Introduction to Fully Homomorphic Encryption Technology and Application Scenarios

Fully homomorphic encryption ( FHE ) is a special encryption scheme that allows function computation on ciphertext without decryption, obtaining the encrypted result of the function output, thus protecting data privacy. Unlike traditional static encryption and encryption in transit, FHE can perform complex computation operations on ciphertext.

A typical application scenario of FHE is online voting systems. Voters can encrypt their voting results and submit them, while an intermediary collects all the encrypted votes, counts the votes, and announces the final result without needing to decrypt each individual's specific voting content. This avoids the problem in traditional encryption schemes where the intermediary must decrypt all data to count it, better protecting privacy.

FHE systems typically include the following types of keys:

1. Decryption Key: The system's master key, used to decrypt FHE ciphertext, typically kept locally by the key holder.

2. Encryption key: used to convert plaintext into ciphertext, can be made public in public key mode.

3. Calculate the key: used for homomorphic operations on ciphertext, it can be made public but cannot be used to crack the ciphertext.

There are several common application patterns for FHE:

1. Outsourcing model: Encrypt sensitive data and hand it over to cloud service providers for computation, applicable to scenarios such as PIR.

2. Both parties compute mode: Both parties provide private data for joint computation, such as the "Millionaire Problem".

3. Aggregation Mode: Aggregating the encrypted data of multiple participants for federated learning, voting systems, etc.

4. Client-Server Model: The server provides private AI model computing services for multiple clients.

The advantage of FHE is that its security is based on cryptographic algorithms rather than hardware, which can prevent side-channel attacks. However, the current computational overhead is significant, and dedicated hardware support is needed for widespread application. In the future, with technological advancements, FHE is expected to play a greater role in the field of privacy computing.