Final answer:
The Data Encryption Standard (DES) is NOT an asymmetric system; it is a symmetric key encryption cipher, meaning the same key is used for both encryption and decryption.
Step-by-step explanation:
To identify which of the provided options is NOT an asymmetric system, let's define what an asymmetric system is. An asymmetric or public key cryptographic system uses a pair of keys: a public key, which is shared openly, and a private key, which is kept secret. The public key is used for encryption and the private key is used for decryption.
- PGP (Pretty Good Privacy) uses an asymmetric system for encrypting emails.
- RSA (Rivest-Shamir-Adleman) is one of the first public-key cryptosystems and is widely used for secure data transmission.
- SSL (Secure Sockets Layer) uses asymmetric cryptography for the initial key exchange and then symmetric encryption for the rest of the session.
- DES (Data Encryption Standard) is the correct answer to this question as it is NOT an asymmetric system but rather a symmetric key encryption cipher, using the same key for both encryption and decryption.