CODEWITHSUNDEEP
c#javaandroidencryptionrsa
Mehdi
Mehdi

Reputation: 49

How can I decrypt an "encrypted string with java" in c sharp?

I have a string. That encrypted with java. Now I have to decrypt it in c sharp.

I use RSA algorithm with same public/private keys in c sharp and java.

But in decryption with c sharp I got a "Bad Data" error.

and an important notice is that: I can decrypt this string in java! and I can encrypt with c sharp and decrypt with c sharp !! But when I try to encrypt with one of them(c sharp or java) and decrypt with the other one it raise an error !

this is my c sharp code :

string privateKey = "<RSAKeyValue><Modulus>rFsMn+idg8jmVMk249DzJc7AFft3+/jcnYDTh9wHee3tgFu1gBRh7e+ao+MWq7NEN0N7kUHa7O4c/ND2Ahcx/h4mXD5KDoixFRBUsxYqCJVA68qYJ7vozVPMjNr4jeOo1xt+oevO5+mUWtcaib5Iw51u1Jq/6qCqLsm8Eq3cnsE=</Modulus><Exponent>AQAB</Exponent><P>5aqTyz3GH655H+vO/BzJvFzpILpxLwXZEvqp3l3NYXKqP0tdkY1g36o6M9YodI3h8ho4VFYofIqA1+V0qPkuDQ==</P><Q>wB45uljBS8Z+WGRE1cRdpZb5aKUv76uLlCp6agtPBBhjXNIQrN8MpOCTvZM2cOsuYpYhDtnwsTY9KKXdBmv6hQ==</Q><DP>KB474uzPhwk7L1BJv9BnjPfN4WGwE765xI70zVslXThidNv9ZEeF/IwHzrZCKtn99gSOgmzqdZbcGtqCHmIooQ==</DP><DQ>eLnFrvsdJJ/sP2Fq/CX0bx0rR34eXG6hPI9g84h9s+YbcnWy8t8LVASn8oYyvMydDminB20e2k1qK0PnW6S4/Q==</DQ><InverseQ>rlPpLse8LJ0KRglnu2D1xzJT90QqzS3o80P0WTpUvm95mF5d8YaVj/d9W7FBdgZ98y6Q7of+wLCmYGKLg56wYQ==</InverseQ><D>Gs8mzZDPP3p2aWXLBfCwgYcBVeoBpc318wHg5VcSSqL5uGeLedqxyOLmOOvP0PFXgQkcJWIK/aOkGqcePQECo3TNiK+uLSwc97V3spZah70FFJVyh23Y+o0wlRGHAm5Nj9QieHlVwhgJPkNUJYgH9qkwB9aCpl+rdAG3da2fQ2E=</D></RSAKeyValue>";
string publicKey = "<RSAKeyValue><Modulus>rFsMn+idg8jmVMk249DzJc7AFft3+/jcnYDTh9wHee3tgFu1gBRh7e+ao+MWq7NEN0N7kUHa7O4c/ND2Ahcx/h4mXD5KDoixFRBUsxYqCJVA68qYJ7vozVPMjNr4jeOo1xt+oevO5+mUWtcaib5Iw51u1Jq/6qCqLsm8Eq3cnsE=</Modulus><Exponent>AQAB</Exponent></RSAKeyValue>";



public string EncryptData(string data2Encrypt )
{
    RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
    rsa.FromXmlString(publicKey);
    byte[] plainbytes = System.Text.Encoding.UTF8.GetBytes(data2Encrypt);
    byte[] cipherbytes = rsa.Encrypt(plainbytes, false);
    return Convert.ToBase64String(cipherbytes);
}

public string DecryptData(string data2Decrypt)
{
    RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
    rsa.FromXmlString(privateKey);
    byte[] plainbytes = rsa.Decrypt(Convert.FromBase64String(data2Decrypt), false);
    return System.Text.Encoding.UTF8.GetString(plainbytes);
}

and my java code is :

byte[] expBytes = Base64.decode("AQAB".getBytes("UTF-8"), Base64.DEFAULT);
byte[] modBytes = Base64.decode("rFsMn+idg8jmVMk249DzJc7AFft3+/jcnYDTh9wHee3tgFu1gBRh7e+ao+MWq7NEN0N7kUHa7O4c/ND2Ahcx/h4mXD5KDoixFRBUsxYqCJVA68qYJ7vozVPMjNr4jeOo1xt+oevO5+mUWtcaib5Iw51u1Jq/6qCqLsm8Eq3cnsE=".getBytes("UTF-8"), Base64.DEFAULT);
byte[] dBytes = Base64.decode("Gs8mzZDPP3p2aWXLBfCwgYcBVeoBpc318wHg5VcSSqL5uGeLedqxyOLmOOvP0PFXgQkcJWIK/aOkGqcePQECo3TNiK+uLSwc97V3spZah70FFJVyh23Y+o0wlRGHAm5Nj9QieHlVwhgJPkNUJYgH9qkwB9aCpl+rdAG3da2fQ2E=".getBytes("UTF-8"), Base64.DEFAULT);

BigInteger modules = new BigInteger(1, modBytes);
BigInteger exponent = new BigInteger(1, expBytes);
BigInteger d = new BigInteger(1, dBytes);

KeyFactory factory = KeyFactory.getInstance("RSA");
Cipher cipher = Cipher.getInstance("RSA");
String input = "test";

RSAPublicKeySpec pubSpec = new RSAPublicKeySpec(modules, exponent);
PublicKey pubKey = factory.generatePublic(pubSpec);
cipher.init(Cipher.ENCRYPT_MODE, pubKey);
byte[] encrypted = cipher.doFinal(input.getBytes());

String strEncrypted = Base64.encodeToString(encrypted, Base64.DEFAULT);

I can not decode strEncrypted value in c sharp.

and at the end encryption value in java is different with c sharp(same keys and algorithm and data) !!!

Upvotes: 4

Views: 1985

Answers (2)

divanov
divanov

Reputation: 6339

Second parameter of RSACryptoServiceProvider.Encrypt(plainbytes, false) means that PKCS#1 padding is used. true is for OAEP padding.

In Java the security provider you use maps "RSA" to "RSA/ECB/NoPadding", which is just encryption without any padding, hence an encryption result is always the same. So there is a need to specify "RSA/ECB/PKCS1Padding" to match C# behavior.

You should always specify the mode and padding otherwise the security provider will choose it's own defaults - and the defaults may differ for each provider.

Upvotes: 3

Mehdi
Mehdi

Reputation: 49

I found it :)

I changed this line :

Cipher cipher = Cipher.getInstance("RSA");

to :

Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1PADDING");

It worked well. But who knows what's different between these ?

Upvotes: 1

Related Questions