refactor: Crypto dep redesign working on Windows

9 files changed, 1085 insertions, 137 deletions

diff --git a/src/internal/impl/bcrypt.c b/src/internal/impl/bcrypt.c
new file mode 100644
index 0000000..8ae6c5a
--- /dev/null
+++ b/src/internal/impl/bcrypt.c
@@ -0,0 +1,297 @@
+/*
+* Copyright (c) 2024 Vaughn Nugent
+*
+* Package: noscrypt
+* File: impl/bcrypt.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/.
+*/
+
+
+/*
+*	This file provides as many fallback implementations on Windows plaforms
+*	as possible using the bcrypt library. This file should be included behind
+*	other libarry implementations, as it is a fallback.
+*/
+
+#ifdef _NC_IS_WINDOWS
+
+#define WIN32_LEAN_AND_MEAN
+#include <Windows.h>
+#include <bcrypt.h>
+
+#include "../../platform.h"
+#include "../nc-util.h"
+
+#define IF_BC_FAIL(x) if(!BCRYPT_SUCCESS(x))
+
+struct _bcrypt_ctx
+{
+	BCRYPT_ALG_HANDLE hAlg;
+	BCRYPT_HASH_HANDLE hHash;
+};
+
+_IMPLSTB NTSTATUS _bcInitSha256(struct _bcrypt_ctx* ctx, DWORD flags)
+{
+	NTSTATUS result;
+
+	result = BCryptOpenAlgorithmProvider(
+		&ctx->hAlg, 
+		BCRYPT_SHA256_ALGORITHM, 
+		NULL, 
+		flags
+	);
+
+	/*
+	*  If operation failed, ensure the algorithm handle is null
+	* to make free code easier to cleanup
+	*/
+	if (!BCRYPT_SUCCESS(result))
+	{
+		ctx->hAlg = NULL;
+	}
+
+	return result;
+}
+
+_IMPLSTB NTSTATUS _bcCreateHmac(struct _bcrypt_ctx* ctx, const cspan_t* key)
+{
+	/*
+	 * NOTE: 
+	 * I am not explicitly managing the hash object buffer. By setting 
+	 * the hash object to NULL, and length to 0, the buffer will be
+	 * managed by the bcrypt library.
+	 * 
+	 * See: https://learn.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptcreatehash
+	 */
+
+	return BCryptCreateHash(
+		ctx->hAlg, 
+		&ctx->hHash, 
+		NULL, 
+		0, 
+		(uint8_t*)key->data, 
+		key->size, 
+		BCRYPT_HASH_REUSABLE_FLAG	/* Enable reusable for expand function */
+	);
+}
+
+_IMPLSTB NTSTATUS _bcCreate(struct _bcrypt_ctx* ctx)
+{
+	cspan_t key;
+	
+	/* Zero out key span for 0 size and NULL data ptr */
+	SecureZeroMemory(&key, sizeof(cspan_t));
+
+	return _bcCreateHmac(ctx, &key);
+}
+
+_IMPLSTB NTSTATUS _bcHashDataRaw(const struct _bcrypt_ctx* ctx, const uint8_t* data, uint64_t len)
+{
+	return BCryptHashData(ctx->hHash, (uint8_t*)data, len, 0);
+}
+
+_IMPLSTB NTSTATUS _bcHashData(const struct _bcrypt_ctx* ctx, const cspan_t* data)
+{
+	return _bcHashDataRaw(ctx, data->data, data->size);
+}
+
+_IMPLSTB NTSTATUS _bcFinishHash(const struct _bcrypt_ctx* ctx, sha256_t digestOut32)
+{
+	return BCryptFinishHash(ctx->hHash, digestOut32, sizeof(sha256_t), 0);
+}
+
+_IMPLSTB void _bcDestroyCtx(struct _bcrypt_ctx* ctx)
+{
+	/* Free the hash memory if it was allocated */
+	if(ctx->hHash) BCryptDestroyHash(ctx->hHash);
+	
+	/* Close the algorithm provider */
+	if (ctx->hAlg) BCryptCloseAlgorithmProvider(ctx->hAlg, 0);
+
+	ctx->hAlg = NULL;
+	ctx->hHash = NULL;
+}
+
+#ifndef _IMPL_SECURE_ZERO_MEMSET
+	/*
+	* On Windows, we can use SecureZeroMemory
+	* as platform zeroing function.
+	*
+	* NOTE:
+	* SecureZeroMemory2 uses volitle function argument
+	* pointers, which is a contested mehtod of compiler
+	* optimization prevention. GNU seems to oppose this method
+	*
+	* https://learn.microsoft.com/en-us/windows/win32/memory/winbase-securezeromemory2
+	*/
+	#define _IMPL_SECURE_ZERO_MEMSET SecureZeroMemory
+#endif /* !_IMPL_SECURE_ZERO_MEMSET */
+
+/*
+* Provide win32 fallback for sha256 digest if needed
+*/
+
+#ifndef _IMPL_CRYPTO_SHA256_DIGEST
+	
+	/* Export function fallack */
+	#define _IMPL_CRYPTO_SHA256_DIGEST			_bcrypt_sha256_digest	
+
+	_IMPLSTB cstatus_t _bcrypt_sha256_digest(const cspan_t* data, sha256_t digestOut32)
+	{
+		cstatus_t result;
+		struct _bcrypt_ctx ctx;
+
+		result = CSTATUS_FAIL;	/* Start in fail state */
+
+		IF_BC_FAIL(_bcInitSha256(&ctx, 0)) goto Exit;
+
+		IF_BC_FAIL(_bcCreate(&ctx)) goto Exit;
+
+		IF_BC_FAIL(_bcHashData(&ctx, data)) goto Exit;
+	
+		IF_BC_FAIL(_bcFinishHash(&ctx, digestOut32)) goto Exit;
+
+		result = CSTATUS_OK;	/* Hash operation completed, so set success */
+
+	Exit:
+
+		_bcDestroyCtx(&ctx);
+
+		return result;
+	}
+
+#endif /* !_IMPL_CRYPTO_SHA256_DIGEST */
+
+#ifndef _IMPL_CRYPTO_SHA256_HMAC
+
+	/* Export function */
+	#define _IMPL_CRYPTO_SHA256_HMAC				_bcrypt_hmac_sha256	
+	
+	_IMPLSTB cstatus_t _bcrypt_hmac_sha256(const cspan_t* key, const cspan_t* data, sha256_t hmacOut32)
+	{
+		cstatus_t result;
+		struct _bcrypt_ctx ctx;
+
+		result = CSTATUS_FAIL;		/* Start in fail state */
+
+		/* Init context with hmac flag set */
+		IF_BC_FAIL(_bcInitSha256(&ctx, BCRYPT_ALG_HANDLE_HMAC_FLAG)) goto Exit;
+
+		IF_BC_FAIL(_bcCreateHmac(&ctx, key)) goto Exit;
+
+		IF_BC_FAIL(_bcHashData(&ctx, data)) goto Exit;
+
+		IF_BC_FAIL(_bcFinishHash(&ctx, hmacOut32)) goto Exit;
+
+		result = CSTATUS_OK;	/* HMAC operation completed, so set success */
+
+	Exit:
+		
+		_bcDestroyCtx(&ctx);
+
+		return result;
+	}
+
+#endif /* !_IMPL_CRYPTO_SHA256_HMAC */
+
+/*
+* Provide a fallback HKDF expand function using the
+* HMAC function as a base.
+*/
+
+#ifndef _IMPL_CRYPTO_SHA256_HKDF_EXPAND
+
+	#define _IMPL_CRYPTO_SHA256_HKDF_EXPAND		_fallbackHkdfExpand
+
+	/* Include string for memmove */
+	#include <string.h>
+
+	static void ncWriteSpanS(span_t* span, uint64_t offset, const uint8_t* data, uint64_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_ASSERT(HKDF_IN_BUF_SIZE > SHA256_DIGEST_SIZE, "HDK Buffer must be at least the size of the underlying hashing alg output")
+
+	/*
+	* The following functions implements the HKDF expand function using an existing 
+	* HMAC function. This is a fallback implementation for Windows platforms at the moment.
+	* 
+	* This follows the guidence from RFC 5869: https://tools.ietf.org/html/rfc5869
+	*/
+
+	#define _BC_MIN(a, b) (a < b ? a : b)
+
+	_IMPLSTB cstatus_t _fallbackHkdfExpand(const cspan_t* prk, const cspan_t* info, span_t* okm)
+	{
+		cstatus_t result;
+		struct _bcrypt_ctx ctx;
+
+		uint8_t counter;
+		uint64_t tLen, okmOffset;
+		uint8_t t[HKDF_IN_BUF_SIZE];
+
+		_IMPL_SECURE_ZERO_MEMSET(t, sizeof(t));
+		
+		tLen = 0;				/* T(0) is an empty string(zero length) */
+		okmOffset = 0;
+		result = CSTATUS_FAIL;	/* Start in fail state */
+
+		/* Init context with hmac flag set, it will be reused */
+		IF_BC_FAIL(_bcInitSha256(&ctx, BCRYPT_ALG_HANDLE_HMAC_FLAG)) goto Exit;
+
+		/* Set hmac key to the prk, alg is set to reusable */
+		IF_BC_FAIL(_bcCreateHmac(&ctx, prk)) goto Exit;
+
+		/* Compute T(N) = HMAC(prk, T(n-1) | info | n) */
+		for (counter = 1; okmOffset < okm->size; counter++)
+		{
+			IF_BC_FAIL(_bcHashDataRaw(&ctx, t, tLen)) goto Exit;
+			IF_BC_FAIL(_bcHashData(&ctx, info)) goto Exit;
+			IF_BC_FAIL(_bcHashDataRaw(&ctx, &counter, sizeof(counter))) goto Exit;
+
+			/* Write current hash state to t buffer */
+			IF_BC_FAIL(_bcFinishHash(&ctx, t)) goto Exit;
+
+			/* Set the length of the current hash state */
+			tLen = _BC_MIN(okm->size - okmOffset, SHA256_DIGEST_SIZE);
+
+			DEBUG_ASSERT(tLen <= sizeof(t));
+			DEBUG_ASSERT((tLen + okmOffset) < okm->size);
+
+			/* write the T buffer back to okm */
+			ncWriteSpanS(okm, okmOffset, t, tLen);
+
+			/* shift base okm pointer by T */
+			okmOffset += tLen;
+		}		
+
+		result = CSTATUS_OK;	/* HMAC operation completed, so set success */
+
+	Exit:
+
+		_bcDestroyCtx(&ctx);
+
+		return result;
+	}
+
+#endif /* !_IMPL_CRYPTO_SHA256_HKDF_EXPAND */
+
+#endif /* _NC_IS_WINDOWS */
\ No newline at end of file
diff --git a/src/internal/impl/mbedtls.c b/src/internal/impl/mbedtls.c
new file mode 100644
index 0000000..54caa44
--- /dev/null
+++ b/src/internal/impl/mbedtls.c
@@ -0,0 +1,158 @@
+/*
+* Copyright (c) 2024 Vaughn Nugent
+*
+* Package: noscrypt
+* File: mbedtls.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/.
+*/
+
+
+/*
+* This file contains implemntation functions for the required 
+* cryptography primitives of noscrypt. This file stubs functionality
+* using the Mbed-TLS library, if the builder desires to link against
+* it. 
+*/
+
+#ifdef MBEDTLS_CRYPTO_LIB
+
+#include <mbedtls/md.h>
+#include <mbedtls/hkdf.h>
+#include <mbedtls/hmac_drbg.h>
+#include <mbedtls/sha256.h>
+#include <mbedtls/chacha20.h>
+#include <mbedtls/constant_time.h>
+
+#include "../../platform.h"
+#include "../nc-util.h"
+
+/*
+*		EXPORT SUPPORTED FUNCTION OVERRIDES
+*/	
+
+_IMPLSTB const mbedtls_md_info_t* _mbed_sha256_alg(void)
+{
+	const mbedtls_md_info_t* info;
+	/* Get sha256 md info for hdkf operations */
+	info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
+	DEBUG_ASSERT2(info != NULL, "Expected SHA256 md info pointer to be valid")
+	return info;
+}
+
+#ifndef _IMPL_CHACHA20_CRYPT
+	
+	/* Export chacha20 computation */
+	#define _IMPL_CHACHA20_CRYPT _mbed_chacha20_encrypt	
+
+	_IMPLSTB int _mbed_chacha20_encrypt(
+		const uint8_t* key,
+		const uint8_t* nonce,
+		const uint8_t* input,
+		uint8_t* output,
+		size_t dataLen
+	)
+	{
+		/* Counter always starts at 0 */
+		return mbedtls_chacha20_crypt(key, nonce, 0x00u, dataLen, input, output);
+	}
+
+#endif
+
+/* Export sha256 if not already defined */
+#ifndef _IMPL_CRYPTO_SHA256_DIGEST	
+	
+	#define _IMPL_CRYPTO_SHA256_DIGEST			_mbed_sha256_digest	
+
+	_IMPLSTB CStatus _mbed_sha256_digest(const uint8_t* data, size_t dataSize,uint8_t* digestOut32)
+	{
+		return mbedtls_sha256(data, dataSize, digestOut32, 0);
+	}
+
+#endif
+
+/* Export Sha256 hmac if not already defined by other libs */
+#ifndef _IMPL_CRYPTO_SHA256_HMAC
+
+	#define _IMPL_CRYPTO_SHA256_HMAC			_mbed_sha256_hmac
+
+	_IMPLSTB CStatus _mbed_sha256_hmac(
+		const uint8_t* key, size_t keyLen,
+		const uint8_t* data, size_t dataLen,
+		void* hmacOut32
+	)
+	{
+		return mbedtls_md_hmac(
+			_mbed_sha256_alg(),
+			key, keyLen,
+			data, dataLen,
+			hmacOut32
+		);
+	}
+#endif
+
+/* Export hkdf expand if not already defined */
+#ifndef _IMPL_CRYPTO_SHA256_HKDF_EXPAND
+
+	#define _IMPL_CRYPTO_SHA256_HKDF_EXPAND		_mbed_sha256_hkdf_expand
+
+	_IMPLSTB int _mbed_sha256_hkdf_expand(
+		const uint8_t* prk, size_t prkLen,
+		const uint8_t* info, size_t infoLen,
+		void* okm, size_t okmLen
+	)
+	{
+		return mbedtls_hkdf_expand(
+			_mbed_sha256_alg(),
+			prk, prkLen,
+			info, infoLen,
+			okm, okmLen
+		);
+	}
+
+#endif
+
+/* Export hkdf extract if not already defined */
+#ifndef _IMPL_CRYPTO_SHA256_HKDF_EXTRACT
+
+	#define _IMPL_CRYPTO_SHA256_HKDF_EXTRACT		_mbed_sha256_hkdf_extract
+
+	_IMPLSTB int _mbed_sha256_hkdf_extract(
+		const uint8_t* salt, size_t saltLen,
+		const uint8_t* ikm, size_t ikmLen,
+		void* prk
+	)
+	{
+		return mbedtls_hkdf_extract(
+			_mbed_sha256_alg(),
+			salt, saltLen,
+			ikm, ikmLen,
+			prk
+		);
+	}
+#endif
+
+/* Export fixed-time compare if not already defined */
+#ifndef _IMPL_CRYPTO_FIXED_TIME_COMPARE
+
+	#define _IMPL_CRYPTO_FIXED_TIME_COMPARE		_mbed_fixed_time_compare
+
+	/* fixed-time memcmp */
+	_IMPLSTB int _mbed_fixed_time_compare(const uint8_t* a, const uint8_t* b, size_t size)
+	{
+		return mbedtls_ct_memcmp(a, b, size);
+	}
+#endif
+
+#endif
\ No newline at end of file
diff --git a/src/internal/impl/monocypher.c b/src/internal/impl/monocypher.c
new file mode 100644
index 0000000..6e93c63
--- /dev/null
+++ b/src/internal/impl/monocypher.c
@@ -0,0 +1,84 @@
+/*
+* Copyright (c) 2024 Vaughn Nugent
+*
+* Package: noscrypt
+* File: impl/monocypher.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/.
+*/
+
+
+/*
+*  This file handles some fallbacks that may not be available on 
+*	some platforms. More specifically:
+*		- Secure memset 0
+* 		- Chacha20 cipher
+* 
+*/
+
+#ifdef NC_ENABLE_MONOCYPHER
+
+#include <monocypher.h>
+
+#include "../../platform.h"
+#include "../nc-util.h"
+
+/* Export secure memse0 */
+#ifndef _IMPL_SECURE_ZERO_MEMSET
+
+	/* export cytpo wipe function as is */
+	#define _IMPL_SECURE_ZERO_MEMSET crypto_wipe	
+#endif
+
+/* Export Chacha20 */
+#ifndef _IMPL_CHACHA20_CRYPT
+
+	#define _IMPL_CHACHA20_CRYPT _mc_chacha20_crypt
+
+	_IMPLSTB cstatus_t _mc_chacha20_crypt(
+		const uint8_t* key,
+		const uint8_t* nonce,
+		const uint8_t* input,
+		uint8_t* output,
+		uint64_t dataLen
+	)
+	{
+		if(dataLen > SIZE_MAX)
+		{
+			return CSTATUS_FAIL;
+		}
+
+		/*
+		* Function returns the next counter value which is not
+		* needed for noscrypt as encryptions are one-shot, and 
+		* require a new nonce for each encryption.
+		* 
+		* ITEF function uses a 12byte nonce which is required for
+		* nip-44 compliant encryption.
+		*/
+		crypto_chacha20_ietf(
+			output,
+			input,
+			(size_t)dataLen,
+			key,
+			nonce,
+			0x00			/* Counter always starts at 0 */
+		);
+
+		return CSTATUS_OK;
+	}
+
+#endif
+
+#endif /* !NC_ENABLE_MONOCYPHER */
\ No newline at end of file
diff --git a/src/internal/impl/openssl.c b/src/internal/impl/openssl.c
new file mode 100644
index 0000000..d0cdb8c
--- /dev/null
+++ b/src/internal/impl/openssl.c
@@ -0,0 +1,47 @@
+/*
+* Copyright (c) 2024 Vaughn Nugent
+*
+* Package: noscrypt
+* File: impl/openssl.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/.
+*/
+
+
+/* Setup openssl */
+
+#ifdef OPENSSL_CRYPTO_LIB
+
+#include <openssl/sha.h>
+
+#include "../../platform.h"
+#include "../nc-util.h"
+
+/*
+*		EXPORT SUPPORTED FUNCTIONS AS MACROS
+*/
+#define _IMPL_CHACHA20_CRYPT				_mbed_chacha20_encrypt			
+#define _IMPL_CRYPTO_SHA256_HMAC			_mbed_sha256_hmac
+#define _IMPL_CRYPTO_SHA256_DIGEST			_ossl_sha256_digest	
+#define _IMPL_CRYPTO_FIXED_TIME_COMPARE		_mbed_fixed_time_compare
+#define _IMPL_CRYPTO_SHA256_HKDF_EXPAND		_mbed_sha256_hkdf_expand
+#define _IMPL_CRYPTO_SHA256_HKDF_EXTRACT	_mbed_sha256_hkdf_extract
+
+_IMPLSTB int _ossl_sha256_digest(const uint8_t* data, uint8_t* digest)
+{
+	
+}
+
+
+#endif	/*!OPENSSL_CRYPTO_LIB */
\ No newline at end of file
diff --git a/src/internal/nc-crypto.c b/src/internal/nc-crypto.c
new file mode 100644
index 0000000..9cd2c3e
--- /dev/null
+++ b/src/internal/nc-crypto.c
@@ -0,0 +1,269 @@
+/*
+* Copyright (c) 2024 Vaughn Nugent
+*
+* Package: noscrypt
+* File: nc-crypto.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 "nc-util.h"
+#include "nc-crypto.h"
+#include "../platform.h"
+
+/*
+*  Functions are not forced inline, just suggested.
+*  So unless it beomes a performance issue, I will leave
+*  most/all impl functions inline and let the compiler 
+*  decide.
+*/
+
+#define _IMPLSTB static _nc_fn_inline
+
+/*
+* Impl .c files may define the following macros for function implementations:
+* 
+*		_IMPL_SECURE_ZERO_MEMSET			secure memset 0 function
+*		_IMPL_CHACHA20_CRYPT				chacha20 cipher function
+*		_IMPL_CRYPTO_FIXED_TIME_COMPARE		fixed time compare function
+*		_IMPL_CRYPTO_SHA256_HMAC			sha256 hmac function
+*		_IMPL_CRYPTO_SHA256_DIGEST			standard sha256 digest function
+* 		_IMPL_CRYPTO_SHA256_HKDF_EXPAND		hkdf expand function
+* 		_IMPL_CRYPTO_SHA256_HKDF_EXTRACT	hkdf extract function
+* 
+* Macros are used to allow the preprocessor to select the correct implementation
+* or raise errors if no implementation is defined.
+*/
+
+
+
+/*
+* Prioritize embedded builds with mbedtls
+*/
+#include "impl/mbedtls.c"
+
+/*
+* Include openssl as an alternative default 
+* implementation
+*/
+#include "impl/openssl.c"
+
+/*
+* Include win32 platform specific fallback support 
+* using bcrypt.
+*/
+#include "impl/bcrypt.c"
+
+/*
+* Handle default implementations of secure 
+* memset 0 functions for each platform.
+*/
+#ifndef _IMPL_SECURE_ZERO_MEMSET
+	#if defined(__GNUC__)	
+		/*
+		*	When using libc, we can use explicit_bzero
+		*	as secure memset implementation.
+		* 
+		*	https://sourceware.org/glibc/manual/2.39/html_mono/libc.html#Erasing-Sensitive-Data
+		*/
+		#include <string.h>
+		#define _IMPL_SECURE_ZERO_MEMSET explicit_bzero
+	#endif
+#endif
+
+/*
+* Finally fall back to monocipher to handle some
+* that are not provided by other libraries.
+*
+* Platform specific opimizations are considered
+* "better" than monocypher options, so this is
+* added as a last resort. Momocypher is "correct"
+* and portable, but not optimized for any specific
+* platform.
+*/
+#include "impl/monocypher.c"
+
+
+#ifdef _IMPL_CRYPTO_SHA256_HMAC
+
+	/*
+	* If a library does not provide a HKDF extract function,
+	* we can just use the HMAC function as a fallback.
+	*
+	* This is a fallback because another library may provide
+	* a more optimized implementation.
+	*/
+
+	#ifndef _IMPL_CRYPTO_SHA256_HKDF_EXTRACT 
+
+		#define _IMPL_CRYPTO_SHA256_HKDF_EXTRACT		_fallbackHkdfExtract
+
+		_IMPLSTB cstatus_t _fallbackHkdfExtract(const cspan_t* salt, const cspan_t* ikm, sha256_t prk)
+		{
+			return _IMPL_CRYPTO_SHA256_HMAC(salt, ikm, prk);
+		}
+
+	#endif /* !_IMPL_CRYPTO_SHA256_HKDF_EXTRACT */
+	
+#endif /* _IMPL_CRYPTO_SHA256_HMAC */
+
+/* Fallback for fixed time comparison for all platforms */
+#ifndef _IMPL_CRYPTO_FIXED_TIME_COMPARE
+
+	#pragma message("Warning: No fixed time compare implementation defined, using fallback. This may not be secure on all platforms")
+
+	#define _IMPL_CRYPTO_FIXED_TIME_COMPARE	_fallbackFixedTimeCompare
+
+	/*
+	* This implemntation is a slightly simplified version of 
+	* MBed TLS constant time memcmp function, knowm to be a 32bit 
+	* integer size
+	*/
+
+	static uint32_t _fallbackFixedTimeCompare(const uint8_t* a, const uint8_t* b, uint64_t size)
+	{
+		size_t i;
+		uint32_t result;
+		uint8_t O;
+		volatile const uint8_t* A, * B;		
+
+		result = 0;
+		O = 0;
+		A = (volatile const uint8_t*)a;
+		B = (volatile const uint8_t*)b;
+
+		/* Compare each byte */
+		for(i = 0; i < size; i++)
+		{
+			/* Handle volatile read */
+			O |= (A[i] ^ B[i]);
+
+			result |= O;
+		}
+
+		return result;
+	}
+
+#endif /* !_IMPL_CRYPTO_FIXED_TIME_COMPARE */
+
+
+/*
+* Internal function implementations that perform
+* basic checking and call the correct implementation
+* for the desired crypto impl.
+*/
+
+void ncCryptoSecureZero(void* ptr, uint64_t size)
+{
+	DEBUG_ASSERT2(ptr != NULL, "Expected ptr to be non-null")
+
+#ifndef _IMPL_SECURE_ZERO_MEMSET
+	#error "No secure memset implementation defined"
+#endif /* _IMPL_SECURE_ZERO_MEMSET */
+
+	_IMPL_SECURE_ZERO_MEMSET(ptr, size);
+}
+
+uint32_t ncCryptoFixedTimeComp(const uint8_t* a, const uint8_t* b, uint64_t size)
+{
+	DEBUG_ASSERT2(a != NULL, "Expected a to be non-null")
+	DEBUG_ASSERT2(b != NULL, "Expected b to be non-null")
+
+#ifndef _IMPL_CRYPTO_FIXED_TIME_COMPARE
+	#error "No fixed time compare implementation defined"
+#endif /* !_IMPL_CRYPTO_FIXED_TIME_COMPARE */
+
+	return _IMPL_CRYPTO_FIXED_TIME_COMPARE(a, b, size);
+}
+
+cstatus_t ncCryptoDigestSha256(const cspan_t* data, sha256_t digestOut32)
+{
+	/* Debug arg validate */
+	DEBUG_ASSERT2(data != NULL && data->data != NULL,	"Expected data to be non-null")
+	DEBUG_ASSERT2(digestOut32 != NULL,					"Expected digestOut32 to be non-null")
+
+#ifndef _IMPL_CRYPTO_SHA256_DIGEST
+	#error "No SHA256 implementation defined"
+#endif /* !_IMPL_CRYPTO_SHA256_DIGEST */
+
+	return _IMPL_CRYPTO_SHA256_DIGEST(data, digestOut32);
+}
+
+cstatus_t ncCryptoHmacSha256(const cspan_t* key, const cspan_t* data, sha256_t hmacOut32)
+{
+	/* Debug arg validate */
+	DEBUG_ASSERT2(key != NULL && key->data != NULL,			"Expected key to be non-null")
+	DEBUG_ASSERT2(data != NULL && data->data != NULL,		"Expected data to be non-null")
+	DEBUG_ASSERT2(hmacOut32 != NULL && data->data != NULL,	"Expected hmacOut32 to be non-null")
+
+#ifndef _IMPL_CRYPTO_SHA256_HMAC
+	#error "No SHA256 HMAC implementation defined"
+#endif /* !_IMPL_CRYPTO_SHA256_HMAC */
+
+	return _IMPL_CRYPTO_SHA256_HMAC(key, data, hmacOut32);
+}
+
+cstatus_t ncCryptoSha256HkdfExpand(const cspan_t* prk, const cspan_t* info, span_t* okm)
+{
+	/* Debug arg validate */
+	DEBUG_ASSERT2(prk != NULL && prk->data != NULL,		"Expected prk to be non-null")
+	DEBUG_ASSERT2(info != NULL && info->data != NULL,	"Expected info to be non-null")
+	DEBUG_ASSERT2(okm != NULL && okm->data != NULL,		"Expected okm to be non-null")
+
+	/*
+	* RFC 5869: 2.3
+	* "length of output keying material in octets (<= 255 * HashLen)"
+	*/
+
+	if(okm->size > (uint64_t)(0xFFu * SHA256_DIGEST_SIZE))
+	{
+		return CSTATUS_FAIL;
+	}
+
+#ifndef _IMPL_CRYPTO_SHA256_HKDF_EXPAND
+	#error "No SHA256 HKDF expand implementation defined"
+#endif /* !_IMPL_CRYPTO_SHA256_HKDF_EXPAND */
+	
+	return _IMPL_CRYPTO_SHA256_HKDF_EXPAND(prk, info, okm);
+}
+
+cstatus_t ncCryptoSha256HkdfExtract(const cspan_t* salt, const cspan_t* ikm, sha256_t prk)
+{
+	/* Debug arg validate */
+	DEBUG_ASSERT2(salt != NULL, "Expected salt to be non-null")
+	DEBUG_ASSERT2(ikm  != NULL, "Expected ikm to be non-null")
+	DEBUG_ASSERT2(prk  != NULL, "Expected prk to be non-null")
+
+#ifndef _IMPL_CRYPTO_SHA256_HKDF_EXTRACT
+	#error "No SHA256 HKDF extract implementation defined"
+#endif /* !_IMPL_CRYPTO_SHA256_HKDF_EXTRACT */
+	
+	return _IMPL_CRYPTO_SHA256_HKDF_EXTRACT(salt, ikm, prk);
+}
+
+cstatus_t ncCryptoChacha20(
+	const uint8_t key[CHACHA_KEY_SIZE],
+	const uint8_t nonce[CHACHA_NONCE_SIZE],
+	const uint8_t* input,
+	uint8_t* output,
+	uint64_t dataSize
+)
+{
+	DEBUG_ASSERT2(key != NULL,		"Expected key to be non-null")
+	DEBUG_ASSERT2(nonce != NULL,	"Expected nonce to be non-null")
+	DEBUG_ASSERT2(input != NULL,	"Expected input to be non-null")
+	DEBUG_ASSERT2(output != NULL,	"Expected output to be non-null")
+
+	return _IMPL_CHACHA20_CRYPT(key, nonce, input, output, dataSize);
+}
diff --git a/src/internal/nc-crypto.h b/src/internal/nc-crypto.h
new file mode 100644
index 0000000..3487b2b
--- /dev/null
+++ b/src/internal/nc-crypto.h
@@ -0,0 +1,73 @@
+
+/*
+* Copyright (c) 2024 Vaughn Nugent
+*
+* Package: noscrypt
+* File: nc-crypto.h
+*
+* 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/.
+*/
+
+#pragma once
+
+#ifndef _NC_CRYPTO_H
+#define _NC_CRYPTO_H
+
+#include <stdint.h>
+
+#define CHACHA_NONCE_SIZE		0x0cu		/* Size of 12 is set by the cipher spec */
+#define CHACHA_KEY_SIZE			0x20u		/* Size of 32 is set by the cipher spec */
+#define SHA256_DIGEST_SIZE		0x20u		/* Size of 32 is set by the cipher spec */
+
+typedef uint8_t cstatus_t;
+#define CSTATUS_OK				((cstatus_t)0x01u)
+#define CSTATUS_FAIL			((cstatus_t)0x00u)
+
+typedef uint8_t sha256_t[SHA256_DIGEST_SIZE];
+
+/*
+* IMPORTANT:
+*	The HKDF_IN_BUF_SIZE defintion sets the internal stack buffer size to use
+*	during fallback HKDF_Expand operations.
+*
+*	128 bytes should be more than enough for most use cases, without going 
+*	overboard. Could be dialed in better for specific use cases later.
+*/
+
+#ifndef HKDF_IN_BUF_SIZE
+	#define HKDF_IN_BUF_SIZE	0x80	
+#endif
+
+
+uint32_t ncCryptoFixedTimeComp(const uint8_t* a, const uint8_t* b, uint64_t size);
+
+void ncCryptoSecureZero(void* ptr, uint64_t size);
+
+cstatus_t ncCryptoDigestSha256(const cspan_t* data, sha256_t digestOut32);
+
+cstatus_t ncCryptoHmacSha256(const cspan_t* key, const cspan_t* data, sha256_t hmacOut32);
+
+cstatus_t ncCryptoSha256HkdfExpand(const cspan_t* prk, const cspan_t* info, span_t* okm);
+
+cstatus_t ncCryptoSha256HkdfExtract(const cspan_t* salt, const cspan_t* ikm, sha256_t prk);
+
+cstatus_t ncCryptoChacha20(
+	const uint8_t key[CHACHA_KEY_SIZE],
+	const uint8_t nonce[CHACHA_NONCE_SIZE],
+	const uint8_t* input,
+	uint8_t* output,
+	uint64_t dataSize
+);
+
+#endif /* !_NC_CRYPTO_H */
diff --git a/src/internal/nc-util.h b/src/internal/nc-util.h
index 9026d29..9f72470 100644
--- a/src/internal/nc-util.h
+++ b/src/internal/nc-util.h
@@ -3,7 +3,7 @@
 * Copyright (c) 2024 Vaughn Nugent
 *
 * Package: noscrypt
-* File: nc-util.c
+* File: nc-util.h
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
@@ -59,4 +59,30 @@
 	#define STATIC_ASSERT(x, m)
 #endif
 
+#include <stdint.h>
+
+typedef struct memory_span_struct
+{
+	uint8_t* data;
+	uint64_t size;
+} span_t;
+
+typedef struct read_only_memory_span_struct
+{
+	const uint8_t* data;
+	uint64_t size;
+} cspan_t;
+
+static void ncSpanInitC(cspan_t* span, const uint8_t* data, uint64_t size)
+{
+	span->data = data;
+	span->size = size;
+}
+
+static void ncSpanInit(span_t* span, uint8_t* data, uint64_t size)
+{
+	span->data = data;
+	span->size = size;
+}
+
 #endif /* NC_UTIL_H */
\ No newline at end of file
diff --git a/src/noscrypt.c b/src/noscrypt.c
index 9271353..4715d50 100644
--- a/src/noscrypt.c
+++ b/src/noscrypt.c
@@ -43,6 +43,7 @@
 	#define CHECK_INVALID_ARG(x, argPos) if(x == NULL) return NCResultWithArgPosition(E_INVALID_ARG, argPos);
 	#define CHECK_NULL_ARG(x, argPos) if(x == NULL) return NCResultWithArgPosition(E_NULL_PTR, argPos);
 	#define CHECK_ARG_RANGE(x, min, max, argPos) if(x < min || x > max) return NCResultWithArgPosition(E_ARGUMENT_OUT_OF_RANGE, argPos);
+	#define CHECK_CONTEXT_STATE(ctx, argPos) CHECK_INVALID_ARG(ctx->secpCtx, argPos)
 #else
 	/* empty macros */
 	#define CHECK_INVALID_ARG(x)
@@ -79,6 +80,7 @@ struct nc_expand_keys {
 	uint8_t hmac_key[NC_HMAC_KEY_SIZE];
 };
 
+
 /* Pointer typecast must work between expanded keys 
 * and message key, size must be identical to work 
 */
@@ -126,7 +128,11 @@ static int _convertToPubKey(const NCContext* ctx, const NCPublicKey* compressedP
 	return result;
 }
 
-static _nc_fn_inline int _convertFromXonly(const NCContext* ctx, const secp256k1_xonly_pubkey* xonly, NCPublicKey* compressedPubKey)
+static _nc_fn_inline int _convertFromXonly(
+	const NCContext* ctx, 
+	const secp256k1_xonly_pubkey* xonly, 
+	NCPublicKey* compressedPubKey
+)
 {
 	DEBUG_ASSERT2(ctx != NULL, "Expected valid context")
 	DEBUG_ASSERT2(xonly != NULL, "Expected valid X-only secp256k1 public key structure.")
@@ -214,23 +220,16 @@ static _nc_fn_inline NCResult _computeConversationKey(
 	struct conversation_key* ck 
 )
 {
-	int opResult;
+	cspan_t saltSpan, ikmSpan;
 	
 	DEBUG_ASSERT2(ctx != NULL, "Expected valid context")
 	DEBUG_ASSERT2(sharedSecret != NULL, "Expected a valid shared-point")
 	DEBUG_ASSERT2(ck != NULL, "Expected a valid conversation key")
-	
-	/* Derive the encryption key */
-	opResult = ncCryptoSha256HkdfExtract(
-		Nip44ConstantSalt,
-		sizeof(Nip44ConstantSalt),
-		(uint8_t*)sharedSecret,			/* Shared secret is the input key */
-		NC_SHARED_SEC_SIZE,
-		(uint8_t*)ck					/* Output produces a conversation key */
-	);
 
-	/* 0 is a successful hdkf result */
-	return opResult == 0 ? NC_SUCCESS : E_OPERATION_FAILED;
+	ncSpanInitC(&saltSpan, Nip44ConstantSalt, sizeof(Nip44ConstantSalt));
+	ncSpanInitC(&ikmSpan, sharedSecret->value, NC_SHARED_SEC_SIZE);
+	
+	return ncCryptoSha256HkdfExtract(&saltSpan, &ikmSpan, ck->value) == CSTATUS_OK ? NC_SUCCESS : E_OPERATION_FAILED;
 }
 
 
@@ -242,7 +241,7 @@ static _nc_fn_inline const struct nc_expand_keys* _expandKeysFromHkdf(const stru
 	return (const struct nc_expand_keys*)hkdf;
 }
 
-static int _chachaEncipher(const struct nc_expand_keys* keys, NCEncryptionArgs* args)
+static cstatus_t _chachaEncipher(const struct nc_expand_keys* keys, NCEncryptionArgs* args)
 {
 	DEBUG_ASSERT2(keys != NULL, "Expected valid keys")
 	DEBUG_ASSERT2(args != NULL, "Expected valid encryption args")
@@ -256,61 +255,65 @@ static int _chachaEncipher(const struct nc_expand_keys* keys, NCEncryptionArgs*
 	);
 }
 
-static _nc_fn_inline NCResult _getMessageKey(
+static _nc_fn_inline cstatus_t _getMessageKey(
 	const struct conversation_key* converstationKey, 
-	const uint8_t* nonce, 
-	size_t nonceSize,
+	const cspan_t* nonce,
 	struct message_key* messageKey
 )
 {
-	int result;
+	cspan_t prkSpan;
+	span_t okmSpan;
+
 	DEBUG_ASSERT2(nonce != NULL, "Expected valid nonce buffer")
 	DEBUG_ASSERT2(converstationKey != NULL, "Expected valid conversation key")
 	DEBUG_ASSERT2(messageKey != NULL, "Expected valid message key buffer")
 
-	/* Another HKDF to derive the message key with nonce */
-	result = ncCryptoSha256HkdfExpand(
-		(uint8_t*)converstationKey,			/* Conversation key is the input key */
-		NC_CONV_KEY_SIZE,
-		nonce,
-		nonceSize,
-		(uint8_t*)messageKey,				/* Output produces a message key (write it directly to struct memory) */
-		NC_MESSAGE_KEY_SIZE
-	);
-
-	return result == 0 ? NC_SUCCESS : E_OPERATION_FAILED;
+	ncSpanInitC(&prkSpan, converstationKey->value, sizeof(struct conversation_key));	/* Conversation key is the input key */
+	ncSpanInit(&okmSpan, messageKey->value, sizeof(struct message_key));				/* Output produces a message key (write it directly to struct memory) */
+	
+	/* Nonce is the info */
+	return ncCryptoSha256HkdfExpand(&prkSpan, nonce, &okmSpan);
 }
 
 static _nc_fn_inline NCResult _encryptEx(
 	const NCContext* ctx, 
 	const struct conversation_key* ck, 
-	uint8_t hmacKey[NC_HMAC_KEY_SIZE],
+	uint8_t* hmacKey,
 	NCEncryptionArgs* args
 )
 {
 	NCResult result;
+	cspan_t nonceSpan;
 	struct message_key messageKey;
 	const struct nc_expand_keys* expandedKeys;
 
-	DEBUG_ASSERT2(ctx != NULL, "Expected valid context")
-	DEBUG_ASSERT2(ck != NULL, "Expected valid conversation key")
-	DEBUG_ASSERT2(args != NULL, "Expected valid encryption args")
-	DEBUG_ASSERT2(hmacKey != NULL, "Expected valid hmac key buffer")
+	DEBUG_ASSERT2(ctx != NULL,		"Expected valid context")
+	DEBUG_ASSERT2(ck != NULL,		"Expected valid conversation key")
+	DEBUG_ASSERT2(args != NULL,		"Expected valid encryption args")
+	DEBUG_ASSERT2(hmacKey != NULL,	"Expected valid hmac key buffer")
+
+	result = NC_SUCCESS;
+
+	ncSpanInitC(&nonceSpan, args->nonce32, NC_ENCRYPTION_NONCE_SIZE);
 	
 	/* Message key will be derrived on every encryption call */
-	if ((result = _getMessageKey(ck, args->nonce32, NC_ENCRYPTION_NONCE_SIZE, &messageKey)) != NC_SUCCESS)
+	if (_getMessageKey(ck, &nonceSpan, &messageKey) != CSTATUS_OK)
 	{
+		result = E_OPERATION_FAILED;
 		goto Cleanup;
 	}
 
-	/* Expand the keys from the hkdf so we can use them in the cipher */
+	/* Split apart the message key into it's expanded form so components can be extracted */
 	expandedKeys = _expandKeysFromHkdf(&messageKey);
 
 	/* Copy the hmac key into the args */
 	MEMMOV(hmacKey, expandedKeys->hmac_key, NC_HMAC_KEY_SIZE);
 
 	/* CHACHA20 (the result will be 0 on success) */
-	result = (NCResult)_chachaEncipher(expandedKeys, args);
+	if (_chachaEncipher(expandedKeys, args) != CSTATUS_OK)
+	{
+		result = E_OPERATION_FAILED;
+	}
 
 Cleanup:
 	ZERO_FILL(&messageKey, sizeof(messageKey));
@@ -318,22 +321,24 @@ Cleanup:
 	return result;
 }
 
-static _nc_fn_inline NCResult _decryptEx(
-	const NCContext* ctx, 
-	const struct conversation_key* ck,
-	NCEncryptionArgs* args
-)
+static _nc_fn_inline NCResult _decryptEx(const NCContext* ctx, const struct conversation_key* ck, NCEncryptionArgs* args)
 {
 	NCResult result;
+	cspan_t nonceSpan;
 	struct message_key messageKey;
 	const struct nc_expand_keys* cipherKeys;
 
 	DEBUG_ASSERT2(ctx != NULL, "Expected valid context")
 	DEBUG_ASSERT2(ck != NULL, "Expected valid conversation key")
 	DEBUG_ASSERT2(args != NULL, "Expected valid encryption args")
+
+	result = NC_SUCCESS;
+
+	ncSpanInitC(&nonceSpan, args->nonce32, NC_ENCRYPTION_NONCE_SIZE);
 	
-	if ((result = _getMessageKey(ck, args->nonce32, NC_ENCRYPTION_NONCE_SIZE, &messageKey)) != NC_SUCCESS)
+	if (_getMessageKey(ck, &nonceSpan, &messageKey) != CSTATUS_OK)
 	{
+		result = E_OPERATION_FAILED;
 		goto Cleanup;
 	}
 
@@ -341,7 +346,10 @@ static _nc_fn_inline NCResult _decryptEx(
 	cipherKeys = _expandKeysFromHkdf(&messageKey);
 
 	/* CHACHA20 (the result will be 0 on success) */
-	result = (NCResult) _chachaEncipher(cipherKeys, args);
+	if (_chachaEncipher(cipherKeys, args) != CSTATUS_OK)
+	{
+		result = E_OPERATION_FAILED;
+	}
 
 Cleanup:
 	ZERO_FILL(&messageKey, sizeof(messageKey));
@@ -349,22 +357,17 @@ Cleanup:
 	return result;
 }
 
-static _nc_fn_inline int _computeHmac(
-	const uint8_t key[NC_HMAC_KEY_SIZE],
-	const NCMacVerifyArgs* args,
-	uint8_t hmacOut[NC_ENCRYPTION_MAC_SIZE]
-) 
+static _nc_fn_inline cstatus_t _computeHmac(const uint8_t key[NC_HMAC_KEY_SIZE], const cspan_t* payload, sha256_t hmacOut)
 {
-	DEBUG_ASSERT2(key != NULL, "Expected valid hmac key")
-	DEBUG_ASSERT2(args != NULL, "Expected valid mac verification args")
-	DEBUG_ASSERT2(hmacOut != NULL, "Expected valid hmac output buffer")
-	DEBUG_ASSERT(args->payload != NULL)
+	cspan_t keySpan;
 
-	return ncCryptoHmacSha256(
-		key, NC_HMAC_KEY_SIZE,
-		args->payload, args->payloadSize,
-		hmacOut
-	);
+	DEBUG_ASSERT2(key != NULL,		"Expected valid hmac key")
+	DEBUG_ASSERT2(payload != NULL,	"Expected valid mac verification args")
+	DEBUG_ASSERT2(hmacOut != NULL,	"Expected valid hmac output buffer")
+
+	ncSpanInitC(&keySpan, key, NC_HMAC_KEY_SIZE);
+
+	return ncCryptoHmacSha256(&keySpan, payload, hmacOut);
 }
 
 static NCResult _verifyMacEx(
@@ -374,26 +377,25 @@ static NCResult _verifyMacEx(
 )
 {
 	NCResult result;
+	cspan_t payloadSpan, nonceSpan;
+	sha256_t hmacOut;
 	const struct nc_expand_keys* keys;
 	struct message_key messageKey;
-	uint8_t hmacOut[NC_ENCRYPTION_MAC_SIZE];
  
 	DEBUG_ASSERT2(ctx != NULL, "Expected valid context")
 	DEBUG_ASSERT2(conversationKey != NULL, "Expected valid conversation key")
 	DEBUG_ASSERT2(args != NULL, "Expected valid mac verification args")
 
+	ncSpanInitC(&nonceSpan, args->nonce32, NC_ENCRYPTION_NONCE_SIZE);
+	ncSpanInitC(&payloadSpan, args->payload, args->payloadSize);
+
 	/*
 	* Message key is again required for the hmac verification
 	*/
-	result = _getMessageKey(
-		(struct conversation_key*)conversationKey,
-		args->nonce32,
-		NC_ENCRYPTION_NONCE_SIZE,
-		&messageKey
-	);
 
-	if (result != NC_SUCCESS)
+	if (_getMessageKey((struct conversation_key*)conversationKey, &nonceSpan, &messageKey) != CSTATUS_OK)
 	{
+		result = E_OPERATION_FAILED;
 		goto Cleanup;
 	}
 
@@ -403,7 +405,7 @@ static NCResult _verifyMacEx(
 	/*
 	* Compute the hmac of the data using the computed hmac key
 	*/
-	if (_computeHmac(keys->hmac_key, args, hmacOut) != 0)
+	if (_computeHmac(keys->hmac_key, &payloadSpan, hmacOut) != CSTATUS_OK)
 	{
 		result = E_OPERATION_FAILED;
 		goto Cleanup;
@@ -419,7 +421,6 @@ Cleanup:
 	return result;
 }
 
-
 /*
 * EXTERNAL API FUNCTIONS
 */
@@ -452,7 +453,7 @@ NC_EXPORT NCResult NC_CC NCReInitContext(
 {
 	CHECK_NULL_ARG(ctx, 0)
 	CHECK_NULL_ARG(entropy, 1)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)	
+	CHECK_CONTEXT_STATE(ctx, 0)
 
 	/* Only randomize again */
 	return secp256k1_context_randomize(ctx->secpCtx, entropy) ? NC_SUCCESS : E_INVALID_ARG;
@@ -460,8 +461,8 @@ NC_EXPORT NCResult NC_CC NCReInitContext(
 
 NC_EXPORT NCResult NC_CC NCDestroyContext(NCContext* ctx)
 {
-	CHECK_NULL_ARG(ctx, 0);
-	CHECK_INVALID_ARG(ctx->secpCtx, 0);
+	CHECK_NULL_ARG(ctx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 
 	/* Destroy secp256k1 context */
 	secp256k1_context_destroy(ctx->secpCtx);
@@ -484,7 +485,7 @@ NC_EXPORT NCResult NC_CC NCGetPublicKey(
 	secp256k1_xonly_pubkey xonly;
 
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(sk, 1)
 	CHECK_NULL_ARG(pk, 2)
 
@@ -508,14 +509,11 @@ NC_EXPORT NCResult NC_CC NCGetPublicKey(
 	return NC_SUCCESS;
 }
 
-NC_EXPORT NCResult NC_CC NCValidateSecretKey(
-	const NCContext* ctx, 
-	const NCSecretKey* sk
-)
+NC_EXPORT NCResult NC_CC NCValidateSecretKey(const NCContext* ctx, const NCSecretKey* sk)
 {
 	CHECK_NULL_ARG(ctx, 0)
 	CHECK_NULL_ARG(sk, 1)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 
 	/* Validate the secret key */
 	return secp256k1_ec_seckey_verify(ctx->secpCtx, sk->key);
@@ -537,7 +535,7 @@ NC_EXPORT NCResult NC_CC NCSignDigest(
 
 	/* Validate arguments */
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(sk, 1)
 	CHECK_NULL_ARG(random32, 2)
 	CHECK_NULL_ARG(digest32, 3)
@@ -571,11 +569,12 @@ NC_EXPORT NCResult NC_CC NCSignData(
 	const NCSecretKey* sk,
 	const uint8_t random32[32],
 	const uint8_t* data,
-	size_t dataSize,
+	uint64_t dataSize,
 	uint8_t sig64[64]
 )
 {
-	uint8_t digest[SHA256_DIGEST_SIZE];
+	cspan_t dataSpan;
+	sha256_t digest;	
 
 	/* Double check is required because arg position differs */
 	CHECK_NULL_ARG(ctx, 0)
@@ -585,8 +584,10 @@ NC_EXPORT NCResult NC_CC NCSignData(
 	CHECK_ARG_RANGE(dataSize, 1, UINT32_MAX, 4)
 	CHECK_NULL_ARG(sig64, 5)
 
+	ncSpanInitC(&dataSpan, data, dataSize);
+
 	/* Compute sha256 of the data before signing */
-	if(ncCryptoDigestSha256(data, dataSize, digest) != 0)
+	if(ncCryptoDigestSha256(&dataSpan, digest) != CSTATUS_OK)
 	{
 		return E_INVALID_ARG;
 	}
@@ -606,7 +607,7 @@ NC_EXPORT NCResult NC_CC NCVerifyDigest(
 	secp256k1_xonly_pubkey xonly;
 
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(pk, 1)
 	CHECK_NULL_ARG(digest32, 2)
 	CHECK_NULL_ARG(sig64, 3)	
@@ -629,11 +630,12 @@ NC_EXPORT NCResult NC_CC NCVerifyData(
 	const NCContext* ctx,
 	const NCPublicKey* pk,
 	const uint8_t* data,
-	const size_t dataSize,
+	const uint64_t dataSize,
 	const uint8_t sig64[64]
 )
 {
-	uint8_t digest[SHA256_DIGEST_SIZE];
+	sha256_t digest;
+	cspan_t dataSpan;
 
 	CHECK_NULL_ARG(ctx, 0)
 	CHECK_NULL_ARG(pk, 1)
@@ -641,8 +643,10 @@ NC_EXPORT NCResult NC_CC NCVerifyData(
 	CHECK_ARG_RANGE(dataSize, 1, UINT32_MAX, 3)
 	CHECK_NULL_ARG(sig64, 4)
 
+	ncSpanInitC(&dataSpan, data, dataSize);
+
 	/* Compute sha256 of the data before verifying */
-	if (ncCryptoDigestSha256(data, dataSize, digest) != 0)
+	if (ncCryptoDigestSha256(&dataSpan, digest) != CSTATUS_OK)
 	{
 		return E_INVALID_ARG;
 	}
@@ -661,7 +665,7 @@ NC_EXPORT NCResult NC_CC NCGetSharedSecret(
 )
 {
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(sk, 1)
 	CHECK_NULL_ARG(otherPk, 2)
 	CHECK_NULL_ARG(sharedPoint, 3)	
@@ -676,7 +680,7 @@ NC_EXPORT NCResult NC_CC NCGetConversationKeyEx(
 )
 {
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(sharedPoint, 1)
 	CHECK_NULL_ARG(conversationKey, 2)	
 
@@ -699,7 +703,7 @@ NC_EXPORT NCResult NC_CC NCGetConversationKey(
 	struct shared_secret sharedSecret;
 
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(sk, 1)
 	CHECK_NULL_ARG(pk, 2)
 	CHECK_NULL_ARG(conversationKey, 3)
@@ -722,35 +726,28 @@ Cleanup:
 NC_EXPORT NCResult NC_CC NCEncryptEx(
 	const NCContext* ctx, 
 	const uint8_t conversationKey[NC_CONV_KEY_SIZE], 
-	uint8_t hmacKeyOut[NC_HMAC_KEY_SIZE],
 	NCEncryptionArgs* args
 )
 {
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(conversationKey, 1)
-	CHECK_NULL_ARG(hmacKeyOut, 2)
-	CHECK_NULL_ARG(args, 3)
+	CHECK_NULL_ARG(args, 2)
 
 	/* Validte ciphertext/plaintext */
-	CHECK_INVALID_ARG(args->inputData, 3)
-	CHECK_INVALID_ARG(args->outputData, 3)
-	CHECK_INVALID_ARG(args->nonce32, 3)
-	CHECK_ARG_RANGE(args->dataSize, NIP44_MIN_ENC_MESSAGE_SIZE, NIP44_MAX_ENC_MESSAGE_SIZE, 3)	
+	CHECK_INVALID_ARG(args->inputData, 2)
+	CHECK_INVALID_ARG(args->outputData, 2)
+	CHECK_INVALID_ARG(args->nonce32, 2)
+	CHECK_INVALID_ARG(args->hmacKeyOut32, 2)
+	CHECK_ARG_RANGE(args->dataSize, NIP44_MIN_ENC_MESSAGE_SIZE, NIP44_MAX_ENC_MESSAGE_SIZE, 2)	
 
-	return _encryptEx(
-		ctx,
-		(struct conversation_key*)conversationKey, 
-		hmacKeyOut,
-		args
-	);
+	return _encryptEx(ctx, (struct conversation_key*)conversationKey, args->hmacKeyOut32, args);
 }
 
 NC_EXPORT NCResult NC_CC NCEncrypt(
 	const NCContext* ctx, 
 	const NCSecretKey* sk, 
-	const NCPublicKey* pk, 
-	uint8_t hmacKeyOut[NC_HMAC_KEY_SIZE],
+	const NCPublicKey* pk,
 	NCEncryptionArgs* args
 )
 {	
@@ -759,17 +756,17 @@ NC_EXPORT NCResult NC_CC NCEncrypt(
 	struct conversation_key conversationKey;	
 
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(sk, 1)
 	CHECK_NULL_ARG(pk, 2)
-	CHECK_NULL_ARG(hmacKeyOut, 3)
-	CHECK_NULL_ARG(args, 4)
+	CHECK_NULL_ARG(args, 3)
 
 	/* Validate input/output data */
-	CHECK_INVALID_ARG(args->inputData, 4)
-	CHECK_INVALID_ARG(args->outputData, 4)
-	CHECK_INVALID_ARG(args->nonce32, 4)
-	CHECK_ARG_RANGE(args->dataSize, NIP44_MIN_ENC_MESSAGE_SIZE, NIP44_MAX_ENC_MESSAGE_SIZE, 4)
+	CHECK_INVALID_ARG(args->inputData, 3)
+	CHECK_INVALID_ARG(args->outputData, 3)
+	CHECK_INVALID_ARG(args->nonce32, 3)
+	CHECK_INVALID_ARG(args->hmacKeyOut32, 3)
+	CHECK_ARG_RANGE(args->dataSize, NIP44_MIN_ENC_MESSAGE_SIZE, NIP44_MAX_ENC_MESSAGE_SIZE, 3)
 
 	/* Compute the shared point */
 	if ((result = _computeSharedSecret(ctx, sk, pk, &sharedSecret)) != NC_SUCCESS)
@@ -783,7 +780,7 @@ NC_EXPORT NCResult NC_CC NCEncrypt(
 		goto Cleanup;
 	}
 
-	result = _encryptEx(ctx, &conversationKey, hmacKeyOut, args);
+	result = _encryptEx(ctx, &conversationKey, args->hmacKeyOut32, args);
 
 Cleanup:
 	/* Clean up sensitive data */
@@ -800,7 +797,7 @@ NC_EXPORT NCResult NC_CC NCDecryptEx(
 )
 {
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(conversationKey, 1)
 	CHECK_NULL_ARG(args, 2)
 
@@ -825,7 +822,7 @@ NC_EXPORT NCResult NC_CC NCDecrypt(
 	struct conversation_key conversationKey;
 
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(sk, 1)
 	CHECK_NULL_ARG(pk, 2)
 	CHECK_NULL_ARG(args, 3)
@@ -860,28 +857,25 @@ NC_EXPORT NCResult NCComputeMac(
 	const NCContext* ctx,
 	const uint8_t hmacKey[NC_HMAC_KEY_SIZE],
 	const uint8_t* payload,
-	size_t payloadSize,
+	uint64_t payloadSize,
 	uint8_t hmacOut[NC_ENCRYPTION_MAC_SIZE]
 )
 {
-	NCMacVerifyArgs args;
+	cspan_t payloadSpan;
 
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(hmacKey, 1)
 	CHECK_NULL_ARG(payload, 2)
 	CHECK_ARG_RANGE(payloadSize, 1, UINT32_MAX, 3)
 	CHECK_NULL_ARG(hmacOut, 4)
 	
-	/*Fill args with 0 before use because we are only using some of the properties*/
-	ZERO_FILL(&args, sizeof(args));
-	args.payload = payload;
-	args.payloadSize = payloadSize;
+	ncSpanInitC(&payloadSpan, payload, payloadSize);
 
 	/*
 	* Compute the hmac of the data using the supplied hmac key
 	*/
-	return _computeHmac(hmacKey, &args, hmacOut) == 0 ? NC_SUCCESS : E_OPERATION_FAILED;
+	return _computeHmac(hmacKey, &payloadSpan, hmacOut) == CSTATUS_OK ? NC_SUCCESS : E_OPERATION_FAILED;
 }
 
 
@@ -892,7 +886,7 @@ NC_EXPORT NCResult NC_CC NCVerifyMacEx(
 )
 {
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(conversationKey, 1)
 	CHECK_NULL_ARG(args, 2)
 
@@ -912,7 +906,7 @@ NC_EXPORT NCResult NC_CC NCVerifyMac(
 )
 {
 	CHECK_NULL_ARG(ctx, 0)
-	CHECK_INVALID_ARG(ctx->secpCtx, 0)
+	CHECK_CONTEXT_STATE(ctx, 0)
 	CHECK_NULL_ARG(sk, 1)
 	CHECK_NULL_ARG(pk, 2)
 	CHECK_NULL_ARG(args, 3)
@@ -937,7 +931,7 @@ NC_EXPORT NCResult NC_CC NCVerifyMac(
 		goto Cleanup;
 	}
 
-	result = _verifyMacEx(ctx, (uint8_t*)&conversationKey, args);
+	result = _verifyMacEx(ctx, conversationKey.value, args);
 
 Cleanup:
 	/* Clean up sensitive data */
diff --git a/src/noscrypt.h b/src/noscrypt.h
index 06746ce..a8a42ee 100644
--- a/src/noscrypt.h
+++ b/src/noscrypt.h
@@ -145,6 +145,10 @@ typedef struct nc_encryption_struct {
 	/* The nonce used for the stream cipher. */
 	const uint8_t* nonce32;
 
+	/* Writes the hmac key to the buffer during encryption events.
+	Set to NULL on decryption */
+	uint8_t* hmacKeyOut32;
+
 	/* The input data buffer to encrypt/decrypt */
 	const uint8_t* inputData;
 
@@ -154,7 +158,7 @@ typedef struct nc_encryption_struct {
 	/* The size of the data buffers. Buffers must 
 	* be the same size or larger than this value
 	*/
-	size_t dataSize;
+	uint64_t dataSize;
 
 } NCEncryptionArgs;
 
@@ -174,7 +178,7 @@ typedef struct nc_mac_verify {
 	const uint8_t* payload;
 
 	/* The size of the payload data */
-	size_t payloadSize;
+	uint64_t payloadSize;
 
 } NCMacVerifyArgs;
 
@@ -217,10 +221,10 @@ that caused the error.
 */
 static _nc_fn_inline int NCParseErrorCode(NCResult result, uint8_t* argPositionOut)
 {
-	/* convert result to a positive value*/
 	NCResult asPositive;
 	int code;
 
+	/* convert result to a positive value*/
 	asPositive = -result;
 
 	/* Get the error code from the lower 8 bits and the argument position from the upper 8 bits*/
@@ -315,7 +319,7 @@ NC_EXPORT NCResult NC_CC NCSignData(
 	const NCSecretKey* sk,
 	const uint8_t random32[32],
 	const uint8_t* data,
-	const size_t dataSize,
+	const uint64_t dataSize,
 	uint8_t sig64[64]
 );
 
@@ -332,7 +336,7 @@ NC_EXPORT NCResult NC_CC NCVerifyData(
 	const NCContext* ctx,
 	const NCPublicKey* pk,
 	const uint8_t* data,
-	const size_t dataSize,
+	const uint64_t dataSize,
 	const uint8_t sig64[64]
 );
 
@@ -396,15 +400,13 @@ the NCEncryptEx functions for extended encryption functionality
 * @param sk The secret key (the local private key)
 * @param pk The compressed public key (x-only serialized public key) the other user's public key
 * @param args The encryption arguments
-* @param hmacKeyOut A pointer to the buffer to write the hmac key to
 * @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
 the error code and positional argument that caused the error
 */
 NC_EXPORT NCResult NC_CC NCEncrypt(
 	const NCContext* ctx, 
 	const NCSecretKey* sk, 
-	const NCPublicKey* pk, 
-	uint8_t hmacKeyOut[NC_HMAC_KEY_SIZE],
+	const NCPublicKey* pk,
 	NCEncryptionArgs* args
 );
 
@@ -500,14 +502,12 @@ NC_EXPORT NCResult NC_CC NCGetConversationKeyEx(
 * @param ctx A pointer to the existing library context
 * @param conversationKey A pointer to the conversation key
 * @param args A pointer to the encryption arguments structure
-* @param hmacKeyOut A pointer to the buffer to write the hmac key to
 * @return NC_SUCCESS if the operation was successful, otherwise an error code. Use NCParseErrorCode to
 the error code and positional argument that caused the error.
 */
 NC_EXPORT NCResult NC_CC NCEncryptEx(
 	const NCContext* ctx, 
 	const uint8_t conversationKey[NC_CONV_KEY_SIZE],
-	uint8_t hmacKeyOut[NC_HMAC_KEY_SIZE],
 	NCEncryptionArgs* args
 );
 
@@ -555,7 +555,7 @@ NC_EXPORT NCResult NCComputeMac(
 	const NCContext* ctx,
 	const uint8_t hmacKey[NC_HMAC_KEY_SIZE],
 	const uint8_t* payload,
-	size_t payloadSize,
+	uint64_t payloadSize,
 	uint8_t hmacOut[NC_ENCRYPTION_MAC_SIZE]
 );