JUCE/modules/juce_cryptography/encryption/juce_RSAKey.cpp

/*
  ==============================================================================

   This file is part of the JUCE 6 technical preview.
   Copyright (c) 2020 - Raw Material Software Limited

   You may use this code under the terms of the GPL v3
   (see www.gnu.org/licenses).

   For this technical preview, this file is not subject to commercial licensing.

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

RSAKey::RSAKey()
{
}

RSAKey::RSAKey (const String& s)
{
    if (s.containsChar (','))
    {
        part1.parseString (s.upToFirstOccurrenceOf (",", false, false), 16);
        part2.parseString (s.fromFirstOccurrenceOf (",", false, false), 16);
    }
    else
    {
        // the string needs to be two hex numbers, comma-separated..
        jassertfalse;
    }
}

RSAKey::~RSAKey()
{
}

bool RSAKey::operator== (const RSAKey& other) const noexcept
{
    return part1 == other.part1 && part2 == other.part2;
}

bool RSAKey::operator!= (const RSAKey& other) const noexcept
{
    return ! operator== (other);
}

bool RSAKey::isValid() const noexcept
{
    return operator!= (RSAKey());
}

String RSAKey::toString() const
{
    return part1.toString (16) + "," + part2.toString (16);
}

bool RSAKey::applyToValue (BigInteger& value) const
{
    if (part1.isZero() || part2.isZero() || value <= 0)
    {
        jassertfalse;   // using an uninitialised key
        value.clear();
        return false;
    }

    BigInteger result;

    while (! value.isZero())
    {
        result *= part2;

        BigInteger remainder;
        value.divideBy (part2, remainder);

        remainder.exponentModulo (part1, part2);

        result += remainder;
    }

    value.swapWith (result);
    return true;
}

BigInteger RSAKey::findBestCommonDivisor (const BigInteger& p, const BigInteger& q)
{
    // try 3, 5, 9, 17, etc first because these only contain 2 bits and so
    // are fast to divide + multiply
    for (int i = 2; i <= 65536; i *= 2)
    {
        const BigInteger e (1 + i);

        if (e.findGreatestCommonDivisor (p).isOne() && e.findGreatestCommonDivisor (q).isOne())
            return e;
    }

    BigInteger e (4);

    while (! (e.findGreatestCommonDivisor (p).isOne() && e.findGreatestCommonDivisor (q).isOne()))
        ++e;

    return e;
}

void RSAKey::createKeyPair (RSAKey& publicKey, RSAKey& privateKey,
                            const int numBits, const int* randomSeeds, const int numRandomSeeds)
{
    jassert (numBits > 16); // not much point using less than this..
    jassert (numRandomSeeds == 0 || numRandomSeeds >= 2); // you need to provide plenty of seeds here!

    BigInteger p (Primes::createProbablePrime (numBits / 2, 30, randomSeeds, numRandomSeeds / 2));
    BigInteger q (Primes::createProbablePrime (numBits - numBits / 2, 30, randomSeeds == nullptr ? nullptr : (randomSeeds + numRandomSeeds / 2), numRandomSeeds - numRandomSeeds / 2));

    const BigInteger n (p * q);
    const BigInteger m (--p * --q);
    const BigInteger e (findBestCommonDivisor (p, q));

    BigInteger d (e);
    d.inverseModulo (m);

    publicKey.part1 = e;
    publicKey.part2 = n;

    privateKey.part1 = d;
    privateKey.part2 = n;
}

} // namespace juce