The East German Encryption Machine T-310 and the Algorithm It Used

Abstract

This article gives an overview on the T-310 encryption machine, which was widely used by East German state authorities in the 1980s. The T-310 was based on a U880 processor and it encrypted 5 bit words as used by the teleprinters of the time. The encryption algorithm the T-310 used is a stream cipher working on 5 bit units. A complete description of this previously unpublished algorithm is given in this article. Although most of the content of this publication is based on information found by Bernd Lippmann in a state-owned archive (Birthler authority archive), additional input came from the former military technician Jö rg Drobick, who maintained several T-310 copies in the 1980s.

Ciphertext-only attacks and weak long-term keys in T-310

“…The original Feistel cipher construction had 2 branches and was invented around 1971 [15]. Then East German cipher designers had already in 1970s [22] mandated a substantially more complex structure. The actual connections depend on the so-called long-term key, a.k.a.…”

“…It remains to specify how the U 1−9 are computed inside one round. In [22] this is defined using a function T : {0, 1} 2+27 → IF 9 2 which is also illustrated in Fig. 3 below.…”

“…Having (exactly) one i s.t. D(i) = 0 is mandatory in [21,22]. The effect of this is that one bit of the left branch is removed, as shown on Fig.…”

“…2. Moreover for so called KT1 class of keys [22,21] and in most of the historical examples of keys in [13] the bit which is removed is um,4j 8 and it is used elsewhere, i.e. we must have P (i) = 4j8 for a certain i.…”

“…T-310 is an important historical cipher which was used in East Germany during the last period of the Cold War. According to [12,22], in 1989 there were some 3,800 T-310 cipher machines in active service across all sorts of government, party and internal security services.…”