code review 130950043: go.crypto/sha3: update to sync with draft FIPS-202

sha3/shake.go

+// 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"
+)
+
+// Shake defines the interface to hash functions that
+// support arbitrary-length output.
+type ShakeHash interface {
+        // Write absorbs more data into the hash's state.
+        // It never returns an error.
+        io.Writer
+        // Read reads more output from the hash; reading affects the hash's
+        // state. (Shake.Read is thus very different from Hash.Sum)
+        // It never returns an error.
+        io.Reader
+
+        // Barrier overwrites (200 - rate) bytes of the hash's state
+        // with zeros, making it computationally infeasible to recover
+        // previous inputs.
+        Barrier()
+
+        // Reset resets the Hash to its initial state.
+        Reset()
+}
+
+// NewShake128 creates a new SHAKE128 variable-output-length Sponge.
+// 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 Sponge.
+// 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)
+}