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Throws error if modInv didn't work

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Barry Brown 2024-06-13 06:43:54 +00:00
parent 7bef120a0a
commit 41585e0d3d
1 changed files with 6 additions and 2 deletions
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8
src/core/lib/Ciphers.mjs
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@ -166,9 +166,13 @@ export function affineEncrypt(input, a, b, alphabet="a-z") {
*/ */
export function affineDecrypt(input, a, b, alphabet="a-z") { export function affineDecrypt(input, a, b, alphabet="a-z") {
const m = Utils.expandAlphRange(alphabet).length; 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 aInv = Utils.modInv(a, m);
const bInv = (m - b) % m; const bInv = (m - b) % m;
return affineApplication(input, aInv, bInv, alphabet, decryptFn); if (aInv === undefined)
throw new OperationError("The value of `a` (" + a + ") must be coprime to " + m + ".");
else return affineApplication(input, aInv, bInv, alphabet, decryptFn);
} }
/** /**
@ -226,7 +230,7 @@ export const AFFINE_ALPHABETS = [
{name: "Letters, match case: a-z", value: "a-z"}, {name: "Letters, match case: a-z", value: "a-z"},
{name: "Letters, case sensitive: A-Za-z", value: "A-Za-z"}, {name: "Letters, case sensitive: A-Za-z", value: "A-Za-z"},
{name: "Word characters: A-Za-z0-9_", value: "A-Za-z0-9_"}, {name: "Word characters: A-Za-z0-9_", value: "A-Za-z0-9_"},
{name: "Printable ASCII: sp-~", value: " -~"} {name: "Printable ASCII: space-~", value: "\\u0020-~"}
]; ];
/** /**