What is "mulabhadra"

Mūlabhadra was a secret method of communication employed by the royal spies of the erstwhile Travancore Kingdom during the medieval period. The scheme was also colloquially referred to as Mūlapatra. It was essentially a cryptographic scheme involving a partial transposition of the letters of the Malayalam alphabet. The scheme had been extensively used by King Marthanda Varma (1706–1758) of Travancore Kingdom and his spies both for oral and written communication of messages. It was a fixed one-time unchangeable code in as much as it did not employ any key in its implementation in contrast to modern methods of substitution ciphers involving the utilisation of a key for generating a system of codes. Mūlabhadra is the only such scheme known to have been used in governance in this part of India during this period.