Design and implementation of encryption algorithm for real time speech signals

This paper presents an FPGA based real time cryptographic algorithm for voice signals. Key concept of cryptography is to hide the data just like putting valuables in a box protected by a lock-key pair. Key(s) are the essential and crucial part of any encryption algorithm, and number and length of keys vary depending upon the purpose. Lengthy keys strengthen the algorithms against brute force attack. We have implemented a multi-key algorithm with real time key updation functionality where keys get updated every time they get used up. Both transmitter and receiver update their keys with proper synchronization. We have used four keys, first key is used to modify the incoming raw sample, second and third keys are used with the permutation table whose job is to shuffle the samples and finally the third key is used for the frame containing the encrypted data and other validation information. 't is predecided by the transmitter whether to update keys or not, this decision gets a position in the final frame telling Rx whether to update keys or not. Algorithm is designed in Verilog IIDL and realization is done on Spartan 3E Starter Kit using Xilinx 'SE 14.7.