?? nbtheory.cpp
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unsigned int trialDivisorBound = (unsigned int)STDMIN((unsigned long)primeTable[primeTableSize-1], (unsigned long)bits*bits/c_opt);
bool success = false;
while (!success)
{
p.Randomize(rng, I, I2, Integer::ANY);
p *= q; p <<= 1; ++p;
if (!TrialDivision(p, trialDivisorBound))
{
a.Randomize(rng, 2, p-1, Integer::ANY);
b = a_exp_b_mod_c(a, (p-1)/q, p);
success = (GCD(b-1, p) == 1) && (a_exp_b_mod_c(b, q, p) == 1);
}
}
}
return p;
}
Integer CRT(const Integer &xp, const Integer &p, const Integer &xq, const Integer &q, const Integer &u)
{
// isn't operator overloading great?
return p * (u * (xq-xp) % q) + xp;
}
Integer CRT(const Integer &xp, const Integer &p, const Integer &xq, const Integer &q)
{
return CRT(xp, p, xq, q, EuclideanMultiplicativeInverse(p, q));
}
Integer ModularSquareRoot(const Integer &a, const Integer &p)
{
if (p%4 == 3)
return a_exp_b_mod_c(a, (p+1)/4, p);
Integer q=p-1;
unsigned int r=0;
while (q.IsEven())
{
r++;
q >>= 1;
}
Integer n=2;
while (Jacobi(n, p) != -1)
++n;
Integer y = a_exp_b_mod_c(n, q, p);
Integer x = a_exp_b_mod_c(a, (q-1)/2, p);
Integer b = (x.Squared()%p)*a%p;
x = a*x%p;
Integer tempb, t;
while (b != 1)
{
unsigned m=0;
tempb = b;
do
{
m++;
b = b.Squared()%p;
if (m==r)
return Integer::Zero();
}
while (b != 1);
t = y;
for (unsigned i=0; i<r-m-1; i++)
t = t.Squared()%p;
y = t.Squared()%p;
r = m;
x = x*t%p;
b = tempb*y%p;
}
assert(x.Squared()%p == a);
return x;
}
bool SolveModularQuadraticEquation(Integer &r1, Integer &r2, const Integer &a, const Integer &b, const Integer &c, const Integer &p)
{
Integer D = (b.Squared() - 4*a*c) % p;
switch (Jacobi(D, p))
{
default:
assert(false); // not reached
return false;
case -1:
return false;
case 0:
r1 = r2 = (-b*(a+a).InverseMod(p)) % p;
assert(((r1.Squared()*a + r1*b + c) % p).IsZero());
return true;
case 1:
Integer s = ModularSquareRoot(D, p);
Integer t = (a+a).InverseMod(p);
r1 = (s-b)*t % p;
r2 = (-s-b)*t % p;
assert(((r1.Squared()*a + r1*b + c) % p).IsZero());
assert(((r2.Squared()*a + r2*b + c) % p).IsZero());
return true;
}
}
Integer ModularRoot(const Integer &a, const Integer &dp, const Integer &dq,
const Integer &p, const Integer &q, const Integer &u)
{
Integer p2 = ModularExponentiation((a % p), dp, p);
Integer q2 = ModularExponentiation((a % q), dq, q);
return CRT(p2, p, q2, q, u);
}
Integer ModularRoot(const Integer &a, const Integer &e,
const Integer &p, const Integer &q)
{
Integer dp = EuclideanMultiplicativeInverse(e, p-1);
Integer dq = EuclideanMultiplicativeInverse(e, q-1);
Integer u = EuclideanMultiplicativeInverse(p, q);
assert(!!dp && !!dq && !!u);
return ModularRoot(a, dp, dq, p, q, u);
}
/*
Integer GCDI(const Integer &x, const Integer &y)
{
Integer a=x, b=y;
unsigned k=0;
assert(!!a && !!b);
while (a[0]==0 && b[0]==0)
{
a >>= 1;
b >>= 1;
k++;
}
while (a[0]==0)
a >>= 1;
while (b[0]==0)
b >>= 1;
while (1)
{
switch (a.Compare(b))
{
case -1:
b -= a;
while (b[0]==0)
b >>= 1;
break;
case 0:
return (a <<= k);
case 1:
a -= b;
while (a[0]==0)
a >>= 1;
break;
default:
assert(false);
}
}
}
Integer EuclideanMultiplicativeInverse(const Integer &a, const Integer &b)
{
assert(b.Positive());
if (a.Negative())
return EuclideanMultiplicativeInverse(a%b, b);
if (b[0]==0)
{
if (!b || a[0]==0)
return Integer::Zero(); // no inverse
if (a==1)
return 1;
Integer u = EuclideanMultiplicativeInverse(b, a);
if (!u)
return Integer::Zero(); // no inverse
else
return (b*(a-u)+1)/a;
}
Integer u=1, d=a, v1=b, v3=b, t1, t3, b2=(b+1)>>1;
if (a[0])
{
t1 = Integer::Zero();
t3 = -b;
}
else
{
t1 = b2;
t3 = a>>1;
}
while (!!t3)
{
while (t3[0]==0)
{
t3 >>= 1;
if (t1[0]==0)
t1 >>= 1;
else
{
t1 >>= 1;
t1 += b2;
}
}
if (t3.Positive())
{
u = t1;
d = t3;
}
else
{
v1 = b-t1;
v3 = -t3;
}
t1 = u-v1;
t3 = d-v3;
if (t1.Negative())
t1 += b;
}
if (d==1)
return u;
else
return Integer::Zero(); // no inverse
}
*/
int Jacobi(const Integer &aIn, const Integer &bIn)
{
assert(bIn.IsOdd());
Integer b = bIn, a = aIn%bIn;
int result = 1;
while (!!a)
{
unsigned i=0;
while (a.GetBit(i)==0)
i++;
a>>=i;
if (i%2==1 && (b%8==3 || b%8==5))
result = -result;
if (a%4==3 && b%4==3)
result = -result;
std::swap(a, b);
a %= b;
}
return (b==1) ? result : 0;
}
Integer Lucas(const Integer &e, const Integer &pIn, const Integer &n)
{
unsigned i = e.BitCount();
if (i==0)
return Integer::Two();
MontgomeryRepresentation m(n);
Integer p=m.ConvertIn(pIn%n), two=m.ConvertIn(Integer::Two());
Integer v=p, v1=m.Subtract(m.Square(p), two);
i--;
while (i--)
{
if (e.GetBit(i))
{
// v = (v*v1 - p) % m;
v = m.Subtract(m.Multiply(v,v1), p);
// v1 = (v1*v1 - 2) % m;
v1 = m.Subtract(m.Square(v1), two);
}
else
{
// v1 = (v*v1 - p) % m;
v1 = m.Subtract(m.Multiply(v,v1), p);
// v = (v*v - 2) % m;
v = m.Subtract(m.Square(v), two);
}
}
return m.ConvertOut(v);
}
// This is Peter Montgomery's unpublished Lucas sequence evalutation algorithm.
// The total number of multiplies and squares used is less than the binary
// algorithm (see above). Unfortunately I can't get it to run as fast as
// the binary algorithm because of the extra overhead.
/*
Integer Lucas(const Integer &n, const Integer &P, const Integer &modulus)
{
if (!n)
return 2;
#define f(A, B, C) m.Subtract(m.Multiply(A, B), C)
#define X2(A) m.Subtract(m.Square(A), two)
#define X3(A) m.Multiply(A, m.Subtract(m.Square(A), three))
MontgomeryRepresentation m(modulus);
Integer two=m.ConvertIn(2), three=m.ConvertIn(3);
Integer A=m.ConvertIn(P), B, C, p, d=n, e, r, t, T, U;
while (d!=1)
{
p = d;
unsigned int b = WORD_BITS * p.WordCount();
Integer alpha = (Integer(5)<<(2*b-2)).SquareRoot() - Integer::Power2(b-1);
r = (p*alpha)>>b;
e = d-r;
B = A;
C = two;
d = r;
while (d!=e)
{
if (d<e)
{
swap(d, e);
swap(A, B);
}
unsigned int dm2 = d[0], em2 = e[0];
unsigned int dm3 = d%3, em3 = e%3;
// if ((dm6+em6)%3 == 0 && d <= e + (e>>2))
if ((dm3+em3==0 || dm3+em3==3) && (t = e, t >>= 2, t += e, d <= t))
{
// #1
// t = (d+d-e)/3;
// t = d; t += d; t -= e; t /= 3;
// e = (e+e-d)/3;
// e += e; e -= d; e /= 3;
// d = t;
// t = (d+e)/3
t = d; t += e; t /= 3;
e -= t;
d -= t;
T = f(A, B, C);
U = f(T, A, B);
B = f(T, B, A);
A = U;
continue;
}
// if (dm6 == em6 && d <= e + (e>>2))
if (dm3 == em3 && dm2 == em2 && (t = e, t >>= 2, t += e, d <= t))
{
// #2
// d = (d-e)>>1;
d -= e; d >>= 1;
B = f(A, B, C);
A = X2(A);
continue;
}
// if (d <= (e<<2))
if (d <= (t = e, t <<= 2))
{
// #3
d -= e;
C = f(A, B, C);
swap(B, C);
continue;
}
if (dm2 == em2)
{
// #4
// d = (d-e)>>1;
d -= e; d >>= 1;
B = f(A, B, C);
A = X2(A);
continue;
}
if (dm2 == 0)
{
// #5
d >>= 1;
C = f(A, C, B);
A = X2(A);
continue;
}
if (dm3 == 0)
{
// #6
// d = d/3 - e;
d /= 3; d -= e;
T = X2(A);
C = f(T, f(A, B, C), C);
swap(B, C);
A = f(T, A, A);
continue;
}
if (dm3+em3==0 || dm3+em3==3)
{
// #7
// d = (d-e-e)/3;
d -= e; d -= e; d /= 3;
T = f(A, B, C);
B = f(T, A, B);
A = X3(A);
continue;
}
if (dm3 == em3)
{
// #8
// d = (d-e)/3;
d -= e; d /= 3;
T = f(A, B, C);
C = f(A, C, B);
B = T;
A = X3(A);
continue;
}
assert(em2 == 0);
// #9
e >>= 1;
C = f(C, B, A);
B = X2(B);
}
A = f(A, B, C);
}
#undef f
#undef X2
#undef X3
return m.ConvertOut(A);
}
*/
Integer InverseLucas(const Integer &e, const Integer &m, const Integer &p, const Integer &q, const Integer &u)
{
Integer d = (m*m-4);
Integer p2 = p-Jacobi(d,p);
Integer q2 = q-Jacobi(d,q);
return CRT(Lucas(EuclideanMultiplicativeInverse(e,p2), m, p), p, Lucas(EuclideanMultiplicativeInverse(e,q2), m, q), q, u);
}
Integer InverseLucas(const Integer &e, const Integer &m, const Integer &p, const Integer &q)
{
return InverseLucas(e, m, p, q, EuclideanMultiplicativeInverse(p, q));
}
unsigned int FactoringWorkFactor(unsigned int n)
{
// extrapolated from the table in Odlyzko's "The Future of Integer Factorization"
// updated to reflect the factoring of RSA-130
if (n<5) return 0;
else return (unsigned int)(2.4 * pow((double)n, 1.0/3.0) * pow(log(double(n)), 2.0/3.0) - 5);
}
unsigned int DiscreteLogWorkFactor(unsigned int n)
{
// assuming discrete log takes about the same time as factoring
if (n<5) return 0;
else return (unsigned int)(2.4 * pow((double)n, 1.0/3.0) * pow(log(double(n)), 2.0/3.0) - 5);
}
// ********************************************************
void PrimeAndGenerator::Generate(signed int delta, RandomNumberGenerator &rng, unsigned int pbits, unsigned int qbits)
{
// no prime exists for delta = -1, qbits = 4, and pbits = 5
assert(qbits > 4);
assert(pbits > qbits);
if (qbits+1 == pbits)
{
Integer minP = Integer::Power2(pbits-1);
Integer maxP = Integer::Power2(pbits) - 1;
bool success = false;
while (!success)
{
p.Randomize(rng, minP, maxP, Integer::ANY, 6+5*delta, 12);
PrimeSieve sieve(p, STDMIN(p+PrimeSearchInterval(maxP)*12, maxP), 12, delta);
while (sieve.NextCandidate(p))
{
assert(IsSmallPrime(p) || SmallDivisorsTest(p));
q = (p-delta) >> 1;
assert(IsSmallPrime(q) || SmallDivisorsTest(q));
if (FastProbablePrimeTest(q) && FastProbablePrimeTest(p) && IsPrime(q) && IsPrime(p))
{
success = true;
break;
}
}
}
if (delta == 1)
{
// find g such that g is a quadratic residue mod p, then g has order q
// g=4 always works, but this way we get the smallest quadratic residue (other than 1)
for (g=2; Jacobi(g, p) != 1; ++g) {}
// contributed by Walt Tuvell: g should be the following according to the Law of Quadratic Reciprocity
assert((p%8==1 || p%8==7) ? g==2 : (p%12==1 || p%12==11) ? g==3 : g==4);
}
else
{
assert(delta == -1);
// find g such that g*g-4 is a quadratic non-residue,
// and such that g has order q
for (g=3; ; ++g)
if (Jacobi(g*g-4, p)==-1 && Lucas(q, g, p)==2)
break;
}
}
else
{
Integer minQ = Integer::Power2(qbits-1);
Integer maxQ = Integer::Power2(qbits) - 1;
Integer minP = Integer::Power2(pbits-1);
Integer maxP = Integer::Power2(pbits) - 1;
do
{
q.Randomize(rng, minQ, maxQ, Integer::PRIME);
} while (!p.Randomize(rng, minP, maxP, Integer::PRIME, delta%q, q));
// find a random g of order q
if (delta==1)
{
do
{
Integer h(rng, 2, p-2, Integer::ANY);
g = a_exp_b_mod_c(h, (p-1)/q, p);
} while (g <= 1);
assert(a_exp_b_mod_c(g, q, p)==1);
}
else
{
assert(delta==-1);
do
{
Integer h(rng, 3, p-1, Integer::ANY);
if (Jacobi(h*h-4, p)==1)
continue;
g = Lucas((p+1)/q, h, p);
} while (g <= 2);
assert(Lucas(q, g, p) == 2);
}
}
}
NAMESPACE_END
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