What is cryptography?
To most people, cryptography is concerned with keeping communications private. Indeed, the protection of sensitive communications has been the emphasis of cryptography throughout much of its history. As the field of cryptography has advanced, the definition has blurred. Cryptography today might be summed up as the study of techniques and applications that depend on the existence of difficult problems.

Encryption is the transformation of data into a form that is as close to impossible as possible to read without the appropriate key. Decryption is the reverse of encryption. But today’s cryptography is more than encryption and decryption.

Why is cryptography important?
Cryptography allows people to carry over the confidence found in the physical world to the electronic world, thus allowing people to do business electronically without worries of deceit and deception. Every day hundreds of thousands of people interact electronically, whether it is through e-mail, e-commerce (business conducted over the Internet), ATM machines, or cellular phones. The perpetual increase of information transmitted electronically has lead to an increased reliance on cryptography.

Cryptography makes secure web sites and electronic safe transmissions possible. For a website to be secure all of the data transmitted between the computers where the data is kept and where it is received must be encrypted. This allows people to do online banking, online trading, and make online purchases with their credit cards, without worrying that any of their account information is being compromised. Cryptography is very important to the continued growth of the Internet and electronic commerce.

What are some of the more popular techniques in cryptography?
There are two types of cryptosystems: secret-key and public-key cryptography. In secret-key cryptography, the same key is used for both encryption and decryption. The most popular secret-key cryptosystem today is the Data Encryption Standard (DES).

In public-key cryptography, each user has a public key and a private key. The public key is made public while the private key remains secret. Encryption is performed with the public key while decryption is done with the private key.

How do identification and authentication work in cryptography?
Identification is the process of verifying someone’s or something’s identity. For example, when withdrawing money from a bank, a teller asks to see identification to verify the identity of the owner of the account. The same process can be done electronically using cryptography. Every automatic teller machine (ATM) card is associated with a ‘secret’ personal identification number (PIN), which binds the owner to the card and thus to the account. When the card is inserted into the ATM, the machine prompts the cardholder for the PIN. If the correct PIN is entered, the machine identifies that person as the rightful owner and grants access. Another important application of cryptography is authentication. Authentication is similar to identification, in that both allow an entity access to resources (such as an Internet account), but authentication is broader because it does not necessarily involve identifying a person or entity. Authentication merely determines whether that person or entity is authorized for .

What is secret-key cryptography?
Secret-key cryptography is sometimes referred to as symmetric cryptography. In it, a single key can be used to encrypt and decrypt a message. Secret-key cryptography not only deals with encryption, but it also deals with authentication. One such technique is called message authentication codes.

The main problem with secret-key cryptosystems is getting the sender and receiver to agree on the secret key without anyone else finding out.

What are the advantages of public-key cryptography over secret-key cryptography?
The primary advantage of public-key cryptography is increased security and convenience: private keys never need to be transmitted or revealed to anyone. In a secret-key system, by contrast, the secret keys must be transmitted (either manually or through a communication channel) since the same key is used for encryption and decryption. A serious concern is that there may be a chance that an enemy can discover the secret key during transmission. Another major advantage of public-key systems is that they can provide digital signatures that cannot be repudiated.

sureshsrini@rsi.ramco.com