RSA (Rivest-Shamir-Adleman) is one of the oldest and most widely deployed asymmetric encryption algorithms. Its security rests on the difficulty of factoring large numbers into their prime components. RSA is used for both encryption and digital signatures. Current recommendations require key lengths of at least 2048 bits; 4096 bits are recommended for long-term protection. With the advent of powerful quantum computers, RSA will eventually need to be replaced by post-quantum-safe algorithms. In your ISMS you document deployed algorithms and key lengths in the cryptography register.