Do you have enough evidence to prove this? @AniccaY

Although LZ4HC compression flag is widely used in many UnityCN-encrypted games, we cannot draw a conclusion that LZ4HC flag is used in ALL the UnityCN-encrypted games.

old version will decrypt type: None Block, cause read bundle error

I'm interested in the asset file you try to decrypt. Could you please provide a sample file and its key to let me investigate deeper?

sample.zip
@isHarryh
2 samples
One will parse error, and raise error info.
Two will parse with no error, but when you extract the only one file in bundle, this file is damaged.
This is a relatively hidden problem.

Thanks.

In your sample files, the blocks with compression flag NONE need no decryption. In another word, for NONE compression, UnityPy should return the data as-is without decryption.

I think you can use:

        if self.decryptor is not None and comp_flag != CompressionFlags.NONE and flags & 0x100:
            ...

instead of simply limiting the decryption to LZ4HC only. As you can see in Studio's implementation, such decryption is applied to all the LZ4-series compression. Here's the reference.

I can only second all of @isHarryh comments.

I did some digging through the TuanjiePlayer just now,
and as far as I can see, there is only an early return path for no compression.
Every other compression type can be encrypted.

As the PR had unwanted changes and was based on "guesswork" based on the work of others,
while I checked the actual engine code, I opted to simply close this PR and push the fix directly myself.