[BUG] Unable to send messages due to "Invalid ciphertext" response from node

[ceodoe]

Code of conduct

• I have read and agree to adhere to the Code of Conduct

Self-training on how to write a bug report

• I have learned how to write a bug report

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

Every message I try to send results in a 400 HTTP response code, with the message "Invalid ciphertext". I am using the F-Droid variant of the app from the official Session F-Droid repository, and I have not modified the app in any way—completely vanilla.

What I've tried:

• Long-pressing a message and tapping "Resend": same error message reappears
• Changing networks (2 different wifi networks, 1 mobile data): no change
• Force-quitting and restarting Session: no change
• Emptying the app cache: no change

I would try to generate a new path, but the app doesn't seem to expose that functionality. I'm getting responses from different IPs in the error messages, so this seems like it's client related instead of node/server related.

Expected Behavior

Messages send.

Steps To Reproduce

1. Attempt to send message
2. Observe that it does not send and instead returns an error

Android Version

15

Session Version

1.33.5 (4525 - 57e3ea)

Anything else?

Screenshot:

Relevant logs (I cut out the 30,000 log lines ahead of when this issue started occurring today):

2026-09-17 17:10:44.558 GMT+02:00 D Poller: MainPoller: Delay next poll for 9998ms
2026-09-17 17:10:44.604 GMT+02:00 D BatchApiExecutor: Sending 1 batched requests, with first=SnodeApiRequest(GetInfoApi, snode=https://51.178.47.243:22021)
2026-09-17 17:10:44.604 GMT+02:00 D OnionSessionApiExecutor: Sending Onion request to Snode destination. Method: batch -- Destination: https://51.178.47.243:22021
2026-09-17 17:10:44.651 GMT+02:00 D OnionSessionApiExecutor: Networking Error, got a non 200 response code: 400, body: Invalid ciphertext
2026-09-17 17:10:44.652 GMT+02:00 W Onion Request: Path test failed for [https://141.144.243.51:22101, https://45.56.90.64:22021, https://198.71.58.236:22021]

org.thoughtcrime.securesms.api.error.ErrorWithFailureDecision: Fail: Onion error with status code 400. Message: Invalid ciphertext. Destination: Snode: https://51.178.47.243
	at org.thoughtcrime.securesms.api.AutoRetryApiExecutor.send(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:81)
	at com.bumptech.glide.integration.ktx.FlowTarget$1.invokeSuspend(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:941)
	at com.bumptech.glide.integration.ktx.FlowTarget$1.invoke(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:228)
	at kotlin.math.MathKt.startUndspatched(Unknown Source:19)
	at kotlinx.coroutines.JobKt.setupTimeout(Unknown Source:29)
	at kotlinx.coroutines.JobKt.withTimeoutOrNull(Unknown Source:75)
	at org.session.libsession.network.onion.PathManager.testPath(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:76)
	at org.session.libsession.network.onion.PathManager.access$rotatePaths(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:464)
	at org.session.libsession.network.onion.PathManager$1.invokeSuspend(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:39)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:8)
	at kotlinx.coroutines.DispatchedTask.run(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:114)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:118)
Caused by: org.session.libsession.network.model.OnionError$PathError: Onion error with status code 400. Message: Invalid ciphertext. Destination: Snode: https://51.178.47.243
	at org.thoughtcrime.securesms.api.onion.OnionSessionApiExecutor.mapHttpError$app(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:345)
	at org.thoughtcrime.securesms.api.onion.OnionSessionApiExecutor.send(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:606)
	at org.thoughtcrime.securesms.api.onion.OnionSessionApiExecutor$send$1.invokeSuspend(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:13)
	... 3 more
2026-09-17 17:10:44.756 GMT+02:00 D BatchApiExecutor: Sending 1 batched requests, with first=SnodeApiRequest(GetInfoApi, snode=https://51.178.47.243:22021)
2026-09-17 17:10:44.757 GMT+02:00 D OnionSessionApiExecutor: Sending Onion request to Snode destination. Method: batch -- Destination: https://51.178.47.243:22021
2026-09-17 17:10:44.919 GMT+02:00 D OnionSessionApiExecutor: Networking Error, got a non 200 response code: 400, body: Invalid ciphertext
2026-09-17 17:10:44.921 GMT+02:00 W Onion Request: Path test failed for [https://194.107.126.33:22021, https://104.244.78.225:22021, https://194.32.79.192:22021]

org.thoughtcrime.securesms.api.error.ErrorWithFailureDecision: Fail: Onion error with status code 400. Message: Invalid ciphertext. Destination: Snode: https://51.178.47.243
	at org.thoughtcrime.securesms.api.AutoRetryApiExecutor.send(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:81)
	at com.bumptech.glide.integration.ktx.FlowTarget$1.invokeSuspend(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:941)
	at com.bumptech.glide.integration.ktx.FlowTarget$1.invoke(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:228)
	at kotlin.math.MathKt.startUndspatched(Unknown Source:19)
	at kotlinx.coroutines.JobKt.setupTimeout(Unknown Source:29)
	at kotlinx.coroutines.JobKt.withTimeoutOrNull(Unknown Source:75)
	at org.session.libsession.network.onion.PathManager.testPath(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:76)
	at org.session.libsession.network.onion.PathManager.access$rotatePaths(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:464)
	at org.session.libsession.network.onion.PathManager$rotatePaths$1.invokeSuspend(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:12)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:8)
	at kotlinx.coroutines.internal.ScopeCoroutine.afterResume(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:7)
	at kotlinx.coroutines.AbstractCoroutine.resumeWith(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:23)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:33)
	at kotlinx.coroutines.DispatchedTask.run(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:114)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:118)
Caused by: org.session.libsession.network.model.OnionError$PathError: Onion error with status code 400. Message: Invalid ciphertext. Destination: Snode: https://51.178.47.243
	at org.thoughtcrime.securesms.api.onion.OnionSessionApiExecutor.mapHttpError$app(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:345)
	at org.thoughtcrime.securesms.api.onion.OnionSessionApiExecutor.send(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:606)
	at org.thoughtcrime.securesms.api.onion.OnionSessionApiExecutor$send$1.invokeSuspend(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:13)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(r8-map-id-e5902e8549df701aeea63ce0067fd87a6016717dec98d83d2f0c6cdf3faa83a5:8)
	... 2 more

[mpretty-cyro]

@ceodoe Thanks for the detailed report, and for the log they were enough to find the defect.

In the two path tests you pasted, the candidate paths share no nodes, but the destination snode is the same in both. The constant is the destination, not the path. That destination is not chosen at random (the path test always targets the first eligible node in the local snode pool) so a single node that rejects onion payloads will fail every path test on your device, indefinitely, no matter how healthy the paths are.

This is a client-side issue, though the reason is a little messy. We deliberately don't penalise a node for most error codes because we can't reliably tell whether the error came from a hop or the destination, and penalising on every unknown error made clients rebuild paths far too aggressively. The safety net for that leniency is supposed to be time-based path rotation, which runs every 10 minutes.

At the moment the safety net on Android cannot do its job. Rotation only commits a new path once it has been verified, the verification always goes to the same node, and the first hop is never replaced during a rotation. So a device that lands on a bad first hop, or on a bad verification target, stays there (and because paths are stored in the database rather than in memory, restarting doesn't clear it either). That is why force-quitting, clearing the cache and changing networks all made no difference.

I'll look at putting together a couple of fixes for this: making the path-test destination a real random choice, and letting rotation replace the first hop instead of keeping it indefinitely. Together those give a device in your state a way out on its own.

[ceodoe]

@mpretty-cyro Thank you for the detailed response! Looking forward to the fix, keep up the great work 😄