1 files changed, 22 insertions, 0 deletions

diff --git a/nacl/crypto_secretbox/wrapper-open.cpp b/nacl/crypto_secretbox/wrapper-open.cpp
new file mode 100644
index 00000000..07989813
--- /dev/null
+++ b/nacl/crypto_secretbox/wrapper-open.cpp
@@ -0,0 +1,22 @@
+#include <string>
+using std::string;
+#include "crypto_secretbox.h"
+
+string crypto_secretbox_open(const string &c,const string &n,const string &k)
+{
+  if (k.size() != crypto_secretbox_KEYBYTES) throw "incorrect key length";
+  if (n.size() != crypto_secretbox_NONCEBYTES) throw "incorrect nonce length";
+  size_t clen = c.size() + crypto_secretbox_BOXZEROBYTES;
+  unsigned char cpad[clen];
+  for (int i = 0;i < crypto_secretbox_BOXZEROBYTES;++i) cpad[i] = 0;
+  for (int i = crypto_secretbox_BOXZEROBYTES;i < clen;++i) cpad[i] = c[i - crypto_secretbox_BOXZEROBYTES];
+  unsigned char mpad[clen];
+  if (crypto_secretbox_open(mpad,cpad,clen,(const unsigned char *) n.c_str(),(const unsigned char *) k.c_str()) != 0)
+    throw "ciphertext fails verification";
+  if (clen < crypto_secretbox_ZEROBYTES)
+    throw "ciphertext too short"; // should have been caught by _open
+  return string(
+    (char *) mpad + crypto_secretbox_ZEROBYTES,
+    clen - crypto_secretbox_ZEROBYTES
+  );
+}