Generating Large Prime Numbers with Py Crypto

Question

I'm trying to generate a large prime number (2048 bits) using the crypto library in python in order to implement RSA. However, I do not really understand the syntax of the getPrime() function. I currently have:

from Crypto.Util import number

n_length = 2048

primeNum = number.getPrime(n_length, randFunc)

I don't understand what the randFunc is supposed to be in the getPrime function.

Solution

n_length is the "size" of the prime number. It will return a number around 2^n_length. randFunc is a callable function that accepts a single argument N and then returns a string of N random bytes. (os.urandom is an example of this). In most cases, randFunc can (and should) be omitted, since the default is PyCrypto's own random number generator.