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Uses new Utils.modInv function

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This commit is contained in:
Barry Brown 2024-06-13 17:32:21 +00:00
parent cb6b1f7509
commit 7ae35bc587
1 changed files with 3 additions and 2 deletions
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5
src/core/lib/Ciphers.mjs
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@ -86,7 +86,7 @@ export function affineApplication(input, a, b, alphabet, affineFn) {
}
if (Utils.gcd(a, modulus) !== 1) {
throw new OperationError("The value of `a` must be coprime to " + modulus + ".");
throw new OperationError("The value of `a` (" + a + ") must be coprime to " + modulus + ".");
}
// Apply affine function to each character in the input
@ -168,9 +168,10 @@ export function affineDecrypt(input, a, b, alphabet="a-z") {
const m = Utils.expandAlphRange(alphabet).length;
if (Utils.gcd(a, m) !== 1)
throw new OperationError("The value of `a` (" + a + ") must be coprime to " + m + ".");
const aInv = Utils.modInv(a, m);
const bInv = (m - b) % m;
if (aInv === undefined)
if (aInv === null)
throw new OperationError("The value of `a` (" + a + ") must be coprime to " + m + ".");
else return affineApplication(input, aInv, bInv, alphabet, decryptFn);
}