pkg: add tweetnacl as a package

pkg/tweetnacl/Makefile

@@ -0,0 +1,12 @@
+PKG_NAME=tweetnacl
+PKG_URL=https://github.com/RIOT-OS/tweetnacl
+PKG_VERSION=7ea05c7098a16c87fa66e9166ce301666f3f2623
+PKG_LICENSE=PD
+
+.PHONY: all
+
+all: git-download
+	@cp $(RIOTBASE)/pkg/tweetnacl/src/* $(PKG_BUILDDIR)
+	"$(MAKE)" -C $(PKG_BUILDDIR)
+
+include $(RIOTBASE)/pkg/pkg.mk

pkg/tweetnacl/Makefile.include

@@ -0,0 +1 @@
+INCLUDES += -I$(BINDIRBASE)/pkg/$(BOARD)/tweetnacl/

pkg/tweetnacl/README.md

@@ -0,0 +1,44 @@
+# TweetNaCl RIOT package
+TweetNaCl is the world's first auditable high-security cryptographic library.
+TweetNaCl fits into just 100 tweets while supporting all 25 of the C NaCl
+functions used by applications. TweetNaCl is a self-contained public-domain C
+library, so it can easily be integrated into applications.
+
+NaCl (pronounced "salt") is a new easy-to-use high-speed software library for
+network communication, encryption, decryption, signatures, etc. NaCl's goal is
+to provide all of the core operations needed to build higher-level
+cryptographic tools.
+
+Of course, other libraries already exist for these core operations. NaCl
+advances the state of the art by improving security, by improving usability,
+and by improving speed.
+
+(from https://nacl.cr.yp.to/ and http://tweetnacl.cr.yp.to/)
+
+You can find the API and more information [here](https://nacl.cr.yp.to/), since
+the sources are not documented due to the aim for fitting in 100 tweets.
+
+## Requirements
+TweetNaCl requires more than 2K of stack, so beware that you're allocating at
+least `THREAD_STACKSIZE_DEFAULT + 2048` bytes.
+
+You can do it easily by adding:
+
+```makefile
+CFLAGS += '-DTHREAD_STACKSIZE_MAIN=(THREAD_STACKSIZE_DEFAULT + 2048)'
+```
+
+to your makefile.
+
+## Usage
+Just add it as a package in your application:
+
+```makefile
+USEPKG += tweetnacl
+```
+
+And don't forget to include the header:
+
+```c
+#include <tweetnacl.h>
+```

pkg/tweetnacl/src/Makefile

@@ -0,0 +1,3 @@
+MODULE=tweetnacl
+
+include $(RIOTBASE)/Makefile.base

pkg/tweetnacl/src/randombytes.c

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2016 Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include "random.h"
+
+#include <stdio.h>
+
+void randombytes(uint8_t *target, uint64_t n)
+{
+    uint32_t random;
+    uint8_t *random_pos = (uint8_t*)&random;
+    unsigned _n = 0;
+
+    while (n--) {
+        if (! (_n++ & 0x3)) {
+            random = random_uint32();
+            random_pos = (uint8_t *) &random;
+        }
+        *target++ = *random_pos++;
+    }
+}