In my previous article, I presented the concept of symmetric encryption, where the same key is used to encrypt and decrypt data. The biggest limitation of symmetric encryption is the key itself. The key used for encryption and decryption has to be kept a secret. If the key is compromised, the encrypted data is no longer secure. While you may feel that it will be easy to keep the key safe, consider the fact that the same key cannot be used to encrypt data between multiple parties. For example, if Alice and Bob agree to use a secret key X for exchanging their messages, the same key X cannot be used to exchange messages between Alice and Jane. This is because such messages can be decrypted by Bob as well. Hence, in addition to keeping the key a secret, each pair that wishes to communicate secretly will have to maintain a key for their conversation.
This problem is overcome by the concept of public key/private key encryption (also known as Public Key Encryption or PKE for short).