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141 lines
4.7 KiB
Go
141 lines
4.7 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build !amd64,!arm gccgo appengine nacl
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package poly1305
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import "encoding/binary"
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// Sum generates an authenticator for msg using a one-time key and puts the
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// 16-byte result into out. Authenticating two different messages with the same
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// key allows an attacker to forge messages at will.
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func Sum(out *[TagSize]byte, msg []byte, key *[32]byte) {
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var (
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h0, h1, h2, h3, h4 uint32 // the hash accumulators
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r0, r1, r2, r3, r4 uint64 // the r part of the key
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)
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r0 = uint64(binary.LittleEndian.Uint32(key[0:]) & 0x3ffffff)
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r1 = uint64((binary.LittleEndian.Uint32(key[3:]) >> 2) & 0x3ffff03)
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r2 = uint64((binary.LittleEndian.Uint32(key[6:]) >> 4) & 0x3ffc0ff)
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r3 = uint64((binary.LittleEndian.Uint32(key[9:]) >> 6) & 0x3f03fff)
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r4 = uint64((binary.LittleEndian.Uint32(key[12:]) >> 8) & 0x00fffff)
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R1, R2, R3, R4 := r1*5, r2*5, r3*5, r4*5
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for len(msg) >= TagSize {
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// h += msg
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h0 += binary.LittleEndian.Uint32(msg[0:]) & 0x3ffffff
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h1 += (binary.LittleEndian.Uint32(msg[3:]) >> 2) & 0x3ffffff
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h2 += (binary.LittleEndian.Uint32(msg[6:]) >> 4) & 0x3ffffff
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h3 += (binary.LittleEndian.Uint32(msg[9:]) >> 6) & 0x3ffffff
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h4 += (binary.LittleEndian.Uint32(msg[12:]) >> 8) | (1 << 24)
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// h *= r
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d0 := (uint64(h0) * r0) + (uint64(h1) * R4) + (uint64(h2) * R3) + (uint64(h3) * R2) + (uint64(h4) * R1)
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d1 := (d0 >> 26) + (uint64(h0) * r1) + (uint64(h1) * r0) + (uint64(h2) * R4) + (uint64(h3) * R3) + (uint64(h4) * R2)
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d2 := (d1 >> 26) + (uint64(h0) * r2) + (uint64(h1) * r1) + (uint64(h2) * r0) + (uint64(h3) * R4) + (uint64(h4) * R3)
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d3 := (d2 >> 26) + (uint64(h0) * r3) + (uint64(h1) * r2) + (uint64(h2) * r1) + (uint64(h3) * r0) + (uint64(h4) * R4)
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d4 := (d3 >> 26) + (uint64(h0) * r4) + (uint64(h1) * r3) + (uint64(h2) * r2) + (uint64(h3) * r1) + (uint64(h4) * r0)
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// h %= p
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h0 = uint32(d0) & 0x3ffffff
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h1 = uint32(d1) & 0x3ffffff
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h2 = uint32(d2) & 0x3ffffff
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h3 = uint32(d3) & 0x3ffffff
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h4 = uint32(d4) & 0x3ffffff
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h0 += uint32(d4>>26) * 5
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h1 += h0 >> 26
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h0 = h0 & 0x3ffffff
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msg = msg[TagSize:]
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}
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if len(msg) > 0 {
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var block [TagSize]byte
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off := copy(block[:], msg)
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block[off] = 0x01
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// h += msg
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h0 += binary.LittleEndian.Uint32(block[0:]) & 0x3ffffff
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h1 += (binary.LittleEndian.Uint32(block[3:]) >> 2) & 0x3ffffff
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h2 += (binary.LittleEndian.Uint32(block[6:]) >> 4) & 0x3ffffff
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h3 += (binary.LittleEndian.Uint32(block[9:]) >> 6) & 0x3ffffff
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h4 += (binary.LittleEndian.Uint32(block[12:]) >> 8)
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// h *= r
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d0 := (uint64(h0) * r0) + (uint64(h1) * R4) + (uint64(h2) * R3) + (uint64(h3) * R2) + (uint64(h4) * R1)
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d1 := (d0 >> 26) + (uint64(h0) * r1) + (uint64(h1) * r0) + (uint64(h2) * R4) + (uint64(h3) * R3) + (uint64(h4) * R2)
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d2 := (d1 >> 26) + (uint64(h0) * r2) + (uint64(h1) * r1) + (uint64(h2) * r0) + (uint64(h3) * R4) + (uint64(h4) * R3)
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d3 := (d2 >> 26) + (uint64(h0) * r3) + (uint64(h1) * r2) + (uint64(h2) * r1) + (uint64(h3) * r0) + (uint64(h4) * R4)
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d4 := (d3 >> 26) + (uint64(h0) * r4) + (uint64(h1) * r3) + (uint64(h2) * r2) + (uint64(h3) * r1) + (uint64(h4) * r0)
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// h %= p
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h0 = uint32(d0) & 0x3ffffff
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h1 = uint32(d1) & 0x3ffffff
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h2 = uint32(d2) & 0x3ffffff
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h3 = uint32(d3) & 0x3ffffff
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h4 = uint32(d4) & 0x3ffffff
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h0 += uint32(d4>>26) * 5
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h1 += h0 >> 26
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h0 = h0 & 0x3ffffff
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}
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// h %= p reduction
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h2 += h1 >> 26
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h1 &= 0x3ffffff
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h3 += h2 >> 26
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h2 &= 0x3ffffff
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h4 += h3 >> 26
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h3 &= 0x3ffffff
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h0 += 5 * (h4 >> 26)
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h4 &= 0x3ffffff
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h1 += h0 >> 26
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h0 &= 0x3ffffff
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// h - p
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t0 := h0 + 5
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t1 := h1 + (t0 >> 26)
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t2 := h2 + (t1 >> 26)
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t3 := h3 + (t2 >> 26)
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t4 := h4 + (t3 >> 26) - (1 << 26)
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t0 &= 0x3ffffff
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t1 &= 0x3ffffff
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t2 &= 0x3ffffff
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t3 &= 0x3ffffff
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// select h if h < p else h - p
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t_mask := (t4 >> 31) - 1
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h_mask := ^t_mask
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h0 = (h0 & h_mask) | (t0 & t_mask)
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h1 = (h1 & h_mask) | (t1 & t_mask)
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h2 = (h2 & h_mask) | (t2 & t_mask)
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h3 = (h3 & h_mask) | (t3 & t_mask)
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h4 = (h4 & h_mask) | (t4 & t_mask)
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// h %= 2^128
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h0 |= h1 << 26
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h1 = ((h1 >> 6) | (h2 << 20))
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h2 = ((h2 >> 12) | (h3 << 14))
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h3 = ((h3 >> 18) | (h4 << 8))
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// s: the s part of the key
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// tag = (h + s) % (2^128)
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t := uint64(h0) + uint64(binary.LittleEndian.Uint32(key[16:]))
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h0 = uint32(t)
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t = uint64(h1) + uint64(binary.LittleEndian.Uint32(key[20:])) + (t >> 32)
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h1 = uint32(t)
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t = uint64(h2) + uint64(binary.LittleEndian.Uint32(key[24:])) + (t >> 32)
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h2 = uint32(t)
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t = uint64(h3) + uint64(binary.LittleEndian.Uint32(key[28:])) + (t >> 32)
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h3 = uint32(t)
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binary.LittleEndian.PutUint32(out[0:], h0)
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binary.LittleEndian.PutUint32(out[4:], h1)
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binary.LittleEndian.PutUint32(out[8:], h2)
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binary.LittleEndian.PutUint32(out[12:], h3)
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}
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