The shortcoming of conventional bus architecture has been overcome by adopting Network on Chip (NoC) in multi core System on Chip (SoC). Many works have been anticipated for NoC, based on network topology, switching methodology and routing techniques. This paper proposes a Modified TACIT algorithm for secure routing in NoC architectures. The key generation is based on four types of HASH function (4H-key) that find hard hitting to the intruder. The algorithm is realized under various block sizes as the 8-bit, 64-bit and 128-bit. The device utilization of the proposed algorithm is determined and the results show that, the maximum frequency achieved by the proposed algorithm (for 8-bit block size) is 640.968 MHz with the total memory usage of 78045 Kb.