tzhash/tz/hash.go

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// Copyright 2018 (c) NSPCC
//
// Package tz implements general Tillich-Zemo
package tz
import (
"errors"
"hash"
"math"
"github.com/nspcc-dev/tzhash/gf127"
)
const (
hashSize = 64
hashBlockSize = 128
)
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type digest struct {
x [4]gf127.GF127
}
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// type assertion
var _ hash.Hash = new(digest)
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var (
minmax = [2]gf127.GF127{{0, 0}, {math.MaxUint64, math.MaxUint64}}
x127x63 = gf127.GF127{1 << 63, 1 << 63}
)
// New returns a new hash.Hash computing the Tillich-Zémor checksum.
func New() hash.Hash {
d := new(digest)
d.Reset()
return d
}
func (d *digest) Sum(in []byte) []byte {
// Make a copy of d so that caller can keep writing and summing.
d0 := *d
h := d0.checkSum()
return append(in, h[:]...)
}
func (d *digest) checkSum() [hashSize]byte {
return d.byteArray()
}
func (d *digest) byteArray() (b [hashSize]byte) {
var t []byte
for i := 0; i < 4; i++ {
t = d.x[i].ByteArray()
copy(b[i*16:], t)
}
return
}
func (d *digest) Reset() {
d.x[0] = gf127.GF127{1, 0}
d.x[1] = gf127.GF127{0, 0}
d.x[2] = gf127.GF127{0, 0}
d.x[3] = gf127.GF127{1, 0}
}
func (d *digest) Write(data []byte) (n int, err error) {
n = len(data)
for _, b := range data {
mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>7)&1])
mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>6)&1])
mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>5)&1])
mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>4)&1])
mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>3)&1])
mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>2)&1])
mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>1)&1])
mulBitRight(&d.x[0], &d.x[1], &d.x[2], &d.x[3], &minmax[(b>>0)&1])
}
return
}
func (d *digest) Size() int {
return hashSize
}
func (d *digest) BlockSize() int {
return hashBlockSize
}
// Sum returnz Tillich-Zémor checksum of data
func Sum(data []byte) [hashSize]byte {
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d := new(digest)
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d.Reset()
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_, _ = d.Write(data) // no errors
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return d.checkSum()
}
// Concat performs combining of hashes based on homomorphic property.
func Concat(hs [][]byte) ([]byte, error) {
var b, c sl2
b = id
for i := range hs {
if err := c.UnmarshalBinary(hs[i]); err != nil {
return nil, err
}
b.Mul(&b, &c)
}
return b.MarshalBinary()
}
// Validate checks if hashes in hs combined are equal to h.
func Validate(h []byte, hs [][]byte) (bool, error) {
var (
b []byte
got, expected [hashSize]byte
err error
)
if len(h) != hashSize {
return false, errors.New("invalid hash")
} else if len(hs) == 0 {
return false, errors.New("empty slice")
}
copy(expected[:], h)
b, err = Concat(hs)
if err != nil {
return false, errors.New("cant concatenate hashes")
}
copy(got[:], b)
return expected == got, nil
}
// SubtractR returns hash a, such that Concat(a, b) == c
// This is possible, because Tillich-Zemor hash is actually a matrix
// which can be inversed.
func SubtractR(c, b []byte) (a []byte, err error) {
var p1, p2, r sl2
if err = r.UnmarshalBinary(c); err != nil {
return nil, err
}
if err = p2.UnmarshalBinary(b); err != nil {
return nil, err
}
p1 = *Inv(&p2)
p1.Mul(&r, &p1)
return p1.MarshalBinary()
}
// SubtractL returns hash b, such that Concat(a, b) == c
// This is possible, because Tillich-Zemor hash is actually a matrix
// which can be inversed.
func SubtractL(c, a []byte) (b []byte, err error) {
var p1, p2, r sl2
if err = r.UnmarshalBinary(c); err != nil {
return nil, err
}
if err = p1.UnmarshalBinary(a); err != nil {
return nil, err
}
p2 = *Inv(&p1)
p2.Mul(&p2, &r)
return p2.MarshalBinary()
}
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func mulBitRight(c00, c01, c10, c11, e *gf127.GF127)