feistel

feistel

This package implements balanced variant of Feistel network (also known as Feistel cipher) for golang.

TLDR: It takes bytes and hashes them to reversable form

features

• small api based on standart data types and interfaces
• additional Block* functions to use it as part of hashing or crypto lib
• 100% test coverage

caveats

• all incoming data slices sizes must be rounded up to selected hash size
• Uint64* methods work with 32 bit hashes only

example

package main

import (
	"fmt"
	"hash"
	"hash/fnv"

	"github.com/google/uuid"
	"github.com/s0rg/feistel"
)

const nRounds = 4

func hashUint64(h hash.Hash, rounds int, value uint64) {
	a, _ := feistel.Uint64Hash(h, rounds, value)
	fmt.Printf("\t%d -> %d\n", value, a)

	h.Reset()

	b, _ := feistel.Uint64Hash(h, rounds, a)
	fmt.Printf("\t%d -> %d\n", a, b)
}

func hashInt64(h hash.Hash, rounds int, value int64) {
	a, _ := feistel.Uint64Hash(h, rounds, uint64(value))
	fmt.Printf("\t%d -> %d\n", value, a)

	h.Reset()

	b, _ := feistel.Uint64Hash(h, rounds, a)
	fmt.Printf("\t%d -> %d\n", a, int64(b))
}

func hashBytes(h hash.Hash, rounds int, value []byte) (rv []byte) {
	a, _ := feistel.BytesHash(h, rounds, value)
	fmt.Printf("\t%v -> %v\n", value, a)

	h.Reset()

	b, _ := feistel.BytesHash(h, rounds, a)
	fmt.Printf("\t%v -> %v\n", a, b)

	return b
}

func main() {
	hash := fnv.New32a()

	fmt.Println("uin64:")
	hashUint64(hash, nRounds, 123456)
	hash.Reset()

	fmt.Println("int64:")
	hashInt64(hash, nRounds, -123456)
	hash.Reset()

	fmt.Println("bytes:")
	id, _ := uuid.NewV7()
	res := hashBytes(hash, nRounds, id[:])
	fmt.Printf("\toriginal : %s\n", id.String())
	fmt.Printf("\tresult   : %s\n", uuid.UUID(res).String())
}

Output:

uin64:
	123456 -> 11152740970488264477
	11152740970488264477 -> 123456
int64:
	-123456 -> 6380474240854226338
	6380474240854226338 -> -123456
bytes:
	[1 156 228 69 159 236 118 49 137 105 96 245 156 183 76 171] -> [217 207 28 95 81 184 4 143 250 166 52 24 222 245 102 47]
	[217 207 28 95 81 184 4 143 250 166 52 24 222 245 102 47] -> [1 156 228 69 159 236 118 49 137 105 96 245 156 183 76 171]
	original : 019ce445-9fec-7631-8969-60f59cb74cab
	result   : 019ce445-9fec-7631-8969-60f59cb74cab

license

MIT