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internal/poly1305: drop Go 1.12 compatibility #239

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internal/poly1305: drop Go 1.12 compatibility #239

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39 changes: 0 additions & 39 deletions internal/poly1305/bits_compat.go
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21 changes: 0 additions & 21 deletions internal/poly1305/bits_go1.13.go
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43 changes: 23 additions & 20 deletions internal/poly1305/sum_generic.go
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,10 @@

package poly1305

import "encoding/binary"
import (
"encoding/binary"
"math/bits"
)

// Poly1305 [RFC 7539] is a relatively simple algorithm: the authentication tag
// for a 64 bytes message is approximately
Expand Down Expand Up @@ -114,13 +117,13 @@ type uint128 struct {
}

func mul64(a, b uint64) uint128 {
hi, lo := bitsMul64(a, b)
hi, lo := bits.Mul64(a, b)
return uint128{lo, hi}
}

func add128(a, b uint128) uint128 {
lo, c := bitsAdd64(a.lo, b.lo, 0)
hi, c := bitsAdd64(a.hi, b.hi, c)
lo, c := bits.Add64(a.lo, b.lo, 0)
hi, c := bits.Add64(a.hi, b.hi, c)
if c != 0 {
panic("poly1305: unexpected overflow")
}
Expand Down Expand Up @@ -155,8 +158,8 @@ func updateGeneric(state *macState, msg []byte) {
// hide leading zeroes. For full chunks, that's 1 << 128, so we can just
// add 1 to the most significant (2¹²⁸) limb, h2.
if len(msg) >= TagSize {
h0, c = bitsAdd64(h0, binary.LittleEndian.Uint64(msg[0:8]), 0)
h1, c = bitsAdd64(h1, binary.LittleEndian.Uint64(msg[8:16]), c)
h0, c = bits.Add64(h0, binary.LittleEndian.Uint64(msg[0:8]), 0)
h1, c = bits.Add64(h1, binary.LittleEndian.Uint64(msg[8:16]), c)
h2 += c + 1

msg = msg[TagSize:]
Expand All @@ -165,8 +168,8 @@ func updateGeneric(state *macState, msg []byte) {
copy(buf[:], msg)
buf[len(msg)] = 1

h0, c = bitsAdd64(h0, binary.LittleEndian.Uint64(buf[0:8]), 0)
h1, c = bitsAdd64(h1, binary.LittleEndian.Uint64(buf[8:16]), c)
h0, c = bits.Add64(h0, binary.LittleEndian.Uint64(buf[0:8]), 0)
h1, c = bits.Add64(h1, binary.LittleEndian.Uint64(buf[8:16]), c)
h2 += c

msg = nil
Expand Down Expand Up @@ -219,9 +222,9 @@ func updateGeneric(state *macState, msg []byte) {
m3 := h2r1

t0 := m0.lo
t1, c := bitsAdd64(m1.lo, m0.hi, 0)
t2, c := bitsAdd64(m2.lo, m1.hi, c)
t3, _ := bitsAdd64(m3.lo, m2.hi, c)
t1, c := bits.Add64(m1.lo, m0.hi, 0)
t2, c := bits.Add64(m2.lo, m1.hi, c)
t3, _ := bits.Add64(m3.lo, m2.hi, c)

// Now we have the result as 4 64-bit limbs, and we need to reduce it
// modulo 2¹³⁰ - 5. The special shape of this Crandall prime lets us do
Expand All @@ -243,14 +246,14 @@ func updateGeneric(state *macState, msg []byte) {

// To add c * 5 to h, we first add cc = c * 4, and then add (cc >> 2) = c.

h0, c = bitsAdd64(h0, cc.lo, 0)
h1, c = bitsAdd64(h1, cc.hi, c)
h0, c = bits.Add64(h0, cc.lo, 0)
h1, c = bits.Add64(h1, cc.hi, c)
h2 += c

cc = shiftRightBy2(cc)

h0, c = bitsAdd64(h0, cc.lo, 0)
h1, c = bitsAdd64(h1, cc.hi, c)
h0, c = bits.Add64(h0, cc.lo, 0)
h1, c = bits.Add64(h1, cc.hi, c)
h2 += c

// h2 is at most 3 + 1 + 1 = 5, making the whole of h at most
Expand Down Expand Up @@ -287,9 +290,9 @@ func finalize(out *[TagSize]byte, h *[3]uint64, s *[2]uint64) {
// in constant time, we compute t = h - (2¹³⁰ - 5), and select h as the
// result if the subtraction underflows, and t otherwise.

hMinusP0, b := bitsSub64(h0, p0, 0)
hMinusP1, b := bitsSub64(h1, p1, b)
_, b = bitsSub64(h2, p2, b)
hMinusP0, b := bits.Sub64(h0, p0, 0)
hMinusP1, b := bits.Sub64(h1, p1, b)
_, b = bits.Sub64(h2, p2, b)

// h = h if h < p else h - p
h0 = select64(b, h0, hMinusP0)
Expand All @@ -301,8 +304,8 @@ func finalize(out *[TagSize]byte, h *[3]uint64, s *[2]uint64) {
//
// by just doing a wide addition with the 128 low bits of h and discarding
// the overflow.
h0, c := bitsAdd64(h0, s[0], 0)
h1, _ = bitsAdd64(h1, s[1], c)
h0, c := bits.Add64(h0, s[0], 0)
h1, _ = bits.Add64(h1, s[1], c)

binary.LittleEndian.PutUint64(out[0:8], h0)
binary.LittleEndian.PutUint64(out[8:16], h1)
Expand Down