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/**************************************************************************/
/* */
/* Copyright (c) Microsoft Corporation. All rights reserved. */
/* */
/* This software is licensed under the Microsoft Software License */
/* Terms for Microsoft Azure RTOS. Full text of the license can be */
/* found in the LICENSE file at https://aka.ms/AzureRTOS_EULA */
/* and in the root directory of this software. */
/* */
/**************************************************************************/
/**************************************************************************/
/**************************************************************************/
/** */
/** NetX Secure Component */
/** */
/** Datagram Transport Layer Security (DTLS) */
/** */
/**************************************************************************/
/**************************************************************************/
#define NX_SECURE_SOURCE_CODE
#include "nx_secure_dtls.h"
#ifdef NX_SECURE_ENABLE_DTLS
static UCHAR _generated_hash[NX_SECURE_TLS_MAX_HASH_SIZE];
/**************************************************************************/
/* */
/* FUNCTION RELEASE */
/* */
/* _nx_secure_dtls_verify_mac PORTABLE C */
/* 6.1 */
/* AUTHOR */
/* */
/* Timothy Stapko, Microsoft Corporation */
/* */
/* DESCRIPTION */
/* */
/* This function verifies the Message Authentication Code (MAC) that */
/* is included in encrypted DTLS records. It hashes the incoming */
/* message data and then compares it to the MAC in the received */
/* record. If there is a mismatch, then the record has been corrupted */
/* in transit and represents a possible security breach. */
/* */
/* INPUT */
/* */
/* dtls_session DTLS control block */
/* header_data DTLS record header data */
/* header_length Length of header data */
/* data DTLS record payload data */
/* length Length of payload data */
/* */
/* OUTPUT */
/* */
/* status Completion status */
/* */
/* CALLS */
/* */
/* _nx_secure_dtls_hash_record Generate payload data hash */
/* */
/* CALLED BY */
/* */
/* _nx_secure_dtls_process_record Process DTLS record data */
/* */
/* RELEASE HISTORY */
/* */
/* DATE NAME DESCRIPTION */
/* */
/* 05-19-2020 Timothy Stapko Initial Version 6.0 */
/* 09-30-2020 Timothy Stapko Modified comment(s), */
/* verified memcpy use cases, */
/* resulting in version 6.1 */
/* */
/**************************************************************************/
UINT _nx_secure_dtls_verify_mac(NX_SECURE_DTLS_SESSION *dtls_session, UCHAR *header_data,
USHORT header_length, UCHAR *data, UINT *length)
{
UCHAR *mac_secret;
USHORT hash_size;
UINT status;
INT compare_result;
USHORT data_length;
UCHAR *received_hash;
UINT hash_length;
UCHAR header[20];
NX_SECURE_TLS_SESSION *tls_session;
tls_session = &dtls_session -> nx_secure_dtls_tls_session;
if (tls_session -> nx_secure_tls_session_ciphersuite == NX_NULL)
{
/* Likely internal error since at this point ciphersuite negotiation was theoretically completed. */
return(NX_SECURE_TLS_UNKNOWN_CIPHERSUITE);
}
/* Get the hash size and MAC secret for our current session. */
hash_size = tls_session -> nx_secure_tls_session_ciphersuite -> nx_secure_tls_hash_size;
/* Select our proper MAC secret for hashing. */
if (tls_session -> nx_secure_tls_socket_type == NX_SECURE_TLS_SESSION_TYPE_SERVER)
{
/* If we are a server, we need to use the client's MAC secret. */
mac_secret = tls_session -> nx_secure_tls_key_material.nx_secure_tls_client_write_mac_secret;
}
else
{
/* We are a client, so use the server's MAC secret. */
mac_secret = tls_session -> nx_secure_tls_key_material.nx_secure_tls_server_write_mac_secret;
}
if (hash_size >= *length)
{
/* The record data was smaller than the selected hash... Error. */
return(NX_SECURE_TLS_HASH_MAC_VERIFY_FAILURE);
}
/* Adjust our length so we only hash the record data, not the hash as well. */
data_length = (USHORT)(*length - hash_size);
/* Copy the header data into our local buffer so we can change it if we need to. */
if (header_length > sizeof(header))
{
return(NX_SECURE_TLS_HASH_MAC_VERIFY_FAILURE);
}
NX_SECURE_MEMCPY(header, header_data, header_length); /* Use case of memcpy is verified. */
/* Adjust the length in the header to match data without hash. */
/* In DTLS, the length is at offset 11. */
header[11] = (UCHAR)((data_length >> 8) & 0x00FF);
header[12] = (UCHAR)(data_length & 0x00FF);
/* Generate the hash on the plaintext data. */
status = _nx_secure_dtls_hash_record(dtls_session, tls_session -> nx_secure_tls_remote_sequence_number, header, header_length,
data, (USHORT)(data_length), _generated_hash, &hash_length, mac_secret);
if (status != NX_SUCCESS)
{
/* The hash operation failed for some reason. */
return(NX_SECURE_TLS_HASH_MAC_VERIFY_FAILURE);
}
/* In DTLS, the sequence number is explicit in the record. In TLS the sequence number would be incremented here. */
/* Now, compare the hash we generated to the one we received. */
received_hash = &data[data_length];
compare_result = NX_SECURE_MEMCMP(received_hash, _generated_hash, hash_size);
/* Before we return, adjust our data size so the caller will only see data, not the hash. */
*length = data_length;
/* If the hashes match, we are all good. Otherwise we have a problem. */
if (compare_result == 0)
{
return(NX_SECURE_TLS_SUCCESS);
}
else
{
return(NX_SECURE_TLS_HASH_MAC_VERIFY_FAILURE);
}
}
#endif /* NX_SECURE_ENABLE_DTLS */
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