Which of the following are MOST susceptible to birthday attacks?

Birthday attacks specifically exploit the probability of finding two different inputs that produce the same hash output (a collision), which is directly applicable to systems that store hashed passwords for authentication. If an attacker can find a collision, they can potentially bypass authentication without knowing the original password.

Digital certificates use hashes as part of their integrity and signing process, but the primary susceptibility of certificates isn't a direct birthday attack on the certificate itself to bypass authentication, but rather on forging signatures or exploiting weaknesses in the Certificate Authority (CA) trust model.

Encryption passwords are used to secure data with cryptographic algorithms, and while a hash might be derived from a password for key generation, the direct impact of a birthday attack targets the collision resistance of the hash function, not the encryption process itself.

One-time passwords rely on a shared secret and a time/counter value to generate unique, ephemeral tokens, and birthday attacks, which aim to find hash collisions, are not the primary threat model for compromising these systems.