My router has a config backup function that downloads a base64-encoded file.
After decoding the file, it's clear that it is encrypted:
I have tried redownloading the config, both after having changed config parameters in the router, and not having changed anything. Every part of the file - except 21 bytes - changes completely every time it is downloaded, regardless of config changes, logged in user etc.
It seems that these bytes will always be present at this position:
000019 BE B0 A9 D4 6B 76 F6 F3 18 FD 31 B7 ¾°©Ôkvöóý1· 000031 1D 50 84 B0 C0 69 3F 35 3F P°Ài?5?
Does this provide any clues as to how these files are encrypted and how one might decrypt them? How do I go about achieving this?
This is a little known proprietary ISP CPE box and the backup feature is undocumented and has to be enabled via an undocumented API, so I haven't been able to find any information regarding this.