88 lines
1.7 KiB
Go
88 lines
1.7 KiB
Go
// Package tz contains Tillich-Zemor checksum implementations
|
|
// using different backends.
|
|
//
|
|
// Copyright 2022 (c) NSPCC
|
|
package tz
|
|
|
|
import (
|
|
"errors"
|
|
)
|
|
|
|
// 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 [Size]byte
|
|
err error
|
|
)
|
|
|
|
if len(h) != Size {
|
|
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()
|
|
}
|