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The check digit is calculated by (()), where s is the sum from step 3. This is the smallest number (possibly zero) that must be added to s {\displaystyle s} to make a multiple of 10. Other valid formulas giving the same value are 9 − ( ( s + 9 ) mod 1 0 ) {\displaystyle 9-((s+9){\bmod {1}}0)} , ( 10 − s ) mod 1 0 {\displaystyle (10-s){\bmod ...
The Luhn mod N algorithm is an extension to the Luhn algorithm (also known as mod 10 algorithm) that allows it to work with sequences of values in any even-numbered base. This can be useful when a check digit is required to validate an identification string composed of letters, a combination of letters and digits or any arbitrary set of N ...
As another example, consider the product 7 ⋅ 15 mod 17 but with R = 10. Using the extended Euclidean algorithm, compute −5 ⋅ 10 + 3 ⋅ 17 = 1, so N′ will be −3 mod 10 = 7. The Montgomery forms of 7 and 15 are 70 mod 17 = 2 and 150 mod 17 = 14, respectively.
However, the linear congruence 4x ≡ 6 (mod 10) has two solutions, namely, x = 4 and x = 9. The gcd(4, 10) = 2 and 2 does not divide 5, but does divide 6. Since gcd(3, 10) = 1, the linear congruence 3x ≡ 1 (mod 10) will have solutions, that is, modular multiplicative inverses of 3 modulo 10 will exist. In fact, 7 satisfies this congruence (i ...
If a modulus just less than a power of 2 is used (the Mersenne primes 2 31 − 1 and 2 61 − 1 are popular, as are 2 32 − 5 and 2 64 − 59), reduction modulo m = 2 e − d can be implemented more cheaply than a general double-width division using the identity 2 e ≡ d (mod m). The basic reduction step divides the product into two e-bit ...
The most direct method of calculating a modular exponent is to calculate b e directly, then to take this number modulo m.Consider trying to compute c, given b = 4, e = 13, and m = 497:
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If the time is 7:00 now, then 8 hours later it will be 3:00. Simple addition would result in 7 + 8 = 15, but 15:00 reads as 3:00 on the clock face because clocks "wrap around" every 12 hours and the hour number starts again at zero when it reaches 12. We say that 15 is congruent to 3 modulo 12, written 15 ≡ 3 (mod 12), so that 7 + 8 ≡ 3 ...