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Although I have no hope really I will leave this here in case someone has the ability and time to help. This is from a modem/router widely used in countries like Germany, Greece and others from Sercomm and labeled as "Speedport Plus"

There is no output from binwalk and entropy is almost 1 (which I guess shows encryption) The *.img file has some info in header enter image description here


enter image description here

enter image description here

File is located here: https://help.cosmote.gr/system/templates/selfservice/gnosisgr/files2/09022001.00.030_OTE5.img

and older version of the firmware: https://help.cosmote.gr/system/templates/selfservice/gnosisgr/files2/09022001.00.030_OTE3.img

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  • How did you collect the file? I suspect the key would have to be on the device in order to decrypt and run the firmware. If you don't readily see the key on the persistent storage, perhaps they're using a TPM to store the key? I've never worked with encrypted firmware, those are just my guesses. – David F. Dec 27 '20 at 13:27
  • File is available from ISP for update/upgrade. As are old firmware files.. – N.K.K. Dec 27 '20 at 15:53
  • High entropy could equally be interpreted as extreme compression. Hard to tell apart without a closer look. – 0xC0000022L Jan 7 at 13:18
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I read about similar issue with ZTE modem: ZTE encrypted backup config file
It was ZLIB-compressed and encrypted with AES in ECB mode with a 16-byte key. You can read this topic, maybe it can work for your modem too.

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