87 lines
1.7 KiB
Go
87 lines
1.7 KiB
Go
// Package tz contains Tillich-Zemor checksum implementations
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// using different backends.
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//
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// Copyright 2022 (c) NSPCC
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package tz
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import (
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"errors"
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)
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// Concat performs combining of hashes based on homomorphic property.
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func Concat(hs [][]byte) ([]byte, error) {
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var b, c sl2
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b = id
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for i := range hs {
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if err := c.UnmarshalBinary(hs[i]); err != nil {
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return nil, err
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}
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b.Mul(&b, &c)
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}
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return b.MarshalBinary()
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}
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// Validate checks if hashes in hs combined are equal to h.
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func Validate(h []byte, hs [][]byte) (bool, error) {
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var (
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b []byte
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got, expected [Size]byte
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err error
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)
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if len(h) != Size {
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return false, errors.New("invalid hash")
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} else if len(hs) == 0 {
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return false, errors.New("empty slice")
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}
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copy(expected[:], h)
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b, err = Concat(hs)
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if err != nil {
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return false, errors.New("cant concatenate hashes")
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}
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copy(got[:], b)
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return expected == got, nil
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}
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// SubtractR returns hash a, such that Concat(a, b) == c
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// This is possible, because Tillich-Zemor hash is actually a matrix
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// which can be inversed.
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func SubtractR(c, b []byte) (a []byte, err error) {
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var p1, p2, r sl2
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if err = r.UnmarshalBinary(c); err != nil {
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return nil, err
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}
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if err = p2.UnmarshalBinary(b); err != nil {
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return nil, err
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}
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p1 = *Inv(&p2)
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p1.Mul(&r, &p1)
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return p1.MarshalBinary()
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}
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// SubtractL returns hash b, such that Concat(a, b) == c
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// This is possible, because Tillich-Zemor hash is actually a matrix
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// which can be inversed.
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func SubtractL(c, a []byte) (b []byte, err error) {
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var p1, p2, r sl2
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if err = r.UnmarshalBinary(c); err != nil {
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return nil, err
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}
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if err = p1.UnmarshalBinary(a); err != nil {
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return nil, err
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}
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p2 = *Inv(&p1)
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p2.Mul(&p2, &r)
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return p2.MarshalBinary()
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}
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