System.IO.IOException: -----END RSA PRIVATE KEY not found

Question

I am trying to create an online database application using PHP for the server and C# form application for the client. On the server I encrypt a simple string using a public RSA key with the PHPSecLib. Then the C# application receives the string and tries to decrypt it using the corresponding private key. The bytes are base64 encoded on the server and decoded to bytes again by C#. I created the key pair using the PHPSecLib.

This is the code I use on the client application:

public string rsa_decrypt(string encryptedText, string privateKey) {
        byte[] bytesToDecrypt = Convert.FromBase64String(encryptedText);
        Pkcs1Encoding decrypter = new Pkcs1Encoding(new RsaEngine());
        //the error occurs on this line:
        AsymmetricCipherKeyPair RSAParams = (AsymmetricCipherKeyPair)new PemReader(new StringReader(privateKey)).ReadObject();

        decrypter.Init(false, RSAParams.Private);
        byte[] decryptedBytes = decrypter.ProcessBlock(bytesToDecrypt, 0, bytesToDecrypt.Length);
        string decryptedString = Convert.ToBase64String(decryptedBytes);
        return decryptedString;
    }

But, I get the following error on the line specified above^.

An unhandled exception of type 'System.IO.IOException' occurred in BouncyCastle.Crypto.dll

Additional information: -----END RSA PRIVATE KEY not found

I believe there's nothing wrong with the key pair combo as I get an error before I even try to decrypt anything. The privateKey parameter is currently hardcoded into the script using this format:

string privateKey = "-----BEGIN RSA PRIVATE KEY-----XXXXXXXX-----END RSA PRIVATE KEY-----";

So it seems to me the footer actually is included in the string... I have debugged and googled everywhere but I can't seem to solve it. I'm pretty new to RSA&Bouncycastle so maybe I'm just using wrong methods.

Hope you can help, thanks! - G4A

P.S. This is my first Stackoverflow question, I just created an account, so if you could also give me some feedback on the way I formulated this question; great!

Menispermaceous

IIRC you need a line between the pre-eb boundary; "-----BEGIN RSA PRIVATE KEY-----\r\nXXXXXXXX\r\n-----END RSA PRIVATE KEY-----" – Strepitous

Welcome to SO, G4A! There is not much wrong with the question, good question, excellent formatting. Four things for further improvement: 1) end with an actual question (you know, something that ends with a question mark) 2) the "Hope you can help, thanks! -4GA" is not required and actually not preferred 3) the PS should be a comment below the question and 4) please try and humor us by replying to e.g. AlexK. when he proposes a solution (which he is unsure of, hence the comment instead of the answer). – Quadroon

That did the trick @AlexK.! I did actually already try that but I forgot the carriage return. Could you please delete your comment and make it into an answer so I can give you karma, or whatever it's called. And thank you @Maarten Bodewes I'll remember it. And finally, sorry for the late answer; I guess my email isn't set up properly yet. – Menispermaceous

This happened to me when moving from a local secrets.json file to Azure settings. I had to .Replace("\\n", "\n") right before using the key and then it worked. – Zashin

Answer 1

You need to add a new line between the pre/post encapsulation boundary text and the Base64 data, so:

 string privateKey = "-----BEGIN RSA PRIVATE KEY-----\r\nXXX\r\n-----END RSA PRIVATE KEY-----";

This is because the pem specification allows for the existence of other textual headers between the two.

Strepitous

Pro tip - make sure you don't use a verbatim string literal (@"...") which would ignore the \n and \r escape sequences. – Germain

Hi, we want to refer from Azure key vault, there @ is required ex: "@Microsoft.KeyVault(SecretUri=dev..)". – Tallowy

Answer 2

If this doesn't work "-----BEGIN RSA PRIVATE KEY-----\r\nXXXXXXXX\r\n-----END RSA PRIVATE KEY-----"

please try this "-----BEGIN RSA PRIVATE KEY-----
XXXXXXXX
-----END RSA PRIVATE KEY-----"

Ganges

This worked with the 
 in Visual Studio .Net Framework 4.8 but not when I ported it over to an Azure Web App. I tried using the \r\n in Azure and that didn't work either. Any ideas? – Kazak

Hi @Alessandro Alves : facing same issue, any solution? – Tallowy

Answer 3

We converted the BOX Private Key to Base64 Format and stored the same in Azure Vault.

• Convert key to Base64 using Base64Encode method, store in Azure Key Vault.

• Retrieve the encoded string in code, decoded back using Base64Decode Method.

  public static string Base64Encode(string plainText) 
  {
      var plainTextBytes = System.Text.Encoding.UTF8.GetBytes(plainText);
      return System.Convert.ToBase64String(plainTextBytes);
  }
  
  public static string Base64Decode(string base64EncodedData) 
  {
      var base64EncodedBytes = System.Convert.FromBase64String(base64EncodedData);
      return System.Text.Encoding.UTF8.GetString(base64EncodedBytes);
  }
  

Tallowy

Answer 4

I recommend use \x0A instead of \r\n and 
. Because only this option worked for me.

So :

"-----BEGIN RSA PRIVATE KEY-----\x0AXXXXXXXX\x0A-----END RSA PRIVATE KEY-----"

Mannes