Long ago, I read an article on Wikipedia which described a cipher algorithm, used by the KGB (if I remember well), with the property that all ciphered letters had the same (or nearly the same) probability to appear, without adding symbols to the alphabet of the ciphered text (i.e. unlike how homophonic encryption does). The algorithm was computable by hand.
But I cannot find this article again. Does anyone know the article I mentioned?
You probably mean the VIC cipher.
It can be set up in a way such that the initial substitution that also achieves fractionation through the use of a so-called straddling checkerboard is followed by a transposition or substitution step. These steps make the distribution of symbols in the cipher text more uniform than in the plain text.
An optional subsequent reverse substitution using the same straddling checkerboard leads to a cipher text that contains only symbols of the original alphabet.
