Hybrid encryption, also known as hybrid encryption, is a combination of asymmetric encryption and symmetric encryption. The sender chooses a random symmetric key called a session key. With this session key, the data to be protected is symmetrically encrypted. The session key is then encrypted asymmetrically with the recipient’s public key. This approach solves the key distribution problem while maintaining the speed advantage of symmetric encryption.
Comparison of the Individual Encryption Methods
In a hybrid encryption method, two different encryption methods are used. For symmetric encryption, all communication partners need the same secret key, which is used to both encrypt and decrypt. For asymmetric encryption, each communication partner needs its own key pair, which consists of a public encryption key and a secret decryption key. Both methods have different properties.
Efficiency
---
- Symmetric encryption methods are very fast, even with large amounts of data.
- Asymmetric encryption methods are very slow and are therefore only suitable for very small amounts of data.
Key
- Symmetric encryption methods have the problem that the communication partners have to agree on a secret key before the message is transmitted. To do this, a secure communication channel must be used, such as a courier.
- Asymmetric encryption methods, on the other hand, solve the problem very elegantly, because only the public key is needed for encryption. To transmit this key, an authenticated channel is sufficient.
Hybrid encryption methods combine the two encryption methods in such a way that their advantages are retained:
- Hybrid encryption methods are very fast and suitable for large amounts of data because the data is encrypted using the symmetric method and the asymmetric method is only used for the session key.
- There is no need to exchange a secret key before sending the message, knowledge of the recipient’s public key is sufficient to encrypt.
How Hybrid Encryption Method Works
Just as with asymmetric encryption methods, each recipient must generate a key pair in hybrid encryption methods.
After the key has been generated, the communication partners exchange their public keys with each other. It must be ensured that the public keys are actually the keys of the participants. Thus, asymmetric encryption reduces the problem of secure (confidential and authenticated) key exchange to the problem of authenticated key exchange.
As a rule, each participant always uses the same asymmetric key pair over a longer period of time. However, a new session key is generated for each encryption operation, which is only valid for that one session. This has the advantage that the symmetric keys of different sessions are independent of each other, so the disclosure of a session key only endangers the security of a single session.
Encryption
If one communication partner wants to send a document to the other in encrypted form, then the as shown in the following example:
- The sender (Alice) produces a document. It is still unencrypted.
Because the document is assumed to be very large, it is encrypted symmetrically:
- For this purpose, a symmetric session key is generated.
- This session key is used to encrypt the document.
The session key is then encrypted asymmetrically:
- The public key of the recipient (Bob) is used for this purpose.
- The encrypted document and the encrypted session key can now be sent to the recipient (Bob).
The combination of the individual encryption methods can be explained as follows:
- The payload data is encrypted symmetrically because high speed is important, which only a symmetric method can provide.
- The session key is encrypted asymmetrically because it is small enough so that the extremely slow computational speed of an asymmetric method is not significant. But only an asymmetrical method offers the advantage that the key management is regulated between Alice and Bob.
Decryption
Below is an example of how the recipient can decrypt the document received:
The recipient (Bob) receives an encrypted document and an encrypted session key from the sender (Alice).
First, the session key is decrypted asymmetrically:
- For this purpose, the secret key of the recipient (Bob) is used.
- With the help of the session key obtained in this way, the document is then decrypted symmetrically.
