Take advantage of Go 1.5 optimized zeroing.

Closes #286.

internal/zero/array.go

@@ -0,0 +1,27 @@
+// Copyright (c) 2015 The btcsuite developers
+//
+// Permission to use, copy, modify, and distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+package zero
+
+// Bytea32 clears the 32-byte array by filling it with the zero value.
+// This is used to explicitly clear private key material from memory.
+func Bytea32(b *[32]byte) {
+	*b = [32]byte{}
+}
+
+// Bytea64 clears the 64-byte array by filling it with the zero value.
+// This is used to explicitly clear sensitive material from memory.
+func Bytea64(b *[64]byte) {
+	*b = [64]byte{}
+}

internal/zero/doc.go

@@ -0,0 +1,3 @@
+// Package zero contains functions to clear data from byte slices and
+// multi-precision integers.
+package zero

internal/zero/slice.go

@@ -0,0 +1,47 @@
+// Copyright (c) 2015 The btcsuite developers
+//
+// Permission to use, copy, modify, and distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+
+// This file implements range-based zeroing, which as of Go 1.5 is
+// optimized using a Duff's device.  See slice14.go for an implementation
+// optimized for previous Go versions.
+//
+// +build !go1.3,!go1.4
+
+package zero
+
+import "math/big"
+
+// Bytes sets all bytes in the passed slice to zero.  This is used to
+// explicitly clear private key material from memory.
+//
+// In general, prefer to use the fixed-sized zeroing functions (Bytea*)
+// when zeroing bytes as they are much more efficient than the variable
+// sized zeroing func Bytes.
+func Bytes(b []byte) {
+	for i := range b {
+		b[i] = 0
+	}
+}
+
+// BigInt sets all bytes in the passed big int to zero and then sets the
+// value to 0.  This differs from simply setting the value in that it
+// specifically clears the underlying bytes whereas simply setting the value
+// does not.  This is mostly useful to forcefully clear private keys.
+func BigInt(x *big.Int) {
+	b := x.Bits()
+	for i := range b {
+		b[i] = 0
+	}
+	x.SetInt64(0)
+}

internal/zero/slice14.go

@@ -12,8 +12,17 @@
 // ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 // OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
-// Package zero contains functions to clear data from byte slices and
+// Go >= 1.5 optimizes range-based zeroing of the form:
-// multi-precision integers.
+//
+//   for i := range slice {
+//           slice[i] = 0
+//   }
+//
+// to an optimized implementation using a Duff's device, but older versions
+// do not and benefit from this custom implementation.
+//
+// +build go1.3 go1.4
+
 package zero
 
 import (
@@ -35,18 +44,6 @@ func Bytes(b []byte) {
 	}
 }
 
-// Bytea32 clears the 32-byte array by filling it with the zero value.
-// This is used to explicitly clear private key material from memory.
-func Bytea32(b *[32]byte) {
-	*b = [32]byte{}
-}
-
-// Bytea64 clears the 64-byte array by filling it with the zero value.
-// This is used to explicitly clear sensitive material from memory.
-func Bytea64(b *[64]byte) {
-	*b = [64]byte{}
-}
-
 // BigInt sets all bytes in the passed big int to zero and then sets the
 // value to 0.  This differs from simply setting the value in that it
 // specifically clears the underlying bytes whereas simply setting the value