Implement HKDF

1 files changed, 53 insertions, 0 deletions

diff --git a/src/hkdf_sha256.c b/src/hkdf_sha256.c
new file mode 100644
index 0000000..a85f5e3
--- /dev/null
+++ b/src/hkdf_sha256.c
@@ -0,0 +1,53 @@
+/*
+  Copyright (c) 2012-2013, Matthias Schiffer <mschiffer@universe-factory.net>
+  All rights reserved.
+
+  Redistribution and use in source and binary forms, with or without
+  modification, are permitted provided that the following conditions are met:
+
+    1. Redistributions of source code must retain the above copyright notice,
+       this list of conditions and the following disclaimer.
+    2. Redistributions in binary form must reproduce the above copyright notice,
+       this list of conditions and the following disclaimer in the documentation
+       and/or other materials provided with the distribution.
+
+  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+
+#include "hkdf_sha256.h"
+
+#include <string.h>
+
+
+void fastd_hkdf_sha256_expand(fastd_sha256_t *out, size_t blocks, fastd_sha256_t *prk, const uint8_t *info, size_t infolen) {
+	if (!blocks)
+		return;
+
+	size_t len = sizeof(fastd_sha256_t) + infolen + 1;
+
+	uint8_t buf[len] __attribute__((align(4)));
+
+	memset(buf, 0, sizeof(fastd_sha256_t));
+	memcpy(buf+sizeof(fastd_sha256_t), info, infolen);
+	buf[len-1] = 0x01;
+
+	fastd_hmacsha256(out, prk->w, (uint32_t*)(buf+sizeof(fastd_sha256_t)), infolen + 1);
+
+	while (--blocks) {
+		memcpy(buf, out, sizeof(fastd_sha256_t));
+		out++;
+		buf[len-1]++;
+
+		fastd_hmacsha256(out, prk->w, (uint32_t*)buf, len);
+	}
+}