Yes and no. Much of cryptography is based on psuedorandom number generators, which output more bits than they are seeded with. If these PRNGs are not secure, th

Yes and no. Much of cryptography is based on psuedorandom number generators, which output more bits than they are seeded with. If these PRNGs are not secure, then almost any piece of cryptography you actually use would be insecure independent of your choice to use random or urandom. Unless all of your cryptography is information-theoretically secure, there is no problem using a PRNG. If you happen to be using a an information-theoretically secure algorithm than you are theoretically weaker using a limited entropy PRNG; but there is no practical implications of this.