問題描述
我需要解密我從服務器接收到的一些數(shù)據(jù)，制作 API 的程序員將我引導到這個 Encrypter 類，看看他用來加密什么.
現(xiàn)在基于該類，我發(fā)現(xiàn)使用的算法是 AES128 CBC，并且我收到的字符串是 Base64 編碼的，并且包含其他數(shù)據(jù)，而不僅僅是密文.
即如果我收到以下字符串:
<預> <代碼> eyJpdiI6InJsSzRlU3pDZTBBUVNwMzdXMjVcL0tBPT0iLCJ2YWx1ZSI6Ik5JOENsSVVWaWk2RGNhNlwvWjJNeG94UzVkclwvMGJOREQreWUyS1UzclRMND0iLCJtYWMiOiJhZTZkYjNkNGM2ZTliNmU0ZTc0MTRiNDBmMzFlZTJhNTczZWIxMjk4N2YwMjlhODA1NTIyMDEzODljNDY2OTk2In0base64 解碼后我得到:
基于 Encrypter 類的 line 99 ( iv = base64_decode($payload['iv']); )，我執(zhí)行了另一個在 iv 和 value 上進行 base64 解碼，得到長度為 16 的 iv.我將這些作為參數(shù)傳遞給下面的函數(shù):
但我收到以下錯誤:
注意:字符串 iv 的長度為 16，但 iv.getBytes() 返回一個長度為 26 的數(shù)組.
誰能指出我哪里出錯了，我該如何解決.謝謝/
編輯
評論后，我做了一些更改，解決了上述錯誤:
在我對 iv 進行 base64 解碼之前，將字節(jié)轉換為字符串，然后將該字符串傳遞給解密方法，該方法反過來調用它的 getBytes().不知何故，這使得字節(jié)數(shù)組的長度為 26.
將我base64解碼后得到的字節(jié)數(shù)組發(fā)送到decrypt方法解決了問題.
現(xiàn)在方法如下:
現(xiàn)在我又遇到了一個奇怪的問題:
我首先加密的文本是 KushtrimPacaj ，但解密后的文本是 s:13:"KushtrimPacaj"; .那另一部分是從哪里來的?13或許代表KushtrimPacaj的長度?
編輯
這是工作代碼，以防萬一有人需要它:
https://gist.github.com/KushtrimPacaj/43a383ab419fc222f80e
可以在padAndMcrypt() 函數(shù)，即給定的 $value 使用 PHP 的 serialize() 函數(shù).你可以重新實現(xiàn) unserialize() 函數(shù)，或者如果您總是在 PHP 中加密字符串，您可以自己拆分字節(jié)數(shù)組.
int firstQuoteIndex = 0;while(decValue[firstQuoteIndex] != (byte)'"') firstQuoteIndex++;return new String(Arrays.copyOfRange(decValue, firstQuoteIndex + 1, decValue.length-2));完整代碼:
public static String decrypt(byte[] keyValue, String ivValue, String encryptedData) 拋出異常 {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);密碼 c = Cipher.getInstance("AES/CBC/PKCS7Padding");//或 PKCS5Paddingc.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));}驗證 MAC 始終是一個好主意，因為它可以防止一些攻擊，例如填充預言攻擊.這也是一種很好的檢測密文一般修改的方法.
帶有 MAC 驗證的完整代碼:
public static String decrypt(byte[] keyValue, String ivValue, String encryptedData, String macValue) 拋出異常 {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))返回空值；//或拋出異常密碼 c = Cipher.getInstance("AES/CBC/PKCS7Padding");//或 PKCS5Paddingc.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));}/* 恒定時間比較以防止對無效身份驗證標簽的定時攻擊.*/公共靜態(tài)布爾secureEquals(最終字節(jié)[]已知，最終字節(jié)[]用戶){int knownLen = known.length;int userLen = user.length;int 結果 = knownLen ^ userLen;for (int i = 0; i < knownLen; i++) {結果 |= 已知[i] ^ 用戶[i % userLen];}返回結果 == 0;}I need to decrypt some data that I receive from the server, and the programmer who made the API directed me to this Encrypter class, to see what he used to encrypt.
Now based on that class, I found that the algorithm used is AES128 CBC, and that the string I receive is Base64 encoded and contains other data, not just the ciphertext.
Namely that if I receive the following String:
after base64 decoding I get:
Based on line 99 of Encrypter class ( iv = base64_decode($payload['iv']); ), I performed another base64 decode on the iv and the value , and got an iv of length 16. Those I passed as parameters to the function below:
But I'm getting the following error:
Note: The String iv has length of 16, but iv.getBytes() returns an array of length 26.
Could someone point me to where I went wrong, and how do I fix it.
Thanks/
EDIT
After the comment, I made some changes, that resolved the above error:
Before I was base64 decoding iv, converting the bytes to String, then passing that String to the decrypt method, which in return called the getBytes() on it. Somehow this made the byte array have a length of 26.
Sending the byte array I obtained after base64 decoding to the decrypt method fixed the problem.
Now the method is as follows:
Now I have another weird problem:
The text I encrypted on the first place was KushtrimPacaj , but the decrypted text is s:13:"KushtrimPacaj"; .
Where is that other part coming from ? 13 perhaps represents the length of KushtrimPacaj ?
Edit
Here's the working code, in case anyone needs it :
https://gist.github.com/KushtrimPacaj/43a383ab419fc222f80e
解決方案 You can see in the padAndMcrypt() function, that the given $value is serialized using PHP's serialize() function. You can re-implement the unserialize() function in Java or you can split the byte array yourself if you're always encrypting strings in PHP.
Full code:
Verifying the MAC is always a good idea, because it prevents some attacks such as the padding oracle attack. It is also a very good way to detect general modifications of ciphertexts.
Full code with MAC verification:
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