GOST is a block algorithm from the former Soviet Union [655,1393]. “GOST” is an acronym for “Gosudarstvennyi Standard,” or Government Standard, sort of similar to a FIPS, except that it can (and does) refer to just about any kind of standard. (Actually, the full name is Gosudarstvennyi Standard Soyuza SSR, or Government Standard of the Union of Soviet Socialist Republics.) This standard is number 28147-89. The Government Committee for Standards of the USSR authorized the standard, whoever they were.
I don't know whether GOST 28147-89 was used for classified traffic or just for civilian encryption. A remark at its beginning states that the algorithm “satisfies all cryptographic requirements and not limits the grade of information to be protected.” I have heard claims that it was initially used for very high-grade communications, including classified military communications, but I have no confirmation.
GOST is a 64-bit block algorithm with a 256-bit key. GOST also has some additional key material that will be discussed later. The algorithm iterates a simple encryption algorithm for 32 rounds.
To encrypt, first break the text up into a left half, L, and a right half, R. The sub-key for round i is Ki. A round, i, of GOST is:
Li = Ri − 1
Ri = Li − 1 f(Ri − 1, Ki)
Figure 14.1 is a single round of GOST. Function f is ...