Coding-decoding

Story hook

In 1942, Alan Turing's team at Bletchley Park stared at lines of ciphered German radio chatter. They had no Enigma machine in front of them — only the output. They worked backwards from frequency of letters, from the German habit of beginning weather reports with Wettervorhersage, and from a single repeated word that gave them the day's rotor setting. Every cipher hides a tiny rule.

A CSAT candidate, decades later, opens her paper and finds: "If FROG is coded as GSPH, how is TREE coded?" She does not know it, but she is doing the same job — guessing the rule, testing it on a known word, and applying it to an unknown one. Two pages later, she is asked to seat eight people around a round table where two are vegetarian, three speak Marathi, and one will not sit beside the chairman. Same skill, different costume: a hidden rule, a fixed number of constraints, a single arrangement that satisfies them all.

Coding and seating arrangements are the cryptography puzzles of the exam hall — quietly mechanical once you see the rule.

Why this matters for UPSC

Together, coding-decoding and seating arrangements contribute four to seven marks per CSAT — about 8% of the qualifying paper. UPSC has asked one or two coding questions in nine of the last ten years and a seating-arrangement set in seven of those ten. They are the second most reliable bucket after blood relations and directions. Neither appears in Mains.