source: box/trunk/lib/crypto/Random.cpp @ 1789

// --------------------------------------------------------------------------
//
// File
//              Name:    Random.cpp
//              Purpose: Random numbers
//              Created: 31/12/03
//
// --------------------------------------------------------------------------

#include "Box.h"

#include <openssl/rand.h>
#include <stdio.h>

#include "Random.h"
#include "CipherException.h"

#include "MemLeakFindOn.h"


// --------------------------------------------------------------------------
//
// Function
//              Name:    Random::Initialise()
//              Purpose: Add additional randomness to the standard library initialisation
//              Created: 18/6/04
//
// --------------------------------------------------------------------------
void Random::Initialise()
{
#ifdef HAVE_RANDOM_DEVICE
        if(::RAND_load_file(RANDOM_DEVICE, 1024) != 1024)
        {
                THROW_EXCEPTION(CipherException, RandomInitFailed)
        }
#else
        BOX_ERROR("No random device -- additional seeding of random number "
                "generator not performed.");
#endif
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    Random::Generate(void *, int)
//              Purpose: Generate Length bytes of random data
//              Created: 31/12/03
//
// --------------------------------------------------------------------------
void Random::Generate(void *pOutput, int Length)
{
        if(RAND_pseudo_bytes((uint8_t*)pOutput, Length) == -1)
        {
                THROW_EXCEPTION(CipherException, PseudoRandNotAvailable)
        }
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    Random::GenerateHex(int)
//              Purpose: Generate Length bytes of hex encoded data. Note that the
//                               maximum length requested is limited. (Returns a string
//                               2 x Length characters long.)
//              Created: 1/11/04
//
// --------------------------------------------------------------------------
std::string Random::GenerateHex(int Length)
{
        uint8_t r[256];
        if(Length > (int)sizeof(r))
        {
                THROW_EXCEPTION(CipherException, LengthRequestedTooLongForRandomHex)
        }
        Random::Generate(r, Length);
        
        std::string o;
        static const char *h = "0123456789abcdef";
        for(int l = 0; l < Length; ++l)
        {
                o += h[r[l] >> 4];
                o += h[r[l] & 0xf];
        }
        
        return o;
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    Random::RandomInt(int)
//              Purpose: Return a random integer between 0 and MaxValue inclusive.
//              Created: 21/1/04
//
// --------------------------------------------------------------------------
uint32_t Random::RandomInt(uint32_t MaxValue)
{
        uint32_t v = 0;

        // Generate a mask
        uint32_t mask = 0;
        while(mask < MaxValue)
        {
                mask = (mask << 1) | 1;
        }

        do
        {
                // Generate a random number
                uint32_t r = 0;
                Random::Generate(&r, sizeof(r));
                
                // Mask off relevant bits
                v = r & mask;
                
                // Check that it's in the right range.
        } while(v > MaxValue);
        
        // NOTE: don't do a mod, because this doesn't give a correct random distribution
        
        return v;
}