On security aspects of the ciphers T-310 and SKS with approved long-term keys
Wolfgang Killmann · Cryptologia · 2023
The cipher T-310 was developed by the Central Cipher Authority of the German Democratic Republic in the 1970s and widely used for protection of teletype communication up to security level secret. After publication of the cipher algorithm in 2006, several articles appeared aiming at the cryptographic properties of the cipher T-310. The cryptographic strength of the cipher T-310 must be assessed as a combination of both the cipher algorithm and the approved long-term keys. This article provides a rationale of the design decisions and the selection of approved long-term keys for T-310. We demonstrate that the attacks involving fundamental equations, linear characteristics, and some of their generalizations do not work if historical approved long-term keys are used. The results are also valid for the cipher SKS and block ciphers, whose groups of round functions are the alternating groups over the blocks.