Symmetric substitution cipher using 13 letter pairs.
The Kamasutra, or Vatsyayana, cipher is a simple substitution cipher where the alphabet is organized into 13 pairs of characters. Each pair directly substitutes for itself, so the same key can encrypt and decrypt.
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Encryption Key Pairs
Keyword letters seed a deduplicated A-Z alphabet, then it splits into 13 pairs (first letter / fourteenth letter, etc.).