Error rate performance analysis of stream and block ciphers in a digital mobile communication channel

This thesis analyses the effect of encrypting data on the bit error rate at the receiver. Block and stream cipher modes based on the Data Encryption Standard (DES) are examined. More specifically, Electronic Code Book (ECB), Cipher Block Chaining (CBC), Output FeedBack (OFB) and Cipher FeedBack (CFB) modes are considered. The ability of binary BCH codes and of bit interleaving to reduce the error rate over fading channels is examined in detail. Experimental results are derived from computer simulations where the digital mobile communication channel is represented by the Gilbert and Fritchman models. Simulations are also carried out over memoryless binary symmetric channels (BSC) to illustrate the difference on the error rate at the receiver (after decryption) as a result of the presence or absence of channel memory.