Donald W. Davies: Data Security - How did they start (Contd...)

BYWAY

Say Hello to Davies
Simple encryption example

You and I are communicating through the internet. We want to send the message to each other so that only you and I are able to read the message and no one else. We set A=1, B=2 … Z=26 and ‘space’ as it is. The key to encrypt the message is to add 2 to all the alphabets.

Example: If you want to send me a message “ZOO” you encrypt it by adding 2 to all the alphabets, resulting “BQQ” (since Z+2 = B). When you send the message to me, an intruder who wants to read the message cannot because it doesn’t give a proper meaning and doesn’t know how the message has been encrypted.

When the message reaches me and since we’ve shared the knowledge of the way of encryption, I subtract 2 from each alphabet, and get the original message “ZOO”. This is a simple way how encryption works.

Let’s say I send you an encrypted message “JGNNQ FCXKGU” encrypted using the same technique above, what actually is the message? Use the same decryption technique.

Answer
HELLO DAVIES

Digital Signature:

Public key systems have a further useful property; they can be used to give a message a digital signature. In this system, the receiver can be sure that it comes from the purported sender and not from an impersonator. For this, sender first encrypts the message using his/her own private key. The receiver tries to decrypt it using the sender's public key. If this reveals a sensible plaintext, the receiver can be sure that the message comes from the purported sender because no one else would have had the private key necessary to scramble it in just that way.

Go Back to Timeline

Prev | Next