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Source file src/crypto/des/block.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 "encoding/binary"
  
  func cryptBlock(subkeys []uint64, dst, src []byte, decrypt bool) {
  	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)
  
  	if decrypt {
  		for i := 0; i < 8; i++ {
  			left, right = feistel(left, right, subkeys[15-2*i], subkeys[15-(2*i+1)])
  		}
  	} else {
  		for i := 0; i < 8; i++ {
  			left, right = feistel(left, right, subkeys[2*i], subkeys[2*i+1])
  		}
  	}
  
  	left = (left << 31) | (left >> 1)
  	right = (right << 31) | (right >> 1)
  
  	// switch left & right and perform final permutation
  	preOutput := (uint64(right) << 32) | uint64(left)
  	binary.BigEndian.PutUint64(dst, permuteFinalBlock(preOutput))
  }
  
  // Encrypt one block from src into dst, using the subkeys.
  func encryptBlock(subkeys []uint64, dst, src []byte) {
  	cryptBlock(subkeys, dst, src, false)
  }
  
  // Decrypt one block from src into dst, using the subkeys.
  func decryptBlock(subkeys []uint64, dst, src []byte) {
  	cryptBlock(subkeys, dst, src, true)
  }
  
  // DES Feistel function
  func feistel(l, r uint32, k0, k1 uint64) (lout, rout uint32) {
  	var t uint32
  
  	t = r ^ uint32(k0>>32)
  	l ^= feistelBox[7][t&0x3f] ^
  		feistelBox[5][(t>>8)&0x3f] ^
  		feistelBox[3][(t>>16)&0x3f] ^
  		feistelBox[1][(t>>24)&0x3f]
  
  	t = ((r << 28) | (r >> 4)) ^ uint32(k0)
  	l ^= feistelBox[6][(t)&0x3f] ^
  		feistelBox[4][(t>>8)&0x3f] ^
  		feistelBox[2][(t>>16)&0x3f] ^
  		feistelBox[0][(t>>24)&0x3f]
  
  	t = l ^ uint32(k1>>32)
  	r ^= feistelBox[7][t&0x3f] ^
  		feistelBox[5][(t>>8)&0x3f] ^
  		feistelBox[3][(t>>16)&0x3f] ^
  		feistelBox[1][(t>>24)&0x3f]
  
  	t = ((l << 28) | (l >> 4)) ^ uint32(k1)
  	r ^= feistelBox[6][(t)&0x3f] ^
  		feistelBox[4][(t>>8)&0x3f] ^
  		feistelBox[2][(t>>16)&0x3f] ^
  		feistelBox[0][(t>>24)&0x3f]
  
  	return l, r
  }
  
  // feistelBox[s][16*i+j] contains the output of permutationFunction
  // for sBoxes[s][i][j] << 4*(7-s)
  var feistelBox [8][64]uint32
  
  // general purpose function to perform DES block permutations
  func permuteBlock(src uint64, permutation []uint8) (block uint64) {
  	for position, n := range permutation {
  		bit := (src >> n) & 1
  		block |= bit << uint((len(permutation)-1)-position)
  	}
  	return
  }
  
  func init() {
  	for s := range sBoxes {
  		for i := 0; i < 4; i++ {
  			for j := 0; j < 16; j++ {
  				f := uint64(sBoxes[s][i][j]) << (4 * (7 - uint(s)))
  				f = permuteBlock(f, permutationFunction[:])
  
  				// Row is determined by the 1st and 6th bit.
  				// Column is the middle four bits.
  				row := uint8(((i & 2) << 4) | i&1)
  				col := uint8(j << 1)
  				t := row | col
  
  				// The rotation was performed in the feistel rounds, being factored out and now mixed into the feistelBox.
  				f = (f << 1) | (f >> 31)
  
  				feistelBox[s][t] = uint32(f)
  			}
  		}
  	}
  }
  
  // permuteInitialBlock is equivalent to the permutation defined
  // by initialPermutation.
  func permuteInitialBlock(block uint64) uint64 {
  	// block = b7 b6 b5 b4 b3 b2 b1 b0 (8 bytes)
  	b1 := block >> 48
  	b2 := block << 48
  	block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
  
  	// block = b1 b0 b5 b4 b3 b2 b7 b6
  	b1 = block >> 32 & 0xff00ff
  	b2 = (block & 0xff00ff00)
  	block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24 // exchange b0 b4 with b3 b7
  
  	// block is now b1 b3 b5 b7 b0 b2 b4 b7, the permutation:
  	//                  ...  8
  	//                  ... 24
  	//                  ... 40
  	//                  ... 56
  	//  7  6  5  4  3  2  1  0
  	// 23 22 21 20 19 18 17 16
  	//                  ... 32
  	//                  ... 48
  
  	// exchange 4,5,6,7 with 32,33,34,35 etc.
  	b1 = block & 0x0f0f00000f0f0000
  	b2 = block & 0x0000f0f00000f0f0
  	block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
  
  	// block is the permutation:
  	//
  	//   [+8]         [+40]
  	//
  	//  7  6  5  4
  	// 23 22 21 20
  	//  3  2  1  0
  	// 19 18 17 16    [+32]
  
  	// exchange 0,1,4,5 with 18,19,22,23
  	b1 = block & 0x3300330033003300
  	b2 = block & 0x00cc00cc00cc00cc
  	block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
  
  	// block is the permutation:
  	// 15 14
  	// 13 12
  	// 11 10
  	//  9  8
  	//  7  6
  	//  5  4
  	//  3  2
  	//  1  0 [+16] [+32] [+64]
  
  	// exchange 0,2,4,6 with 9,11,13,15:
  	b1 = block & 0xaaaaaaaa55555555
  	block ^= b1 ^ b1>>33 ^ b1<<33
  
  	// block is the permutation:
  	// 6 14 22 30 38 46 54 62
  	// 4 12 20 28 36 44 52 60
  	// 2 10 18 26 34 42 50 58
  	// 0  8 16 24 32 40 48 56
  	// 7 15 23 31 39 47 55 63
  	// 5 13 21 29 37 45 53 61
  	// 3 11 19 27 35 43 51 59
  	// 1  9 17 25 33 41 49 57
  	return block
  }
  
  // permuteInitialBlock is equivalent to the permutation defined
  // by finalPermutation.
  func permuteFinalBlock(block uint64) uint64 {
  	// Perform the same bit exchanges as permuteInitialBlock
  	// but in reverse order.
  	b1 := block & 0xaaaaaaaa55555555
  	block ^= b1 ^ b1>>33 ^ b1<<33
  
  	b1 = block & 0x3300330033003300
  	b2 := block & 0x00cc00cc00cc00cc
  	block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
  
  	b1 = block & 0x0f0f00000f0f0000
  	b2 = block & 0x0000f0f00000f0f0
  	block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
  
  	b1 = block >> 32 & 0xff00ff
  	b2 = (block & 0xff00ff00)
  	block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24
  
  	b1 = block >> 48
  	b2 = block << 48
  	block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
  	return block
  }
  
  // creates 16 28-bit blocks rotated according
  // to the rotation schedule
  func ksRotate(in uint32) (out []uint32) {
  	out = make([]uint32, 16)
  	last := in
  	for i := 0; i < 16; i++ {
  		// 28-bit circular left shift
  		left := (last << (4 + ksRotations[i])) >> 4
  		right := (last << 4) >> (32 - ksRotations[i])
  		out[i] = left | right
  		last = out[i]
  	}
  	return
  }
  
  // creates 16 56-bit subkeys from the original key
  func (c *desCipher) generateSubkeys(keyBytes []byte) {
  	// apply PC1 permutation to key
  	key := binary.BigEndian.Uint64(keyBytes)
  	permutedKey := permuteBlock(key, permutedChoice1[:])
  
  	// rotate halves of permuted key according to the rotation schedule
  	leftRotations := ksRotate(uint32(permutedKey >> 28))
  	rightRotations := ksRotate(uint32(permutedKey<<4) >> 4)
  
  	// generate subkeys
  	for i := 0; i < 16; i++ {
  		// combine halves to form 56-bit input to PC2
  		pc2Input := uint64(leftRotations[i])<<28 | uint64(rightRotations[i])
  		// apply PC2 permutation to 7 byte input
  		c.subkeys[i] = unpack(permuteBlock(pc2Input, permutedChoice2[:]))
  	}
  }
  
  // Expand 48-bit input to 64-bit, with each 6-bit block padded by extra two bits at the top.
  // By doing so, we can have the input blocks (four bits each), and the key blocks (six bits each) well-aligned without
  // extra shifts/rotations for alignments.
  func unpack(x uint64) uint64 {
  	var result uint64
  
  	result = ((x>>(6*1))&0xff)<<(8*0) |
  		((x>>(6*3))&0xff)<<(8*1) |
  		((x>>(6*5))&0xff)<<(8*2) |
  		((x>>(6*7))&0xff)<<(8*3) |
  		((x>>(6*0))&0xff)<<(8*4) |
  		((x>>(6*2))&0xff)<<(8*5) |
  		((x>>(6*4))&0xff)<<(8*6) |
  		((x>>(6*6))&0xff)<<(8*7)
  
  	return result
  }
  

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