Concatenation and Turbo Principle of Channel Coding and Cryptography

The transmission of data coded by a convolutional or turbo code and secured by cryptographic check values is improved by using of Soft Input Decryption. An additional coding gain can be reached, when coded data with cryptographic check values are interleaved, decoded and decrypted in an iterative process with feedback from decryptor to channel decoder. The coding gains are given complimentary, because the cryptographic redundancy is added by security aspects, which become more and more important and common. This paper observes the method of iterative Soft Input Decryption with feedback for concatenated codes of an inner convolutional or turbo code and cryptography as an outer error recognizing code. In this case the code rate diminished by the outer code has to be considered if the advantages of this method are exhibited. The coding gain of this method is so great that the code rate of the outer code can be compensated by puncturing. The extension of this method to more than two iterations leads to a Turbo principle of concatenated codes Key words