Symmetric keys are a type of encryption method where the same key is used for both encrypting and decrypting data. This means that both the sender and the receiver must have access to the same secret key to communicate securely. Because of this shared key, symmetric key encryption is generally faster and more efficient than other methods. However, the main challenge with symmetric keys is securely sharing the key between parties. If the key is intercepted or compromised, the security of the communication is at risk. Common algorithms that use symmetric keys include AES and DES, which are widely used in various applications to protect sensitive information.