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Reject IBAN check digits 00, 01 and 99 [patch] - #439
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ISO 13616 issues check digits as 98 - (n mod 97), so only 02-98 occur. 00, 01 and 99 are congruent to 97, 98 and 02 modulo 97, so the mod-97 test alone accepted an invalid twin of every IBAN with those digits. Fixes #438 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_016AQEMQSRnmweax4URvCpi3
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Fixes #438
Summary
IsIbanAttributenow rejects check digits outside 02–98 before running the mod-97 test, with the message "The value must be a valid IBAN (check digits must be 02-98)."98 - (n mod 97), so 00, 01 and 99 never occur. They are congruent to 97, 98 and 02, so the remainder test alone accepted them.Tests
Create_CheckDigitsAtEdgeOfRange_Succeeds:GB98…,GB97…,GB02WEST00000000000029still validate.Create_CheckDigitsNeverIssued_Throws:GB01WEST12340000000012,GB00WEST12340000000030,GB99WEST00000000000029throw, and the message names the check digits.Semantics.Testsuite passes (1697 passed, 8 skipped).Generated by Claude Code