Access Pseudo-Random Bytes from /dev/urandom

Random numbers have many important uses in applied cryptography. Yet you can't compute true randomness arithmetically.

This project sources randomness from /dev/urandom - this is a character special file in Linux (including Android) that provides access to a source of randomness generated by the Kernel. The randomness is sourced from environmental noise from device drivers and other sources - stored in an entropy pool.

Most userspace random number generators ultimately rely on /dev/urandom. This project provides a convenient wrapper around /dev/urandom to source random bytes.

Build Instructions

Run make in the project root directory.

The Makefile expects a bin directory. Running make will build some example programmes:

g++ -W -Wall -std=c++17 -g -I. -o bin/main random.cpp main.cpp
g++ -W -Wall -std=c++17 -g -I. -o bin/diceroll random.cpp examples/diceroll.cpp
g++ -W -Wall -std=c++17 -g -I. -o bin/random-bytes random.cpp examples/random-bytes.cpp
g++ -W -Wall -std=c++17 -g -I. -o bin/code-usage random.cpp examples/code-usage.cpp

Initialise with a Size

Initialise the Random object with size_t n.

Access a std::vector<unsigned char> that contains n random bytes using getRandomBytes().

Member function printHex() prints random bytes in zero-padded hexadecimal format.

Member function printInt() prints random bytes in space-separated decimal format.

size_t n = 10;
Random r{n}; // Initialise with a size n
r.printInt(); // Prints n random bytes to stdout, decimal integers.
r.printHex(); // Prints n random bytes to stdout, hexadecimal format.

Initialise with a Buffer

Initialise the Random object with a suitable buffer to fill the buffer with random bytes.

std::vector<unsigned char> randVec(10);
Random r(randVec); // randVec now has 10 random bytes

Get Random Bytes

Once the Random object has been initialised, get it's randomBytes member using getRandomBytes().

Returns a std::vector<unsigned char> filled with random bytes.

std::vector<unsigned char> randBytes = r.getRandomBytes(); // Assign random bytes to a vector.

Reset Pseudo Random Bytes

Call setRandomBytes() to reset random bytes held by the object:

r.setRandomBytes(); // Bytes have been refreshed.

Next call to getRandomBytes() return different values.

Assign Pseudo Random Bytes to a Buffer

Passing a suitable buffer to getRandomBytes() populates the buffer with random bytes.

Random r;
std::vector<unsigned char> buf;
r.getRandomBytes(buf);
// buf now contains random bytes
for (auto& el : buf)
	std::cout << (int)el << " ";
std::cout << '\n';

// If initialised with a vector, fill vector with random values.
// -------------------------------------------------------------
std::vector<unsigned char> v(32);
Random r2{v};

std::cout << "printRandomBytes(v) =\n";
r2.printRandomBytes(v);

return 0;
}

Static Methods

Get a Random Byte

unsigned char r = Random::getRandomByte();
std::cout << "r is a random byte, value " << (int)r << '\n';