| RESEARCH HIGHLIGHTS |


between the phosphorene atoms will break and an alloy may form.” The researchers compared the effect of


two different substrates on the growth of the phosphorene nanoflake — a copper substrate, commonly used for growing graphene, which bonds with the phosphorene through strong chemical processes, and a hexagonal hydrogen


boron nitride (h-BN) substrate that couples with the phosphorene via weak van der Waals bonds. The copper substrate caused the nanoflake


to break, whereas the h-BN was unable to stabilize its flat structure. By boosting the strength of the bonding between the nanoflake and the h-BN substrate, their simulations showed that the 2D growth of the


phosphorene was maintained. “Our work is the first attempt to explore the direct growth of phosphorene and provides guidance in the search for suitable substrates,” says Gao.


1. Gao, J., Zhang, G., Zhang, Y.-W. The critical role of substrate in stabilizing phosphorene nanoflake: A theoretical exploration. Journal of the American Chemical Society 138, 4763–4771 (2016).


Cyber security:


WEAKNESS OF 2G MOBILE PHONE NETWORKS REVEALED


A FAST AND RELATIVELY SIMPLE ATTACK ON SECOND GENERATION DIGITAL MOBILE PHONE COMMUNICATIONS HIGHLIGHTS THE NEED TO UPDATE SECURITY ON OLDER MOBILE NETWORKS


The encryption scheme used for second generation (2G) mobile phone data can be hacked within seconds by exploiting weak- nesses and using common hardware, A*STAR researchers show. The ease of the attack shows an urgent need for the 2G Global System for Mobile Communications (GSM) encryption scheme to be updated. GSM was first deployed 25 years ago and


has since become the global standard for mobile communications, used in nearly every country and comprising more than 90 per cent of the global user base. “GSM uses an encryption scheme called


the A5/1 stream cipher to protect data,” explains Jiqiang Lu from the A*STAR


40 A*STAR RESEARCH


Institute for Infocomm Research. “A5/1 uses a 64-bit secret key and a complex keystream generator to make it resistant to elementary attacks such as exhaustive key searches and dictionary attacks.” Any encryption scheme can be hacked


given sufficient time and data, so security engineers usually try to create an encryption scheme that would demand an unfeasible amount of time to crack. But, as GSM gets older, weaknesses in the A5/1 cipher and advances in technology have rendered GSM communications susceptible to attack. Straightforward ‘brute force’ attacks by


guessing the secret key from the data stream are still intensively time consuming, and


A*STAR researchers have shown that the 2G GSM encryption scheme can be hacked within seconds and urgently needs to be updated.


although A5/1 was reported to have been successfully attacked in 2010, the details of the attack were kept secret. By exploiting weaknesses in the A5/1 cipher, Lu and his colleagues have now demonstrated the first real-time attack using a relatively small amount of data. “We used a rainbow table, which is


constructed iteratively offline as a set of chains relating the secret key to the cipher output,” says Lu. “When an output is received during an attack, the attacker identifies the relevant chain in the rainbow table and regenerates it, which gives a result that is very likely to be the secret key of the cipher.”


ISSUE 5 | OCTOBER – DECEMBER 2016


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