65 lines
2.0 KiB
Dart
65 lines
2.0 KiB
Dart
import 'dart:typed_data';
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//图片解密：前 100 字节与 key 循环异或
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class ImageCrypto {
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//jpg/png/gif 文件头，都对不上视为加密图
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static final List<Uint8List> _featuresList = [
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Uint8List.fromList([0xff, 0xd8, 0xff]), //jpg,jpeg
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Uint8List.fromList([0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A]), //png
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Uint8List.fromList([0x47, 0x49, 0x46]), //gif
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];
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static const int _minLen = 6; //最小字节数
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static const int _encryptedLen = 100; //加密图片的数据长度
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static final Uint8List _decryptKey = Uint8List.fromList('2019ysapp7527'.codeUnits); //加密key
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static Uint8List? decrypt(Uint8List? imgBytes) {
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if (imgBytes?.isNotEmpty != true) {
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return imgBytes;
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}
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//不足 6 字节视为坏图，抛给调用方走失败（沿用老逻辑比对 6 字节魔数时越界抛错的行为）
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if (imgBytes!.length < _minLen) {
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throw RangeError.range(imgBytes.length, 0, imgBytes.length - 1, 'length');
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}
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if (_isEncrypted(imgBytes)) {
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imgBytes = _xor(imgBytes, _decryptKey, _encryptedLen);
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}
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return imgBytes;
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}
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static bool _isEncrypted(Uint8List imgBytes) {
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bool isMismatch = false;
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int featuresLen = _featuresList.length;
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for (int i = 0; i < featuresLen; i++) {
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isMismatch = false;
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for (int j = 0; j < _featuresList[i].length; j++) {
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if (_featuresList[i][j] != imgBytes[j]) {
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isMismatch = true;
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break;
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}
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}
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if (isMismatch) {
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continue;
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} else {
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break;
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}
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}
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return isMismatch;
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}
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//前 length 字节与 key 循环异或（原地修改）
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static Uint8List _xor(Uint8List src, Uint8List key, int length) {
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int srcLen = src.length;
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int keyLen = key.length;
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if (length > srcLen || length <= 0) {
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length = srcLen;
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}
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for (var i = 0; i < length; i += keyLen) {
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for (var j = 0; j < keyLen && i + j < length; j++) {
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src[i + j] ^= key[j];
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}
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}
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return src;
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}
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}
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