Hans Peter Luhn’s 1954 patent on a number-verifying computer is a direct ancestor of modern checksums and hash tables, predating widespread cryptographic hashing by decades.
Key Takeaways
The Luhn Algorithm (Modulus 10) detects all single-digit errors and all adjacent-digit transpositions except 09/90 swaps, where substitution values are identical.
The algorithm works by doubling alternating digits, summing results, and checking that the total mod 10 equals zero – simple enough for mechanical or manual verification.
It is explicitly not cryptographically secure: two-digit errors can cancel out and produce a valid checksum, making it unsuitable against malicious tampering.
One year earlier, in 1953, Luhn proposed using math to bucket searchable data in an internal IBM memo – the conceptual seed for hash tables, later refined to ensure even distribution and minimize collisions.
Modern credit card and ID number schemes layer additional algorithms on top of or instead of Luhn because of its collision weakness.
