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using System;
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.Math.EC.Multiplier;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Crypto.Generators
{
/**
* an RSA key pair generator.
*/
public class RsaKeyPairGenerator
: IAsymmetricCipherKeyPairGenerator
{
private static readonly int[] SPECIAL_E_VALUES = new int[]{ 3, 5, 17, 257, 65537 };
private static readonly int SPECIAL_E_HIGHEST = SPECIAL_E_VALUES[SPECIAL_E_VALUES.Length - 1];
private static readonly int SPECIAL_E_BITS = BigInteger.ValueOf(SPECIAL_E_HIGHEST).BitLength;
protected static readonly BigInteger One = BigInteger.One;
protected static readonly BigInteger DefaultPublicExponent = BigInteger.ValueOf(0x10001);
protected const int DefaultTests = 100;
protected RsaKeyGenerationParameters parameters;
public virtual void Init(
KeyGenerationParameters parameters)
{
if (parameters is RsaKeyGenerationParameters)
{
this.parameters = (RsaKeyGenerationParameters)parameters;
}
else
{
this.parameters = new RsaKeyGenerationParameters(
DefaultPublicExponent, parameters.Random, parameters.Strength, DefaultTests);
}
}
public virtual AsymmetricCipherKeyPair GenerateKeyPair()
{
for (;;)
{
//
// p and q values should have a length of half the strength in bits
//
int strength = parameters.Strength;
int pBitlength = (strength + 1) / 2;
int qBitlength = strength - pBitlength;
int mindiffbits = strength / 3;
int minWeight = strength >> 2;
BigInteger e = parameters.PublicExponent;
// TODO Consider generating safe primes for p, q (see DHParametersHelper.generateSafePrimes)
// (then p-1 and q-1 will not consist of only small factors - see "Pollard's algorithm")
BigInteger p = ChooseRandomPrime(pBitlength, e);
BigInteger q, n;
//
// generate a modulus of the required length
//
for (;;)
{
q = ChooseRandomPrime(qBitlength, e);
// p and q should not be too close together (or equal!)
BigInteger diff = q.Subtract(p).Abs();
if (diff.BitLength < mindiffbits)
continue;
//
// calculate the modulus
//
n = p.Multiply(q);
if (n.BitLength != strength)
{
//
// if we get here our primes aren't big enough, make the largest
// of the two p and try again
//
p = p.Max(q);
continue;
}
/*
* Require a minimum weight of the NAF representation, since low-weight composites may
* be weak against a version of the number-field-sieve for factoring.
*
* See "The number field sieve for integers of low weight", Oliver Schirokauer.
*/
if (WNafUtilities.GetNafWeight(n) < minWeight)
{
p = ChooseRandomPrime(pBitlength, e);
continue;
}
break;
}
if (p.CompareTo(q) < 0)
{
BigInteger tmp = p;
p = q;
q = tmp;
}
BigInteger pSub1 = p.Subtract(One);
BigInteger qSub1 = q.Subtract(One);
//BigInteger phi = pSub1.Multiply(qSub1);
BigInteger gcd = pSub1.Gcd(qSub1);
BigInteger lcm = pSub1.Divide(gcd).Multiply(qSub1);
//
// calculate the private exponent
//
BigInteger d = e.ModInverse(lcm);
if (d.BitLength <= qBitlength)
continue;
//
// calculate the CRT factors
//
BigInteger dP = d.Remainder(pSub1);
BigInteger dQ = d.Remainder(qSub1);
BigInteger qInv = q.ModInverse(p);
return new AsymmetricCipherKeyPair(
new RsaKeyParameters(false, n, e),
new RsaPrivateCrtKeyParameters(n, e, d, p, q, dP, dQ, qInv));
}
}
/// <summary>Choose a random prime value for use with RSA</summary>
/// <param name="bitlength">the bit-length of the returned prime</param>
/// <param name="e">the RSA public exponent</param>
/// <returns>a prime p, with (p-1) relatively prime to e</returns>
protected virtual BigInteger ChooseRandomPrime(int bitlength, BigInteger e)
{
bool eIsKnownOddPrime = (e.BitLength <= SPECIAL_E_BITS) && Arrays.Contains(SPECIAL_E_VALUES, e.IntValue);
for (;;)
{
BigInteger p = new BigInteger(bitlength, 1, parameters.Random);
if (p.Mod(e).Equals(One))
continue;
if (!p.IsProbablePrime(parameters.Certainty, true))
continue;
if (!eIsKnownOddPrime && !e.Gcd(p.Subtract(One)).Equals(One))
continue;
return p;
}
}
}
}
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