230 lines
6.1 KiB
Go
230 lines
6.1 KiB
Go
// Copyright (c) 2016 Andreas Auernhammer. All rights reserved.
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// Use of this source code is governed by a license that can be
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// found in the LICENSE file.
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// +build !amd64 gccgo appengine nacl
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package poly1305
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import "encoding/binary"
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const (
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msgBlock = uint32(1 << 24)
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finalBlock = uint32(0)
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)
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// Sum generates an authenticator for msg using a one-time key and returns the
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// 16-byte result. Authenticating two different messages with the same key allows
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// an attacker to forge messages at will.
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func Sum(msg []byte, key [32]byte) [TagSize]byte {
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var (
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h, r [5]uint32
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s [4]uint32
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)
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var out [TagSize]byte
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initialize(&r, &s, &key)
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// process full 16-byte blocks
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n := len(msg) & (^(TagSize - 1))
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if n > 0 {
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update(msg[:n], msgBlock, &h, &r)
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msg = msg[n:]
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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] = 1
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update(block[:], finalBlock, &h, &r)
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}
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finalize(&out, &h, &s)
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return out
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}
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// New returns a hash.Hash computing the poly1305 sum.
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// Notice that Poly1305 is insecure if one key is used twice.
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func New(key [32]byte) *Hash {
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p := new(Hash)
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initialize(&(p.r), &(p.s), &key)
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return p
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}
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// Hash implements a Poly1305 writer interface.
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// Poly1305 cannot be used like common hash.Hash implementations,
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// because using a poly1305 key twice breaks its security.
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// So poly1305.Hash does not support some kind of reset.
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type Hash struct {
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h, r [5]uint32
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s [4]uint32
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buf [TagSize]byte
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off int
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done bool
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}
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// Size returns the number of bytes Sum will append.
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func (p *Hash) Size() int { return TagSize }
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// Write adds more data to the running Poly1305 hash.
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// This function should return a non-nil error if a call
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// to Write happens after a call to Sum. So it is not possible
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// to compute the checksum and than add more data.
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func (p *Hash) Write(msg []byte) (int, error) {
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if p.done {
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return 0, errWriteAfterSum
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}
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n := len(msg)
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if p.off > 0 {
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dif := TagSize - p.off
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if n <= dif {
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p.off += copy(p.buf[p.off:], msg)
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return n, nil
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}
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copy(p.buf[p.off:], msg[:dif])
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msg = msg[dif:]
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update(p.buf[:], msgBlock, &(p.h), &(p.r))
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p.off = 0
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}
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// process full 16-byte blocks
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if nn := len(msg) & (^(TagSize - 1)); nn > 0 {
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update(msg[:nn], msgBlock, &(p.h), &(p.r))
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msg = msg[nn:]
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}
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if len(msg) > 0 {
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p.off += copy(p.buf[p.off:], msg)
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}
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return n, nil
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}
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// Sum appends the Pol1305 hash of the previously
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// processed data to b and returns the resulting slice.
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// It is safe to call this function multiple times.
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func (p *Hash) Sum(b []byte) []byte {
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var out [TagSize]byte
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h := p.h
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if p.off > 0 {
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var buf [TagSize]byte
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copy(buf[:], p.buf[:p.off])
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buf[p.off] = 1 // invariant: p.off < TagSize
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update(buf[:], finalBlock, &h, &(p.r))
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}
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finalize(&out, &h, &(p.s))
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p.done = true
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return append(b, out[:]...)
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}
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func initialize(r *[5]uint32, s *[4]uint32, key *[32]byte) {
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r[0] = binary.LittleEndian.Uint32(key[0:]) & 0x3ffffff
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r[1] = (binary.LittleEndian.Uint32(key[3:]) >> 2) & 0x3ffff03
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r[2] = (binary.LittleEndian.Uint32(key[6:]) >> 4) & 0x3ffc0ff
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r[3] = (binary.LittleEndian.Uint32(key[9:]) >> 6) & 0x3f03fff
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r[4] = (binary.LittleEndian.Uint32(key[12:]) >> 8) & 0x00fffff
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s[0] = binary.LittleEndian.Uint32(key[16:])
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s[1] = binary.LittleEndian.Uint32(key[20:])
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s[2] = binary.LittleEndian.Uint32(key[24:])
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s[3] = binary.LittleEndian.Uint32(key[28:])
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}
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func update(msg []byte, flag uint32, h, r *[5]uint32) {
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h0, h1, h2, h3, h4 := h[0], h[1], h[2], h[3], h[4]
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r0, r1, r2, r3, r4 := uint64(r[0]), uint64(r[1]), uint64(r[2]), uint64(r[3]), uint64(r[4])
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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) | flag
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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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h[0], h[1], h[2], h[3], h[4] = h0, h1, h2, h3, h4
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}
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func finalize(out *[TagSize]byte, h *[5]uint32, s *[4]uint32) {
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h0, h1, h2, h3, h4 := h[0], h[1], h[2], h[3], h[4]
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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(s[0])
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h0 = uint32(t)
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t = uint64(h1) + uint64(s[1]) + (t >> 32)
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h1 = uint32(t)
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t = uint64(h2) + uint64(s[2]) + (t >> 32)
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h2 = uint32(t)
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t = uint64(h3) + uint64(s[3]) + (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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