c25519: Initial support for c25519 package

c25519[1] is a library optimized for embedded applications handling ed25519
signing and x25519 crypto. It uses significantly less memory and flash
compared to TweetNaCl and is significantly faster when used on a
samr21-xpro

[1]: https://www.dlbeer.co.nz/oss/c25519.html

pkg/c25519/Makefile

@@ -0,0 +1,36 @@
+PKG_NAME    = c25519
+PKG_URL     = https://www.dlbeer.co.nz/downloads
+PKG_VERSION = 2017-10-05
+PKG_EXT     = zip
+PKG_LICENSE = PD
+PKG_SHA512  = dbfb4285837ab2ea3d99c448b22877cc7a139ccbaebb1de367e2bec1fd562fe629b389d86603915448078b8fd7e631c8fc9a7d126eb889a1ba0c17611369b190
+
+PKG_BUILDDIR ?= $(PKGDIRBASE)/$(PKG_NAME)
+PKG_ZIPFILE = $(PKGDIRBASE)/$(PKG_NAME)-$(PKG_VERSION).$(PKG_EXT)
+
+ifneq ($(RIOTBASE),)
+include $(RIOTBASE)/Makefile.base
+endif
+
+.PHONY: all clean distclean
+
+prepare: $(PKG_BUILDDIR)/
+
+all: $(PKG_BUILDDIR)/
+	"$(MAKE)" -C $(PKG_BUILDDIR)/src -f $(CURDIR)/Makefile.c25519
+
+$(PKG_BUILDDIR)/: $(PKGDIRBASE)/$(PKG_NAME)-$(PKG_VERSION).$(PKG_EXT)
+	test "$(PKG_SHA512)  $(PKG_ZIPFILE)" =  "$$(sha512sum "${PKG_ZIPFILE}")"
+	$(Q)$(UNZIP_HERE) -D -d $(PKGDIRBASE) $<
+
+$(PKG_ZIPFILE):
+	mkdir -p $(PKGDIRBASE)
+	$(Q)$(DOWNLOAD_TO_FILE) $@ $(PKG_URL)/$(PKG_NAME)-$(PKG_VERSION).$(PKG_EXT)
+
+clean::
+	# Reset package to checkout state.
+	rm -rf $(PKG_BUILDDIR)
+
+distclean::
+	rm -rf $(PKG_BUILDDIR) $(PKGDIRBASE)/$(PKG_NAME)-$(PKG_VERSION).$(PKG_EXT)
+	rm -rf $(PKG_SHAFILE)

pkg/c25519/Makefile.c25519

@@ -0,0 +1,11 @@
+MODULE := c25519
+
+SRC += c25519.c
+SRC += ed25519.c
+SRC += edsign.c
+SRC += f25519.c
+SRC += fprime.c
+SRC += morph25519.c
+SRC += sha512.c
+
+include $(RIOTBASE)/Makefile.base

pkg/c25519/Makefile.include

@@ -0,0 +1 @@
+INCLUDES += -I$(PKGDIRBASE)/c25519/src

pkg/c25519/doc.txt

@@ -0,0 +1,36 @@
+/**
+ * @defgroup pkg_c25519 C25519 cryptographic library
+ * @ingroup  pkg
+ * @ingroup  sys
+ * @brief    Curve25519 and Ed25519 for low-memory systems
+ *
+ * This package contains portable public-domain implementations of Daniel J.
+ * Bernstein's Curve255191 Diffie-Hellman function, and of the Ed25519
+ * signature system. The memory consumption is low enough that they could be
+ * reasonably considered for most microcontroller applications. In particular,
+ * Curve25519 scalar multiplication uses less than half a kB of peak stack
+ * usage.
+ *
+ * ## Requirements
+ *
+ * C25519 requires around 1K of stack, so beware that you're allocating at
+ * least `THREAD_STACKSIZE_DEFAULT + 1K` bytes.
+ *
+ * You can do it easily by adding:
+ *
+ * ```makefile
+ * CFLAGS += '-DTHREAD_STACKSIZE_MAIN=(THREAD_STACKSIZE_DEFAULT + 1024)'
+ * ```
+ *
+ * to your makefile.
+ *
+ * ## Usage
+ *
+ * Just add it as a package in your application:
+ *
+ * ```makefile
+ * USEPKG += c25519
+ * ```
+ *
+ * @see      https://www.dlbeer.co.nz/oss/c25519.html
+ */