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utils: make equalBytes constant-time

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Paul Miller 2023-12-10 22:04:01 +00:00
parent 4ffb68853d
commit 8e6c19de2b
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1 changed files with 7 additions and 5 deletions
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12
src/abstract/utils.ts
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@ -20,6 +20,7 @@ function isBytes(a: any): a is Uint8Array {
return a instanceof Uint8Array || a.constructor.name === 'Uint8Array'; return a instanceof Uint8Array || a.constructor.name === 'Uint8Array';
} }
// Array where index 0xf0 (240) is mapped to string 'f0'
const hexes = /* @__PURE__ */ Array.from({ length: 256 }, (_, i) => const hexes = /* @__PURE__ */ Array.from({ length: 256 }, (_, i) =>
i.toString(16).padStart(2, '0') i.toString(16).padStart(2, '0')
); );
@ -147,11 +148,12 @@ export function concatBytes(...arrays: Uint8Array[]): Uint8Array {
return res; return res;
} }
export function equalBytes(b1: Uint8Array, b2: Uint8Array) { // Compares 2 u8a-s in kinda constant time
// We don't care about timing attacks here export function equalBytes(a: Uint8Array, b: Uint8Array) {
if (b1.length !== b2.length) return false; if (a.length !== b.length) return false;
for (let i = 0; i < b1.length; i++) if (b1[i] !== b2[i]) return false; let diff = 0;
return true; for (let i = 0; i < a.length; i++) diff |= a[i] ^ b[i];
return diff === 0;
} }
// Global symbols in both browsers and Node.js since v11 // Global symbols in both browsers and Node.js since v11