Posts tagged: Eavesdropping

Dec 25 2013

4096-bit RSA Key Extraction Attack via Acoustic Cryptanalysis

A trio of scientists have verified that results they first presented nearly 10 years ago are in fact valid, proving that they can extract a 4096-bit RSA key from a laptop using an acoustic side-channel attack that enables them to record the noise coming from the laptop during decryption, using a smartphone placed nearby. The attack, laid out in a new paper, can be used to reveal a large RSA key in less than an hour.

Acoustic Cryptanalysis
Parabolic microphone extracting an RSA key from a target laptop

The attack relies on a number of factors, including proximity to the machine performing the decryption operation and being able to develop chosen ciphertexts that incite certain observable numerical cancellations in the GnuPG algorithm. Over several thousand repetitions of the algorithm’s operation, the researchers discovered that there was sound leakage they could record over the course of fractions of a second and interpret, resulting in the discovery of the RSA key in use.

Their attack works against a number of laptop models and they said that there are a number of ways that they could implement it, including through a malicious smartphone app running on a device near a target machine. They could also implement it through software on a compromised mobile device of through the kind of eavesdropping bugs used by intelligence agencies and private investigators.

The developers of GnuPG have developed a patch for the vulnerability that the Israeli researchers used, implementing a technique known as blinding. The patch is included in version 1.4.16 of GnuPG. Shamir and his co-authors, Daniel Genkin and Eran Tromer, said that they also could perform their attack from a greater distance using a parabolic microphone and may also work with a laser microphone or vibrometer.

Research Paper: RSA Key Extraction via Low-Bandwidth Acoustic Cryptanalysis

Jan 05 2011

Researchers hack GSM mobile calls

Researchers have demonstrated an alarmingly simple technique for eavesdropping on individual GSM mobile calls without the need to use expensive, specialised equipment.

During a session at the Chaos Computer Club Congress (CCC) in Berlin, Karsten Nohl and Sylvain Munaut used cheap Motorola handsets running a replacement firmware based on open source code to intercept data coming from a network base station.

Armed with this, they were able to locate the unique ID for any phone using this base, breaking the encryption keys with a rainbow table lookup.

Although far from trivial as hacks go, the new break does lower the bar considerably compared to previous hacks shown by the same reasearchers. In 2009, Nohl published a method for cracking open GSM’s A5/1 encryption design using a lookup table in near real time.

Another important detail is that Nohl was able to replace the firmware of the handsets with custom software. According to the BBC report on which most stories are being based, this was only possible because the Motorola handsets in question had been reverse engineered after an unspecified leak.

How easy would it be to exploit the new hack? In short, not particularly easy. Creating a custom lookup table similar to Nohl’s would take months of work and any eavesdropper would still need to break into the handset in question.

The crack does lower the bar from being a hardware problem to one of software expertise, which will cause some alarm in the GSM engineering community.

By John E Dunn,