Function write_block

libcppcryptfs/file/cryptio.cpp:117–202

}

int
write_block(CryptContext *con, unsigned char *cipher_buf, HANDLE hfile, const unsigned char *fileid, unsigned long long block, const unsigned char *ptbuf, int ptlen, EVP_CIPHER_CTX* openssl_crypt_context, const unsigned char *iv)
{


	long long offset = FILE_HEADER_LEN + block*CIPHER_BS;

	if (!iv)
		return -1;

	OVERLAPPED ov;

	if (hfile != INVALID_HANDLE_VALUE) {
		SetOverlapped(&ov, offset);
	}

	unsigned long long be_block = MakeBigEndian(block);

	unsigned char auth_data[sizeof(be_block) + FILE_ID_LEN];

	memcpy(auth_data, &be_block, sizeof(be_block));

	memcpy(auth_data + sizeof(be_block), fileid, FILE_ID_LEN);

	unsigned char tag[BLOCK_TAG_LEN];

	if (!con->GetConfig()->m_reverse) {
		memcpy(cipher_buf, iv, BLOCK_IV_LEN);
	} else {
		const unsigned char* block0iv = iv;

		// On a 128-bit big-endian machine, this would be the low-order 64 bits
		// hence the name block0IVlow
		unsigned long long block0IVlow; 

		static_assert(BLOCK_SIV_LEN == 16, "BLOCK_SIV_LEN != 16.");
		static_assert(sizeof(block0IVlow) == 8, "sizeof(block0IVlow) != 8.");
		memcpy(&block0IVlow, block0iv + 8, sizeof(block0IVlow));

		block0IVlow = MakeBigEndianNative(block0IVlow);

		block0IVlow += block;

		block0IVlow = MakeBigEndian(block0IVlow);

		memcpy(cipher_buf, block0iv, 8);
		memcpy(cipher_buf + 8, &block0IVlow, sizeof(block0IVlow));
		
		
	}

	bool siv = con->GetConfig()->m_AESSIV;

	int ctlen;

	if (siv) {
		ctlen = encrypt_siv(ptbuf, ptlen, auth_data, sizeof(auth_data), 
			cipher_buf, cipher_buf + BLOCK_IV_LEN + BLOCK_SIV_LEN, cipher_buf + BLOCK_IV_LEN, &con->m_siv);