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import Base64 from "../base64.js";
import { modPow, bigIntToU8Array, u8ArrayToBigInt } from "./bigint.js";
export class RSACipher {
constructor() {
this._keyLength = 0;
this._keyBytes = 0;
this._n = null;
this._e = null;
this._d = null;
this._nBigInt = null;
this._eBigInt = null;
this._dBigInt = null;
this._extractable = false;
}
get algorithm() {
return { name: "RSA-PKCS1-v1_5" };
}
_base64urlDecode(data) {
data = data.replace(/-/g, "+").replace(/_/g, "/");
data = data.padEnd(Math.ceil(data.length / 4) * 4, "=");
return Base64.decode(data);
}
_padArray(arr, length) {
const res = new Uint8Array(length);
res.set(arr, length - arr.length);
return res;
}
static async generateKey(algorithm, extractable, _keyUsages) {
const cipher = new RSACipher;
await cipher._generateKey(algorithm, extractable);
return { privateKey: cipher };
}
async _generateKey(algorithm, extractable) {
this._keyLength = algorithm.modulusLength;
this._keyBytes = Math.ceil(this._keyLength / 8);
const key = await window.crypto.subtle.generateKey(
{
name: "RSA-OAEP",
modulusLength: algorithm.modulusLength,
publicExponent: algorithm.publicExponent,
hash: {name: "SHA-256"},
},
true, ["encrypt", "decrypt"]);
const privateKey = await window.crypto.subtle.exportKey("jwk", key.privateKey);
this._n = this._padArray(this._base64urlDecode(privateKey.n), this._keyBytes);
this._nBigInt = u8ArrayToBigInt(this._n);
this._e = this._padArray(this._base64urlDecode(privateKey.e), this._keyBytes);
this._eBigInt = u8ArrayToBigInt(this._e);
this._d = this._padArray(this._base64urlDecode(privateKey.d), this._keyBytes);
this._dBigInt = u8ArrayToBigInt(this._d);
this._extractable = extractable;
}
static async importKey(key, _algorithm, extractable, keyUsages) {
if (keyUsages.length !== 1 || keyUsages[0] !== "encrypt") {
throw new Error("only support importing RSA public key");
}
const cipher = new RSACipher;
await cipher._importKey(key, extractable);
return cipher;
}
async _importKey(key, extractable) {
const n = key.n;
const e = key.e;
if (n.length !== e.length) {
throw new Error("the sizes of modulus and public exponent do not match");
}
this._keyBytes = n.length;
this._keyLength = this._keyBytes * 8;
this._n = new Uint8Array(this._keyBytes);
this._e = new Uint8Array(this._keyBytes);
this._n.set(n);
this._e.set(e);
this._nBigInt = u8ArrayToBigInt(this._n);
this._eBigInt = u8ArrayToBigInt(this._e);
this._extractable = extractable;
}
async encrypt(_algorithm, message) {
if (message.length > this._keyBytes - 11) {
return null;
}
const ps = new Uint8Array(this._keyBytes - message.length - 3);
window.crypto.getRandomValues(ps);
for (let i = 0; i < ps.length; i++) {
ps[i] = Math.floor(ps[i] * 254 / 255 + 1);
}
const em = new Uint8Array(this._keyBytes);
em[1] = 0x02;
em.set(ps, 2);
em.set(message, ps.length + 3);
const emBigInt = u8ArrayToBigInt(em);
const c = modPow(emBigInt, this._eBigInt, this._nBigInt);
return bigIntToU8Array(c, this._keyBytes);
}
async decrypt(_algorithm, message) {
if (message.length !== this._keyBytes) {
return null;
}
const msgBigInt = u8ArrayToBigInt(message);
const emBigInt = modPow(msgBigInt, this._dBigInt, this._nBigInt);
const em = bigIntToU8Array(emBigInt, this._keyBytes);
if (em[0] !== 0x00 || em[1] !== 0x02) {
return null;
}
let i = 2;
for (; i < em.length; i++) {
if (em[i] === 0x00) {
break;
}
}
if (i === em.length) {
return null;
}
return em.slice(i + 1, em.length);
}
async exportKey() {
if (!this._extractable) {
throw new Error("key is not extractable");
}
return { n: this._n, e: this._e, d: this._d };
}
}
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