Android常见加密算法实现

逆向的时候，经常会遇到各种加密算法，google查起来比较乱，这里整理下。

编码：base64、
哈希算法：md5、sha-1、sha-256
对称加密：AES、DES、3DES
非对称加密：RSA

一、常见算法的Android实现

base64

//编码
byte[] data = text.getBytes("UTF-8");
String base64 = Base64.encodeToString(data, Base64.DEFAULT);

//解码
String x = ""
byte[] data = Base64.decode(x, Base64.DEFAULT);
String text = new String(data, "UTF-8");

md5、sha-1、sha-256

写法都一样，区别在于MessageDigest.getInstance(“MD5”)指明要使用的算法，

fun md5(str: String): String {
    val digest = MessageDigest.getInstance("MD5")
    val result = digest.digest(str.toByteArray())
    //没转16进制之前是16位
    println("result${result.size}")
    //转成16进制后是32字节
    return toHex(result)
}

fun sha1(str:String): String {
    val digest = MessageDigest.getInstance("SHA-1")
    val result = digest.digest(str.toByteArray())
    return toHex(result)
}

fun sha256(str:String): String {
    val digest = MessageDigest.getInstance("SHA-256")
    val result = digest.digest(str.toByteArray())
    return toHex(result)
}

DES

这里DES加解密的区别只有一点，
cipher.init(Cipher.DECRYPT_MODE, securekey, sr)，Cipher.DECRYPT_MODE为解密，Cipher.ENCRYPT_MODE为加密。

//DES加密
	//DES加密的key必须是8个字节
	String key="mykeysss"; 
    // 生成一个可信任的随机数
    SecureRandom sr = new SecureRandom();

    // 从原始密钥数据创建DESKeySpec对象
    DESKeySpec dks = new DESKeySpec(key.getBytes());

    // 创建一个密钥工厂，然后用它把DESKeySpec转换成SecretKey对象
    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
    SecretKey securekey = keyFactory.generateSecret(dks);

    // Cipher对象实际完成加密操作
    Cipher cipher = Cipher.getInstance("DES"); //默认为DES/ECB/PKCS5Padding

    // 用密钥初始化Cipher对象
    cipher.init(Cipher.ENCRYPT_MODE, securekey, sr);

    return cipher.doFinal(data);

//DES解密
	//DES解密的key必须是8个字节
	String key="mykeysss";
    // 生成一个可信任的随机数源
    SecureRandom sr = new SecureRandom();

    // 从原始密钥数据创建DESKeySpec对象
    DESKeySpec dks = new DESKeySpec(key.getBytes());

    // 创建一个密钥工厂，然后用它把DESKeySpec转换成SecretKey对象
    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("DES");
    SecretKey securekey = keyFactory.generateSecret(dks);

    // Cipher对象实际完成解密操作
    Cipher cipher = Cipher.getInstance("DES"); //默认为DES/ECB/PKCS5Padding

    // 用密钥初始化Cipher对象
    cipher.init(Cipher.DECRYPT_MODE, securekey, sr);

    return cipher.doFinal(data);

AES

AES加解密的区别也是只有一个地方，cipher.init(Cipher.DECRYPT_MODE, skeySpec)，Cipher.DECRYPT_MODE为解密，Cipher.ENCRYPT_MODE 加密

//AES加密	
    String key = "mysecret";
    byte[] raw = key.getBytes("utf-8");
    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");

    //初始化cipher 算法/模式/补码方式
    Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
    cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

    //加密
    byte[] bytesContent;
    byte[] enc = cipher.doFinal(bytesContent);
    return enc;
    
    
//AES解密
    //key相关
    byte[] raw = key.getBytes("utf-8");
    SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");

    //"算法/模式/补码方式" 初始化cipher
    Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
    cipher.init(Cipher.DECRYPT_MODE, skeySpec);

    //执行解密
    byte[] bytesContent;
    byte[] dec = cipher.doFinal(bytesContent);
    return dec;

RSA

//秘钥长度为1024 生成公钥和私钥
KeyPairGenerator keyPairGenerator=KeyPairGenerator.getInstance("RSA");
keyPairGenerator.initialize(1024);
KeyPair keyPair= keyPairGenerator.generateKeyPair();

//获取公钥 私钥
PublicKey publicKey=keyPair.getPublic();
PrivateKey privateKey=keyPair.getPrivate();

//公钥加密 java默认"RSA"="RSA/ECB/PKCS1Padding"
Cipher cipher=Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
byte[] encBytes = cipher.doFinal(bytesData);



//私钥解密 java默认"RSA"="RSA/ECB/PKCS1Padding"
Cipher cipher1=Cipher.getInstance("RSA");
cipher1.init(Cipher.DECRYPT_MODE, privateKey);
byte[] decBytes = cipher1.doFinal(encBytes);
Log.d("xxx",new String(decBytes));

二、python实现

逆向时需要进行算法验证，比较讨厌java代码的写法，可以用python进行验证。

python base64

import base64

s = "mykey"
# 必须为byte类型
encoder = base64.b64encode(s.encode("utf-8"))
print(encoder) # byte类型 b'5oiR5piv5LiA5Liq5a2X56ym5Liy'
print(encoder.decode('utf-8')) # str类型 5oiR5piv5LiA5Liq5a2X56ym5Liy

# 解码过程
#参数为string类型
s = '5oiR5piv5LiA5Liq5a2X56ym5Liy'
decoder = base64.b64decode(s)
print(decoder.decode('utf-8')) # str类型

python DES

需要保证ECB或CBC模式、padmode与java实现一致。例如java的Cipher.getInstance(“DES”)默认为DES/ECB/PKCS5Padding模式。

from pyDes import *

def des_encrypt(s):
    secret_key = 'QExW+yCC'
    iv = secret_key
    k = des(secret_key, ECB, iv, pad=None, padmode=PAD_PKCS5)
    en = k.encrypt(s, padmode=PAD_PKCS5)
    return en


def des_descrypt(s):
    secret_key = 'QExW+yCC'
    iv = secret_key
    k = des(secret_key, ECB, iv, pad=None, padmode=PAD_PKCS5)
    de = k.decrypt(s, padmode=PAD_PKCS5)
    return de

python AES

#pip3 install pycryptodome
from Crypto.Cipher import AES
data = b"aaaaaaa"
key = b'Sixteen byte key'
cipher = AES.new(key, AES.MODE_EAX)
nonce = cipher.nonce
ciphertext, tag = cipher.encrypt_and_digest(data)
print(ciphertext, tag)


key = b'Sixteen byte key'
cipher = AES.new(key, AES.MODE_EAX, nonce=nonce)
plaintext = cipher.decrypt(ciphertext)
try:
    cipher.verify(tag)
    print("The message is authentic:", plaintext)
except ValueError:
    print("Key incorrect or message corrupted")

python RSA

>>> from Crypto.PublicKey import RSA
>>>
>>> key = RSA.generate(2048)
>>> f = open('mykey.pem','wb')
>>> f.write(key.export_key('PEM'))
>>> f.close()
...
>>> f = open('mykey.pem','r')
>>> key = RSA.import_key(f.read())

三、openssl命令

使用openssl命令似乎更方便

base64

编码

1	echo m4bln \| openssl base64

解码

1	echo YWJjCg== \| openssl base64 -d

md5/sha1/sha256

1
2
3

echo abc | openssl md5
echo abc | openssl sha1
echo abc | openssl sha256

des/aes/rsa

待补充

参考资料：

android官方文档-加密 https://developer.android.com/guide/topics/security/cryptography?hl=zh-cn
frida hook AES DES RSA 自吐算法 https://zhuanlan.zhihu.com/p/320229007