FA-72500 / Check-digit algorithms / Member archive

IBAN accepts check digits 00 and 01 · case 05

An IBAN whose check digits are the out-of-range aliases 00 or 01 is accepted.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

IBAN validation for the countries DE 22, GB 22, FR 27, NL 18, BE 16, NO 15, MT 31 (other countries: "malformed"). Spaces (print format) are removed and letters are upper-cased. The check digits must be 02..98. Move the first four characters to the end, replace letters with 10..35, and the IBAN is "valid" when the number is 1 mod 97.

Why this case matters

Payment initiation rejects mistyped account identifiers before submitting transfers.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression ["DE01435241396484727591"]	`"valid"`	`"malformed"`	Failed

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