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The Wire web app can relatively easily lose conversation history completely when the browser's storage gets deleted or corrupted. The history is also not displayed (though unclear if it's lost or just kept from the user) when the user logs in from a new device.

When asked to warn users specifically about this data loss, a Wire developer stated that,

History loss due to storage loss in inherit with end-to-end encryption

Is this claim correct? (I assume they meant "History loss due to storage loss is inherent with end-to-end encryption".) Can't the server store the conversation history encrypted at rest, deliver it to the client on request, which will be able to decrypt it using the private key? After all, that's how E2E email services like Protonmail seem to work.

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No, loss off message history isn't inherent to end to end encryption, but it's inherent to forward secrecy.

It might be either the Wire developer conflating between e2e and FS, or they consider FS to be a crucial component of e2e, which is not entirely unreasonable viewpoint but is not one that's common.

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  • I find this bizarre, I can't imagine a way to support end-to-end encryption without the storage loss that Wire is stating, without exposing your private key. How could an app with end-to-end encryption sync history with a new device? Oh, I suppose you could sync it from the other person's history...
    – Mooing Duck
    Mar 1, 2018 at 1:24
  • It's not necessarily inherent to forward secrecy. OTR provides forward secrecy, but if you are using ZNC while having an encrypted conversation and then you disconnect and come back later, the ZNC will send you the encrypted ciphertext you missed and you will be able to decrypt it (assuming you haven't closed the program using OTR).
    – forest
    Mar 1, 2018 at 3:38
  • @forest: I guess I should clarify what I meant by loss of history in FS is that if you record the ciphertext of all communications, and clients have deleted their chat history and session key (i.e. the OTR session is closed), then there will be no way to recover the history even if you have the ciphertext and everyone's private key. Note that the encryption session is not necessarily the same as the connection session. An encryption session can last over multiple reconnection and there can be multiple encryption sessions in a single connection when clients rekeys.
    – Lie Ryan
    Mar 1, 2018 at 8:52
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One thing strictly speaking has nothing to do with the other. The goal of end-to-end encrypted instant messaging is to protect the contents of the messages from being eavesdropped on a public network, but once the message has been received and decrypted in the client, it's silent on whether the messages should be stored or not.

Some apps do try to help users dispose of messages promptly, by offering features to automatically delete messages immediately after they're read. That's a choice of the app's designer; the end-to-end transit encryption doesn't dictate this. Storing a message history does provide an avenue for somebody who's targeting you to get their hands on the messages by breaking into your devices' storage, but it's also a very convenient feature, and security is about striking balances between convenience and safety.

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  • The question isn't about weather or not to store messages, but that the messages are lost when storage is cleared and not shared between devices. You appear to have misread the question.
    – Mooing Duck
    Mar 1, 2018 at 1:25

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