Which algorithm is based on factoring prime numbers?

The algorithm that is based on factoring prime numbers is RSA. This asymmetric cryptographic algorithm relies on the mathematical difficulty of factoring the product of two large prime numbers. When two large primes are multiplied together, the result is a number that is easy to compute but difficult to reverse back into the original prime factors without knowledge of those primes. This property underpins the security of RSA, making it a widely used method for secure data transmission, particularly in scenarios like web encryption and digital signatures.

In contrast, the other options provided do not utilize prime factorization in the same way. DES (Data Encryption Standard) and Blowfish are symmetric key algorithms that are based on substitution and permutation rather than the complexity of factoring large numbers. Diffie-Hellman, while related to key exchange and using discrete logarithms, does not rely on the factoring of primes either. The unique foundation of RSA on prime factorization not only establishes its security framework but also highlights the complexity challenges involved in breaking the encryption.