Hello, i went thru lots and lots of searchs and results and pages considering this matter but havent found the solution yet. Like i described in the title i want to decrypt data using my Public Key which is something i am able to do with my PHP code, my certificate is generated from my PHP page. Here is a sample of what i am trying: public string Decrypt(string data) { X509Certificate2 cert = new X509Certificate2(); cert.Import(Encoding.ASCII.GetBytes(webApi["PublicDefaultKey"])); RSACryptoServiceProvider rsa = (RSACryptoServiceProvider)cert.PublicKey.Key; byte[] ciphertextBytes = Convert.FromBase64String(data); byte[] plaintextBytes = rsa.Decrypt(ciphertextBytes, false); return System.Text.Encoding.UTF8.GetString(plaintextBytes); } MessageBox.Show(Decrypt("pgcl93TpVfyHubuRlL72/PZN0nA4Q+HHx8Y15qGvUyTNpI6y7J13YG07ZVEyB7Dbgx63FSw9vEw1D1Z3bvNbI0gqalVfKTfHv5tKVc7Y6nQwQYwoODpUhVpa/K9OP1lqx4esnxqwJx95G0rqgJTdS+Yo773s5UcJrHzzbsX2z+w=")); here is the public key i am using for tests: -----BEGIN CERTIFICATE----- MIIDxDCCAy2gAwIBAgIBADANBgkqhkiG9w0BAQUFADCBozELMAkGA1UEBhMCVUsx EDAOBgNVBAgTB0VuZ2xhbmQxDzANBgNVBAcTBkxvbmRvbjESMBAGA1UEChMJTU1P Q2xldmVyMSMwIQYDVQQLExpNTU9DbGV2ZXIgRGV2ZWxvcGVyJ3MgVGVhbTESMBAG A1UEAxMJTU1PQ2xldmVyMSQwIgYJKoZIhvcNAQkBFhVzdXBwb3J0QG1tb2NsZXZl ci5jb20wHhcNMTAwNTE2MTkxNDQ4WhcNMTEwNTE2MTkxNDQ4WjCBozELMAkGA1UE BhMCVUsxEDAOBgNVBAgTB0VuZ2xhbmQxDzANBgNVBAcTBkxvbmRvbjESMBAGA1UE ChMJTU1PQ2xldmVyMSMwIQYDVQQLExpNTU9DbGV2ZXIgRGV2ZWxvcGVyJ3MgVGVh bTESMBAGA1UEAxMJTU1PQ2xldmVyMSQwIgYJKoZIhvcNAQkBFhVzdXBwb3J0QG1t b2NsZXZlci5jb20wgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBAMozHr17PL+N seZyadobUmpIV+RKqmRUGX0USIdj0i0yvwvltu3AIKAyRhGz16053jZV2WeglCEj qfiewF9sYTAAoIVGtdd/sZvO4uUcng9crSzDo0CrEPs/Tn5SunmlmyFlZfdlqpAM XXLno/HMo9cza0CrcMnRokaTiu8szBeBAgMBAAGjggEEMIIBADAdBgNVHQ4EFgQU zip+3/hBIpjvdcSoWQ2rW+xDEWAwgdAGA1UdIwSByDCBxYAUzip+3/hBIpjvdcSo WQ2rW+xDEWChgamkgaYwgaMxCzAJBgNVBAYTAlVLMRAwDgYDVQQIEwdFbmdsYW5k MQ8wDQYDVQQHEwZMb25kb24xEjAQBgNVBAoTCU1NT0NsZXZlcjEjMCEGA1UECxMa TU1PQ2xldmVyIERldmVsb3BlcidzIFRlYW0xEjAQBgNVBAMTCU1NT0NsZXZlcjEk MCIGCSqGSIb3DQEJARYVc3VwcG9ydEBtbW9jbGV2ZXIuY29tggEAMAwGA1UdEwQF MAMBAf8wDQYJKoZIhvcNAQEFBQADgYEAyU6RLifBXSyQUkBFnTcI6h5ryujh+6o6 eQ1wuPOPmRdYJZuWx/5mjMpIF13sYlNorcOv5WaEnp8/Jfuwc9h/jXlcujser0UE WoaaFwK81O801Xkv2zEm2UUWiOabrGTIT4FVy3gCUXJYjaCnvfSdmkfLJOQxNHVt 4NTMp7IeF60= -----END CERTIFICATE----- by default, the PHP generates the key in PKCS as far as i know, from my C# code i can encrypt using my publick key with out any problems and decrypt it on my php page but so far i was not able to decrypt data sent from my php page encrypted with the private key which is something i can do on my php... i did like some help to understand what i am doing wrong... the error when i run the functions is "bad data" at rsa.Decrypt(ciphertextBytes, false); which i couldnt found anymore information at it... Thanks for any and all the help :)