Historically, messages in languages that use alphabets have been encrypted manually according to some kind of algorithm (e.g. mono- and poly-alphabetic ciphers). But how were messages encrypted in a semagram-based language like Chinese?
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$\begingroup$ One possibility according to Wikipedia: Transposition Ciphers. $\endgroup$– SEJPMOct 26, 2015 at 13:35
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$\begingroup$ Aggregating the answers: treat them as digits. $\endgroup$– DannyNiuAug 14, 2021 at 8:31
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2 Answers
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There was a telegraphic code that mapped the comparatively frequently used 10000 words (that's very much more than for common daily use, e.g. newspapers) of Chinese to [0,9999]. There was once also a patented mechanical device that effected a poly-alphabetical substitution of [0,9] with a set of disks containing certain scrambled alphabet of [0,9], which the user selected 4 of them (aggreed upon with the partner) to encrypt the 4 digits from the telegraphic code. Since frequency analysis of the digits barely helps, the result from that device isn't bad IMHO even today (anyway assuming one has a somewhat larger set of disks than at that time.)
answered Oct 26, 2015 at 13:45
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The Chinese used digits. So there is an encoding into digit groups, like a code book. This code book could be standard (like the Chinese used for telegraphy and radio as well, which used a publicly available book), or for extra secrecy could be kept a secret. The cipher could then be made to work on digit groups (and there standard techniques like addition mod 10 with a key stream, permuations, etc could be used).
The Japanese also used digit based codes a lot, or they used (in their WW2 era machines) the transliteration (there are only a finite number of syllables) into a Latin alphabet, and then used rotor machine techniques (as for the enigma) etc.
But the digit route seems the more common.
