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Securing messages against prying eyes

We’ve all had those occasional texts cautioning us against sending confidential e-mails since these may be opened before being delivered. It’s actually possible that your texts and private messages might be read before they’re passed on to the final destination! But Prof. Navin Kashyap and his Code Design and Analysis (CoDA) team at the Indian Institute of Science assure us that there’s nothing to worry about.

Today, we take wireless communication for granted. From the advent of smartphones to 4G  enabled ones, there are a number of challenges that engineers face while modelling a wireless channel. Noise and interference that distort the transmitted signal are common challenges, making it all the more important to work on information security.

“Our cellphones, laptops, wifi access points, cellular base stations, are all "nodes" in huge wireless networks,” explains Shashank, Prof. Kashyap’s student.

The base station is like the mediator between your mobile phone and numerous others. It acts as the “intermediate node” between one mobile unit and another. Such intermediate nodes are called relays.

It’s rather unsettling to know that the base station can listen to the messages that are transmitted. The CoDA lab is making strides in securing relays from unauthorized use and protecting our communication. The lab is working on securing the ‘compute-and-forward’ strategy used in the transmission of messages. The team proposes the use of a coding scheme called “nested lattice codes”, for providing security in the presence of untrusted relays. ‘Untrusted’ relays, as the name suggests, can be of two types: one that delivers your message faithfully but reads the contents beforehand; the other that steals or changes the content of the message. The former is called “honest-but-curious” relay. “This means that the relay would honestly deliver your email to the intended destination, but may open it and read it (hence, the term "curious") before delivering it,” explains Prof. Navin Kashyap.

The lab is also working on different types of encryption techniques. Encryption offers a secure form of communication where only authorized users can read messages. In asymmetric encryption, a public key is used to encrypt a message and a ‘secret key’ is used to decrypt it. So it’s impossible to know what’s in an encrypted file or a message if you don’t have both the keys. However, there is a bit of a problem when you want to share this secret key with a select number of people. Transmitting private data to different receivers or terminals first requires ‘public communication’.

“The legitimate parties agree upon a common bit string, call it K, using communication over an insecure public channel. Being insecure and public, the communication could be observed by an eavesdropper. The communication must therefore be such that the eavesdropper is not able to infer anything about the common bit string K”, explains Prof. Kashyap.

The maximum ‘rate’ of a secret key is defined as the largest length of the bit string that can be used in a particular group of terminals. It’s important to keep the communication between parties minimum in order to save battery power since these terminals are usually remotely located. The minimum total amount of communication, measured in terms of bits transmitted, required in order to generate a maximal-rate secret key is termed as the communication complexity. The team has managed to find good estimates of this communication complexity, while still giving us a maximal-rate secret key.

“Our more recent work has focused on making these protocols more practical, more computationally efficient. We have developed polynomial-time algorithms for secure and reliable communication using these nested lattice codes,” says Shashank.

The CoDA lab is striving to keep our messages off prying eyes and their breakthrough research enables a better and secure means of communication over an insecure, public channel. Here is wishing the team good luck for their future endeavors!

Navin Kashyap is an Associate Professor in the Department of Electrical Communication Engineering, Indian Institute of Science. He can be contacted at +91-80-2293 3385