Source file src/pkg/crypto/cipher/cipher.go

     1	// Copyright 2010 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	// Package cipher implements standard block cipher modes that can be wrapped
     6	// around low-level block cipher implementations.
     7	// See http://csrc.nist.gov/groups/ST/toolkit/BCM/current_modes.html
     8	// and NIST Special Publication 800-38A.
     9	package cipher
    10	
    11	// A Block represents an implementation of block cipher
    12	// using a given key.  It provides the capability to encrypt
    13	// or decrypt individual blocks.  The mode implementations
    14	// extend that capability to streams of blocks.
    15	type Block interface {
    16		// BlockSize returns the cipher's block size.
    17		BlockSize() int
    18	
    19		// Encrypt encrypts the first block in src into dst.
    20		// Dst and src may point at the same memory.
    21		Encrypt(dst, src []byte)
    22	
    23		// Decrypt decrypts the first block in src into dst.
    24		// Dst and src may point at the same memory.
    25		Decrypt(dst, src []byte)
    26	}
    27	
    28	// A Stream represents a stream cipher.
    29	type Stream interface {
    30		// XORKeyStream XORs each byte in the given slice with a byte from the
    31		// cipher's key stream. Dst and src may point to the same memory.
    32		XORKeyStream(dst, src []byte)
    33	}
    34	
    35	// A BlockMode represents a block cipher running in a block-based mode (CBC,
    36	// ECB etc).
    37	type BlockMode interface {
    38		// BlockSize returns the mode's block size.
    39		BlockSize() int
    40	
    41		// CryptBlocks encrypts or decrypts a number of blocks. The length of
    42		// src must be a multiple of the block size. Dst and src may point to
    43		// the same memory.
    44		CryptBlocks(dst, src []byte)
    45	}
    46	
    47	// Utility routines
    48	
    49	func shift1(dst, src []byte) byte {
    50		var b byte
    51		for i := len(src) - 1; i >= 0; i-- {
    52			bb := src[i] >> 7
    53			dst[i] = src[i]<<1 | b
    54			b = bb
    55		}
    56		return b
    57	}
    58	
    59	func dup(p []byte) []byte {
    60		q := make([]byte, len(p))
    61		copy(q, p)
    62		return q
    63	}