// The vote is stored as {number of voters + 1}^{# of candidate - 1}.

paillier_plaintext_t* ptVote = paillier_plaintext_from_ui(numVotersPlusOne);

mpz_pow_ui(ptVote->m, ptVote->m, zCandidate - 1);

// Encrypt the vote.

paillier_ciphertext_t* ctVote = paillier_enc(NULL, pub, ptVote, paillier_get_rand_devurandom);

os << "BEGIN:ENVELOPE\nBEGIN:BALLOT\n" << ciphertext_base64(ctVote) << "END:BALLOT" << endl;

paillier_freeplaintext(ptVote);

// The backwards vote is {number of voters + 1}^({number of candidates} - {# of candidate}).

paillier_plaintext_t* ptVoteReversed = paillier_plaintext_from_ui(numVotersPlusOne);

mpz_pow_ui(ptVoteReversed->m, ptVoteReversed->m, numCandidates - zCandidate);

// Encrypt the backwards vote.

paillier_ciphertext_t* ctVoteReversed = paillier_enc(NULL, pub, ptVoteReversed, paillier_get_rand_devurandom);

os << "BEGIN:RBALLOT\n" << ciphertext_base64(ctVoteReversed) << "END:RBALLOT" << endl;

paillier_freeplaintext(ptVoteReversed);

paillier_freeciphertext(ctVoteReversed);

// Get the SHA-256 sum of the ciphertext.

mpz_t checksum;

ciphertext_sha256(checksum, ctVote);

paillier_freeciphertext(ctVote);

// Create an authenticity value, which is the voter token bitshifted 256 bits to the left + the SHA-256 sum.

paillier_plaintext_t* ptAuthentic = paillier_plaintext_from_ui(0);

mpz_mul_2exp(ptAuthentic->m, zVoterToken, 256);

mpz_add(ptAuthentic->m, ptAuthentic->m, checksum);

mpz_clear(checksum);

// Encrypt the authenticity value.

paillier_ciphertext_t* ctAuthentic = paillier_enc(NULL, pub, ptAuthentic, paillier_get_rand_devurandom);

os << "BEGIN:MAC\n" << ciphertext_base64(ctAuthentic) << "END:MAC\nEND:ENVELOPE" << endl;

paillier_freeplaintext(ptAuthentic);

paillier_freeciphertext(ctAuthentic);

cout << "Welcome! ";

// Read the public key from a file.

string electionName, electionEmailAddress;

int numCandidates, numVotersPlusOne;

paillier_pubkey_t* pub;

if(!read_pubkey_from_file(numCandidates, numVotersPlusOne, &pub, electionName, electionEmailAddress)){

cerr << "The public key file is missing or corrupt.\n";

return 2;

}

cout << "You are voting in the election: " << electionName << '\n' << endl;

// Prompt the user for the voter token. The token should be represented as a base 10 number.

// There may be dashes every few digits to make it easier for the user to enter, but they

// will be removed from the string here.

string strVoterToken;

cout << "Please enter your voter ID code (dashes optional):\n>>> ";

cout.flush();

getline(cin, strVoterToken);

cout << '\n';

// Remove hyphens from the voter token.

if(!sanitize_voter_token(strVoterToken)){

// Non-numeric characters, other than hyphens, were found!

cerr << "The voter ID code should contain numbers only. Hyphens are acceptable but ignored.\n";

return 3;

}

// Convert the base 10 string into a GMP integer.

mpz_t zVoterToken;

if(mpz_init_set_str(zVoterToken, strVoterToken.c_str(), 10) == -1){

cerr << "Fatal error: the integer parsing failed.\n";

return 4;

}

// Make sure that the token is at most TOKEN_LENGTH bits long.

if(mpz_sizeinbase(zVoterToken, 2) > TOKEN_LENGTH){

cerr << "Error: That token seems to be too big.\n";

return 5;

}

cout << "Your token was successfully verified to be a number. Note that this program does not check whether your token was\n"

<< "actually issued by the election authority. Once your vote is submitted, the election authority should send you a\n"

<< "confirmation. If you do not receive a confirmation, please contact the election authority.\n";

// Prompt the user to choose a candidate.

char confirmation;

int zCandidate;

do {

cout << '\n'

<< "Please pick a candidate between 1 and " << numCandidates << ", inclusive. If you do not know who the candidates are, please contact\n"

<< "your election authority.\n"

<< "Enter the number of the candidate that you want to vote for: ";

cout.flush();

cin >> zCandidate;

if(0 < zCandidate && zCandidate <= numCandidates){

cout << "You picked candidate " << zCandidate << ". Are you sure? (Y/N): ";

cout.flush();

cin >> confirmation;

}else{

cout << "That was not one of the choices.\n";

confirmation = 'n';

}

while(cin.get() != '\n');

}while(confirmation != 'y' && confirmation != 'Y');

cout << '\n';

// Open a file for writing the encrypted ballot and authenticity value.

ofstream ofsEmail(EMAIL_TXT);

if(ofsEmail){

ofsEmail << "Subject: Vote: " << electionName << "\n\n";

print_envelope(ofsEmail, numCandidates, numVotersPlusOne, zCandidate, zVoterToken, pub);

ofsEmail.close();

cout << "Your vote was successfully encrypted. To send your vote, run the following command:\n"

<< " ssmtp " << electionEmailAddress << " <" << EMAIL_TXT << endl;

}else{

cout << "A text file could not be created in the current directory!\n"

<< "You can manually send your vote via e-mail. Just send the following contents to " << electionEmailAddress << ".\n"

<< "Use \"Vote: " << electionName << "\" as the subject.\n\n";

print_envelope(cout, numCandidates, numVotersPlusOne, zCandidate, zVoterToken, pub);

}

// Clean up.

// TODO: also clean up when something fails above

mpz_clear(zVoterToken);

paillier_freepubkey(pub);

return 0;