control rotor stepping. As part of the key setup, the stepping control pins can be rotated relative to the outer ring. The inner, electrical ring can also be rotated relative to the outer ring and can be inserted in one of two ways, with side 1 or side 2 up. unitary rotors, used with the M-125-MN. These have both electrical contacts and mechanical pins. The only key adjustment is the order of the rotors on the axle and the initial rotor settings. There is one combination for the disassemblable rotors that is compatible with the unitary rotor. One East German manual that has become public contains typed-in and hand written addenda that suggest the East Germans, at least, later stopped using the added features of the disassemblable rotors and only used them in unitary compatibility mode. Adjacent rotors step in opposite directions. A spare rotor assembly could be kept in the unit's top cover. The Fialka machines were originally delivered with two sets of rotors, one in the machine assemblage and one set supplied in a metal cylinder inside the dustcover. The singly most crucial flaw in the Enigma design was that letter substitutions were reciprocal and that in particular a letter could never encrypt to itself. The Russians clearly learned from this in designing Fialka such that it is possible for a letter to encrypt to itself. Keying material The keying material for the Fialka consists of a daily key book, a message key book and a message identifier book for broadcast traffic. The daily key book contains day keys for one month. A day key consists of a key table (in Cyrillic) and a punched card. For fixed rotor systems, the key table specifies the order of the rotors on the axle and the initial rotor settings to be used to decrypt the indicator of broadcast messages. As its name implies, the day key is valid (has a cryptoperiod in NSA parlance) for 24 hours and was changed at 00:01 hours. For the disassemblable rotors, the table also specifies the electrical insert for each outer rotor, which side was to be up, and the orientation of the insert relative to the outer rotor. Here is a sample M-125-3NM day key table for use on the 14th of the month: ИДЖЗА ВКБГЕ 14 OCAHE PTБВЕ БДВИА ГЕЗКЖ 2II22 I22I2 КУЛКЮ ЫХВУГ The message key table contained the initial rotor