What is Hybrid System?

Hybrid system is a basic key transport protocol that incorporates both Asymmetric and Symmetric Algorithms. In another word, this system uses a combination of both (public-key) and (private-key). This Hybrid system provides the following:

  1. Key Exchange: for Symmetric schemes; and digital signatures are performed with (slow) Asymmetric algorithms.
  2. Encryption of data is done using (fast) Symmetric Ciphers such as, Block Ciphers or Stream Ciphers.


The following example shows both Symmetric and Asymmetric Cryptography to achieve Hybrid protocol (using the AES operation to exchange data).

Hybrid Protocol.png

Description: The figure above shows the process of Hybrid Protocol that provides both Symmetric and Asymmetric Algorithm to eventually exchange data securely.

  1. Any party can start this communication, but in this case Bob started by generating two different keys (public-key and private-key).
  2. Bob will send his public-key to Alice.
  3. Alice generates a random number and encrypt her number using Bob’s public-key; and send the result to Bob; as an encrypted message. Note: if the message get corrupted, it means nothing because it is only an encrypted number (useful for Alice and Bob, but useless for anyone else).
  4. Bob will use his private-key to decrypt the message to know Alice’s key.
  5. Asymmetric algorithm has been achieved by exchanging the key between Alice and Bob.
  6. Now, Alice can encrypt any message and send it to Bob security, where Bob can only decrypt this message.
  7. Symmetric algorithm has been achieved by exchanging the data between Alice and Bob.

Note: the public-key can be public to anyone; and we do not care if any third party, Oscar for example, got a copy of it. However, the private-key must be kept secret and should be available to no one by the generator himself/herself (in our case Bob).


The attached link shows an animation video about the hybrid-protocol process and how it works step-by-step.


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