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 } 142
