block.go

     1  // Copyright 2011 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 des
     6  
     7  import (
     8  	"internal/byteorder"
     9  	"sync"
    10  )
    11  
    12  func cryptBlock(subkeys []uint64, dst, src []byte, decrypt bool) {
    13  	b := byteorder.BeUint64(src)
    14  	b = permuteInitialBlock(b)
    15  	left, right := uint32(b>>32), uint32(b)
    16  
    17  	left = (left << 1) | (left >> 31)
    18  	right = (right << 1) | (right >> 31)
    19  
    20  	if decrypt {
    21  		for i := 0; i < 8; i++ {
    22  			left, right = feistel(left, right, subkeys[15-2*i], subkeys[15-(2*i+1)])
    23  		}
    24  	} else {
    25  		for i := 0; i < 8; i++ {
    26  			left, right = feistel(left, right, subkeys[2*i], subkeys[2*i+1])
    27  		}
    28  	}
    29  
    30  	left = (left << 31) | (left >> 1)
    31  	right = (right << 31) | (right >> 1)
    32  
    33  	// switch left & right and perform final permutation
    34  	preOutput := (uint64(right) << 32) | uint64(left)
    35  	byteorder.BePutUint64(dst, permuteFinalBlock(preOutput))
    36  }
    37  
    38  // DES Feistel function. feistelBox must be initialized via
    39  // feistelBoxOnce.Do(initFeistelBox) first.
    40  func feistel(l, r uint32, k0, k1 uint64) (lout, rout uint32) {
    41  	var t uint32
    42  
    43  	t = r ^ uint32(k0>>32)
    44  	l ^= feistelBox[7][t&0x3f] ^
    45  		feistelBox[5][(t>>8)&0x3f] ^
    46  		feistelBox[3][(t>>16)&0x3f] ^
    47  		feistelBox[1][(t>>24)&0x3f]
    48  
    49  	t = ((r << 28) | (r >> 4)) ^ uint32(k0)
    50  	l ^= feistelBox[6][(t)&0x3f] ^
    51  		feistelBox[4][(t>>8)&0x3f] ^
    52  		feistelBox[2][(t>>16)&0x3f] ^
    53  		feistelBox[0][(t>>24)&0x3f]
    54  
    55  	t = l ^ uint32(k1>>32)
    56  	r ^= feistelBox[7][t&0x3f] ^
    57  		feistelBox[5][(t>>8)&0x3f] ^
    58  		feistelBox[3][(t>>16)&0x3f] ^
    59  		feistelBox[1][(t>>24)&0x3f]
    60  
    61  	t = ((l << 28) | (l >> 4)) ^ uint32(k1)
    62  	r ^= feistelBox[6][(t)&0x3f] ^
    63  		feistelBox[4][(t>>8)&0x3f] ^
    64  		feistelBox[2][(t>>16)&0x3f] ^
    65  		feistelBox[0][(t>>24)&0x3f]
    66  
    67  	return l, r
    68  }
    69  
    70  // feistelBox[s][16*i+j] contains the output of permutationFunction
    71  // for sBoxes[s][i][j] << 4*(7-s)
    72  var feistelBox [8][64]uint32
    73  
    74  var feistelBoxOnce sync.Once
    75  
    76  // general purpose function to perform DES block permutations.
    77  func permuteBlock(src uint64, permutation []uint8) (block uint64) {
    78  	for position, n := range permutation {
    79  		bit := (src >> n) & 1
    80  		block |= bit << uint((len(permutation)-1)-position)
    81  	}
    82  	return
    83  }
    84  
    85  func initFeistelBox() {
    86  	for s := range sBoxes {
    87  		for i := 0; i < 4; i++ {
    88  			for j := 0; j < 16; j++ {
    89  				f := uint64(sBoxes[s][i][j]) << (4 * (7 - uint(s)))
    90  				f = permuteBlock(f, permutationFunction[:])
    91  
    92  				// Row is determined by the 1st and 6th bit.
    93  				// Column is the middle four bits.
    94  				row := uint8(((i & 2) << 4) | i&1)
    95  				col := uint8(j << 1)
    96  				t := row | col
    97  
    98  				// The rotation was performed in the feistel rounds, being factored out and now mixed into the feistelBox.
    99  				f = (f << 1) | (f >> 31)
   100  
   101  				feistelBox[s][t] = uint32(f)
   102  			}
   103  		}
   104  	}
   105  }
   106  
   107  // permuteInitialBlock is equivalent to the permutation defined
   108  // by initialPermutation.
   109  func permuteInitialBlock(block uint64) uint64 {
   110  	// block = b7 b6 b5 b4 b3 b2 b1 b0 (8 bytes)
   111  	b1 := block >> 48
   112  	b2 := block << 48
   113  	block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
   114  
   115  	// block = b1 b0 b5 b4 b3 b2 b7 b6
   116  	b1 = block >> 32 & 0xff00ff
   117  	b2 = (block & 0xff00ff00)
   118  	block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24 // exchange b0 b4 with b3 b7
   119  
   120  	// block is now b1 b3 b5 b7 b0 b2 b4 b6, the permutation:
   121  	//                  ...  8
   122  	//                  ... 24
   123  	//                  ... 40
   124  	//                  ... 56
   125  	//  7  6  5  4  3  2  1  0
   126  	// 23 22 21 20 19 18 17 16
   127  	//                  ... 32
   128  	//                  ... 48
   129  
   130  	// exchange 4,5,6,7 with 32,33,34,35 etc.
   131  	b1 = block & 0x0f0f00000f0f0000
   132  	b2 = block & 0x0000f0f00000f0f0
   133  	block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
   134  
   135  	// block is the permutation:
   136  	//
   137  	//   [+8]         [+40]
   138  	//
   139  	//  7  6  5  4
   140  	// 23 22 21 20
   141  	//  3  2  1  0
   142  	// 19 18 17 16    [+32]
   143  
   144  	// exchange 0,1,4,5 with 18,19,22,23
   145  	b1 = block & 0x3300330033003300
   146  	b2 = block & 0x00cc00cc00cc00cc
   147  	block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
   148  
   149  	// block is the permutation:
   150  	// 15 14
   151  	// 13 12
   152  	// 11 10
   153  	//  9  8
   154  	//  7  6
   155  	//  5  4
   156  	//  3  2
   157  	//  1  0 [+16] [+32] [+64]
   158  
   159  	// exchange 0,2,4,6 with 9,11,13,15:
   160  	b1 = block & 0xaaaaaaaa55555555
   161  	block ^= b1 ^ b1>>33 ^ b1<<33
   162  
   163  	// block is the permutation:
   164  	// 6 14 22 30 38 46 54 62
   165  	// 4 12 20 28 36 44 52 60
   166  	// 2 10 18 26 34 42 50 58
   167  	// 0  8 16 24 32 40 48 56
   168  	// 7 15 23 31 39 47 55 63
   169  	// 5 13 21 29 37 45 53 61
   170  	// 3 11 19 27 35 43 51 59
   171  	// 1  9 17 25 33 41 49 57
   172  	return block
   173  }
   174  
   175  // permuteFinalBlock is equivalent to the permutation defined
   176  // by finalPermutation.
   177  func permuteFinalBlock(block uint64) uint64 {
   178  	// Perform the same bit exchanges as permuteInitialBlock
   179  	// but in reverse order.
   180  	b1 := block & 0xaaaaaaaa55555555
   181  	block ^= b1 ^ b1>>33 ^ b1<<33
   182  
   183  	b1 = block & 0x3300330033003300
   184  	b2 := block & 0x00cc00cc00cc00cc
   185  	block ^= b1 ^ b2 ^ b1>>6 ^ b2<<6
   186  
   187  	b1 = block & 0x0f0f00000f0f0000
   188  	b2 = block & 0x0000f0f00000f0f0
   189  	block ^= b1 ^ b2 ^ b1>>12 ^ b2<<12
   190  
   191  	b1 = block >> 32 & 0xff00ff
   192  	b2 = (block & 0xff00ff00)
   193  	block ^= b1<<32 ^ b2 ^ b1<<8 ^ b2<<24
   194  
   195  	b1 = block >> 48
   196  	b2 = block << 48
   197  	block ^= b1 ^ b2 ^ b1<<48 ^ b2>>48
   198  	return block
   199  }
   200  
   201  // creates 16 28-bit blocks rotated according
   202  // to the rotation schedule.
   203  func ksRotate(in uint32) (out []uint32) {
   204  	out = make([]uint32, 16)
   205  	last := in
   206  	for i := 0; i < 16; i++ {
   207  		// 28-bit circular left shift
   208  		left := (last << (4 + ksRotations[i])) >> 4
   209  		right := (last << 4) >> (32 - ksRotations[i])
   210  		out[i] = left | right
   211  		last = out[i]
   212  	}
   213  	return
   214  }
   215  
   216  // creates 16 56-bit subkeys from the original key.
   217  func (c *desCipher) generateSubkeys(keyBytes []byte) {
   218  	feistelBoxOnce.Do(initFeistelBox)
   219  
   220  	// apply PC1 permutation to key
   221  	key := byteorder.BeUint64(keyBytes)
   222  	permutedKey := permuteBlock(key, permutedChoice1[:])
   223  
   224  	// rotate halves of permuted key according to the rotation schedule
   225  	leftRotations := ksRotate(uint32(permutedKey >> 28))
   226  	rightRotations := ksRotate(uint32(permutedKey<<4) >> 4)
   227  
   228  	// generate subkeys
   229  	for i := 0; i < 16; i++ {
   230  		// combine halves to form 56-bit input to PC2
   231  		pc2Input := uint64(leftRotations[i])<<28 | uint64(rightRotations[i])
   232  		// apply PC2 permutation to 7 byte input
   233  		c.subkeys[i] = unpack(permuteBlock(pc2Input, permutedChoice2[:]))
   234  	}
   235  }
   236  
   237  // Expand 48-bit input to 64-bit, with each 6-bit block padded by extra two bits at the top.
   238  // By doing so, we can have the input blocks (four bits each), and the key blocks (six bits each) well-aligned without
   239  // extra shifts/rotations for alignments.
   240  func unpack(x uint64) uint64 {
   241  	return ((x>>(6*1))&0xff)<<(8*0) |
   242  		((x>>(6*3))&0xff)<<(8*1) |
   243  		((x>>(6*5))&0xff)<<(8*2) |
   244  		((x>>(6*7))&0xff)<<(8*3) |
   245  		((x>>(6*0))&0xff)<<(8*4) |
   246  		((x>>(6*2))&0xff)<<(8*5) |
   247  		((x>>(6*4))&0xff)<<(8*6) |
   248  		((x>>(6*6))&0xff)<<(8*7)
   249  }
   250
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