Quantum Leap: cryptography of the future
CRYPTOGRAPHY FOR BEGINNERS
The fundamentals of cryptography (the art of writing THE RSA 1024 CHALLENGE
in and deciphering codes) haven’t changed in over a The mathematical formulae underpinning public
millennium. The sender uses a set of rules to convert key encryption are based upon the factorisation
a sensitive message into something with no meaning. (multiplication) of two prime numbers. Solutions
This message can then be sent to the recipient, who are so difficult to calculate that RSA (a leading IT
uses a set of rules to decode the message back to its Security company) offered $100,000 to anyone
original form. Anyone who intercepts the message in who can work out which two prime numbers
transit learns nothing, as they don’t know the rules for multiplied together result in this 309 digit figure:
encoding and decoding the message.
1350664108659952233496032162788059699388
Good, but there is a fundamental problem. How do the 8147560566702752448514385152651060485953
sender and receiver agree on the rules to be used? In 3833940287150571909441798207282164471551
modern cryptography, this is called the key exchange 3736804197039641917430464965892742562393
problem. If an eavesdropper listens in when the keys are 4102086438320211037295872576235850964311
swapped, they can sit back and decode all the messages 0564073501508187510676594629205563685529
that follow. Worse still, the sender and receiver won’t 4752135008528794163773285339061097505443
even know their messages have been intercepted. 34999811150056977236890927563
SOLvING THE KEY ExCHANGE PROBLEM Before you reach for your calculators, consider
Modern cryptography solved this problem via public key that the last RSA challenge to be broken was
encryption, using a public key (shared with the receiver) RSA-200 in 2005. The computer power involved
to encode the message and a different private key to in factoring this 200 digit number was the
decode the message. Public key encryption is expensive equivalent of a high-end desktop running 24
(in terms of processing cost) so it is normally used to hours a day for 70 years. This revealed the key
solve the key exchange problem and create a secure used for just one message.
channel, which is used for all future communication.
Source: RSA.com, March 2008
Most IT cryptographic solutions used today are
underpinned by public key encryption. When you logon
to your online banking service, enter your payment details
into a website, retrieve a balance from an ATM or use
Chip and Pin at a supermarket, public key encryption will
have been used to establish the secure channel.

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