/*
* PKCS1 Pad Operation
*/
secure_vector<byte> EME_PKCS1v15::pad(const byte in[], size_t inlen,
size_t olen,
RandomNumberGenerator& rng) const
{
olen /= 8;
if(olen < 10)
throw Encoding_Error("PKCS1: Output space too small");
if(inlen > olen - 10)
throw Encoding_Error("PKCS1: Input is too large");
secure_vector<byte> out(olen);
out[0] = 0x02;
for(size_t j = 1; j != olen - inlen - 1; ++j)
while(out[j] == 0)
out[j] = rng.next_byte();
buffer_insert(out, olen - inlen, in, inlen);
return out;
}
/*
* Generate a random prime
*/
BigInt random_prime(RandomNumberGenerator& rng,
u32bit bits, const BigInt& coprime,
u32bit equiv, u32bit modulo)
{
if(bits <= 1)
throw Invalid_Argument("random_prime: Can't make a prime of " +
to_string(bits) + " bits");
else if(bits == 2)
return ((rng.next_byte() % 2) ? 2 : 3);
else if(bits == 3)
return ((rng.next_byte() % 2) ? 5 : 7);
else if(bits == 4)
return ((rng.next_byte() % 2) ? 11 : 13);
if(coprime <= 0)
throw Invalid_Argument("random_prime: coprime must be > 0");
if(modulo % 2 == 1 || modulo == 0)
throw Invalid_Argument("random_prime: Invalid modulo value");
if(equiv >= modulo || equiv % 2 == 0)
throw Invalid_Argument("random_prime: equiv must be < modulo, and odd");
while(true)
{
BigInt p(rng, bits);
p.set_bit(bits - 2);
p.set_bit(0);
if(p % modulo != equiv)
p += (modulo - p % modulo) + equiv;
const u32bit sieve_size = std::min(bits / 2, PRIME_TABLE_SIZE);
SecureVector<u32bit> sieve(sieve_size);
for(u32bit j = 0; j != sieve.size(); ++j)
sieve[j] = p % PRIMES[j];
u32bit counter = 0;
while(true)
{
if(counter == 4096 || p.bits() > bits)
break;
bool passes_sieve = true;
++counter;
p += modulo;
if(p.bits() > bits)
break;
for(u32bit j = 0; j != sieve.size(); ++j)
{
sieve[j] = (sieve[j] + modulo) % PRIMES[j];
if(sieve[j] == 0)
passes_sieve = false;
}
if(!passes_sieve || gcd(p - 1, coprime) != 1)
continue;
if(passes_mr_tests(rng, p))
return p;
}
}
}
PointGFp Blinded_Point_Multiply::blinded_multiply(const BigInt& scalar_in,
RandomNumberGenerator& rng)
{
if(scalar_in.is_negative())
throw std::invalid_argument("Blinded_Point_Multiply scalar must be positive");
#if BOTAN_POINTGFP_SCALAR_BLINDING_BITS > 0
// Choose a small mask m and use k' = k + m*order (Coron's 1st countermeasure)
const BigInt mask(rng, BOTAN_POINTGFP_SCALAR_BLINDING_BITS, false);
const BigInt scalar = scalar_in + m_order * mask;
#else
const BigInt& scalar = scalar_in;
#endif
const size_t scalar_bits = scalar.bits();
// Randomize each point representation (Coron's 3rd countermeasure)
for(size_t i = 0; i != m_U.size(); ++i)
m_U[i].randomize_repr(rng);
#if BOTAN_POINTGFP_BLINDED_MULTIPLY_USE_MONTGOMERY_LADDER
PointGFp R = m_U.at(3*m_h + 2); // base point
int32_t alpha = 0;
R.randomize_repr(rng);
/*
Algorithm 7 from "Randomizing the Montgomery Powering Ladder"
Duc-Phong Le, Chik How Tan and Michael Tunstall
http://eprint.iacr.org/2015/657
It takes a random walk through (a subset of) the set of addition
chains that end in k.
*/
for(size_t i = scalar_bits; i > 0; i--)
{
const int32_t ki = scalar.get_bit(i);
// choose gamma from -h,...,h
const int32_t gamma = static_cast<int32_t>((rng.next_byte() % (2*m_h))) - m_h;
const int32_t l = gamma - 2*alpha + ki - (ki ^ 1);
R.mult2(m_ws);
R.add(m_U.at(3*m_h + 1 + l), m_ws);
alpha = gamma;
}
const int32_t k0 = scalar.get_bit(0);
R.add(m_U[3*m_h + 1 - alpha - (k0 ^ 1)], m_ws);
#else
// N-bit windowing exponentiation:
size_t windows = round_up(scalar_bits, m_h) / m_h;
PointGFp R = m_U[0];
if(windows > 0)
{
windows--;
const u32bit nibble = scalar.get_substring(windows*m_h, m_h);
R.add(m_U[nibble], m_ws);
/*
Randomize after adding the first nibble as before the addition R
is zero, and we cannot effectively randomize the point
representation of the zero point.
*/
R.randomize_repr(rng);
while(windows)
{
for(size_t i = 0; i != m_h; ++i)
R.mult2(m_ws);
const u32bit nibble = scalar.get_substring((windows-1)*m_h, m_h);
R.add(m_U[nibble], m_ws);
windows--;
}
}
#endif
//BOTAN_ASSERT(R.on_the_curve(), "Output is on the curve");
return R;
}
