Mumbai, Oct 6: Telephone tapping is done under strict authorisation, according to the Mahanagar Telephone Nigam Ltd (MTNL. However, legal luminary Nani Palkivala says that except in the interest of the state or public, phones cannot be tapped.

Telephones can be tapped or monitored only by investigating agencies such as the Central Bureau of Investigation (CBI), Intelligence Bureau (IB), Central Economic Intelligence Bureau (CEIB), Directorate of Revenue Intelligence (DRI), Enforcement Directorate (ED) and the Research & Analysis Wing (RAW).

These agencies, in turn, need to get prior approval from the courts. Permission for tapping or monitoring is only for a particular period of time decided by the courts.

Tapping of telephones is not restricted only to MTNL or the Department of Telecommunication (DoT). Investigating agencies can also monitor or tap cellular phones, which are operated by private service providers.

Even private basic service providers on commencement of operations will have to adhere to the same rules and regulations that are applicable to MTNL.

Telephones are tapped at the exchange, which routes all the calls. A parallel line is drawn from the switch which routes all the calls and the conversations are recorded. However, in case of a mobile , tapping is done from two ends depending on where the call is headed.

In case of a call from a mobile phone to a land line, the calls are tapped at the exchange end. But in case of a call between two mobile phones, monitoring becomes difficult as the voice is continously encrypted.

Calls, even when tapped, cannot be heard till the time they are not decoded. The calls are decoded using special keys, which are provided by mobile phone operators. Even if a telephone is being tapped, by attaching some devices to the instrument, it can be made redundant.

One such device, Secraphone, can be attached to the instrument which encodes the voice before it goes to the exchange.

However, a similar device would be needed at the receiving end to decode the encrypted voice. But Secraphone is not freely available. Its usage has to be authorised by the government and the device is issued by DoT. MTNL sources say it is restricted to top government officials .such as the prime minister or the president.

Copyright © 1997 Indian Express Newspapers (Bombay) Ltd.