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Fix password generator modulo bias with rejection sampling

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Use single-byte rejection sampling: generate byte, reject if >= largest multiple of charset length, then modulo. Eliminates bias from c.charAt(arr[i] % c.length).
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Zaki
2026-05-09 22:28:54 +01:00
parent 46d7ca3694
commit 69b17e4505
1 changed files with 1 additions and 1 deletions
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js/app.js
+1 -1
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@@ -425,7 +425,7 @@ function genPreset(len, chars) {
genPwd(); genPwd();
playSound('click'); playSound('click');
} }
function genPwd() { const l = parseInt(document.getElementById('pwdLen').value); let c = ''; if (document.getElementById('useUpper').checked) c += 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'; if (document.getElementById('useLower').checked) c += 'abcdefghijklmnopqrstuvwxyz'; if (document.getElementById('useNum').checked) c += '0123456789'; if (document.getElementById('useSym').checked) c += '!@#$%^&*()_+-=[]{}|;:,.<>?'; if (!c) { document.getElementById('genPreview').textContent = 'Select option'; return; } let p = ''; const arr = new Uint32Array(l); crypto.getRandomValues(arr); for (let i = 0; i < l; i++) p += c.charAt(arr[i] % c.length); genPwdVal = p; document.getElementById('genPreview').textContent = p; } function genPwd() { const l = parseInt(document.getElementById('pwdLen').value); let c = ''; if (document.getElementById('useUpper').checked) c += 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'; if (document.getElementById('useLower').checked) c += 'abcdefghijklmnopqrstuvwxyz'; if (document.getElementById('useNum').checked) c += '0123456789'; if (document.getElementById('useSym').checked) c += '!@#$%^&*()_+-=[]{}|;:,.<>?'; if (!c) { document.getElementById('genPreview').textContent = 'Select option'; return; } let p = ''; const max = 256 - (256 % c.length); const buf = new Uint8Array(1); for (let i = 0; i < l; i++) { do { crypto.getRandomValues(buf); } while (buf[0] >= max); p += c.charAt(buf[0] % c.length); } genPwdVal = p; document.getElementById('genPreview').textContent = p; }
function useGen() { function useGen() {
if (!genPwdVal) genPwd(); if (!genPwdVal) genPwd();
// Put the generated password into the add‑modal’s password field // Put the generated password into the add‑modal’s password field