Rajeh Taher
66 lines
1.9 KiB
TypeScript
66 lines
1.9 KiB
TypeScript
import { hkdf } from './crypto'
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/**
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* LT Hash is a summation based hash algorithm that maintains the integrity of a piece of data
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* over a series of mutations. You can add/remove mutations and it'll return a hash equal to
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* if the same series of mutations was made sequentially.
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*/
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const o = 128
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class LTHash {
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salt: string
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constructor(e: string) {
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this.salt = e
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}
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async add(e: ArrayBuffer, t: ArrayBuffer[]): Promise<ArrayBuffer> {
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for (const item of t) {
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e = await this._addSingle(e, item)
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}
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return e
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}
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async subtract(e: ArrayBuffer, t: ArrayBuffer[]): Promise<ArrayBuffer> {
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for (const item of t) {
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e = await this._subtractSingle(e, item)
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}
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return e
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}
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async subtractThenAdd(e: ArrayBuffer, addList: ArrayBuffer[], subtractList: ArrayBuffer[]): Promise<ArrayBuffer> {
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const subtracted = await this.subtract(e, subtractList)
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return this.add(subtracted, addList)
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}
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private async _addSingle(e: ArrayBuffer, t: ArrayBuffer): Promise<ArrayBuffer> {
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const derived = new Uint8Array(await hkdf(Buffer.from(t), o, { info: this.salt })).buffer
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return this.performPointwiseWithOverflow(e, derived, (a, b) => a + b)
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}
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private async _subtractSingle(e: ArrayBuffer, t: ArrayBuffer): Promise<ArrayBuffer> {
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const derived = new Uint8Array(await hkdf(Buffer.from(t), o, { info: this.salt })).buffer
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return this.performPointwiseWithOverflow(e, derived, (a, b) => a - b)
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}
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private performPointwiseWithOverflow(
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e: ArrayBuffer,
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t: ArrayBuffer,
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op: (a: number, b: number) => number
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): ArrayBuffer {
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const n = new DataView(e)
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const i = new DataView(t)
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const out = new ArrayBuffer(n.byteLength)
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const s = new DataView(out)
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for (let offset = 0; offset < n.byteLength; offset += 2) {
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s.setUint16(offset, op(n.getUint16(offset, true), i.getUint16(offset, true)), true)
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}
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return out
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}
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}
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export const LT_HASH_ANTI_TAMPERING = new LTHash('WhatsApp Patch Integrity')
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