# Cryptography

Leave a commentMay 18, 2014 by Ozgur Ozden

Before we discuss the topic it will be a good idea to take a look at what public and private key encryption is. But let start from cryptography first. Ayushi (2010) describes this concept very elegantly in his article as “Cryptography is the art of achieving security by encoding messages to make them non-readable. Cryptography is the practice and study of hiding information.” and it has been around since 1900 BC with the invention of old hieroglyphs in Egypt.

There are two basic type of cryptography as Ayushi (2010) mentioned.

Symmetric-key algorithm: In this system, both sides use the same or very similar keys for encryption and decryption. Users must keep the key securely. Stream ciphers which encrypts the texts into digits or bytes, block ciphers which assumes certain size of bits and encrypt them as one unit. 64 is the most common one. One of the disadvantages of this this system is that secure way of sharing the common key is required. Also authenticity of the message is also questionable. As Kerckhoff’s Principle explained a system is secure only details can be shared with the rest of the world.

Asymmetric-key algorithm:

This is a system that requires two different keys one of them is public that anyone can see it and the other one is private. Even though these two keys are different they are linked to each other by a mathematical algorithm. One of the keys encrypts the message and the other one is simply decrypts the ciphertext. Very basically system can be illustrated as; suppose Jane would like to send a message to John. Jane prepares the message and encrypt by Johns’s public key. So message become and encrypted text. When John receives the message decrypt by his private key so message become a readable text again. Digital signatures can be used to make sure that the message is sent by a known and trustable source.

There are many mathematical algorithms are in use to create the public and private keys. Pretty Good Privacy (PGP) is one of the most common one. It is created by Philip Zimmerman.. It is a free system that you can get it from certain sources. Algorithm was so successful that US gov’t actually open a lawsuit against Zimmerman for sharing this crucial system with public. But later on case was dropped.

Another famous algorithm is Diffie–Hellman key exchange Algorithm. In this system two sides share a secret and this secret is used during the communications.

Asymmetric key algorithm systems also have some disadvantages. Alan Hughes (2012) explains these as:

1- The system is slow and not suitable for encrypting long messages. 2- It widely uses computer resources. 3- Private key must be kept very securely and any loss of the key may results in decrypting the messages by third parties.

I believe that whatever the system we use or develop, we will still have people out there to hack into systems. This is the nature of mankind and also carried mankind to this date. Curiosity and challenge.

References:

1- Alan Hughes, (2012) Advantages & Disadvantages of Private Key Encryption (Online) Available at: http://www.ehow.com/info_8738577_advantages-disadvantages-private-key-encryption.html#ixzz2T4eq3QBR [Accessed: 11 May 2013]

2- Ayushi (2010) A Symmetric Key Cryptographic Algorithm International Journal of Computer Applications (0975 – 8887) Volume 1 – No. 15 (online) Available at: http://www.ijcaonline.org/journal/number15/pxc387502.pdf [Accessed: 11 May 2013]

3- Rahul Banerjee (year unknown) Introduction to symmetric key algorithm Lecture notes (online) Available at: http://discovery.bits-pilani.ac.in/rahul/netsec/network%20security-lecture-2-2005-2006-secure.pdf [Accessed: 12 May 2013]