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44 lines
2 KiB
Markdown
44 lines
2 KiB
Markdown
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Migrating smack-omemo from 4.2.1 to 4.x.x
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=========================================
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The implementation of smack-omemo and smack-omemo-signal was originally started as an
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academic project under pressure of time.
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For that reason, the API was not perfect when OMEMO support was first introduced in
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Smack in version 4.2.1.
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Many issues of smack-omemo have been resolved over the course of the last year in
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a major effort, which is why smack-omemo and smack-omemo-signalwere excluded from
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the 4.2.2 release.
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During this time major parts of the implementation were redone and the API changed
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as a consequence of that. This guide will go through all notable changes in order
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to make the process of upgrading as easy and straight forward as possible.
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## Trust
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One major change is, that the OmemoStore implementations no longer store trust decisions.
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Methods related to trust have been removed from OmemoStore implementations.
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Instead the client is now responsible to store those.
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Upon startup, the client now must pass an `OmemoTrustCallback` to the `OmemoManager`
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which is used to access and change trust decisions.
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It is recommended for the client to store trust decisions as tuples of (omemo device,
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fingerprint of identityKey, trust state).
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When querying a trust decision (aka. "Is this fingerprint trusted for that device?),
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the local fingerprint should be compared to the provided fingerprint.
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The method signatures for setting and querying trust from inside the OmemoManager are
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still the same. Internally they access the `OmemoTrustCallback` set by the client.
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## Encryption
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Message encryption in smack-omemo 4.2.1 was ugly. Encryption for multiple devices
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could fail because session negotiation could go wrong, which resulted in an
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exception, which contained all devices with working sessions.
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That exception could then be used in
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`OmemoManager.encryptForExistingSessions(CannotEstablishOmemoSessionException exception, String message)`,
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to encrypt the message for all devices with a session.
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The new API is
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