text: // Copyright 2014 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package sha3
  
  // This file defines the ShakeHash interface, and provides
  // functions for creating SHAKE instances, as well as utility
  // functions for hashing bytes to arbitrary-length output.
  
  import (
  	"io"
  )
  
  // ShakeHash defines the interface to hash functions that
  // support arbitrary-length output.
  type ShakeHash interface {
  	// Write absorbs more data into the hash's state. It panics if input is
  	// written to it after output has been read from it.
  	io.Writer
  
  	// Read reads more output from the hash; reading affects the hash's
  	// state. (ShakeHash.Read is thus very different from Hash.Sum)
  	// It never returns an error.
  	io.Reader
  
  	// Clone returns a copy of the ShakeHash in its current state.
  	Clone() ShakeHash
  
  	// Reset resets the ShakeHash to its initial state.
  	Reset()
  }
  
  func (d *state) Clone() ShakeHash {
  	return d.clone()
  }
  
  // NewShake128 creates a new SHAKE128 variable-output-length ShakeHash.
  // Its generic security strength is 128 bits against all attacks if at
  // least 32 bytes of its output are used.
  func NewShake128() ShakeHash { return &state{rate: 168, dsbyte: 0x1f} }
  
  // NewShake256 creates a new SHAKE128 variable-output-length ShakeHash.
  // Its generic security strength is 256 bits against all attacks if
  // at least 64 bytes of its output are used.
  func NewShake256() ShakeHash { return &state{rate: 136, dsbyte: 0x1f} }
  
  // ShakeSum128 writes an arbitrary-length digest of data into hash.
  func ShakeSum128(hash, data []byte) {
  	h := NewShake128()
  	h.Write(data)
  	h.Read(hash)
  }
  
  // ShakeSum256 writes an arbitrary-length digest of data into hash.
  func ShakeSum256(hash, data []byte) {
  	h := NewShake256()
  	h.Write(data)
  	h.Read(hash)
  }
  