我需要解密从服务器接收到的一些数据,编写API的程序员将我定向到此Encrypter类,以查看他过去用于加密的内容。
现在基于该类,我发现所使用的算法是AES128 CBC,并且我接收到的字符串是Base64编码的,并且包含其他数据,而不仅仅是密文。
即,如果我收到以下字符串:
eyJpdiI6InJsSzRlU3pDZTBBUVNwMzdXMjVcL0tBPT0iLCJ2YWx1ZSI6Ik5JOENsSVVWaWk2RGNhNlwvWjJNeG94UzVkclwvMGJOREQreWUyS1UzclRMND0iLCJtYWMiOiJhZTZkYjNkNGM2ZTliNmU0ZTc0MTRiNDBmMzFlZTJhNTczZWIxMjk4N2YwMjlhODA1NTIyMDEzODljNDY2OTk2In0
经过base64解码后,我得到:
{"iv":"rlK4eSzCe0AQSp37W25\/KA==","value":"NI8ClIUVii6Dca6\/Z2MxoxS5dr\/0bNDD+ye2KU3rTL4=","mac":"ae6db3d4c6e9b6e4e7414b40f31ee2a573eb12987f029a80552201389c466996"}
基于line 99的Encrypter类(iv = base64_decode($payload['iv']);),I执行另一解码的base64上iv和value,并得到了一个iv长度为16的那些我作为参数下面的传递函数:
line 99
Encrypter
iv = base64_decode($payload['iv']);
iv
value
public static String decrypt(String iv, String encryptedData) throws Exception { byte[] keyValue = "zy2dEd1pKG5i3WuWbvOBolFQR84AYbvN".getBytes(); Key key = new SecretKeySpec(keyValue, "AES"); Cipher c = Cipher.getInstance("AES/CBC/PKCS7Padding"); c.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv.getBytes())); byte[] decordedValue = Base64.decode(encryptedData.getBytes(), Base64.DEFAULT); byte[] decValue = c.doFinal(decordedValue); return new String(decValue); }
但是我收到以下错误:
10-06 19:13:33.601 12895-12895/? W/System.err: java.security.InvalidAlgorithmParameterException: expected IV length of 16 10-06 19:13:33.601 12895-12895/? W/System.err: at com.android.org.conscrypt.OpenSSLCipher.engineInitInternal(OpenSSLCipher.java:281) 10-06 19:13:33.601 12895-12895/? W/System.err: at com.android.org.conscrypt.OpenSSLCipher.engineInit(OpenSSLCipher.java:323) 10-06 19:13:33.601 12895-12895/? W/System.err: at javax.crypto.Cipher.init(Cipher.java:751) 10-06 19:13:33.601 12895-12895/? W/System.err: at javax.crypto.Cipher.init(Cipher.java:701) 10-06 19:13:33.601 12895-12895/? W/System.err: at com.example.kushtrim.testproject.MainActivity.decrypt(MainActivity.java:62) 10-06 19:13:33.601 12895-12895/? W/System.err: at com.example.kushtrim.testproject.MainActivity.onCreate(MainActivity.java:45) 10-06 19:13:33.601 12895-12895/? W/System.err: at android.app.Activity.performCreate(Activity.java:5990) 10-06 19:13:33.601 12895-12895/? W/System.err: at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106) 10-06 19:13:33.601 12895-12895/? W/System.err: at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278) 10-06 19:13:33.601 12895-12895/? W/System.err: at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 10-06 19:13:33.601 12895-12895/? W/System.err: at android.app.ActivityThread.access$800(ActivityThread.java:151) 10-06 19:13:33.601 12895-12895/? W/System.err: at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 10-06 19:13:33.602 12895-12895/? W/System.err: at android.os.Handler.dispatchMessage(Handler.java:102) 10-06 19:13:33.602 12895-12895/? W/System.err: at android.os.Looper.loop(Looper.java:135) 10-06 19:13:33.602 12895-12895/? W/System.err: at android.app.ActivityThread.main(ActivityThread.java:5254) 10-06 19:13:33.602 12895-12895/? W/System.err: at java.lang.reflect.Method.invoke(Native Method) 10-06 19:13:33.602 12895-12895/? W/System.err: at java.lang.reflect.Method.invoke(Method.java:372) 10-06 19:13:33.602 12895-12895/? W/System.err: at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) 10-06 19:13:33.602 12895-12895/? W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
注意: 字符串的iv长度为16,但iv.getBytes()返回长度为26的数组。
iv.getBytes()
有人可以指出我出了问题的地方,以及如何解决它。谢谢/
编辑 注释之后,我进行了一些更改,解决了上述错误: 在进行base64解码之前iv,将字节转换为String,然后将该String传递给解密方法,该方法在其上调用了getBytes()。不知何故,字节数组的长度为26。 将我在base64解码后获得的字节数组发送给解密方法解决了该问题。 现在的方法如下:
public static String decrypt(byte[] iv, String encryptedData) throws Exception { byte[] keyValue = "zy2dEd1pKG5i3WuWbvOBolFQR84AYbvN".getBytes(); Key key = new SecretKeySpec(keyValue, "AES"); Cipher c = Cipher.getInstance("AES/CBC/PKCS7Padding"); c.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv)); byte[] decordedValue = Base64.decode(encryptedData.getBytes(), Base64.DEFAULT); byte[] decValue = c.doFinal(decordedValue); return new String(decValue); }
现在,我又 遇到了 一个 奇怪的 问题: 首先加密的文本是KushtrimPacaj,但是解密的文本是 s:13:"KushtrimPacaj";。那另一部分是哪里来的呢?13也许代表长度KushtrimPacaj?
KushtrimPacaj
s:13:"KushtrimPacaj";
您可以在padAndMcrypt()函数中看到,给定的$ value是使用PHP的serialize()function序列化的。您可以用Java 重新实现该unserialize()功能,或者如果您始终使用PHP加密字符串,则可以自己拆分字节数组。
padAndMcrypt()
serialize()
unserialize()
int firstQuoteIndex = 0; while(decValue[firstQuoteIndex] != (byte)'"') firstQuoteIndex++; return new String(Arrays.copyOfRange(decValue, firstQuoteIndex + 1, decValue.length-2));
完整代码:
public static String decrypt(byte[] keyValue, String ivValue, String encryptedData) throws Exception { Key key = new SecretKeySpec(keyValue, "AES"); byte[] iv = Base64.decode(ivValue.getBytes("UTF-8"), Base64.DEFAULT); byte[] decodedValue = Base64.decode(encryptedData.getBytes("UTF-8"), Base64.DEFAULT); Cipher c = Cipher.getInstance("AES/CBC/PKCS7Padding"); // or PKCS5Padding c.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv)); byte[] decValue = c.doFinal(decodedValue); int firstQuoteIndex = 0; while(decValue[firstQuoteIndex] != (byte)'"') firstQuoteIndex++; return new String(Arrays.copyOfRange(decValue, firstQuoteIndex + 1, decValue.length-2)); }
验证MAC始终是一个好主意,因为它可以防止某些攻击,例如padding oracle攻击。这也是检测密文的一般修改的一种非常好的方法。
具有MAC验证的完整代码:
public static String decrypt(byte[] keyValue, String ivValue, String encryptedData, String macValue) throws Exception { Key key = new SecretKeySpec(keyValue, "AES"); byte[] iv = Base64.decode(ivValue.getBytes("UTF-8"), Base64.DEFAULT); byte[] decodedValue = Base64.decode(encryptedData.getBytes("UTF-8"), Base64.DEFAULT); SecretKeySpec macKey = new SecretKeySpec(keyValue, "HmacSHA256"); Mac hmacSha256 = Mac.getInstance("HmacSHA256"); hmacSha256.init(macKey); hmacSha256.update(ivValue.getBytes("UTF-8")); byte[] calcMac = hmacSha256.doFinal(encryptedData.getBytes("UTF-8")); byte[] mac = Hex.decodeHex(macValue.toCharArray()); if (!secureEquals(calcMac, mac)) return null; // or throw exception Cipher c = Cipher.getInstance("AES/CBC/PKCS7Padding"); // or PKCS5Padding c.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv)); byte[] decValue = c.doFinal(decodedValue); int firstQuoteIndex = 0; while(decValue[firstQuoteIndex] != (byte)'"') firstQuoteIndex++; return new String(Arrays.copyOfRange(decValue, firstQuoteIndex + 1, decValue.length-2)); } /* Constant-time compare to prevent timing attacks on invalid authentication tags. */ public static boolean secureEquals(final byte[] known, final byte[] user) { int knownLen = known.length; int userLen = user.length; int result = knownLen ^ userLen; for (int i = 0; i < knownLen; i++) { result |= known[i] ^ user[i % userLen]; } return result == 0; }