20 lines
820 B
Forth
20 lines
820 B
Forth
ROT13 ("rotate by 13 places", sometimes hyphenated ROT-13) is a simple
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letter substitution cipher that replaces a letter with the letter 13
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letters after it in the alphabet. ROT13 is a special case of the Caesar
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cipher, developed in ancient Rome.
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Because there are 26 letters (21^3) in the basic Latin alphabet, ROT13
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is its own inverse; that is, to undo ROT13, the same algorithm is
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applied, so the same action can be used for encoding and decoding. The
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algorithm provides virtually no cryptographic security, and is often
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cited as a canonical example of weak encryption.
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(Taken from https://en.m.wikipedia.org/wiki/ROT13)
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This is an implementation of ROT13 in RETRO.
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~~~
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'nopqrstuvwxyzabcdefghijklm 'MAP s:const
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:encode (c-c) $a - MAP + fetch ;
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:rot13 (s-s) s:to-lower [ dup c:letter? [ encode ] if ] s:map ;
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~~~
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