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web/src/decrypt/qmcv2.ts

95 lines
3.1 KiB

import QMCCryptoModule from '@jixun/qmc2-crypto';
// EOF Magic detection.
const DETECTION_SIZE = 40;
// Process in 2m buffer size
const DECRYPTION_BUF_SIZE = 2 * 1024 * 1024;
/**
* 解密一个 QMC2 加密的文件。
*
* 如果检测并解密成功,返回解密后的 Uint8Array 数组,按顺序拼接即可得到完整文件。
* 若失败,返回 `null`。
* @param {ArrayBuffer} mggBlob 读入的文件 Blob
* @param {string} name 文件名
* @return {Promise<Uint8Array[]|null>}
*/
export async function decryptMGG(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");
const detectionError = QMCCrypto.UTF8ToString(pDetectionResult + 8);
// 释放内存
QMCCrypto._free(pDetectionBuf);
QMCCrypto._free(pDetectionResult);
if (detectOK) {
// 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;
// $prog.max = decryptedSize;
// 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;
// $prog.value = offset;
// 避免网页卡死,让 event loop 处理一下其它事件。
// Worker 应该不需要等待也可以?
// await new Promise((resolve) => setTimeout(resolve));
}
QMCCrypto._free(buf);
hCrypto.delete();
return decryptedParts;
} else {
throw new Error("ERROR: could not decrypt\n " + detectionError);
}
}