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IDProjectCategoryView StatusLast Update
0011192Talermerchant portal webuipublic2026-09-19 14:43
Reportersebasjm Assigned ToFlorian Dold Resolution deadline
ImplementerReviewer 
Release signed byDeployed by 
VerifierCommunicator 
Data protection authority notification requiredNo  
CSIRT notification requiredNo  
Estimated effort (hours)Actual effort (hours)0 
Fast-trackNo
Work packagenone
PrioritynormalSeverityfeatureReproducibilityhave not tried
Status closedResolutionwon't fix 
Target Version1.6Fixed in Version1.6 
Summary0011192: dd 89: no enough info to distinguish between two emails if they come togheter
DescriptionMy email server had a big delay sending email and some emails reached at the same time.
I left the SPA open waiting for the email to enter the code but when I tried both code failed (maybe it was a third one that never reached, didn't test)

There should be a unique information in the email for the user to match the correct email with the verification the backend is waiting.

One way I thought this could be is instead of sending 1234-5678 we send ABC-1234-5678 (3 random upper cased letters in addition to the 8 random numbers). We can achieve this by 2 ways:

 1) extending the protocol by adding a new fiend in the response of https://docs.taler.net/core/api-merchant.html#post-[-instances-$INSTANCE]-challenge-$CHALLENGE_ID

interface ChallengeRequestResponse {
...
  // The characters sent additionally as a TAN code prefix.
  // The client should show this in the UI so the user only needs to input the other 8 numbers
  tan_id: String;
}

2) Using the last 3 characters of the challenge id for this purpose. We don't modify the protocol but this id will be the send on "resend".

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Christian Grothoff

2026-03-04 19:35

manager   ~0027985

Eh, the latest version of the backend includes the instance name, expiration date, and the purpose of the TAN. How is that not sufficient?

sebasjm

2026-03-04 19:48

developer   ~0027986

The only piece of info that is unique to the tan code is the expiration date but we don't show it in the MFA screen, we show the remaining time if is close to be expired. So no.

it's not a matter of sending more information, more also means that is more confusing (specially plain text email, or sms).
Adding 3 letter as a prefix of the code doesn't require parse the full email and the SPA should very prominently asking

Verification code: A F G - [ ][ ][ ][ ] - [ ][ ][ ][ ]

Christian Grothoff

2026-03-04 20:55

manager   ~0027987

I don't think we should do this, this is uncommon, we need to make sure e-mails are delivered quickly anyway, and having some strange prefix can lead to bad results. Just imagine the random prefix being FCK-1234 for some sensitive user. Nobody else does it, and it also is not good for auto-detection of TANs in SMS by mobile OSes for easy copy & paste.

Florian Dold

2026-08-27 12:01

manager   ~0029698

Closing this as won't fix, since as Christian noted, we've never seen any relevant service do this in the wild.

Issue History

Date ModifiedUsernameFieldChange
2026-03-04 19:09sebasjmNew Issue
2026-03-04 19:09sebasjmStatusnew => assigned
2026-03-04 19:09sebasjmAssigned To => Christian Grothoff
2026-03-04 19:35Christian GrothoffNote Added: 0027985
2026-03-04 19:36Christian GrothoffAssigned ToChristian Grothoff => sebasjm
2026-03-04 19:36Christian GrothoffStatusassigned => feedback
2026-03-04 19:48sebasjmNote Added: 0027986
2026-03-04 19:48sebasjmAssigned Tosebasjm => Christian Grothoff
2026-03-04 20:55Christian GrothoffNote Added: 0027987
2026-03-04 20:56Christian GrothoffStatusfeedback => acknowledged
2026-03-04 20:56Christian GrothoffTarget Version => post-2.0
2026-03-04 20:56Christian GrothoffAssigned ToChristian Grothoff =>
2026-03-04 20:56Christian GrothoffSeverityminor => feature
2026-03-26 14:56vecirexRelationship addedparent of 0011296
2026-03-26 14:57vecirexRelationship deletedparent of 0011296
2026-08-23 14:18Florian DoldCategorymerchant backoffice SPA => merchant portal webui
2026-08-27 12:01Florian DoldAssigned To => Florian Dold
2026-08-27 12:01Florian DoldStatusacknowledged => closed
2026-08-27 12:01Florian DoldResolutionopen => won't fix
2026-08-27 12:01Florian DoldNote Added: 0029698
2026-09-19 14:43Christian GrothoffFixed in Version => 1.6
2026-09-19 14:43Christian GrothoffTarget Versionpost-2.0 => 1.6