Age and Authenticated Encryption

https://words.filippo.io/dispatches/age-authentication/

by akalin • 4 years ago

56 19 4 years ago

words.filippo.io

hutley• 4 years ago

I remain unconvinced by their arguments on this, and so will keep using good old reliable `gpg -se`.

woodruffw4• 4 years ago

Is there a specific argument you found unconvincing? I thought this was a very well-written summary of (1) why age doesn't provide authenticated encryption by default, (2) how you can do authenticated encryption with age, and (3) why age won't make "simple" authenticated encryption simpler.

Edit: I forgot to point out: GPG does sign-then-encrypt, which has a potential failure mode that the post notes (i.e., that your recipient retains your signature, and can encrypt-and-forward it to any additional recipient they please.)

upofadown3• 4 years ago

...that your recipient retains your signature, and can encrypt-and-forward it to any additional recipient they please.

So just like signatures made on paper? You can take a signed paper document and put it in an envelope and send it anywhere you want. What is wrong with that? It is what someone living in this world would normally expect. We need more things that work as expected, not less...

michelpp• 4 years ago

Another signcryption scheme as described in the article is also implemented by the libsodium author as an extension:

https://github.com/jedisct1/libsodium-signcryption

It's unclear from the article if this is the same implementation age uses.

Signcryption schemes are also a good candidate algorithm for replacing JWTs and PASETO as they suffer from no algorithm confusion, and don't need what PASETO calls "Algorithm Lucidity" and serve both plaintext authentication, authenticated encryption, sender receiver verification, and shared key generation that can be used for unlimited encrypted streaming, for example with libsodium's crypto_secretstream API.

https://doc.libsodium.org/secret-key_cryptography/secretstre...

https://github.com/paseto-standard/paseto-spec/blob/master/d...

chlorion2• 4 years ago

This is very interesting, thanks for sharing!

I have considered switching from GPG to age quite a lot, but I mostly use GPG for file encryption so this issue was a deal breaker for me. I did consider signing the encrypted backups with minisign, but then I needed two unrelated key pairs to safely access my backups instead of just one.

waynesonfire2• 4 years ago

In response to your post, I'm very happy with gpg.

technion• 4 years ago

The hypothetical I want to pose people is, let's say your server is corrupted or I.pacted by ransomware. So you pull your gpg backups and hit restore. The data somehow looks correct and in line with expectations, but the signature fails to verify.

You can say 'well I know there was tampering, or possible one bit of bitrot' but then what? Let's say my backup was a poatgresql backup that restored correctly and had no obvious issues.

People often state backups mist be signed but just not sure how you would even respond. You cannot just not use the backup if all your backups are the same and you just had an incident. You could say "now we don't trust the data" but again what is meaningful action here?

Is it really a plausible threat that an attacker wiped put production, gained access to your backup infrastructure, but instead of just wiping it in order to force you to pay a ransom they took a new backup and quietly modified it? Surely such a person would just modify production if they wanted such a game.

waynesonfire2• 4 years ago

Huh? What's your concern? Yeah there was tempering, good idea you signed. Maybe go freeze your credit? I don't know, you tell me?

chlorion2• 4 years ago

For me, it's about uploading files to the "cloud" such as Google Drive or Github and wanting to make sure that the data I uploaded is the same data that I am getting back. If the signatures fail I could unpack the file and manually review them to see what's up.

In your case, I think the problem is having backups that are attackable from production, and likely only having one set of backups.

You cannot just not use the backup

What would you do if instead of tampering with the backups or production they just deleted everything outright?

akerl_• 4 years ago

If I pulled a backup and it looked like it had been tampered with, I wouldn’t use the backup. Using a medium that protects against bit rot for backups, and testing the backups often enough to notice if they’ve been tampered with or malformed, are both key tenets of production systems.

normaler• 4 years ago

My main use case for gpg is actually signing things. Outbound unencrypted mail and gut commits e.g. .

aborsy• 4 years ago

I use Gpg heavily, no reason to change (well, unless perhaps Age provides ChaCha-20 Poly1305 with 256 bits file keys not 128, and someone creates a good backup software with it).

youainti• 4 years ago

Can someone explain if sign-encrypt-sign doesn't achieve the same objective of message authentication? It seems like it would to me.

Age and Authenticated Encryption

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