Which of the following is not a type of symmetric encryption?

RSA is a well-known asymmetric encryption algorithm, which distinguishes it from symmetric encryption methods. In asymmetric encryption, two keys are utilized: a public key for encryption and a private key for decryption. This key pair model is fundamentally different from symmetric encryption, where a single secret key is used for both encryption and decryption operations.

In contrast, AES, 3DES, and Blowfish are all types of symmetric encryption. They rely on the same key for both encrypting and decrypting data, making them suitable for scenarios where a secure key-sharing mechanism can be established. Symmetric encryption algorithms are known for their speed and efficiency, especially when handling large amounts of data. Therefore, RSA's reliance on a public/private key pair confirms it as not belonging to the category of symmetric encryption.