From 46da5280eb7fe9fafabaee5c7202732fa15a034a Mon Sep 17 00:00:00 2001
From: "Joe Richey joerichey@google.com" <joerichey@google.com>
Date: Mon, 17 Jul 2017 17:15:15 -0700
Subject: [PATCH] crypto: Conversion to/from C strings

---
 crypto/key.go | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/crypto/key.go b/crypto/key.go
index cffe2b4..e440ca1 100644
--- a/crypto/key.go
+++ b/crypto/key.go
@@ -20,6 +20,12 @@
 
 package crypto
 
+/*
+#include <stdlib.h>
+#include <string.h>
+*/
+import "C"
+
 import (
 	"bytes"
 	"crypto/subtle"
@@ -148,13 +154,6 @@ func (key *Key) Len() int {
 	return len(key.data)
 }
 
-// UnsafeData exposes the underlying protected slice. This is unsafe because the
-// data can be paged to disk if the buffer is copied, or the slice may be
-// wiped while being used.
-func (key *Key) UnsafeData() []byte {
-	return key.data
-}
-
 // Equals compares the contents of two keys, returning true if they have the same
 // key data. This function runs in constant time.
 func (key *Key) Equals(key2 *Key) bool {
@@ -178,6 +177,30 @@ func (key *Key) resize(requestedSize int) (*Key, error) {
 	return resizedKey, nil
 }
 
+// UnsafeToCString makes a copy of the string's data into a null-terminated C
+// string allocated by C. Note that this method is unsafe as this C copy has no
+// locking or wiping functionality. The key shouldn't contain any `\0` bytes.
+func (key *Key) UnsafeToCString() unsafe.Pointer {
+	// Memory for the key must be moved into a C string allocated by C.
+	size := C.size_t(key.Len())
+	data := C.calloc(size+1, 1)
+	C.memcpy(data, util.Ptr(key.data), size)
+	return data
+}
+
+// NewKeyFromCString creates of a copy of some C string's data in a key. Note
+// that the original C string is not modified at all, so steps must be taken to
+// ensure that this original copy is secured.
+func NewKeyFromCString(str unsafe.Pointer) (*Key, error) {
+	size := C.strlen((*C.char)(str))
+	key, err := newBlankKey(int(size))
+	if err != nil {
+		return nil, err
+	}
+	C.memcpy(util.Ptr(key.data), str, size)
+	return key, nil
+}
+
 // NewKeyFromReader constructs a key of abritary length by reading from reader
 // until hitting EOF.
 func NewKeyFromReader(reader io.Reader) (*Key, error) {
-- 
2.39.5