  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.
