refactor: Crypto dep redesign working on Windows

7 files changed, 955 insertions, 1 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