某guo安卓apk题库破解加密并解密

此apk各种脱壳混淆导致很难反编译，记录核心内容方便解密

 解密内容 = (com.dep.xxx.utils.p.b(加密串, 解密KEY));

p.b的class还原

package com.dep.xxx.utils;

import android.util.Base64;
import java.io.Closeable;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.net.SocketException;
import java.net.URL;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Random;
import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

/* loaded from: classes12.dex */
public class p {
    private static final String a = "AES";

    /* renamed from: b  reason: collision with root package name */
    public static final int f20374b = 16;

    /* renamed from: c  reason: collision with root package name */
    private static final Charset f20375c = StandardCharsets.UTF_8;

    /* renamed from: d  reason: collision with root package name */
    private static final String f20376d = "0";

    /* renamed from: e  reason: collision with root package name */
    private static final String f20377e = "AES/ECB/PKCS7Padding";

    /* renamed from: f  reason: collision with root package name */
    private static final String f20378f = "AES/CBC/PKCS7Padding";

    private static void a(Closeable closeable) {
        if (closeable != null) {
            try {
                closeable.close();
            } catch (Exception e2) {
                e2.printStackTrace();
                com.biguo.utils.b.e.c("dddd", Arrays.toString(e2.getStackTrace()), e2);
            }
        }
    }

    public static String b(String str, String str2) {
        try {
            byte[] decode = Base64.decode(str, 2);
            Cipher cipher = Cipher.getInstance(f20377e);
            cipher.init(2, f(str2));
            return new String(cipher.doFinal(decode), f20375c);
        } catch (Exception e2) {
            e2.printStackTrace();
            return null;
        }
    }

    public static File c(String str, String str2, String str3, String str4) throws Exception {
        try {
            CipherInputStream cipherInputStream = new CipherInputStream(new URL(str).openStream(), g(str4, 2));
            File file = new File(str2, str3);
            FileOutputStream fileOutputStream = new FileOutputStream(file);
            byte[] bArr = new byte[8192];
            while (true) {
                int read = cipherInputStream.read(bArr);
                if (read != -1) {
                    fileOutputStream.write(bArr, 0, read);
                    fileOutputStream.flush();
                } else {
                    fileOutputStream.close();
                    cipherInputStream.close();
                    return file;
                }
            }
        } catch (Exception e2) {
            e2.printStackTrace();
            com.biguo.utils.b.e.c("dddd", Arrays.toString(e2.getStackTrace()), e2);
            throw new SocketException();
        }
    }

    public static String d(String str, String str2) {
        try {
            Cipher cipher = Cipher.getInstance(f20377e);
            cipher.init(1, f(str2));
            return Base64.encodeToString(cipher.doFinal(str.getBytes(f20375c)), 0);
        } catch (Exception e2) {
            e2.printStackTrace();
            com.biguo.utils.b.e.c("dddd", Arrays.toString(e2.getStackTrace()), e2);
            return null;
        }
    }

    public static File e(String str, String str2, String str3, String str4) {
        try {
            CipherInputStream cipherInputStream = new CipherInputStream(new FileInputStream(str), g(str4, 1));
            File file = new File(str2, str3);
            FileOutputStream fileOutputStream = new FileOutputStream(file);
            byte[] bArr = new byte[8192];
            while (true) {
                int read = cipherInputStream.read(bArr);
                if (read != -1) {
                    fileOutputStream.write(bArr, 0, read);
                    fileOutputStream.flush();
                } else {
                    cipherInputStream.close();
                    a(fileOutputStream);
                    return file;
                }
            }
        } catch (Exception e2) {
            e2.printStackTrace();
            com.biguo.utils.b.e.c("dddd", Arrays.toString(e2.getStackTrace()), e2);
            return null;
        }
    }

    public static SecretKeySpec f(String str) {
        return new SecretKeySpec(i(str).getBytes(f20375c), a);
    }

    private static Cipher g(String str, int i2) {
        try {
            SecretKeySpec f2 = f(str);
            Cipher cipher = Cipher.getInstance(f20378f);
            cipher.init(i2, f2, new IvParameterSpec(new byte[cipher.getBlockSize()]));
            return cipher;
        } catch (Exception e2) {
            e2.printStackTrace();
            com.biguo.utils.b.e.c("dddd", Arrays.toString(e2.getStackTrace()), e2);
            return null;
        }
    }

    public static String h() {
        StringBuilder sb = new StringBuilder();
        Random random = new Random(System.currentTimeMillis());
        while (sb.length() < 16) {
            int nextInt = random.nextInt(26);
            if (random.nextInt(2) % 2 == 0) {
                sb.append((char) (nextInt + 65));
            } else {
                sb.append((char) (nextInt + 97));
            }
        }
        return sb.toString();
    }

    private static String i(String str) {
        int length = str.length();
        if (length < 16) {
            StringBuilder sb = new StringBuilder();
            sb.append(str);
            for (int i2 = 0; i2 < 16 - length; i2++) {
                sb.append("0");
            }
            return sb.toString();
        }
        return str;
    }
}

再看看解密Key来源

 String b2 = com.dep.xxx.utils.n0.b(baseResponse.getData().getKey(), PracticeV3Presenter.this.f15272q[1]);

可以看到需要找到f15272q，核心代码如下

    public String i0() {
        try {
            String[] e2 = com.dep.xxx.utils.n0.e();
            this.f15272q = e2;
            com.biguo.utils.b.e.a("dddd", e2);
            if (this.f15272q[0].startsWith(c.c.f1719m)) {
                this.f15272q[0] = this.f15272q[0].substring(1);
            }
            if (this.f15272q[0].endsWith(c.c.f1719m)) {
                this.f15272q[0] = this.f15272q[0].substring(0, this.f15272q[0].length() - 1);
            }
            return Base64.encodeToString(String.format("-----BEGIN PUBLIC KEY-----\n%s\n-----END PUBLIC KEY-----", this.f15272q[0]).getBytes(), 0);
        } catch (NoSuchAlgorithmException unused) {
            ((e4.b) this.f36061d).U3("秘钥生成失败，请联系客服");
            return "";
        }
    }

核心还是在utils.n0.e()

    public static String[] e() throws NoSuchAlgorithmException {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(1024);
        KeyPair generateKeyPair = keyPairGenerator.generateKeyPair();
        PrivateKey privateKey = generateKeyPair.getPrivate();
        return new String[]{Base64.encodeToString(generateKeyPair.getPublic().getEncoded(), 0), Base64.encodeToString(privateKey.getEncoded(), 0)};
    }

本地生成了rsa证书，公钥转base64请求通过get发送给服务端，例如

https://www.xxx.com/api/v5/exams/getQuestionBank?code=03708&mainType=4&public_key=LS0tLS1CRUdJTiBQVUJMSUMgS0VZLS0tLS0KTUlHZk1BMEdDU3FHU0liM0RRRUJBUVVBQTRHTkFEQ0JpUUtCZ1FDVFJqRUhDc3pZNFo3VENVdlBueFphNE1yUQp4MzJoQy8zd2MrNW9wNWQyWWo5SitJNTZzT0NkUC9McVB2Yzlna1lPeTUrblg3QXFyVEovOVhOYmZjN3E4WENRCjFxblQ5ZW1TRm9XR3Y1WjUrY29oeHlhV21CVnVkMkZYUlhoUldlL295aDlZUk9EMStnbUxidEU1RVBnTHcwdzQKZFVBOFhreG41VTJHdjF6b0hRSURBUUFCCi0tLS0tRU5EIFBVQkxJQyBLRVktLS0tLQ==&isAllExam=1&professions_id=4626&cert_type=0&layer_id=1&school_id=92&province_id=21&users_id=1851315&city_id=220

待验证数据

{"result_code":1,"result_info":"请求成功","data":{"source":"file","key":"ghIIs6gpDPsGf4gqZfY2UYLqYe\/7Fr\/b2BYDWtze8U0Bl7R3SAiXhD3CXRHY62V9OKO9lqCNXDQ9vO+ncmhovXq76eEPTs00xuu01+\/rOu6vllUtx\/dBP+oxKKJEmLg5m7Ul\/m6Tk2fVqknJ\/Uzu0xfcwQzOseNhl49VKF7Sag4=","topics":[],"fileUrls":["masterTopicList\/topicList-mainType_4-code_00910-topicType_1-version_1729066317.json","masterTopicList\/topicList-mainType_4-code_00910-topicType_2-version_1729066317.json","masterTopicList\/topicList-mainType_4-code_00910-topicType_4-version_1729066317.json"]}}