230 lines
6.1 KiB
Go
230 lines
6.1 KiB
Go
|
// Copyright (c) 2016 Andreas Auernhammer. All rights reserved.
|
||
|
// Use of this source code is governed by a license that can be
|
||
|
// found in the LICENSE file.
|
||
|
|
||
|
// +build !amd64 gccgo appengine nacl
|
||
|
|
||
|
package poly1305
|
||
|
|
||
|
import "encoding/binary"
|
||
|
|
||
|
const (
|
||
|
msgBlock = uint32(1 << 24)
|
||
|
finalBlock = uint32(0)
|
||
|
)
|
||
|
|
||
|
// Sum generates an authenticator for msg using a one-time key and returns the
|
||
|
// 16-byte result. Authenticating two different messages with the same key allows
|
||
|
// an attacker to forge messages at will.
|
||
|
func Sum(msg []byte, key [32]byte) [TagSize]byte {
|
||
|
var (
|
||
|
h, r [5]uint32
|
||
|
s [4]uint32
|
||
|
)
|
||
|
var out [TagSize]byte
|
||
|
|
||
|
initialize(&r, &s, &key)
|
||
|
|
||
|
// process full 16-byte blocks
|
||
|
n := len(msg) & (^(TagSize - 1))
|
||
|
if n > 0 {
|
||
|
update(msg[:n], msgBlock, &h, &r)
|
||
|
msg = msg[n:]
|
||
|
}
|
||
|
if len(msg) > 0 {
|
||
|
var block [TagSize]byte
|
||
|
off := copy(block[:], msg)
|
||
|
block[off] = 1
|
||
|
update(block[:], finalBlock, &h, &r)
|
||
|
}
|
||
|
finalize(&out, &h, &s)
|
||
|
return out
|
||
|
}
|
||
|
|
||
|
// New returns a hash.Hash computing the poly1305 sum.
|
||
|
// Notice that Poly1305 is insecure if one key is used twice.
|
||
|
func New(key [32]byte) *Hash {
|
||
|
p := new(Hash)
|
||
|
initialize(&(p.r), &(p.s), &key)
|
||
|
return p
|
||
|
}
|
||
|
|
||
|
// Hash implements a Poly1305 writer interface.
|
||
|
// Poly1305 cannot be used like common hash.Hash implementations,
|
||
|
// because using a poly1305 key twice breaks its security.
|
||
|
// So poly1305.Hash does not support some kind of reset.
|
||
|
type Hash struct {
|
||
|
h, r [5]uint32
|
||
|
s [4]uint32
|
||
|
|
||
|
buf [TagSize]byte
|
||
|
off int
|
||
|
done bool
|
||
|
}
|
||
|
|
||
|
// Size returns the number of bytes Sum will append.
|
||
|
func (p *Hash) Size() int { return TagSize }
|
||
|
|
||
|
// Write adds more data to the running Poly1305 hash.
|
||
|
// This function should return a non-nil error if a call
|
||
|
// to Write happens after a call to Sum. So it is not possible
|
||
|
// to compute the checksum and than add more data.
|
||
|
func (p *Hash) Write(msg []byte) (int, error) {
|
||
|
if p.done {
|
||
|
return 0, errWriteAfterSum
|
||
|
}
|
||
|
n := len(msg)
|
||
|
|
||
|
if p.off > 0 {
|
||
|
dif := TagSize - p.off
|
||
|
if n <= dif {
|
||
|
p.off += copy(p.buf[p.off:], msg)
|
||
|
return n, nil
|
||
|
}
|
||
|
copy(p.buf[p.off:], msg[:dif])
|
||
|
msg = msg[dif:]
|
||
|
update(p.buf[:], msgBlock, &(p.h), &(p.r))
|
||
|
p.off = 0
|
||
|
}
|
||
|
|
||
|
// process full 16-byte blocks
|
||
|
if nn := len(msg) & (^(TagSize - 1)); nn > 0 {
|
||
|
update(msg[:nn], msgBlock, &(p.h), &(p.r))
|
||
|
msg = msg[nn:]
|
||
|
}
|
||
|
|
||
|
if len(msg) > 0 {
|
||
|
p.off += copy(p.buf[p.off:], msg)
|
||
|
}
|
||
|
|
||
|
return n, nil
|
||
|
}
|
||
|
|
||
|
// Sum appends the Pol1305 hash of the previously
|
||
|
// processed data to b and returns the resulting slice.
|
||
|
// It is safe to call this function multiple times.
|
||
|
func (p *Hash) Sum(b []byte) []byte {
|
||
|
var out [TagSize]byte
|
||
|
h := p.h
|
||
|
|
||
|
if p.off > 0 {
|
||
|
var buf [TagSize]byte
|
||
|
copy(buf[:], p.buf[:p.off])
|
||
|
buf[p.off] = 1 // invariant: p.off < TagSize
|
||
|
|
||
|
update(buf[:], finalBlock, &h, &(p.r))
|
||
|
}
|
||
|
|
||
|
finalize(&out, &h, &(p.s))
|
||
|
p.done = true
|
||
|
return append(b, out[:]...)
|
||
|
}
|
||
|
|
||
|
func initialize(r *[5]uint32, s *[4]uint32, key *[32]byte) {
|
||
|
r[0] = binary.LittleEndian.Uint32(key[0:]) & 0x3ffffff
|
||
|
r[1] = (binary.LittleEndian.Uint32(key[3:]) >> 2) & 0x3ffff03
|
||
|
r[2] = (binary.LittleEndian.Uint32(key[6:]) >> 4) & 0x3ffc0ff
|
||
|
r[3] = (binary.LittleEndian.Uint32(key[9:]) >> 6) & 0x3f03fff
|
||
|
r[4] = (binary.LittleEndian.Uint32(key[12:]) >> 8) & 0x00fffff
|
||
|
|
||
|
s[0] = binary.LittleEndian.Uint32(key[16:])
|
||
|
s[1] = binary.LittleEndian.Uint32(key[20:])
|
||
|
s[2] = binary.LittleEndian.Uint32(key[24:])
|
||
|
s[3] = binary.LittleEndian.Uint32(key[28:])
|
||
|
}
|
||
|
|
||
|
func update(msg []byte, flag uint32, h, r *[5]uint32) {
|
||
|
h0, h1, h2, h3, h4 := h[0], h[1], h[2], h[3], h[4]
|
||
|
r0, r1, r2, r3, r4 := uint64(r[0]), uint64(r[1]), uint64(r[2]), uint64(r[3]), uint64(r[4])
|
||
|
R1, R2, R3, R4 := r1*5, r2*5, r3*5, r4*5
|
||
|
|
||
|
for len(msg) > 0 {
|
||
|
// h += msg
|
||
|
h0 += binary.LittleEndian.Uint32(msg[0:]) & 0x3ffffff
|
||
|
h1 += (binary.LittleEndian.Uint32(msg[3:]) >> 2) & 0x3ffffff
|
||
|
h2 += (binary.LittleEndian.Uint32(msg[6:]) >> 4) & 0x3ffffff
|
||
|
h3 += (binary.LittleEndian.Uint32(msg[9:]) >> 6) & 0x3ffffff
|
||
|
h4 += (binary.LittleEndian.Uint32(msg[12:]) >> 8) | flag
|
||
|
|
||
|
// h *= r
|
||
|
d0 := (uint64(h0) * r0) + (uint64(h1) * R4) + (uint64(h2) * R3) + (uint64(h3) * R2) + (uint64(h4) * R1)
|
||
|
d1 := (d0 >> 26) + (uint64(h0) * r1) + (uint64(h1) * r0) + (uint64(h2) * R4) + (uint64(h3) * R3) + (uint64(h4) * R2)
|
||
|
d2 := (d1 >> 26) + (uint64(h0) * r2) + (uint64(h1) * r1) + (uint64(h2) * r0) + (uint64(h3) * R4) + (uint64(h4) * R3)
|
||
|
d3 := (d2 >> 26) + (uint64(h0) * r3) + (uint64(h1) * r2) + (uint64(h2) * r1) + (uint64(h3) * r0) + (uint64(h4) * R4)
|
||
|
d4 := (d3 >> 26) + (uint64(h0) * r4) + (uint64(h1) * r3) + (uint64(h2) * r2) + (uint64(h3) * r1) + (uint64(h4) * r0)
|
||
|
|
||
|
// h %= p
|
||
|
h0 = uint32(d0) & 0x3ffffff
|
||
|
h1 = uint32(d1) & 0x3ffffff
|
||
|
h2 = uint32(d2) & 0x3ffffff
|
||
|
h3 = uint32(d3) & 0x3ffffff
|
||
|
h4 = uint32(d4) & 0x3ffffff
|
||
|
|
||
|
h0 += uint32(d4>>26) * 5
|
||
|
h1 += h0 >> 26
|
||
|
h0 = h0 & 0x3ffffff
|
||
|
|
||
|
msg = msg[TagSize:]
|
||
|
}
|
||
|
|
||
|
h[0], h[1], h[2], h[3], h[4] = h0, h1, h2, h3, h4
|
||
|
}
|
||
|
|
||
|
func finalize(out *[TagSize]byte, h *[5]uint32, s *[4]uint32) {
|
||
|
h0, h1, h2, h3, h4 := h[0], h[1], h[2], h[3], h[4]
|
||
|
|
||
|
// h %= p reduction
|
||
|
h2 += h1 >> 26
|
||
|
h1 &= 0x3ffffff
|
||
|
h3 += h2 >> 26
|
||
|
h2 &= 0x3ffffff
|
||
|
h4 += h3 >> 26
|
||
|
h3 &= 0x3ffffff
|
||
|
h0 += 5 * (h4 >> 26)
|
||
|
h4 &= 0x3ffffff
|
||
|
h1 += h0 >> 26
|
||
|
h0 &= 0x3ffffff
|
||
|
|
||
|
// h - p
|
||
|
t0 := h0 + 5
|
||
|
t1 := h1 + (t0 >> 26)
|
||
|
t2 := h2 + (t1 >> 26)
|
||
|
t3 := h3 + (t2 >> 26)
|
||
|
t4 := h4 + (t3 >> 26) - (1 << 26)
|
||
|
t0 &= 0x3ffffff
|
||
|
t1 &= 0x3ffffff
|
||
|
t2 &= 0x3ffffff
|
||
|
t3 &= 0x3ffffff
|
||
|
|
||
|
// select h if h < p else h - p
|
||
|
t_mask := (t4 >> 31) - 1
|
||
|
h_mask := ^t_mask
|
||
|
h0 = (h0 & h_mask) | (t0 & t_mask)
|
||
|
h1 = (h1 & h_mask) | (t1 & t_mask)
|
||
|
h2 = (h2 & h_mask) | (t2 & t_mask)
|
||
|
h3 = (h3 & h_mask) | (t3 & t_mask)
|
||
|
h4 = (h4 & h_mask) | (t4 & t_mask)
|
||
|
|
||
|
// h %= 2^128
|
||
|
h0 |= h1 << 26
|
||
|
h1 = ((h1 >> 6) | (h2 << 20))
|
||
|
h2 = ((h2 >> 12) | (h3 << 14))
|
||
|
h3 = ((h3 >> 18) | (h4 << 8))
|
||
|
|
||
|
// s: the s part of the key
|
||
|
// tag = (h + s) % (2^128)
|
||
|
t := uint64(h0) + uint64(s[0])
|
||
|
h0 = uint32(t)
|
||
|
t = uint64(h1) + uint64(s[1]) + (t >> 32)
|
||
|
h1 = uint32(t)
|
||
|
t = uint64(h2) + uint64(s[2]) + (t >> 32)
|
||
|
h2 = uint32(t)
|
||
|
t = uint64(h3) + uint64(s[3]) + (t >> 32)
|
||
|
h3 = uint32(t)
|
||
|
|
||
|
binary.LittleEndian.PutUint32(out[0:], h0)
|
||
|
binary.LittleEndian.PutUint32(out[4:], h1)
|
||
|
binary.LittleEndian.PutUint32(out[8:], h2)
|
||
|
binary.LittleEndian.PutUint32(out[12:], h3)
|
||
|
}
|