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/*
* (C) 2015,2016 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include "driver.h"
#include <botan/numthry.h>
void fuzz(const uint8_t in[], size_t len)
{
/*
* This allows two values (a,p) up to 768 bits in length, which is
* sufficient to test ressol (modular square root) for since it is
* mostly used for ECC.
*/
if(len % 2 != 0 || len > 2 * (768 / 8))
return;
const BigInt a = BigInt::decode(in, len / 2);
const BigInt n = BigInt::decode(in + len / 2, len / 2);
try {
BigInt a_sqrt = ressol(a, n);
if(a_sqrt > 0)
{
/*
* If n is not prime then the result of ressol will be bogus. But
* this function is exposed to untrusted inputs (via OS2ECP) so
* should not hang or crash even with composite modulus.
* If the result is incorrect, check if n is a prime: if it is
* then z != a is a bug.
*/
BigInt z = (a_sqrt * a_sqrt) % n;
BigInt a_redc = a % n;
if(z != a_redc)
{
if(is_prime(n, fuzzer_rng(), 64))
{
std::cout << "A = " << a << "\n";
std::cout << "N = " << n << "\n";
std::cout << "Ressol = " << a_sqrt << "\n";
std::cout << "recomputed = " << z << "\n";
abort();
}
}
}
}
catch(Botan::Exception& e) {}
return;
}
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