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Communications of the ACM


Future-Proof Encryption

Norbert Ltkenhaus of the University of Waterloo

Norbert Ltkenhaus, associate professor in the physics department at the University of Waterloo and a member of the Institute for Quantum Computing (IQC), is involved in research on the theory of practical quantum key distribution systems.

Credit: The Institute for Quantum Computing

This summer, the controversial former National Security Agency (NSA) analyst Edward Snowden answered a series of security-related questions in an online forum hosted by the Guardian newspaper. One worried reader asked if there was any way to hide email from the inquisitive eyes of the NSA. Snowden replied, in brief: "Encryption works. Properly implemented strong crypto systems are one of the few things you can rely on."

When these systems fail, the cause is typically human error—someone installing malware on their machine, for example—and not the result of a fundamental flaw. Yet researchers say this will not remain true if quantum computers, machines with exponentially more processing power than today's technology, become a reality. "It is reasonably clear that the classical encryption methods we are using today are going to become insecure in the long term," says physicist Vadim Makarov of the Institute for Quantum Computing at the University of Waterloo. "Once the technology to crack classical encryption becomes available in the future, all the secrets become compromised retroactively. This is just not acceptable for many kinds of secrets, like medical, political, military secrets, which have very long-term value."


K.R. Chowdhary

The article very clearly indicates that present Internet security, which is based on factoring of large numbers, is not sustainable as processors are becoming more and more powerful. As we note the trend, the DES (digital encryption standard) -- a 54 bit symmetric cryptography, orginally developed by IBM -- is no more secure. The RSA security, which is based on large prime numbers, where for breaking it one need to first generate the other prime number, by the processes of factoring. And, for factoring there is no efficient algorithm exists yet, and this is the strength of RSA. However, the RSA can be easily broken at least for not too large prime number based keys; either by running a powerful system for a long time, or by connecting many PCs in parallel, and sharing the work of generating prime numbers and attempting to crack the RSA key.

RSA has one fundamental weakness; if encrypted information while in transmission is copied in an intermediate station through eavesdropping, the packets are not able to sense that they have been copied. This copied information can be attempted to dug up later, to find out the contents.

However, in case of quantum cryptography, which is based on photons, you cannot copy the photons, at the middle station; in fact you can only steal some photons, which will result to tempering in the message (photons, and their counts, spins, etc.), and this will be detected at the destination easily.

Another important point about this article is that it talks about the information while in transmission, which can be in the form of photons, for quantum cryptography. But, it appears that a vast amount of information, which remains stored in media, if required to be secured, the conventional cryptography will continue to prevail. Because, photons cannot be stored. Hence, it requires to strengthen the existing RSA cryptography, as well as, and to investigate new methods to encrypt the stored information.

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