Which of the following is an asymmetric encryption algorithm?

Blowfish is a symmetric block cipher that uses the same key for both encryption and decryption, not an asymmetric algorithm.

RC5 is a symmetric block cipher designed by Ron Rivest that uses a single shared secret key for encryption and decryption.

Diffie-Hellman is an asymmetric cryptographic protocol that allows two parties to establish a shared secret over an insecure channel without prior key exchange. It relies on the mathematical difficulty of the discrete logarithm problem and uses a key pair concept - making it asymmetric - even though its primary use is key agreement rather than bulk encryption.

RC4 is a symmetric stream cipher that uses one shared key for both encrypting and decrypting data.