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RSA encryption using modulus and exponent public key

I need to encrypt my steam login password. Before sending the auth data, steam sends this: "publickey_mod":"c511d72db5ebbba01977983eec2...","publickey_exp":"010001".
The browser encrypts password with this script:
var pubKey = RSA.getPublicKey(results.publickey_mod, results.publickey_exp);
password = password.replace(/[^\x00-\x7F]/g, ''); // remove non-standard-ASCII characters
var encryptedPassword = RSA.encrypt(password, pubKey);
I can't write a working algorithm in c# which will encrypt the password using modulus and exponent.
Here is what i tried:
static async Task Main()
{
var pubKey = SetPublicKey($"{response["publickey_mod"]}", $"{response["publickey_exp"]}");
string password = "123456";
byte[] password_byte = Encoding.ASCII.GetBytes(password);
byte[] encryptedPassword;
using (RSACryptoServiceProvider RSA = new RSACryptoServiceProvider())
{
RSA.ImportParameters(pubKey);
encryptedPassword = RSA.Encrypt(password_byte, false);
}
string encodingPassword = Convert.ToHexString(encryptedPassword);
Console.WriteLine(encodingPassword);
}
public static RSAParameters SetPublicKey(string modulus, string exponent)
{
RSAParameters result = new RSAParameters();
result.Modulus = Convert.FromHexString(modulus);
result.Exponent = Convert.FromHexString(exponent);
return result;
}

working algorithm:
byte[] encryptedPasswordBytes;
using (var rsaEncryptor = new RSACryptoServiceProvider())
{
var passwordBytes = Encoding.ASCII.GetBytes(password);
var rsaParameters = rsaEncryptor.ExportParameters(false);
rsaParameters.Exponent = Convert.FromHexString($"{_response_getrsakey["publickey_exp"]}");
rsaParameters.Modulus = Convert.FromHexString($"{_response_getrsakey["publickey_mod"]}");
rsaEncryptor.ImportParameters(rsaParameters);
encryptedPasswordBytes = rsaEncryptor.Encrypt(passwordBytes, false);
}
string encryptedPassword = Convert.ToBase64String(encryptedPasswordBytes);

Export RSA public key into byte array

I create public and private key for RSA algorithm. I would like to export public key into byte[]. I did method called FunctionA bellow, later i got suggestion to use the ExportSubjectPublicKeyInfo which is included in FunctionB bellow. I have to store the public key in byte[] and sent it into server which isn't in .NET.
I'd like to know if some of these approaches are correct or i should consider some other solution.
private RSAParameters RSAParamsPublicKey;
private RSAParameters RSAParamsPrivateKey;
private byte[] keyPublicKeyArray;
private void FunctionA() {
var csp = new RSACryptoServiceProvider();
RSAParamsPrivateKey = csp.ExportParameters(true);
RSAParamsPublicKey = csp.ExportParameters(false);
List < byte > keyPublicKeyList = new List < byte > ();
foreach(byte b in RSAParamsPublicKey.Exponent) {
keyPublicKeyList.Add(b);
}
foreach(byte b in RSAParamsPublicKey.Modulus) {
keyPublicKeyList.Add(b);
}
keyPublicKeyArray = keyPublicKeyList.ToArray();
}
private void FunctionB() {
var csp = new RSACryptoServiceProvider();
csp.ExportParameters(true);
csp.ExportParameters(false);
keyPublicKeyArray = csp.ExportSubjectPublicKeyInfo();
}

C# AES-GCM and RSA Encryption using Sytem.Secuirty.Cryptography

I am developing the post data request in c# and using AES GCM encryption and RSA encryption. As compared to the C# code with Node.js / Python for encryption, we found that C# AES GCM encryption does not have tag value in the method.
e.g How do I return below data in C# after encryption.
return {
key: aesKey,
cipher_text: encrypted,
tag,
iv
}
In Python and Node.js using JsEncrypt, forge.js.... and implementations are working fine. But, now developing the same client in the C#, do not find such libraries which I can use directly.
However, I found two classes in C# AesGcm and AesManaged for AES Encryption. But I think AesManages is only for AES not GCM encryption. Therefore, I am using AesGcm class in below example, but not sure.
The code executes the following steps:
Request client certificate from DSG.
Extract the public key from the certificate.
Encrypt PII with AES key.
Encrypt AES key with RSA public key.
Send wrapped key and PII payload to DSG tokenization.
class Program
{
static void Main(string[] args)
{
string _ApiKey = "--- YOUR API KEY ----";
string _SecretKey = " ---- YOUR SECRET KEY --------";
string jsonPlainText = "<JSON TExT>";
#region Certificate
string certificate = GetCertificate();
Certificate rawSigningCert = JsonConvert.DescrializeObject<Certificate>(certificate);
var certBytes = Encoding.UTF8.GetBytes(rawSigningCert.crt);
// X509Certificate2
var x509Certificate2 = new System.Security.Cryptography.X509Certificates.X509Certificate2(certBytes);
byte[] publicKey = x509Certificate2.GetPublicKey();
#endregion
#region AES GCM Encryption
byte[] aesGcmKey = new byte[16];
RandomNumberGenerator.Fill(aesGcmKey);
byte[] nonce = new byte[12];
RandomNumberGenerator.Fill(nonce);
byte[] tag = new byte[16];
byte[] dataToEncrypt = Encoding.UTF8.GetBytes(jsonPlainText);
byte[] cipherText = new byte[dataToEncrypt.Length];
using (AesGcm aesGcm = new AesGcm(aesGcmKey))
{
aesGcm.Encrypt(nonce, dataToEncrypt, cipherText, tag);
}
string encryptedCipher = Convert.ToBase64String(cipherText);
var keyString = Convert.ToBase64String(aesGcmKey);
var iVString = Convert.ToBase64String(nonce);
var tagString = Convert.ToBase64String(tag);
string aesGcmEncryptionString = string.Format("{0}:{1}:{2}", keyString, iVString, tagString);
#endregion
#region RSA Encryption
var rsa = new RSACryptoServiceProvider();
RSAParameters RSAKeyInfo = rsa.ExportParameters(false);
RSAKeyInfo.Modulus = publicKey;
rsa.ImportParameters(RSAKeyInfo);
byte[] encryptedSymmetricKey = RSAEncrypt(Encoding.UTF8.GetBytes(aesGcmEncryptionString), RSAKeyInfo, false);
var enc_key = Convert.ToBase64String(encryptedSymmetricKey);
var requestBodyObject = new { message = encryptedCipher, enckey = enc_key };
string jsonRequestBody = JsonConvert.SerializeObject(requestBodyObject);
#endregion
#region Calculating Message Signature
Random random = new Random();
int ClientRequestId = random.Next(0, 99999999);
var time = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
var rawSignature = _ApiKey + ClientRequestId + time + jsonRequestBody;
HMACSHA256 hashObject = new HMACSHA256(Encoding.UTF8.GetBytes(_SecretKey));
var signature = hashObject.ComputeHash(Encoding.UTF8.GetBytes(rawSignature));
var computedHmac = Convert.ToBase64String(signature);
#endregion
#region Make Request
try
{
var client = new RestClient("< API URL>");
client.Timeout = -1;
var request = new RestRequest(Method.POST);
request.AddHeader("contentType", "application/json");
request.AddHeader("clientRequestId", ClientRequestId.ToString());
request.AddHeader("apiKey", _ApiKey);
request.AddHeader("timestamp", time.Tostring);
request.AddHeader("messageSignature", computedHmac);
request.AddJsonBody(jsonRequestBody);
request.RequestFormat = DataFormat.Json;
IRestResponse response = client.Execute(request);
Console.WriteLine(response.Content);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
#endregion
}
static string GetCertificate()
{
string cer = string.Empty;
// Code to get certicate .crt from the service.
//"<GET CERTICATE HERE>";
return cer;
}
static public byte[] RSAEncrpt(byte[] data, RSAParameters keyInfo, bool doOAEPPadding)
{
byte[] encryptedData;
using (RSACryptoServiceProvider rsa = new RSACryptoServiceProvider())
{
rsa.ImportParameters(keyInfo);
encryptedData = rsa.Encrypt(data, RSAEncryptionPadding.Pkcs1);
}
return encryptedData;
}
}
class Certificate
{
public string crt { get; set; }
}
How I can trace each steps as service is responding with incorrect message signature. Any way to verify and trace the above code steps?
Help!
Thanks in advance

How can I create a SHA1WithRSA signature

I have a signature generator in Java:
private static String getPvtKeyFromConfig = "merchantPvtKey";
private static String getPubKeyFromConfig = "merchantPubKey";
private static String getSaltFromConfig = "merchant_salt";
public static void main(String[] args) throws Exception {
// Generate Signature
String uniqueId="ab123";
byte[] data = Base64.decodeBase64(uniqueId);
java.security.Signature sig =java.security.Signature.getInstance("SHA1WithRSA");
sig.initSign(getPrivateFromSpec(getPvtKeyFromConfig));
sig.update(data);
byte[] signatureBytes = sig.sign();
System.out.println("Signature for uniqueId - "+uniqueId+": "+ Base64.encodeBase64String(signatureBytes));
}
How can I do it in C#?

I think this is what you are looking for:
static byte[] Sign(string text, string certSubject)
{
// Access a store
using (X509Store store = new X509Store(StoreName.My, StoreLocation.CurrentUser))
{
store.Open(OpenFlags.ReadOnly);
// Find the certificate used to sign
RSACryptoServiceProvider provider = null;
foreach (X509Certificate2 cert in store.Certificates)
{
if (cert.Subject.Contains(certSubject))
{
// Get its associated CSP and private key
provider = (RSACryptoServiceProvider)cert.PrivateKey;
break;
}
}
if (provider == null)
throw new Exception("Certificate not found.");
// Hash the data
var hash = HashText(text);
// Sign the hash
var signature = provider.SignHash(hash, CryptoConfig.MapNameToOID("SHA1"));
return signature;
}
}
static bool Verify(string text, byte[] signature, string certPath)
{
// Load the certificate used to verify the signature
X509Certificate2 certificate = new X509Certificate2(certPath);
// Get its associated provider and public key
RSACryptoServiceProvider provider = (RSACryptoServiceProvider)certificate.PublicKey.Key;
// Hash the data
var hash = HashText(text);
// Verify the signature with the hash
var result = provider.VerifyHash(hash, CryptoConfig.MapNameToOID("SHA1"), signature);
return result;
}
static byte[] HashText(string text)
{
SHA1Managed sha1Hasher = new SHA1Managed();
UnicodeEncoding encoding = new UnicodeEncoding();
byte[] data = encoding.GetBytes(text);
byte[] hash = sha1Hasher.ComputeHash(data);
return hash;
}
Sample usage:
var signature = Sign("To be or not to be, that is the question.", "CN=some_cert");
var result = Verify("To be or not to be, that is the question.", signature, "C:\\temp\\some_cert.cer");
Console.WriteLine("Verified: {0}", result);

Below C# code works for me for the exact java code mentioned in the question.
Few Notes :
.) Your project should have Target frameworks as 4.8
.) You should have existing private key
.) Using this Private key we can generate the .pfx certificate by using the OpenSSL commands.( we will have to generate the .crt first and then .pfx)
static string GenerateSignatureUsingCert(string dataToSign)
{
X509Certificate2 certificate = new X509Certificate2(#"C:\PFX\MyCertificate.pfx", "****", X509KeyStorageFlags.Exportable);
RSA privateKey1 = certificate.GetRSAPrivateKey();
Encoding unicode = Encoding.UTF8;
byte[] bytesInUni = unicode.GetBytes(dataToSign);
return Convert.ToBase64String(privateKey1.SignData(bytesInUni, HashAlgorithmName.SHA256,RSASignaturePadding.Pkcs1));
}
Usage
string canonicalizeData = CanonicalizeHeaders(headers);
String data = null;
try
{
data = GenerateSignatureUsingCert(canonicalizeData);
}
catch(Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.WriteLine("Signature: " + data);

How to Generate Unique Public and Private Key via RSA

I am building a custom shopping cart where CC numbers and Exp date will be stored in a database until processing (then deleted). I need to encrypt this data (obviously).
I want to use the RSACryptoServiceProvider class.
Here is my code to create my keys.
public static void AssignNewKey(){
const int PROVIDER_RSA_FULL = 1;
const string CONTAINER_NAME = "KeyContainer";
CspParameters cspParams;
cspParams = new CspParameters(PROVIDER_RSA_FULL);
cspParams.KeyContainerName = CONTAINER_NAME;
cspParams.Flags = CspProviderFlags.UseMachineKeyStore;
cspParams.ProviderName = "Microsoft Strong Cryptographic Provider";
rsa = new RSACryptoServiceProvider(cspParams);
string publicPrivateKeyXML = rsa.ToXmlString(true);
string publicOnlyKeyXML = rsa.ToXmlString(false);
// do stuff with keys...
}
Now the plan is to store the private key xml on a USB drive attached to the managers key chain.
Whenever a manager leaves the company I want to be able to generate new public and private keys (and re-encrypt all currently stored CC numbers with the new public key).
My problem is that the keys generated by this code are always the same. How would I generate a unique set of keys every time?
UPDATE. My test code is below.:
note: the "privatekey" parameter here is the original private key. In order for the keys to be changed I need to verify that the private key is valid.
In Default.aspx.cs
public void DownloadNewPrivateKey_Click(object sender, EventArgs e)
{
StreamReader reader = new StreamReader(fileUpload.FileContent);
string privateKey = reader.ReadToEnd();
Response.Clear();
Response.ContentType = "text/xml";
Response.End();
Response.Write(ChangeKeysAndReturnNewPrivateKey(privateKey));
}
In Crytpography.cs:
public static privateKey;
public static publicKey;
public static RSACryptoServiceProvider rsa;
public static string ChangeKeysAndReturnNewPrivateKey(string _privatekey)
{
string testData = "TestData";
string testSalt = "salt";
// encrypt the test data using the exisiting public key...
string encryptedTestData = EncryptData(testData, testSalt);
try
{
// try to decrypt the test data using the _privatekey provided by user...
string decryptTestData = DecryptData(encryptedTestData, _privatekey, testSalt);
// if the data is successfully decrypted assign new keys...
if (decryptTestData == testData)
{
AssignNewKey();
// "AssignNewKey()" should set "privateKey" to the newly created private key...
return privateKey;
}
else
{
return string.Empty;
}
}
catch (Exception ex)
{
return string.Empty;
}
}
public static void AssignParameter(){
const int PROVIDER_RSA_FULL = 1;
const string CONTAINER_NAME = "KeyContainer";
CspParameters cspParams;
cspParams = new CspParameters(PROVIDER_RSA_FULL);
cspParams.KeyContainerName = CONTAINER_NAME;
cspParams.Flags = CspProviderFlags.UseMachineKeyStore;
cspParams.ProviderName = "Microsoft Strong Cryptographic Provider";
rsa = new RSACryptoServiceProvider(cspParams);
}
public static void AssignNewKey()
{
AssignParameter();
using (SqlConnection myConn = new SqlConnection(Utilities.ConnectionString))
{
SqlCommand myCmd = myConn.CreateCommand();
string publicPrivateKeyXML = rsa.ToXmlString(true);
privateKey = publicPrivateKeyXML; // sets the public variable privateKey to the new private key.
string publicOnlyKeyXML = rsa.ToXmlString(false);
publicKey = publicOnlyKeyXML; // sets the public variable publicKey to the new public key.
myCmd.CommandText = "UPDATE Settings SET PublicKey = #PublicKey";
myCmd.Parameters.AddWithValue("#PublicKey", publicOnlyKeyXML);
myConn.Open();
myComm.ExecuteScalar();
}
}
public static string EncryptData(string data2Encrypt, string salt)
{
AssignParameter();
using (SqlConnection myConn = new SqlConnection(Utilities.ConnectionString))
{
SqlCommand myCmd = myConn.CreateCommand();
myCmd.CommandText = "SELECT TOP 1 PublicKey FROM Settings";
myConn.Open();
using (SqlDataReader sdr = myCmd.ExecuteReader())
{
if (sdr.HasRows)
{
DataTable dt = new DataTable();
dt.Load(sdr);
rsa.FromXmlString(dt.Rows[0]["PublicKey"].ToString());
}
}
}
//read plaintext, encrypt it to ciphertext
byte[] plainbytes = System.Text.Encoding.UTF8.GetBytes(data2Encrypt + salt);
byte[] cipherbytes = rsa.Encrypt(plainbytes, false);
return Convert.ToBase64String(cipherbytes);
}
public static string DecryptData(string data2Decrypt, string privatekey, string salt)
{
AssignParameter();
byte[] getpassword = Convert.FromBase64String(data2Decrypt);
string publicPrivateKeyXML = privatekey;
rsa.FromXmlString(publicPrivateKeyXML);
//read ciphertext, decrypt it to plaintext
byte[] plain = rsa.Decrypt(getpassword, false);
string dataAndSalt = System.Text.Encoding.UTF8.GetString(plain);
return dataAndSalt.Substring(0, dataAndSalt.Length - salt.Length);
}

When you use a code like this:
using (var rsa = new RSACryptoServiceProvider(1024))
{
// Do something with the key...
// Encrypt, export, etc.
}
.NET (actually Windows) stores your key in a persistent key container forever.
The container is randomly generated by .NET
This means:
Any random RSA/DSA key you have EVER generated for the purpose of protecting data, creating custom X.509 certificate, etc. may have been exposed without your awareness in the Windows file system. Accessible by anyone who has access to your account.
Your disk is being slowly filled with data. Normally not a big concern but it depends on your application (e.g. it might generates hundreds of keys every minute).
To resolve these issues:
using (var rsa = new RSACryptoServiceProvider(1024))
{
try
{
// Do something with the key...
// Encrypt, export, etc.
}
finally
{
rsa.PersistKeyInCsp = false;
}
}
ALWAYS

The RSACryptoServiceProvider(CspParameters) constructor creates a keypair which is stored in the keystore on the local machine. If you already have a keypair with the specified name, it uses the existing keypair.
It sounds as if you are not interested in having the key stored on the machine.
So use the RSACryptoServiceProvider(Int32) constructor:
public static void AssignNewKey(){
RSA rsa = new RSACryptoServiceProvider(2048); // Generate a new 2048 bit RSA key
string publicPrivateKeyXML = rsa.ToXmlString(true);
string publicOnlyKeyXML = rsa.ToXmlString(false);
// do stuff with keys...
}
EDIT:
Alternatively try setting the PersistKeyInCsp to false:
public static void AssignNewKey(){
const int PROVIDER_RSA_FULL = 1;
const string CONTAINER_NAME = "KeyContainer";
CspParameters cspParams;
cspParams = new CspParameters(PROVIDER_RSA_FULL);
cspParams.KeyContainerName = CONTAINER_NAME;
cspParams.Flags = CspProviderFlags.UseMachineKeyStore;
cspParams.ProviderName = "Microsoft Strong Cryptographic Provider";
rsa = new RSACryptoServiceProvider(cspParams);
rsa.PersistKeyInCsp = false;
string publicPrivateKeyXML = rsa.ToXmlString(true);
string publicOnlyKeyXML = rsa.ToXmlString(false);
// do stuff with keys...
}

What I ended up doing is create a new KeyContainer name based off of the current DateTime (DateTime.Now.Ticks.ToString()) whenever I need to create a new key and save the container name and public key to the database. Also, whenever I create a new key I would do the following:
public static string ConvertToNewKey(string oldPrivateKey)
{
// get the current container name from the database...
rsa.PersistKeyInCsp = false;
rsa.Clear();
rsa = null;
string privateKey = AssignNewKey(true); // create the new public key and container name and write them to the database...
// re-encrypt existing data to use the new keys and write to database...
return privateKey;
}
public static string AssignNewKey(bool ReturnPrivateKey){
string containerName = DateTime.Now.Ticks.ToString();
// create the new key...
// saves container name and public key to database...
// and returns Private Key XML.
}
before creating the new key.