Crossword clue: relating to cryptography; written in secret characters or in cipher, or with sympathetic ink.

cryptographic, cryptographical.

The most common answer is cryptographic (13 letters).

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

Possible answers

cryptographic 13 letters web-def

of or relating to cryptanalysis

cryptographical 15 letters web-def

Relating to cryptography; written in secret characters or in cipher, or with sympathetic ink.