Which of the following is an example of an asymmetric encryption implementation?

SHA1 is a one-way cryptographic hash function that produces a fixed-length digest and cannot encrypt or decrypt data.

PGP (Pretty Good Privacy) uses asymmetric algorithms such as RSA or DSA to encrypt and exchange a session key, then applies a symmetric cipher to encrypt the actual data payload. This reliance on a public/private key pair for key exchange classifies PGP as an asymmetric encryption implementation. The other options are either symmetric ciphers or one-way hash functions.

3DES (Triple DES) is a symmetric encryption algorithm that uses the same shared key for both encryption and decryption.

MD5 is a cryptographic hash function used for data integrity verification, not an encryption algorithm.