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/*
* (C) 2015,2016 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include "fuzzers.h"
#include <botan/numthry.h>
namespace {
Botan::BigInt inverse_mod_ref(const Botan::BigInt& n, const Botan::BigInt& mod)
{
if(n == 0)
return 0;
Botan::BigInt u = mod, v = n;
Botan::BigInt B = 0, D = 1;
while(u.is_nonzero())
{
const size_t u_zero_bits = low_zero_bits(u);
u >>= u_zero_bits;
for(size_t i = 0; i != u_zero_bits; ++i)
{
//B.cond_sub(B.is_odd(), mod);
if(B.is_odd())
{ B -= mod; }
B >>= 1;
}
const size_t v_zero_bits = low_zero_bits(v);
v >>= v_zero_bits;
for(size_t i = 0; i != v_zero_bits; ++i)
{
if(D.is_odd())
{ D -= mod; }
D >>= 1;
}
if(u >= v) { u -= v; B -= D; }
else { v -= u; D -= B; }
}
if(v != 1)
return 0; // no modular inverse
while(D.is_negative()) D += mod;
while(D >= mod) D -= mod;
return D;
}
}
void fuzz(const uint8_t in[], size_t len)
{
if(len % 2 == 1 || len > 2*4096/8)
return;
const Botan::BigInt x = Botan::BigInt::decode(in, len / 2);
Botan::BigInt mod = Botan::BigInt::decode(in + len / 2, len / 2);
mod.set_bit(0);
if(mod < 3 || x >= mod)
return;
Botan::BigInt ref = inverse_mod_ref(x, mod);
Botan::BigInt ct = Botan::ct_inverse_mod_odd_modulus(x, mod);
//Botan::BigInt mon = Botan::normalized_montgomery_inverse(x, mod);
if(ref != ct)
{
FUZZER_WRITE_AND_CRASH("X = " << x << "\n"
<< "P = " << mod << "\n"
<< "GCD = " << gcd(x, mod) << "\n"
<< "Ref = " << ref << "\n"
<< "CT = " << ct << "\n"
<< "RefCheck = " << (ref*ref)%mod << "\n"
<< "CTCheck = " << (ct*ct)%mod << "\n");
}
}
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