Iterative method for improvement of coding and decryption
Cryptographic check values (digital signatures, MACs and H-MACs) are useful only if they are free of errors. For that reason all of errors in cryptographic check values should be corrected after the transmission over a noisy channel before their verification is performed. Soft Input Decryption is a method of combining SISO convolutional decoding and decrypting of cryptographic check values to improve the correction of errors in themselves. If Soft Input Decryption is successful, i.e. all wrong bit of a cryptographic check value are corrected, these bit are sent as feedback information to the channel decoder for a next iteration. The bit of the next iteration are corrected by channel decoding followed by another Soft Input Decryption. Iterative Soft Input Decryption uses interleaved blocks. If one block can be corrected by Soft Input Decryption, the decoding of the interleaved block is improved (serial scheme). If Soft Input Decryption is applied on both blocks and one of the blocks can be corrected, the corrected block is used for an improved decoding of the other block (parallel scheme). Both schemes show significant coding gains compared to convolutional decoding without iterative Soft Input Decryption.