Symmetric key encryption and asymmetric key encryption are two different methods of securing data. Symmetric key encryption uses a single secret key for both encryption and decryption, while asymmetric key encryption uses a pair of keys (public and private). Symmetric key encryption has challenges with key distribution as the secret key must be shared securely between the sender and receiver without being intercepted by an attacker. In contrast, asymmetric key encryption has easier key distribution as the public key can be shared openly without compromising security. In terms of computational complexity, symmetric key encryption is generally faster and more efficient than asymmetric key encryption due to simpler mathematical operations involved. However, asymmetric key encryption is slower and more computationally intensive due to complex mathematical algorithms used.