Re: Encryption and authentication

On 23/06/2023 05:44, John Goerzen wrote:
> Hi,

Hi John

> 
> I hope you'll excuse all my dar enthusiasm... I really am enjoying it
> and just had a lengthy Mastodon thread about it.

no worries, this is a place for open discussions :)

> 
> Anyhow, in researching the encryption and signature options, I believe
> that what I have found it this:
> 
> - The encryption itself is not authenticated (not using AEAD or some
>    such)

correct

> 
> - The signature applies only to the session key

"session" usually means a set of events linked together over time (start 
session, do transactions in that session, end a session). Not sure this 
concept of session applies to dar/libdar but:

you can have more info about the way strong encryption is used in libdar 
here:

http://dar.linux.free.fr/doc/Notes.html#strong_encryption


> 
> - (And the key seems to be derived using SHA-1; not sure how important
>    that is)

this is not exact: actually if libargon2 is available the key derivation 
function is argon2 protocol with salt (see --kdf option)

> 
> So it looks to me that --sign doesn't actually guarantee the integrity
> of the data.

No, it should. There is just one known restriction when signing an 
archive for multiple recipients as documented here:

http://dar.linux.free.fr/doc/Notes.html#asym

> 
> Related, does the encryption also encrypt metadata such as filename at
> every occurrence?

Please have a look at this paragraph: a drawing worth thousand words!

http://dar.linux.free.fr/doc/Notes.html#archive_structure

> 
> Thanks!
> 
> - John
> 

Cheers,
Denis