libgo/go/golang_org/x/crypto/poly1305/sum_ref.go

   1 // Copyright 2012 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 // +build !amd64,!arm gccgo appengine nacl
   6
   7 package poly1305
   8
   9 import "encoding/binary"
  10
  11 // Sum generates an authenticator for msg using a one-time key and puts the
  12 // 16-byte result into out. Authenticating two different messages with the same
  13 // key allows an attacker to forge messages at will.
  14 func Sum(out *[TagSize]byte, msg []byte, key *[32]byte) {
  15         var (
  16                 h0, h1, h2, h3, h4 uint32 // the hash accumulators
  17                 r0, r1, r2, r3, r4 uint64 // the r part of the key
  18         )
  19
  20         r0 = uint64(binary.LittleEndian.Uint32(key[0:]) & 0x3ffffff)
  21         r1 = uint64((binary.LittleEndian.Uint32(key[3:]) >> 2) & 0x3ffff03)
  22         r2 = uint64((binary.LittleEndian.Uint32(key[6:]) >> 4) & 0x3ffc0ff)
  23         r3 = uint64((binary.LittleEndian.Uint32(key[9:]) >> 6) & 0x3f03fff)
  24         r4 = uint64((binary.LittleEndian.Uint32(key[12:]) >> 8) & 0x00fffff)
  25
  26         R1, R2, R3, R4 := r1*5, r2*5, r3*5, r4*5
  27
  28         for len(msg) >= TagSize {
  29                 // h += msg
  30                 h0 += binary.LittleEndian.Uint32(msg[0:]) & 0x3ffffff
  31                 h1 += (binary.LittleEndian.Uint32(msg[3:]) >> 2) & 0x3ffffff
  32                 h2 += (binary.LittleEndian.Uint32(msg[6:]) >> 4) & 0x3ffffff
  33                 h3 += (binary.LittleEndian.Uint32(msg[9:]) >> 6) & 0x3ffffff
  34                 h4 += (binary.LittleEndian.Uint32(msg[12:]) >> 8) | (1 << 24)
  35
  36                 // h *= r
  37                 d0 := (uint64(h0) * r0) + (uint64(h1) * R4) + (uint64(h2) * R3) + (uint64(h3) * R2) + (uint64(h4) * R1)
  38                 d1 := (d0 >> 26) + (uint64(h0) * r1) + (uint64(h1) * r0) + (uint64(h2) * R4) + (uint64(h3) * R3) + (uint64(h4) * R2)
  39                 d2 := (d1 >> 26) + (uint64(h0) * r2) + (uint64(h1) * r1) + (uint64(h2) * r0) + (uint64(h3) * R4) + (uint64(h4) * R3)
  40                 d3 := (d2 >> 26) + (uint64(h0) * r3) + (uint64(h1) * r2) + (uint64(h2) * r1) + (uint64(h3) * r0) + (uint64(h4) * R4)
  41                 d4 := (d3 >> 26) + (uint64(h0) * r4) + (uint64(h1) * r3) + (uint64(h2) * r2) + (uint64(h3) * r1) + (uint64(h4) * r0)
  42
  43                 // h %= p
  44                 h0 = uint32(d0) & 0x3ffffff
  45                 h1 = uint32(d1) & 0x3ffffff
  46                 h2 = uint32(d2) & 0x3ffffff
  47                 h3 = uint32(d3) & 0x3ffffff
  48                 h4 = uint32(d4) & 0x3ffffff
  49
  50                 h0 += uint32(d4>>26) * 5
  51                 h1 += h0 >> 26
  52                 h0 = h0 & 0x3ffffff
  53
  54                 msg = msg[TagSize:]
  55         }
  56
  57         if len(msg) > 0 {
  58                 var block [TagSize]byte
  59                 off := copy(block[:], msg)
  60                 block[off] = 0x01
  61
  62                 // h += msg
  63                 h0 += binary.LittleEndian.Uint32(block[0:]) & 0x3ffffff
  64                 h1 += (binary.LittleEndian.Uint32(block[3:]) >> 2) & 0x3ffffff
  65                 h2 += (binary.LittleEndian.Uint32(block[6:]) >> 4) & 0x3ffffff
  66                 h3 += (binary.LittleEndian.Uint32(block[9:]) >> 6) & 0x3ffffff
  67                 h4 += (binary.LittleEndian.Uint32(block[12:]) >> 8)
  68
  69                 // h *= r
  70                 d0 := (uint64(h0) * r0) + (uint64(h1) * R4) + (uint64(h2) * R3) + (uint64(h3) * R2) + (uint64(h4) * R1)
  71                 d1 := (d0 >> 26) + (uint64(h0) * r1) + (uint64(h1) * r0) + (uint64(h2) * R4) + (uint64(h3) * R3) + (uint64(h4) * R2)
  72                 d2 := (d1 >> 26) + (uint64(h0) * r2) + (uint64(h1) * r1) + (uint64(h2) * r0) + (uint64(h3) * R4) + (uint64(h4) * R3)
  73                 d3 := (d2 >> 26) + (uint64(h0) * r3) + (uint64(h1) * r2) + (uint64(h2) * r1) + (uint64(h3) * r0) + (uint64(h4) * R4)
  74                 d4 := (d3 >> 26) + (uint64(h0) * r4) + (uint64(h1) * r3) + (uint64(h2) * r2) + (uint64(h3) * r1) + (uint64(h4) * r0)
  75
  76                 // h %= p
  77                 h0 = uint32(d0) & 0x3ffffff
  78                 h1 = uint32(d1) & 0x3ffffff
  79                 h2 = uint32(d2) & 0x3ffffff
  80                 h3 = uint32(d3) & 0x3ffffff
  81                 h4 = uint32(d4) & 0x3ffffff
  82
  83                 h0 += uint32(d4>>26) * 5
  84                 h1 += h0 >> 26
  85                 h0 = h0 & 0x3ffffff
  86         }
  87
  88         // h %= p reduction
  89         h2 += h1 >> 26
  90         h1 &= 0x3ffffff
  91         h3 += h2 >> 26
  92         h2 &= 0x3ffffff
  93         h4 += h3 >> 26
  94         h3 &= 0x3ffffff
  95         h0 += 5 * (h4 >> 26)
  96         h4 &= 0x3ffffff
  97         h1 += h0 >> 26
  98         h0 &= 0x3ffffff
  99
 100         // h - p
 101         t0 := h0 + 5
 102         t1 := h1 + (t0 >> 26)
 103         t2 := h2 + (t1 >> 26)
 104         t3 := h3 + (t2 >> 26)
 105         t4 := h4 + (t3 >> 26) - (1 << 26)
 106         t0 &= 0x3ffffff
 107         t1 &= 0x3ffffff
 108         t2 &= 0x3ffffff
 109         t3 &= 0x3ffffff
 110
 111         // select h if h < p else h - p
 112         t_mask := (t4 >> 31) - 1
 113         h_mask := ^t_mask
 114         h0 = (h0 & h_mask) | (t0 & t_mask)
 115         h1 = (h1 & h_mask) | (t1 & t_mask)
 116         h2 = (h2 & h_mask) | (t2 & t_mask)
 117         h3 = (h3 & h_mask) | (t3 & t_mask)
 118         h4 = (h4 & h_mask) | (t4 & t_mask)
 119
 120         // h %= 2^128
 121         h0 |= h1 << 26
 122         h1 = ((h1 >> 6) | (h2 << 20))
 123         h2 = ((h2 >> 12) | (h3 << 14))
 124         h3 = ((h3 >> 18) | (h4 << 8))
 125
 126         // s: the s part of the key
 127         // tag = (h + s) % (2^128)
 128         t := uint64(h0) + uint64(binary.LittleEndian.Uint32(key[16:]))
 129         h0 = uint32(t)
 130         t = uint64(h1) + uint64(binary.LittleEndian.Uint32(key[20:])) + (t >> 32)
 131         h1 = uint32(t)
 132         t = uint64(h2) + uint64(binary.LittleEndian.Uint32(key[24:])) + (t >> 32)
 133         h2 = uint32(t)
 134         t = uint64(h3) + uint64(binary.LittleEndian.Uint32(key[28:])) + (t >> 32)
 135         h3 = uint32(t)
 136
 137         binary.LittleEndian.PutUint32(out[0:], h0)
 138         binary.LittleEndian.PutUint32(out[4:], h1)
 139         binary.LittleEndian.PutUint32(out[8:], h2)
 140         binary.LittleEndian.PutUint32(out[12:], h3)
 141 }