Soft Input Decryption

Abstract:
This paper presents an approach to integrate decryption into the decoding process, and also gives an example to prove its advantages. The general idea considers the decryptor as a decoding component and not as an isolated unit in the decoding path between the channel and the source decoder. A decryptor produces useless output, if only one bit of its input, compared to the output of the encryptor, is modified. Therefore, it is important to improve the capability to correct input errors by the decryptor in case the channel decoder does not deliver correct bits. The presented solution supports the decryptor with soft output of the channel decoder. As far as known today, soft output has never been used by cryptographic mechanisms before. The example of a decryptor, which provides data origin authentication, proves that after decryption the error rate can drastically be reduced by using soft output from a Convolutional or Turbo Decoder as soft input to the decryptor. Results are given for digital signature verification based on elliptic curve cryptography transmitted over channels with a wide range of Signal-to-Noise Ratios.