user121614: Phoenix wallet is a unique Lightning wallet in that, among other things, it allows the user to restore channels by simply entering their seed. According to ACINQ's blogpost, this is how they achieve it:

TL; DR: Each time channels are updated, Phoenix sends an encrypted version of their data to its peer. This allows for easy backup/restore of channels while maintaining privacy.

In the case of Phoenix wallet, the peer is always ACINQ, but my question applies to any similar peer backup solutions: what's to stop the peer from making me recover an old channel state, and claim all my funds when I try to close it?

user101498: Nothing.
If you have lost the last state and are recovering it from your peer then you are trusting it, no matter if it's encrypted or not.
This could include having you close the channel with a previous state where they had a higher balance, or for Phoenix (if i read the blog post correctly) even continuing the channel operation from a past state when they had a higher balance, or even the catastrophic scenario you mentioned (if Phoenix is at all able to force close..).

121614: <p>Phoenix wallet is a unique Lightning wallet in that, among other things, it allows the user to restore channels by simply entering their seed. According to ACINQ's <a href="https://medium.com/@ACINQ/phoenix-wallet-part-3-backup-f63a9470d4e7" rel="nofollow noreferrer">blogpost</a>, this is how they achieve it:</p>
<blockquote>
<p>TL; DR: Each time channels are updated, Phoenix sends an encrypted version of their data to its peer. This allows for easy backup/restore of channels while maintaining privacy.</p>
</blockquote>
<p>In the case of Phoenix wallet, the peer is always ACINQ, but my question applies to any similar peer backup solutions: what's to stop the peer from making me recover an old channel state, and claim all my funds when I try to close it?</p>
 101498: <p>Nothing.</p>
<p>If you have lost the last state and are recovering it from your peer then <strong>you are trusting it</strong>, no matter if it's encrypted or not.</p>
<p>This could include having you close the channel with a previous state where they had a higher balance, or for Phoenix (if i read the blog post correctly) even continuing the channel operation from a past state when they had a higher balance, or even the catastrophic scenario you mentioned (if Phoenix is at all able to force close..).</p>
