Invalid Cipher bytes in Encryption method in Android using RSA

Question

We are facing an issue while trying to Encrypt data in Android and Decrypt it in a WCF Service. The Android code to encrypt data is as follows:

try{
String strModulus = "tr82UfeGetV7yBKcOPjFTWs7pHqqr/5YKKWMUZ/HG4HnCmWrZsOhuR1FBnMZ/g2YiosoSlu0zd7Ukz9lX7wv2RLfWXfMvZYGpAAvfYWwzbyQ2i1q+tKE/thgKNscoSRellDD+uJcYn1H4hnaudVyYJH9miVhOKhKlExMzw8an6U=";
String strExponent = "AQAB";
byte[] modulusBytes = Base64.decode(strModulus, Base64.DEFAULT);
byte[] exponentBytes = Base64.decode(strExponent, Base64.DEFAULT);

BigInteger modulus = new BigInteger(1, modulusBytes );               
BigInteger exponent = new BigInteger(1, exponentBytes);

RSAPublicKeySpec rsaPubKey = new RSAPublicKeySpec(modulus, exponent);
KeyFactory fact = KeyFactory.getInstance("RSA/ECB/PKCS1Padding");
PublicKey pubKey = fact.generatePublic(rsaPubKey);    

Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pubKey);   

byte[] plainBytes = new String("Manchester United").getBytes("UTF-8");
byte[] cipherData = cipher.doFinal(plainBytes); 
encryptedString = Base64.encodeToString(cipherData, Base64.DEFAULT);
}
catch(Exception e){
Log.e("Error", e.toString());
}

return encryptedString;

The same code in Java:

try{
        String strModulus = "tr82UfeGetV7yBKcOPjFTWs7pHqqr/5YKKWMUZHG4HnCmWrZsOhuR1FBnMZ/g2YiosoSlu0zd7Ukz9lX7wv2RLfWXfMvZYGpAAvfYWwzbyQ2i1q+tKE/thgKNscoSRellDD+uJcYn1H4hnaudVyYJH9miVhOKhKlExMzw8an6U=";
        String strExponent = "AQAB";
        byte[] modulusBytes = DatatypeConverter.parseBase64Binary("tr82UfeGetV7yBKcOPjFTWs7pHqqr/5YKKWMUZ/HG4HnCmWrZsOhuR1FBnMZ/g2YiosoSlu0zd7Ukz9lX7wv2RLfWXfMvZYGpAAvfYWwzbyQ2i1q+tKE/thgKNscoSRellDD+uJcYn1H4hnaudVyYJH9miVhOKhKlExMzw8an6U=");
        byte[] exponentBytes = DatatypeConverter.parseBase64Binary("AQAB");

        BigInteger modulus = new BigInteger(1, modulusBytes );
        BigInteger exponent = new BigInteger(1, exponentBytes);

        RSAPublicKeySpec rsaPubKey = new RSAPublicKeySpec(modulus, exponent);
        KeyFactory fact = KeyFactory.getInstance("RSA");
        PublicKey pubKey = fact.generatePublic(rsaPubKey);

        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, pubKey);

        byte[] plainBytes = new String("Manchester United").getBytes("UTF-8");
        byte[] cipherData = cipher.doFinal(plainBytes);
        //String encryptedString = Base64.encodeToString(cipherData, Base64.NO_PADDING);
        String encryptedString = DatatypeConverter.printBase64Binary(cipherData);
        String encryptedData = encryptedString;
    }
    catch(Exception e){
    }       
}

WCF Service:

public string Decrypt()
{
    const int PROVIDER_RSA_FULL = 1;
    const string CONTAINER_NAME = "Tracker";
    CspParameters cspParams;
    cspParams = new CspParameters(PROVIDER_RSA_FULL);
    cspParams.KeyContainerName = CONTAINER_NAME;
    RSACryptoServiceProvider rsa1 = new RSACryptoServiceProvider(cspParams);
    rsa1.FromXmlString("<RSAKeyValue><Modulus>tr82UfeGetV7yBKcOPjFTWs7pHqqr/5YKKWMUZ/HG4HnCmWrZsOhuR1FBnMZ/g2YiosoSlu0zd7Ukz9lX7wv2RLfWXfMvZYGpAAvfYWwzbyQ2i1q+tKE/thgKNscoSRellDD+uJcYn1H4hnaudVyYJH9miVhOKhKlExMzw8an6U=</Modulus><Exponent>AQAB</Exponent><P>6e0nv7EBFBugtpoB+ozpg1J4js8E+DVyWCuBsERBPzqu4H7Z/oeLIRSC8Gi5GZgrCpBf3EvyIluM7rzaIfNThQ==</P><Q>x/29X9ns1WcXC42IJjLDjscz5ygdVh79dm8B2tQVbqwyhDsQ6OIOQdu5+eHf4hUMoTrM9KkS2F6FGlLXuaOFoQ==</Q><DP>kTS2LMaJ/dpce5zDx6w6s1q5HSSiWBSNIu/2s9zah448yXvUg6vNkD40PVk0NRAA/7C44H2AExWzOOqfmN17JQ==</DP><DQ>xtAx9drQPWnpl/uQUOEAVa0kpPTVDStrr9Q1FNTnpYkcAyYw7kLkB4anAIoSpk9kqdeprsNxz5VPXtbiTFMKYQ==</DQ><InverseQ>O0594NMjnjSp+/NAa1kQxoQNzn1qqq+p1Zb+kT3/jRc/0d7ZnqSSpxFMXfxx3yZkNAOPDOdbckPQbRZ13RKBHg==</InverseQ><D>bjVEagwvkrZaTt9CTW1hd3362weLFlX6DpE/3R3RcrpVfkSwKGpEhqGrNeeGPlsuqiaf5rAFir4eTqrF1QVliKsU4XE0RyzP5lHGc7dlX4DOHMjs2R9nNWv8QOTPoaRuLrLGorqBXlw/jQPxFI6gQzkIIjzuf//lDVnFam3dw4E=</D></RSAKeyValue>");
    string data2Decrypt = "LyVNDhkdJ5jNgwZDiVZ1R0lmd10AQgqNDFHh2vJB1676eg8wj0MOdTyChAGrvEjha0uXg+f/aNBAc4+/LFbCgsA1e+O3wnXr27sXznGJ9G15avZzQHG4JWUS42MXBahAkcJ80pcihTbL9edfQCkEuj9RzQ/zFJyDEMssfd/EPDM=";
    byte[] encyrptedBytes = Convert.FromBase64String(data2Decrypt);
    byte[] plain = rsa1.Decrypt(encyrptedBytes, false);
    string decryptedString = System.Text.Encoding.UTF8.GetString(plain);
}

Original Data : 'Manchester United'

The strange thing is that if I encrypt a string with the Java code it can be decrypted at the WCF service end, however, if it is encrypted using the above Android code, the decryption provides the error: "The data to be decrypted exceeds the maximum for this modulus of 128 bytes".

On debugging, I realized that the byte[] cipherData is not the same for Android and Java. All the previous values happen to be in sync. This generates different Encrypted Strings in Java and Android.

My question is why does this happen? Is there a silly mistake? Is there a way to work around it? Or something else that can be done in Android to get the 'Cipher Data' right?

Any help will be appreciated.

PKCS #1 padding includes random data, so if you repeatedly encrypt the same data over and over, you will always get different results. This is not the cause of your WCF problems. Can you share code for your WCF service? Is it possible you are forgetting to base64-decode the data prior to decryption? — Duncan Jones, Jun 23 '14 at 10:19
@Duncan WCF code has been added. And as you can see in the code i have converted the code into base64 prior decrypting the data. Still doesn't work. I don't understand how it works perfectly fine with java code and not in android. — Rohit Sonawane, Jun 24 '14 at 04:58

score 0 · Answer 1 · answered Jun 21 '14 at 10:35

0

You are using a different padding on Android. Use the exact same padding on Android as well:

Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");

answered Jun 21 '14 at 10:35

HHK

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@RohitSonawane It's good advice anyway. Always specify the full transformation in your code. You may wish to edit your question code examples to make it clear you've tried this. – Duncan Jones Jun 23 '14 at 10:20

Invalid Cipher bytes in Encryption method in Android using RSA

1 Answers1