Digital Signatures That Use Public-key Can’t be Repudiated

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