web/src/decrypt/qmc_wasm.ts

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import QMCCryptoModule from '@jixun/qmc2-crypto/QMC2-wasm-bundle';
// 检测文件末端使用的缓冲区大小
const DETECTION_SIZE = 40;
// 每次处理 2M 的数据
const DECRYPTION_BUF_SIZE = 2 * 1024 * 1024;
function MergeUint8Array(array: Uint8Array[]): Uint8Array {
let length = 0;
array.forEach(item => {
length += item.length;
});
let mergedArray = new Uint8Array(length);
let offset = 0;
array.forEach(item => {
mergedArray.set(item, offset);
offset += item.length;
});
return mergedArray;
}
/**
* QMC2
*
* Uint8Array
* @param {ArrayBuffer} mggBlob Blob
* @return {Promise<Uint8Array|false>}
*/
export async function DecryptQMCWasm(mggBlob: ArrayBuffer) {
// 初始化模组
const QMCCrypto = await QMCCryptoModule();
// 申请内存块,并文件末端数据到 WASM 的内存堆
const detectionBuf = new Uint8Array(mggBlob.slice(-DETECTION_SIZE));
const pDetectionBuf = QMCCrypto._malloc(detectionBuf.length);
QMCCrypto.writeArrayToMemory(detectionBuf, pDetectionBuf);
// 检测结果内存块
const pDetectionResult = QMCCrypto._malloc(QMCCrypto.sizeof_qmc_detection());
// 进行检测
const detectOK = QMCCrypto.detectKeyEndPosition(
pDetectionResult,
pDetectionBuf,
detectionBuf.length
);
// 提取结构体内容:
// (pos: i32; len: i32; error: char[??])
const position = QMCCrypto.getValue(pDetectionResult, "i32");
const len = QMCCrypto.getValue(pDetectionResult + 4, "i32");
// 释放内存
QMCCrypto._free(pDetectionBuf);
QMCCrypto._free(pDetectionResult);
if (!detectOK) {
return false;
}
// 计算解密后文件的大小。
// 之前得到的 position 为相对当前检测数据起点的偏移。
const decryptedSize = mggBlob.byteLength - DETECTION_SIZE + position;
// 提取嵌入到文件的 EKey
const ekey = new Uint8Array(
mggBlob.slice(decryptedSize, decryptedSize + len)
);
// 解码 UTF-8 数据到 string
const decoder = new TextDecoder();
const ekey_b64 = decoder.decode(ekey);
// 初始化加密与缓冲区
const hCrypto = QMCCrypto.createInstWidthEKey(ekey_b64);
const buf = QMCCrypto._malloc(DECRYPTION_BUF_SIZE);
const decryptedParts = [];
let offset = 0;
let bytesToDecrypt = decryptedSize;
while (bytesToDecrypt > 0) {
const blockSize = Math.min(bytesToDecrypt, DECRYPTION_BUF_SIZE);
// 解密一些片段
const blockData = new Uint8Array(
mggBlob.slice(offset, offset + blockSize)
);
QMCCrypto.writeArrayToMemory(blockData, buf);
QMCCrypto.decryptStream(hCrypto, buf, offset, blockSize);
decryptedParts.push(QMCCrypto.HEAPU8.slice(buf, buf + blockSize));
offset += blockSize;
bytesToDecrypt -= blockSize;
}
QMCCrypto._free(buf);
hCrypto.delete();
return MergeUint8Array(decryptedParts);
}