The Kamasutra cipher is one of the oldest monographic monoalphabetic substitution methods. The cipher was described in the Kamasutra around 400 BC.
The plaintext and ciphertext alphabets are identical. The key of the cipher is obtained by permuting the alphabet. Then the alphabet is divided into two halves and written under each other. This allows letters to be easily assigned to each other, as in Atbasch.