file/file_encrypt/encrypt.c

gos_result_t encrypt_buffer_to_file(const uint8_t *key, uint8_t *buffer, uint32_t buffer_length, const char *encrypted_filename)

{

gos_handle_t handle;

gos_result_t result;

uint8_t mac[MAC_SIZE];

gos_aes128_iv_t init_iv;

crypt_context_t context;

int32_t remaining_bytes;

// Initialize the AES context with the supplied key

gos_aes_setkey_enc(&context.aes, key, AES128_BLOCK_BITS);

// Generate random initialization vector (IV)

gos_get_random_buffer(init_iv.buf, IV_SIZE);

memcpy(context.iv.buf, init_iv.buf, IV_SIZE);

gos_dump_buffer(init_iv.buf, IV_SIZE, "IV", GOS_DUMP_FLAGS(16, 1, LITTLE, ADD_SPACE, NO_ADDRESSES, NO_ASCII ));

// Calculate the file's MAC

calculate_mac(key, buffer, buffer_length, mac);

gos_dump_buffer(mac, MAC_SIZE, "MAC", GOS_DUMP_FLAGS(16, 1, LITTLE, ADD_SPACE, NO_ADDRESSES, NO_ASCII ));

// Create the output file

// Notes:

// * The encrypted file is 32 bytes longer to store the IV and MAC

// * The GOS_FILE_OWNER_USER owner types indicates that the file is encrypted with the 'user key'

// * The GOS_FILE_FLAG_PRE_ENCRYPTED flag indicates that the file is encrypted

// * The GOS_FILE_FLAG_PRE_ENCRYPTED flag indicates that the file is pre-encrypted (i.e. Gecko OS will NOT encrypt the file as it's written)

gos_file_t file = GOS_FILE_DEFAULT_USER_FILE_INFO;

file.owner = GOS_FILE_OWNER_USER;

file.size = sizeof(init_iv) + sizeof(mac) + buffer_length;

file.flags = GOS_FILE_FLAG_ENCRYPTED|GOS_FILE_FLAG_PRE_ENCRYPTED;

strcpy(file.name, encrypted_filename);

// Delete the file if it already exists

gos_file_delete(encrypted_filename, GOS_FILE_LOCATION_ANY);

// Create the file

if (GOS_FAILED(result, gos_file_create(&file, &handle)))

{

GOS_LOG("Failed to create file: %d", result);

return result;

}

// Write the initial IV

if (GOS_FAILED(result, gos_file_write(handle, init_iv.buf, sizeof(init_iv))))

{

GOS_LOG("Failed to write IV: %d", result);

return result;

}

// Encrypt the MAC and write to the file

encrypt_block(&context, mac);

if (GOS_FAILED(result, gos_file_write(handle, mac, sizeof(mac))))

{

GOS_LOG("Failed to write MAC: %d", result);

return result;

}

// Encrypt the input file data AES128_BLOCK_SIZE bytes at a time and write to the output file

uint8_t *file_ptr = buffer;

remaining_bytes = buffer_length;

while (remaining_bytes > 0)

{

encrypt_block(&context, file_ptr);

if (GOS_FAILED(result, gos_file_write(handle, file_ptr, MIN(remaining_bytes, AES128_BLOCK_SIZE))))

{

GOS_LOG("Failed to write encrypted data: %d", result);

return result;

}

remaining_bytes -= AES128_BLOCK_SIZE;

file_ptr += AES128_BLOCK_SIZE;

}

gos_file_close(handle);

return GOS_SUCCESS;

}