ISC2016训练赛 phrackCTF--Smali

测试文件：https://static2.ichunqiu.com/icq/resources/fileupload/phrackCTF/REVERSE/Crackme.smali

参考资料：https://www.cnblogs.com/lz2017/p/6917049.html

1.文件分析

使用SmaliJavaUI反编译文件，得到

/**
  * Generated by smali2java 1.0.0.558
  * Copyright (C) 2013 Hensence.com
  */

package net.bluelotus.tomorrow.easyandroid;

import android.util.Base64;
import java.io.PrintStream;
import java.security.NoSuchAlgorithmException;
import javax.crypto.NoSuchPaddingException;
import java.security.InvalidKeyException;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.BadPaddingException;
import javax.crypto.spec.SecretKeySpec;
import javax.crypto.Cipher;
import java.security.Key;
import java.security.GeneralSecurityException;

public class Crackme {
    private String str2 = "cGhyYWNrICBjdGYgMjAxNg==";
    
    public Crackme() {
        GetFlag("sSNnx1UKbYrA1+MOrdtDTA==");
    }
    
    private String GetFlag(String p1) {//将上面两段字符串经过base64解密
        byte[] "content" = Base64.decode(p1.getBytes(), 0x0);
        String "kk" = new String(Base64.decode(str2.getBytes(), 0x0));
        System.out.println(decrypt("content", "kk"));
        return null;
    }
    
    private String decrypt(byte[] p1, String p2) {//将解密后的序列，一段用来生成key，一段作为被AES加密的字符串。
        String "m" = 0x0;
        try {
            byte[] "keyStr" = p2.getBytes();
            SecretKeySpec "key" = new SecretKeySpec("keyStr", "AES");
            Cipher "cipher" = Cipher.getInstance("AES/ECB/NoPadding");
            "cipher".init(0x2, "key");
            byte[] "result" = "cipher".doFinal(p1);
            return "m";
        } catch(NoSuchPaddingException "e") {
            "e".printStackTrace();
        }
        return  "m";
    }
}

2.脚本获取

from Crypto.Cipher import AES
import base64

key = base64.b64decode("cGhyYWNrICBjdGYgMjAxNg==")
str1 = base64.b64decode("sSNnx1UKbYrA1+MOrdtDTA==")

cryptor = AES.new(key, AES.MODE_ECB)
result = cryptor.decrypt(str1)
print(result)

3.get flag！

PCTF{Sm4liRiver}