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Source file src/crypto/des/cipher.go

Documentation: crypto/des

  // Copyright 2011 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 des
  
  import (
  	"crypto/cipher"
  	"encoding/binary"
  	"strconv"
  )
  
  // The DES block size in bytes.
  const BlockSize = 8
  
  type KeySizeError int
  
  func (k KeySizeError) Error() string {
  	return "crypto/des: invalid key size " + strconv.Itoa(int(k))
  }
  
  // desCipher is an instance of DES encryption.
  type desCipher struct {
  	subkeys [16]uint64
  }
  
  // NewCipher creates and returns a new cipher.Block.
  func NewCipher(key []byte) (cipher.Block, error) {
  	if len(key) != 8 {
  		return nil, KeySizeError(len(key))
  	}
  
  	c := new(desCipher)
  	c.generateSubkeys(key)
  	return c, nil
  }
  
  func (c *desCipher) BlockSize() int { return BlockSize }
  
  func (c *desCipher) Encrypt(dst, src []byte) { encryptBlock(c.subkeys[:], dst, src) }
  
  func (c *desCipher) Decrypt(dst, src []byte) { decryptBlock(c.subkeys[:], dst, src) }
  
  // A tripleDESCipher is an instance of TripleDES encryption.
  type tripleDESCipher struct {
  	cipher1, cipher2, cipher3 desCipher
  }
  
  // NewTripleDESCipher creates and returns a new cipher.Block.
  func NewTripleDESCipher(key []byte) (cipher.Block, error) {
  	if len(key) != 24 {
  		return nil, KeySizeError(len(key))
  	}
  
  	c := new(tripleDESCipher)
  	c.cipher1.generateSubkeys(key[:8])
  	c.cipher2.generateSubkeys(key[8:16])
  	c.cipher3.generateSubkeys(key[16:])
  	return c, nil
  }
  
  func (c *tripleDESCipher) BlockSize() int { return BlockSize }
  
  func (c *tripleDESCipher) Encrypt(dst, src []byte) {
  	b := binary.BigEndian.Uint64(src)
  	b = permuteInitialBlock(b)
  	left, right := uint32(b>>32), uint32(b)
  
  	left = (left << 1) | (left >> 31)
  	right = (right << 1) | (right >> 31)
  
  	for i := 0; i < 8; i++ {
  		left, right = feistel(left, right, c.cipher1.subkeys[2*i], c.cipher1.subkeys[2*i+1])
  	}
  	for i := 0; i < 8; i++ {
  		right, left = feistel(right, left, c.cipher2.subkeys[15-2*i], c.cipher2.subkeys[15-(2*i+1)])
  	}
  	for i := 0; i < 8; i++ {
  		left, right = feistel(left, right, c.cipher3.subkeys[2*i], c.cipher3.subkeys[2*i+1])
  	}
  
  	left = (left << 31) | (left >> 1)
  	right = (right << 31) | (right >> 1)
  
  	preOutput := (uint64(right) << 32) | uint64(left)
  	binary.BigEndian.PutUint64(dst, permuteFinalBlock(preOutput))
  }
  
  func (c *tripleDESCipher) Decrypt(dst, src []byte) {
  	b := binary.BigEndian.Uint64(src)
  	b = permuteInitialBlock(b)
  	left, right := uint32(b>>32), uint32(b)
  
  	left = (left << 1) | (left >> 31)
  	right = (right << 1) | (right >> 31)
  
  	for i := 0; i < 8; i++ {
  		left, right = feistel(left, right, c.cipher3.subkeys[15-2*i], c.cipher3.subkeys[15-(2*i+1)])
  	}
  	for i := 0; i < 8; i++ {
  		right, left = feistel(right, left, c.cipher2.subkeys[2*i], c.cipher2.subkeys[2*i+1])
  	}
  	for i := 0; i < 8; i++ {
  		left, right = feistel(left, right, c.cipher1.subkeys[15-2*i], c.cipher1.subkeys[15-(2*i+1)])
  	}
  
  	left = (left << 31) | (left >> 1)
  	right = (right << 31) | (right >> 1)
  
  	preOutput := (uint64(right) << 32) | uint64(left)
  	binary.BigEndian.PutUint64(dst, permuteFinalBlock(preOutput))
  }
  

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