1 files changed, 83 insertions, 0 deletions
diff --git a/board/cr50/dcrypto/hkdf.c b/board/cr50/dcrypto/hkdf.c
new file mode 100644
index 0000000000..3afdc6b2eb
--- /dev/null
+++ b/board/cr50/dcrypto/hkdf.c
@@ -0,0 +1,83 @@
+/* Copyright 2016 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+/* An implementation of HKDF as per RFC 5869. */
+
+#include "dcrypto.h"
+#include "internal.h"
+
+#include "cryptoc/sha256.h"
+#include "cryptoc/util.h"
+
+static int hkdf_extract(uint8_t *PRK, const uint8_t *salt, size_t salt_len,
+			const uint8_t *IKM, size_t IKM_len)
+{
+	LITE_HMAC_CTX ctx;
+
+	if (PRK == NULL)
+		return 0;
+	if (salt == NULL && salt_len > 0)
+		return 0;
+	if (IKM == NULL && IKM_len > 0)
+		return 0;
+
+	DCRYPTO_HMAC_SHA256_init(&ctx, salt, salt_len);
+	HASH_update(&ctx.hash, IKM, IKM_len);
+	memcpy(PRK, DCRYPTO_HMAC_final(&ctx), SHA256_DIGEST_SIZE);
+	return 1;
+}
+
+static int hkdf_expand(uint8_t *OKM, size_t OKM_len, const uint8_t *PRK,
+		const uint8_t *info, size_t info_len)
+{
+	uint8_t count = 1;
+	const uint8_t *T = OKM;
+	size_t T_len = 0;
+	uint32_t num_blocks = (OKM_len / SHA256_DIGEST_SIZE) +
+		(OKM_len % SHA256_DIGEST_SIZE ? 1 : 0);
+
+	if (OKM == NULL || OKM_len == 0)
+		return 0;
+	if (PRK == NULL)
+		return 0;
+	if (info == NULL && info_len > 0)
+		return 0;
+	if (num_blocks > 255)
+		return 0;
+
+	while (OKM_len > 0) {
+		LITE_HMAC_CTX ctx;
+		const size_t block_size = OKM_len < SHA256_DIGEST_SIZE ?
+			OKM_len : SHA256_DIGEST_SIZE;
+
+		DCRYPTO_HMAC_SHA256_init(&ctx, PRK, SHA256_DIGEST_SIZE);
+		HASH_update(&ctx.hash, T, T_len);
+		HASH_update(&ctx.hash, info, info_len);
+		HASH_update(&ctx.hash, &count, sizeof(count));
+		memcpy(OKM, DCRYPTO_HMAC_final(&ctx), block_size);
+
+		T += T_len;
+		T_len = SHA256_DIGEST_SIZE;
+		count += 1;
+		OKM += block_size;
+		OKM_len -= block_size;
+	}
+	return 1;
+}
+
+int DCRYPTO_hkdf(uint8_t *OKM, size_t OKM_len,
+		const uint8_t *salt, size_t salt_len,
+		const uint8_t *IKM, size_t IKM_len,
+		const uint8_t *info, size_t info_len)
+{
+	int result;
+	uint8_t PRK[SHA256_DIGEST_SIZE];
+
+	if (!hkdf_extract(PRK, salt, salt_len, IKM, IKM_len))
+		return 0;
+
+	result = hkdf_expand(OKM, OKM_len, PRK, info, info_len);
+	always_memset(PRK, 0, sizeof(PRK));
+	return result;
+}