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AA-005
Self-Invertible Encryption Key on Cipher Trigraphic Polyfunction

Asmaa Zafirah Kamaluzaman 1, a) ,Faridah Yunos 2,b) , and Mohd Syafiq Jamaludin 3,c)

1,2,3 Department of Mathematics and Statistics, Faculty of Science, Universiti Putra Malaysia,
43400 UPM Serdang, Selangor, Malaysia.
2 Institute for Mathematical Research, Universiti Putra Malaysia,
43400 UPM Serdang, Selangor, Malaysia.

a) asmaazafirah@gmail.com
b) Corresponding author: faridahy@upm.edu.my
c) syafiqjamaludinmtmkc1819@gmail.com

Abstract. Cipher Trigraphic Polyfunction developed by previous researchers is a modification of Hill
Cipher technique in modern cryptography. It was built on the system using three symbols or letters and
more than one transformation of the original message. The modular arithmetic of a key matrix plays an
important role in the encryption and decryption processes. To get the inverse matrix in the decryption
process is a crucial aspect. Some matrices do not have inverses, and, in that case, the receiver needs to
choose a different key matrix to decrypt a cipher. To make sure every ciphertext block can be decrypted;
an inverse key matrix is not needed for decryption, and this definitely simplifies the computational
complexity and saves the computational time. The objective of this paper is to obtain some patterns of
secret keys and subsequently generate a self-invertible key which will be used in the encryption and
decryption process of Cipher Trigraphic Polyfunction.

Keywords: Encryption, decryption, hill cipher, self-invertible, secret key

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