[Standards] XEP-0384 and inbox/omemo-filetransfer: Variable length of MAC

Andrey Gursky andrey.gursky at e-mail.ua
Sun Dec 11 18:07:23 UTC 2016


Hi,

> The 16 bytes key and the GCM authentication tag (The tag SHOULD have at
> least 128 bit) are concatenated and for each intended recipient
> device...

Once received due to the predefined length of the first field (key),
the length of the tag can be calculated. Considering OMEMO
file-transfer: the tag is appended at the end of the encrypted file and
the total length is reported to the receiver. It seems to me not
possible to derive the used authentication tag length in this case.

Thanks,
Andrey


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