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Last active June 18, 2022 05:36
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OPPOENCRYPT! ozip Specs
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help-wanted.md

Help-Wanted

  1. Find out the exact encryption algorithm used by aes_decrypt (hint: use IDA Pro against /sbin/recovery ) it is aes-ecb
  2. Extract the 128-bit ECB Key (binary is here, aarch64 elf, 0x23f08)
  3. Implement external decryptor
Raw
ozip.md

OPPOENCRYPT OZIP Specs

Schema

An ordinary OZIP file is constructed with following schema:

Overall

offset size type description
0 4176 header See Meta header
4177 rest Data encrypted zip

Meta header

offset size type description
0 16 header Always contain 4F 50 50 4F 45 4E 43 52 59 50 54 21 00 00 00 00 ; OPPOENCRYPT!.... (by vendor)
17 16 decompressed size in bytes (append 00 ; .)
33 48 hash SHA1 of the decrypted data (40 bytes, append 00 ; .)
81 variant recovery instruction Example: ota-id=R9s_11.A.14_014_201611261040 (0A) ota_version=R9s_11.A.14_014_201611261040 (0A) patch_type=1 (0A) post-timestamp=1480130654 (0A) version_name=R9s_11_A.14_161126 (0A) wipe=0

Data

(The following offset have meta-header stripped)

The Data section contains an ordinary encrypted zip file.

Encryption

  1. From offset:00000000 , for every offset+:00004010 , the following 16 bytes is encrypted by AES-128-ECB (key unknown)
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