The suspicion surrounding the Electronic Voting Machines (EVMs) was heightened when mock polling was conducted in Kasaragod on April 17.

Agents of the Congress and CPM candidates complained that four of the 190 EVMs tested had reportedly given extra votes to the BJP's lotus symbol. Even when the BJP symbol was not pressed, it was said that the Voter Verifiable Paper Audit Trial (VVPAT) units of these four EVMs gave one vote to the party. When the lotus symbol was pressed, the charge was that the VVPATs of these four EVMs gave the BJP candidate two votes.

After the Supreme Court asked the Election Commission of India to verify, the ECI submitted that the allegations of EVMs throwing up extra votes for the BJP were false. Later, Kerala's chief electoral officer Sanjay Kaul too put out a statement terming the allegations "baseless". He said the twin VVPAT slip that caused confusion during the mock poll was nothing but the VVPAT slip that was not printed during the preliminary check. On the slip, it was also printed "not to be counted".

Yet, if doubt persists, there are reasons. The ECI has not been able to offer convincing answers for various EVM-related issues. For instance, the discrepancies in the votes polled data on the EVMs and the votes counted data on EVMs in over 373 constituencies; in four cases, the difference was over 10,000 votes. The ECI has also not been able to account for the missing of nearly 20 lakh EVMs.

What is the design of an EVM?
The EVM is not a monolithic unit. It has three components. The Ballot Unit (BU), on which the names and symbols of the candidates are given and on which the voter presses her choice. The Control Unit (CU) receives the vote and is placed on the presiding officer’s desk. The CU is connected to the Voter Verifiable Paper Audit Trail (VVPAT) printer, which is then connected to the BU.

The VVPAT prints the symbol that a voter has pressed. VVPAT has a transparent glass screen that shows the printed paper slip having the name, serial number and election symbol of the chosen candidate. The slip can be seen through the screen for seven seconds.

The EVM is not connected to wi-fi, Bluetooth or even to the internet. And so, the ECI argues that it would be foolish to believe that the EVM could be remotely controlled.

Can EVMs be hacked or manipulated?
Since Indian EVMs are standalone devices unconnected to units outside the system, a large number of experts have ruled out the possibility of hacking or control from remote locations.

Nonetheless, manipulation has not been ruled out. This possibility stems from the peculiar design of the EVM unit. The BU is not directly connected to the CU. It is linked to the CU through the VVPAT.

Meaning, a voter's choice made on the BU is not directly received by the CU. It goes through the VVPAT before reaching the CU. However, the ECI disputes the observation of civil rights activists and election integrity experts. According to the Commission, it is the CU that communicates with both the BU and the VVPAT. The ECI says that when a voter presses a candidate button on the BU, the BU sends the button number to the CU, contradicting the view of activists, and the CU in turn communicates with the VVPAT to print the slip.

However, experts like Madhav Deshpande, a computer scientist who had worked for the Obama administration, and even former civil servants like Kannan Gopinathan say that it is theoretically possible to rig the VVPAT unit to alter the voter's choice before it reaches the CU.

The VVPAT is said to be the weakest link in the EVM ecosystem. The BU and CU are location blind and are not fed details of candidates; they are randomised at least three times before reaching the booth. Not so with the VVPAT. It is location-specific and is fed candidate info from external devices.

How can EVMs be manipulated?
Candidate-specific data is uploaded in the VVPAT using the Symbol Upload Module (SUM) a fortnight before the polls. For this, ECI-authorised engineers will connect to the ECI website, download into their laptop the specific SUM for the constituency in which they are going to operate, and then connect this laptop to the VVPAT to upload candidate data. Incidentally, this uploading process using external devices contradicts the ECI claim that the EVM is a standalone unit.

The VVPAT has a customised programme written specifically to recognise the signals (votes) that come from the ballot unit so that it can print the information on a paper trail. Experts say that this VVPAT programme can be bugged to make the VVPAT adulterate the voter's choice.

The VVPAT has been fed various data sets - names of candidates, their symbols and party names - in its programme code. It is possible to contaminate this code by providing additional information, say an asterisk or a hash sign, for the candidate to be favoured, say Candidate A. By using this additional data, the code can be tweaked in such a way that the VVPAT is prompted to read every third or fifth or seventh vote as made for A even if it was actually for B or C.

Is VVPAT truly voter-verifiable?
The Indian VVPAT system does not allow the voter to verify the slip before the vote is cast.

The correct VVPAT protocol, according to election integrity researchers, has three steps. One, it allows a voter to approve the VVPAT slip before the vote is cast. Two, it allows the voter to cancel her vote if there is a discrepancy. And three, it allows the voter to vote from another machine.

None of the three rights are granted to an Indian voter.

How many EVMs are crosschecked with VVPATs?
The Supreme Court has said that five EVMs per Assembly constituency should be crosschecked. This translates to 20,625 EVMs across the country. Nearly 11 lakh EVMs are used in a general election. There was clamour for at least 50 per cent by civil society activists but the apex court ruled that it was not necessary.

Before the SC order, the ECI had concluded that only 479 EVMs needed to be tallied with VVPATs to detect problematic EVMs. This was based on a study by the Indian Statistical Institute, Delhi. This was less than one EVM per Lok Sabha constituency, forget Assembly constituencies.

It has also been argued that auditing a fixed number of EVMs per constituency is not sufficient to verify elections with narrow margins.