function ElG_KeyGen($lambda, $r)
{
//Generate the proper parameter q, with |q| >= lambda
//The idea is to take the minimum q just above 2^lambda
$powlambda = pow(2, $lambda);
$max_retries = 5;
$i = 0;
do {
$safe_primes = get_safe_primes($powlambda * pow(2, 1 + $i) * $r, $r);
$nb_safe_primes = count($safe_primes);
if ($nb_safe_primes == 0 || $safe_primes[$nb_safe_primes - 1][1] < $powlambda) {
$q = 0;
} else {
if ($nb_safe_primes == 1) {
$q = $safe_primes[0][1];
} else {
$candidate_q = $safe_primes[$nb_safe_primes - 1][1];
$j = 1;
while ($candidate_q > $powlambda) {
$candidate_q = $safe_primes[$nb_safe_primes - $j - 1][1];
$j++;
}
$q = $safe_primes[$nb_safe_primes - $j + 1][1];
}
}
$i++;
} while ($q < $powlambda && $i < $max_retries);
//If no possible q was found, return false
if ($i == $max_retries) {
if (_DEBUG >= 1) {
echo "KeyGen : impossible to find a suitable q for lambda = {$lambda} and r = {$r}. Aborting key generation.\n";
}
return false;
}
return ElG_KeyGen_alt($r, $q);
}
}
if ($INIT_ROUTE) {
echo "Route initialization";
}
echo " on {$limit} sets of parameters. All is OK !\n";
echo "Mean time for route proposition : ", 1000 * $total_time_prop_route / $limit, "ms, mean time for route initialization: ", 1000 * $total_time_init_route / $limit, "ms \n\n";
}
if ($TIMINGS_ELGAMAL) {
echo "Measuring running times of ElGamal primitives and homomorphic operations...\n";
$limit = 1000;
$cumul = array("keygen" => 0, "enc" => 0, "dec" => 0, "mult" => 0, "plainmult" => 0, "scexp" => 0, "rerand" => 0);
$keys = ElG_KeyGen($lambda, $r);
$q = $keys["pk"]["group"]["order"];
for ($i = 0; $i < $limit; $i++) {
$begin_time = microtime(true);
$keys = ElG_KeyGen_alt($r, $q);
if ($keys == false) {
echo "Error at key generation...";
exit;
}
$end_time = microtime(true);
$cumul["keygen"] += 1000 * ($end_time - $begin_time);
list($pk, $sk) = array_values($keys);
$group = $pk["group"];
$a = $group["G"][array_rand($group["G"])];
$b = $group["G"][array_rand($group["G"])];
$begin_time = microtime(true);
$ca = ElG_Enc($a, $pk);
$end_time = microtime(true);
$cumul["enc"] += 1000 * ($end_time - $begin_time);
$begin_time = microtime(true);
