The transmission of data between sender and receiver must be secure and accurate. For secure transmission, cryptography techniques are widely used. Many of the variants of algorithm use symmetric and public keys. In this paper, symmetric key encryption algorithm is designed using division algorithm a = qb + r, 0 r < b, where q and r are unique positive integers. The algorithm can be applied in decimal, binary or hexadecimal number system. The key space, the set of all possible keys, depends on the choice of 8 or 16-bit or even more number of bits in a key. The key space is generated using quotient q and remainder r in a division algorithm. The algorithm given in Narayana and Veereswara Swamy (2012) uses 8-bit key and is shown to be of this particular case.

Communication system consists of a network of systems. System consists of related components that participate in communication. The system can be a sender or a receiver. The data to be transmitted over a communication channel can be either in text, audio, image, video or audiovisual form and must not be exposed to the third party other than the sender or the receiver. The security requirements include:

• Authentication: To prove one’s identity.
• Privacy or Confidentiality: Third party should not read the message.
• Integrity: To ensure that the original message and the received message are same.
• Non-repudiation: To confirm that the sender really sent this message.

The above issues can be addressed through cryptography. Cryptography is used to protect data from theft or alteration and for user authentication. It is an ancient art adopted by Egyptians for writing plain text into secret code which is either readable or unreadable and uninterpretable.

Substitution is a very old art invented some 2000 years ago. It was utilized by Julius Caesar and later by the Arabs. The message is encrypted by substituting each letter of the alphabet with a particular substitution letter. Caesar was the first one to use this method of ciphering text. He used substitution based on shifting mechanism, like replacing a with D, b with E, c with F, etc. For example, the word ‘cryptography’ can be encrypted as ‘FUBSWRJUDSKB’.

The following terminologies are commonly used in the context of Cryptography.

Computer Sciences Journal, Division algorithm, Cryptography, Symmetric key, Secret key, Asymmetric key, Public key, Cipher text, Encryption, Decryption.