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?