Encryption, Part 3: Hybrid Encryption

In part one of the series, I covered the topic of symmetric encryption (SE). While in part two, I covered public/ private key encryption, also known as public key encryption (PKE). The limitation of symmetric encryption is that the key used for encryption and decryption is one and the same. Hence, the key needs to be kept a secret. PKE overcomes the problem of key sharing by using two keys — one private and one public. To share a message, it is typically encrypted using the public key. Then, the private key counterpart of the public key can be used to decrypt the message. Thus, PKE achieves security.

But using PKE for large messages is very difficult for two reasons. The first reason is that the longer text that can be encrypted in one go has to be less than the length of the key used for encryption. The second reason is that PKE is more time consuming, compared to symmetric encryption. The third reason why PKE is not used for encrypting long messages is that after encryption, the length of the encrypted text is much larger than the length of the original text.

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