The Krypto - Funkfernschreiber 58 (Ciphering radio teletype system 58) consists of the keyboard and the printing system of the ETK with it's fourteen character elements. In contrast to the CCITT No.2 Baudot code, most characters are still discernible, if the transmission of one of the character steps did fail.

The ciphering process is done in the encryption unit, which is set atop the teleprinter unit. Only the encryption unit was classified as being "secret".
The key consists of a password with twelve characters and a number key with four out of eight numbers. The four permutation wheels at the left side and the advancement wheels at the right side of the key display window are moved electrically to set the key to start decryption. According to the number key, the switches 1 - 8 are set to the correct position.
A major improvement over the TC 53 is the "SYN KRYPTO" mode, with synchronisation pulses, the ciphering machines at the transmitting and receiving side are kept synchroneous while the machines are idle. If the synchronisation pulses are not received properly due to propagation disturbances, they are replaced by impulses from an internal crystal oscillator. The machines can be kept "in pace" over a time of several minutes, when reception is poor.

The KFF 58 comes also with the SPG (Schlüsselproduktionsgerät), which is nothing else then a mechanical password generator. It is used to generate a true random message key, so that the operators did not use standard passwords.

Because of the KFF 58 used the fourteen segment code, it cannot be used in conjunction with other ciphering equipment which uses the 7 element Baudot code. The KPP 58 has been withdrawn from troop use in 1991, the ciphering modules have been destroyed nearly completely, the teleprinter parts have been sold to the public as surplus.