Create a gist now

Instantly share code, notes, and snippets.

@mimoo /cshake.go
Last active Apr 21, 2017

What would you like to do?
Cshake implementation in Go (to place in golang.org/x/crypto/sha3)
package sha3
// This allows you to customize SHAKE with a custom string,
// see shake.go for more comments on usage and security.
import (
"io"
"bytes"
"encoding/binary"
)
type CShakeHash interface {
io.Writer
io.Reader
Clone() ShakeHash
Reset()
}
// NewcShake128 creates a new custom cSHAKE128 variable-output-length CShakeHash.
// Its generic security strength is 128 bits against all attacks if at
// least 32 bytes of its output are used.
func NewcShake128(custom []byte) CShakeHash {
cshake := &state{rate: 168, dsbyte: 0x04}
cshake.initcShake(custom)
return cshake
}
// NewcShake256 creates a new custom cSHAKE128 variable-output-length CShakeHash.
// Its generic security strength is 256 bits against all attacks if
// at least 64 bytes of its output are used.
func NewcShake256(custom []byte) CShakeHash {
cshake := &state{rate: 136, dsbyte: 0x04}
cshake.initcShake(custom)
return cshake
}
// CShakeSum128 writes an arbitrary-length digest of data into hash.
// custom string should be of length smaller than uint64
func CShakeSum128(hash, data, custom []byte) {
h := NewcShake128(custom)
h.Write(data)
h.Read(hash)
}
// CShakeSum256 writes an arbitrary-length digest of data into hash.
// custom string should be of length smaller than uint64
func CShakeSum256(hash, data, custom []byte) {
h := NewcShake256(custom)
h.Write(data)
h.Read(hash)
}
// The initialization of cShake
func (cshake *state) initcShake(custom []byte) {
cShakePad := make([]byte, 0)
cShakePad = append(cShakePad, left_encode(uint64(cshake.rate))...)
cShakePad = append(cShakePad, []byte{1, 0}...) // left_encode(0)
cShakePad = append(cShakePad, left_encode(uint64(len(custom) * 8))...)
cShakePad = append(cShakePad, custom...)
padding_len := cshake.rate - (len(cShakePad) % cshake.rate)
cShakePad = append(cShakePad, bytes.Repeat([]byte{0}, padding_len)...)
cshake.Write(cShakePad)
}
// Helper function for the initialization of cShake
func left_encode(value uint64) []byte {
var input [9]byte
var offset uint
if value == 0 {
offset = 8
} else {
binary.BigEndian.PutUint64(input[1:], value)
for offset = 0; offset < 9; offset ++ {
if input[offset] != 0 {
break
}
}
}
input[offset - 1] = byte(9 - offset)
return input[offset - 1:]
}
//
// This is an example on how to use this code
// first get the sha-3 library: `go get golang.org/x/crypto/sha3`
// then place the `cshake.go` file in there (`$GOPATH/src/golang.org/x/crypto/sha3`)
//
package main
import(
"golang.org/x/crypto/sha3"
"fmt"
"encoding/hex"
)
func main(){
// output will be 16 bytes
hash := make([]byte, 16)
// hashing "message" with the customization string "custom"
sha3.CShakeSum128(hash, []byte("message"), []byte("custom"))
// printing the result
fmt.Println(hex.EncodeToString(hash))
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment