hls: check the length of the downloaded AES-128 key

[pzhlkj6612]

Hello! Thank you for making this great project.

I'm from https://github.com/yt-dlp/yt-dlp/issues/2537#issuecomment-1256555973 . I tried to download a stream by hlsdl (this project) at that time but kept getting "Error: AES128_CBC_DecryptUpdate failed: 0, in_size: ..., out_size: ...". After debugging, I found that the key was just 9 bytes. I didn't specify the correct HTTP header, and then the server replied with a HTTP 200 and a body with the string "Forbidden". It should reply with a failed status code, shouldn't it ;)

To make the error message a little more detailed in this case, I think we can check the key length after getting it. The length of the AES-128 key must be 16 bytes, so the logic is simple.

Also, the "memcpy" always copy 16 bytes data from "key_value" (code). If the key is shorter, it will read dirty data.

It's worth noting that the return value of the "int fill_key_value(struct enc_aes128 *)" function is ignored, so currently we are not able to stop the program when the key is wrong.

Test

Before (883acbdb59ada7739f3ae75207bb74bac1994f75):

$ ...
> START media_playlist_get_links
> END media_playlist_get_links
HLS Stream is AES-128 encrypted.
{"d_t":"live"}
Downloading part ...
Error: AES128_CBC_DecryptUpdate failed: 0, in_size: ..., out_size: ...
{"t_d":...,"d_d":...,"d_s":...}
Downloading part ...
Error: AES128_CBC_DecryptUpdate failed: 0, in_size: ..., out_size: ...
Downloading part ...

After (771a2a6510c7f74c060fef09d313d181e3bb352f):

$ ...
> START media_playlist_get_links
> END media_playlist_get_links
HLS Stream is AES-128 encrypted.
{"d_t":"live"}
Downloading part ...
Error: Wrong length key-file. Expected 16 bytes but got 9.
Error: AES128_CBC_DecryptUpdate failed: 0, in_size: ..., out_size: ...
{"t_d":...,"d_d":...,"d_s":...}
Downloading part ...
Error: Wrong length key-file. Expected 16 bytes but got 9.
Error: AES128_CBC_DecryptUpdate failed: 0, in_size: ..., out_size: ...
Downloading part ...

[selsta]

Thank you :)