a byte from the
	// cipher's key stream. Dst and src may point to the same memory.
	XORKeyStream(dst, src []byte)
}

A Stream represents a stream cipher.

func NewCFBDecrypter

func NewCFBDecrypter(block Block, iv []byte) Stream

NewCFBDecrypter returns a Stream which decrypts with cipher feedback mode, using the given Block. The iv must be the same length as the Block's block size.

func NewCFBEncrypter

func NewCFBEncrypter(block Block, iv []byte) Stream

NewCFBEncrypter returns a Stream which encrypts with cipher feedback mode, using the given Block. The iv must be the same length as the Block's block size.

func NewCTR

func NewCTR(block Block, iv []byte) Stream

NewCTR returns a Stream which encrypts/decrypts using the given Block in counter mode. The length of iv must be the same as the Block's block size.

func NewOFB

func NewOFB(b Block, iv []byte) Stream

NewOFB returns a Stream that encrypts or decrypts using the block cipher b in output feedback mode. The initialization vector iv's length must be equal to b's block size.

type StreamReader

type StreamReader struct {
	S Stream
	R io.Reader
}

StreamReader wraps a Stream into an io.Reader. It calls XORKeyStream to process each slice of data which passes through.

func (StreamReader) Read

func (r StreamReader) Read(dst []byte) (n int, err error)

type StreamWriter

type StreamWriter struct {
	S   Stream
	W   io.Writer
	Err error // unused
}

StreamWriter wraps a Stream into an io.Writer. It calls XORKeyStream to process each slice of data which passes through. If any Write call returns short then the StreamWriter is out of sync and must be discarded. A StreamWriter has no internal buffering; Close does not need to be called to flush write data.

func (StreamWriter) Close

func (w StreamWriter) Close() error

Close closes the underlying Writer and returns its Close return value, if the Writer is also an io.Closer. Otherwise it returns nil.

func (StreamWriter) Write

func (w StreamWriter) Write(src []byte) (n int, err error)