Encrypt in C# using RSACryptoServiceProvide and decrypt using openssl_private_decrypt in PHP

Question

I spent whole day for trying to get it work but no luck:(

I use these code in C# for encryption:

RSACryptoServiceProvider rsa = new RSACryptoServiceProvider();
RSAParameters rsaParam = rsa.ExportParameters(false);
rsaParam.Modulus = Convert.FromBase64String("MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCwlhAsNcNCDRgzCc49u/0iSDrdJn7yoiH/HHipbQp0QSejzg/48mMA6wb32OPQ7qzBgJNvwiQbMvi89BvGNAJ9K8vM0RW7WOqtnb/8IK9BAJVtEwJ3vvKTf5EluiUgWVbGYpWPjbl/lsD3/hRTR0uF46h7q4OlARxOupl9xVS2wQIDAQAB");
rsa.ImportParameters(rsaParam);
string msg = "This is a test.";
byte[] encValue = rsa.Encrypt(Encoding.UTF8.GetBytes(msg), true);
Console.WriteLine(Convert.ToBase64String(encValue));

This is the PHP code I use to decrypt.

// Read key
$fp = fopen($KeyPath,"r");
$Key = fread($fp,8192);
fclose($fp);
openssl_private_decrypt($data, $decrypted, openssl_get_privatekey($Key, "123456"));

The private key I used(Passphase "123456"):

I am not familiar with encryption, can some one please tell how to get it work? PS: I think the code in php is fine since I tested the code seperately.

score 0 · Answer 1 · answered May 01 '13 at 14:28

You can use this code for encrypt your string.

public string EncodeData(string sData)
{
    try {
        byte[] encData_byte = new byte[sData.Length];
        encData_byte = System.Text.Encoding.UTF8.GetBytes(sData);
        string encodedData = Convert.ToBase64String(encData_byte);
        return encodedData;
    } catch (Exception ex) {
        throw new Exception("Error in base64Encode" + ex.Message);
    }
}

and for decrypt your string you can use this code.

public string DecodeData(string sData)
{
    System.Text.UTF8Encoding encoder = new System.Text.UTF8Encoding();
    System.Text.Decoder utf8Decode = encoder.GetDecoder();
    byte[] todecode_byte = Convert.FromBase64String(sData);
    int charCount = utf8Decode.GetCharCount(todecode_byte, 0, todecode_byte.Length);
    char[] decoded_char = new char[charCount];
    utf8Decode.GetChars(todecode_byte, 0, todecode_byte.Length, decoded_char, 0);
    string result = new String(decoded_char);
    return result;
}

Try this this will work.

Thank you.

No, that is not what I want. I need to use key pairs to encrypt data for transfer. — user1510539, May 01 '13 at 14:38

score 0 · Answer 2 · edited May 23 '17 at 11:57

Are you sure RSACryptoProvider is working with the key in the format you're providing it in?

A lot of examples of RSACryptoProvider I've seen use XML-based private keys. eg.

RSA Signing with PHP and verifying with C#

"<RSAKeyValue><Modulus>3BqiIB3ouyXHDMpW43TlZrx8fkts2FVVARJKNXFRQ/WIlsthDzL2jY2KEJVN6BKE4A51X+8LMzAI+2z3vIgAQT3bRSfOwygpGBjdhhnXJwFlQ6Gf/+z0ffQfVx/DHw3+QWphcwGDBst+KIA6u6ayy+RDE+jEityyyWDiWqkR9J8=</Modulus><Exponent>AQAB</Exponent><P>8a8nuVhIANh7J2TLn4wWTXhZY1tvlyFKaslOeAOVr+wgEWLQpLZ0Jpjm8aUyyOYPXlk7xrA5BOebtz41diu4RQ==</P><Q>6SQ9y3sEMjrf/c4bHGVlhOj4LUVykradWWUNC0ya7llnR8y1djJ1uUut+EoAa1JQCGukuv4K8NvN1Ieo72Fhkw==</Q><DP>cg0VMusNN5DxNRrk2IrUL4TesfuBQpGMO6554DrY1acZTvsRuNj9IQXA3kH2IEYo9H4prk6U6dKeci/iLLze/Q==</DP><DQ>m/pZNXeZ+RkWnrFzxe24m9FZqMAbxThT0Wkf7v1Tcj9yL8EvbmKYDF4riD/KRAMP9HJABbLNExObg6M3TOAz7Q==</DQ><InverseQ>w8PvW8srrPCuOcphBKXSyoZxCZn81+rovBxuE8AB95m5X+URE8SunK7f+g7hBBin6nUOaVGohBP8jzkQEsdx1Q==</InverseQ>  <D>AsVPDypxOJHkLJQLffeFv8JVqt1WNG72j/nj90JC7KEVpBhRU3inw+ZpO4Y1odtB0vQ7pAaFVJKhOlEH2Va48hNUEQujML8rE+LZXgI3lu0TlqOCIqTHIljeJry0ca30XFtFDp9kh0Kr/0CgGMqgIed+hDUjAad8ke9D2YicDok=</D></RSAKeyValue>"

Yes, the code above had successfully encrypted the data, but somehow I just cant decrypt it in PHP. I think it maybe some sort of reverse thing. But I try every combination of reversing the array. Doesn't work. — user1510539, May 01 '13 at 14:58

score 0 · Accepted Answer · answered May 03 '13 at 13:41

I searched for days and finally figured out myself:)
I am loading the parameters in the wrong way.

According to the RSA Public key structures(PEM):

MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCwlhAsNcNCDRgzCc49u/0iSDrdJn7yoiH/HHipbQp0QSejzg/48mMA6wb32OPQ7qzBgJNvwiQbMvi89BvGNAJ9K8vM0RW7WOqtnb/8IK9BAJVtEwJ3vvKTf5EluiUgWVbGYpWPjbl/lsD3/hRTR0uF46h7q4OlARxOupl9xVS2wQIDAQAB

Which I split the string into 3 parts(base64 encoded):

Header

MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC

Modulus:

wlhAsNcNCDRgzCc49u/0iSDrdJn7yoiH/HHipbQp0QSejzg/48mMA6wb32OPQ7qzBgJNvwiQbMvi89BvGNAJ9K8vM0RW7WOqtnb/8IK9BAJVtEwJ3vvKTf5EluiUgWVbGYpWPjbl/lsD3/hRTR0uF46h7q4OlARxOupl9xVS2wQ

Exponent:

IDAQAB

(Note that I still didn't get a clear idea of the RSA key strutures. Those above are just a blurry view of a key structure, but for those who interested in, I recommend you to read the API Documentation "RSAParameters" or the RSA specification)

Obviously what I was doing is to import the entire key string to the RSAParameters.Modulus. That is not the way to import the key. So that's why it didn't work.

The way to do it is to extract the modulus and exponent which was needed for a public encryption from the key file. And import into RSAParameters

RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
RSAParameters RSAKeyInfo = new RSAParameters();
RSAKeyInfo.Modulus = modulus;
RSAKeyInfo.Exponent = exponent;
RSA.ImportParameters(RSAKeyInfo);

Then encrypt the string:

RSA.Encrypt("HAHA I GOT IT!!", false);

The way to extract. I recommend going to JavaScience for more info. There are bunch of cryptographic utilities there.

Encrypt in C# using RSACryptoServiceProvide and decrypt using openssl_private_decrypt in PHP

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