[FEATURE] Validate the provided decryption key against an encrypted backup and exit

[ritiek]

Hi, thanks for creating this tool!

I do automated periodic snapshots of my WhatsApp backup. I'm also interested in automating whether the decryption key I currently posses is valid for the latest snapshot. Currently it seems tricky to perform such a check without having the exporter write the decrypted db file to disk.

Does it seem interesting to have a param such as --dry-run, which'll only check whether the provided decryption key is valid for a given backup file and then exit with an appropriate return code? It'll help me keep in check whether my snapshots are dependable or not in the time of need.

[KnugiHK]

I added a dry-run logic to the decrypt_backup function. I hope that will be useful for you!

[KnugiHK]

Moreover, rather than adding the --dry-run option to the exporter (which doesn't seem right to me), I think it would be better to load the decrypted database into memory and work with the in-memory version. In this way, no decrypted database will be written into disk.

I am not sure if the sqlite3.Connection.deserialize method introduced in Python 3.11 will help.

[ritiek]

I added a dry-run logic to the decrypt_backup function. I hope that will be useful for you!

Much thanks!

Moreover, rather than adding the --dry-run option to the exporter (which doesn't seem right to me), I think it would be better to load the decrypted database into memory and work with the in-memory version. In this way, no decrypted database will be written into disk.

I am not sure if the sqlite3.Connection.deserialize method introduced in Python 3.11 will help.

Yep, I guess this area could be improved a lil. Currently it's not very clear that the tool writes the decrypted msgstore.db in current working directory. On my first try, it seemed like it was normal to take a while to decrypt the messages (when in fact the tool was almost immediately done with decrypting the db and was on the next stage taking its time to write the html files).

Although I think some people may also play around with decrypted db itself (in addition to post processed html/txt), so we might want to keep some way to write the decrypted db to disk.

[KnugiHK]

I have moved the decrypt_backup function to a separate module called android_crypt in commit b2bcf36. You should now import it using from Whatsapp_Chat_Exporter.android_crypt import decrypt_backup. Additionally, please note that the dry_run parameter is now a keyword argument. See the function signiture below:

def decrypt_backup(
    database: bytes,
    key: Union[str, io.IOBase],
    output: str = None,
    crypt: Crypt = Crypt.CRYPT14,
    show_crypt15: bool = False,
    db_type: DbType = DbType.MESSAGE,
    *,
    dry_run: bool = False,
    keyfile_stream: bool = False
)

[ritiek]

That does it for me. Thanks again.

[KnugiHK]

Good to hear that! I will leave this open until release.