there is a function of compress,but there is no function of decompress.if I compress ciphertext,I will how to decompress

`Compress`

is a way to reduce the size of a ciphertext before sending it to the decryption party (to minimize communication costs). `Uncompress`

is not expected to be called in this scenario. One could â€śuncompressâ€ť a ciphertext by calling bootstrapping, e.g., when using CKKS bootstrapping. I would suggest looking at the documentation/examples for bootstrapping for more details.

Can you give an example?I donâ€™t understand how to use bootstrapping for decompress?

You can look at https://github.com/openfheorg/openfhe-development/blob/v1.0.4/src/pke/examples/simple-ckks-bootstrapping.cpp to get familiar with CKKS bootstrapping.

I donâ€™t understand the relationship between bootstrapping and compressionă€‚Is it possible to recover by bootstrapping after compressionďĽź

I suggest watching the Introduction to FHE webinar to get familiar with how noise increases in FHE with every computation (see slides 11-15). Eventually, no more computations are allowed. Bootstrapping is what resets the noise and enables more computations (by expanding the ciphertext). A compressed ciphertext is the one that does not support any more computations (and hence it can be much smaller).

I understand it ,thank you!