vendor/golang.org/x/crypto/blake2s/blake2x.go

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// Copyright 2017 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 blake2s

import (
	"encoding/binary"
	"errors"
	"io"
)

// XOF defines the interface to hash functions that
// support arbitrary-length output.
type XOF interface {
	// Write absorbs more data into the hash's state. It panics if called
	// after Read.
	io.Writer

	// Read reads more output from the hash. It returns io.EOF if the limit
	// has been reached.
	io.Reader

	// Clone returns a copy of the XOF in its current state.
	Clone() XOF

	// Reset resets the XOF to its initial state.
	Reset()
}

// OutputLengthUnknown can be used as the size argument to NewXOF to indicate
// the length of the output is not known in advance.
const OutputLengthUnknown = 0

// magicUnknownOutputLength is a magic value for the output size that indicates
// an unknown number of output bytes.
const magicUnknownOutputLength = 65535

// maxOutputLength is the absolute maximum number of bytes to produce when the
// number of output bytes is unknown.
const maxOutputLength = (1 << 32) * 32

// NewXOF creates a new variable-output-length hash. The hash either produce a
// known number of bytes (1 <= size < 65535), or an unknown number of bytes
// (size == OutputLengthUnknown). In the latter case, an absolute limit of
// 128GiB applies.
//
// A non-nil key turns the hash into a MAC. The key must between
// zero and 32 bytes long.
func NewXOF(size uint16, key []byte) (XOF, error) {
	if len(key) > Size {
		return nil, errKeySize
	}
	if size == magicUnknownOutputLength {
		// 2^16-1 indicates an unknown number of bytes and thus isn't a
		// valid length.
		return nil, errors.New("blake2s: XOF length too large")
	}
	if size == OutputLengthUnknown {
		size = magicUnknownOutputLength