Researchers Successfully Eavesdrop On Quantum Encrypted Communications
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A team of quantum cryptography researchers from Singapore and Norway have managed to eavesdrop on a communication that was encrypted by quantum key distribution (QKD) without being detected.
QKD is one variety of quantum cryptography, and is probably the most well known. In a nutshell, a communication encrypted by QKD is one where both the sender (known in the literature as “Alice”) and the receiver (“Bob”). Like the most common encryption protocol used today, public-key encryption, QKD relies on electronic “keys” to decrypt messages sent back and forth between Alice and Bob. In public-key encryption, the keys are very large prime numbers, which are difficult to current computers to calculate and determine through brute force.
In QKD, the key is actually in the form of stream of photons, where each photon consists of one bit of information about the key, depending on the photon’s state. In theory, this would prevent an eavesdropper (“Eve”) from breaking into the communication, because the very act of Eve trying to measure the state of the photons will actually change their state. That change would enable Bob and Alice to know that Eve was trying to listen in on their conversation, and also prevent Eve from obtaining the complete key.
In practice, however, this has turned out to be more difficult, due to the physical limitations of a QKD system. This has enabled several successful attacks on QKD systems, including the ability of Eve to obtain the key and listen to the communications. However, all of these methods still introduce some errors into the communcations and key receptions, meaning that it’s possible for Alice and Bob to notice the eavesdropping and act accordingly.
The researchers at the University of Singapore, however, have managed to go one step further — they’ve developed a method of producing a full exploit of a QKD system that allows for Eve to eavedrop on Alice’s and Bob’s communication — without introducing enough errors to allow her to be detected. Her eavesdropping appeared to be no different from the random background errors that are inevitable in the physical implementation of a QKD system.
Although the researchers were able to infiltrate this system with basically off-the-shelf parts, it’s worth noting that this exploit doesn’t mean that QKD isn’t a viable method of encryption. The researchers themselves suggest several countermeasures, and no doubt other countermeasures will be developed as this research continues. As the researchers themselves note: ”a more pointed question is what problems still lurk unnoticed in the gap between the theoretical description and the practical systems. Just as in classical cryptography, an ongoing search for backdoors is required to build hardened implementations of quantum cryptography for real-world use.”
Quantum cryptography is still in its infancy, but it’s still more than likely the future of encrypted communications once its been further refined and developed.
By on 27/06/2011