Subversion Repositories openrisc

// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// 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.
package cipher

// 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 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 Stream represents a stream cipher.
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 BlockMode represents a block cipher running in a block-based mode (CBC,
// ECB etc).
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)
}

// Utility routines

func shift1(dst, src []byte) byte {
        var b byte
        for i := len(src) - 1; i >= 0; i-- {
                bb := src[i] >> 7
                dst[i] = src[i]<<1 | b
                b = bb
        }
        return b
}

func dup(p []byte) []byte {
        q := make([]byte, len(p))
        copy(q, p)
        return q
}