1 files changed, 131 insertions, 0 deletions
diff --git a/src/crypto/hkdf.c b/src/crypto/hkdf.c
new file mode 100644
index 0000000..0d91d14
--- /dev/null
+++ b/src/crypto/hkdf.c
@@ -0,0 +1,131 @@
+/*
+* Copyright (c) 2024 Vaughn Nugent
+*
+* Package: noscrypt
+* File: hkdf.c
+*
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU Lesser General Public License
+* as published by the Free Software Foundation; either version 2.1
+* of the License, or  (at your option) any later version.
+*
+* This library is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+* Lesser General Public License for more details.
+*
+* You should have received a copy of the GNU Lesser General Public License
+* along with noscrypt. If not, see http://www.gnu.org/licenses/.
+*/
+
+
+#include "hkdf.h"
+
+/* Include string for memmove */
+#include <string.h>
+
+#define HKDF_MIN(a, b) (a < b ? a : b)
+
+STATIC_ASSERT(HKDF_IN_BUF_SIZE > SHA256_DIGEST_SIZE, "HDK Buffer must be at least the size of the underlying hashing alg output")
+
+static _nc_fn_inline void ncWriteSpanS(span_t* span, uint32_t offset, const uint8_t* data, uint32_t size)
+{
+	DEBUG_ASSERT2(span != NULL, "Expected span to be non-null")
+	DEBUG_ASSERT2(data != NULL, "Expected data to be non-null")
+	DEBUG_ASSERT2(offset + size <= span->size, "Expected offset + size to be less than span size")
+
+	/* Copy data to span */
+	memmove(span->data + offset, data, size);
+}
+
+static _nc_fn_inline void debugValidateHandler(const struct nc_hkdf_fn_cb_struct* handler)
+{
+	DEBUG_ASSERT(handler != NULL)
+	DEBUG_ASSERT(handler->update != NULL)
+	DEBUG_ASSERT(handler->finish != NULL)
+}
+
+/*
+* The following functions implements the HKDF expand function using an existing
+* HMAC function.
+*
+* This follows the guidence from RFC 5869: https://tools.ietf.org/html/rfc5869
+*/
+
+cstatus_t hkdfExpandProcess(
+	const struct nc_hkdf_fn_cb_struct* handler,
+	void* ctx,
+	const cspan_t* info,
+	span_t* okm
+)
+{
+	cstatus_t result;
+
+	uint8_t counter;
+	uint32_t tLen, okmOffset;
+	uint8_t t[HKDF_IN_BUF_SIZE];
+	cspan_t tSpan, counterSpan;
+
+	debugValidateHandler(handler);
+
+	ncCryptoSecureZero(t, sizeof(t));
+
+	tLen = 0;				/* T(0) is an empty string(zero length) */
+	okmOffset = 0;
+	counter = 1;			/* counter is offset by 1 for init */
+	result = CSTATUS_FAIL;	/* Start in fail state */
+
+	/* counter as a span */
+	ncSpanInitC(&counterSpan, &counter, sizeof(counter));
+
+	/* Compute T(N) = HMAC(prk, T(n-1) | info | n) */
+	while (okmOffset < okm->size)
+	{
+		ncSpanInitC(&tSpan, t, tLen);
+
+		if (handler->update(ctx, &tSpan) != CSTATUS_OK)
+		{
+			goto Exit;
+		}
+
+		if (handler->update(ctx, info) != CSTATUS_OK)
+		{
+			goto Exit;
+		}
+
+		if (handler->update(ctx, &counterSpan) != CSTATUS_OK)
+		{
+			goto Exit;
+		}
+
+		/* 
+		* Write current hash state to t buffer. It is known
+		* that the t buffer must be at least the size of the
+		* underlying hash function output.
+		*/
+		if (handler->finish(ctx, t) != CSTATUS_OK)
+		{
+			goto Exit;
+		}
+
+		/* tlen becomes the hash size or remaining okm size */
+		tLen = HKDF_MIN(okm->size - okmOffset, SHA256_DIGEST_SIZE);
+
+		DEBUG_ASSERT(tLen <= sizeof(t));
+
+		/* write the T buffer back to okm */
+		ncWriteSpanS(okm, okmOffset, t, tLen);
+
+		/* shift base okm pointer by T */
+		okmOffset += tLen;
+
+		/* increment counter */
+		counter++;
+	}
+
+	result = CSTATUS_OK;	/* HMAC operation completed, so set success */
+
+Exit:
+
+	return result;
+}