# Real-world applications of prime numbers?

I am going through the problems from Project Euler and I notice a strong insistence on Primes and efficient algorithms to compute large primes efficiently.

The problems are interesting per se, but I am still wondering what the real-world applications of primes would be.

What real tasks require the use of prime numbers?

Edit: A bit more context to the question:
I am trying to improve myself as a programmer, and having learned a few good algorithms for calculating primes, I am trying to figure out where I could apply them.

The explanations concerning cryptography are great, but is there nothing else that primes can be used for?