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Modulo-97

Modulo-97 checksum algorithm used in IBAN (International Bank Account Number) validation per ISO 7064. Detects up to 99% of single-digit errors and all transposition errors. Uses mod-97-10 check digit calculation.

Properties

Property	Value
Category	Checksums
Sub-category	Modular Arithmetic
Security status	🎓 Educational Only
Complexity	Beginner
Inventor	ISO 7064 standard
Year	1983
Origin	Not specified
Source	`algorithms/checksum/modulo.js`

Security

Status: 🎓 Educational Only

No vulnerabilities are recorded for this implementation.

Notes

Algorithm: Convert digits to number, compute mod 97
Used in: IBAN validation (mod-97-10)
Check digit calculation: 98 - (number mod 97)
Validation: (number with check digits) mod 97 == 1
Detects: ~99% single-digit errors
Detects: All adjacent transposition errors
For IBAN: letters converted A=10, B=11, …, Z=35
Output: remainder (0-96), or check digits (02-98)

Documentation

References

python-stdnum ISO 7064 mod 97-10 implementation

Test vectors

3 vectors ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — Simple digit sequence

Source: Modulo-97 calculation

Field	Value
`input`	`313233343536`
`expected`	`48`

Vector 2 — IBAN check digit validation

Source: Valid IBAN check digit

Field	Value
`input`	`3938`
`expected`	`01`

Vector 3 — Large digit sequence

Source: Modulo-97 overflow handling

Field	Value
`input`	`393939393939`
`expected`	`1a`

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