DecodeOpenSSLPrivateKey

// NOT MADE BY ME

public static byte[] DecodeOpenSSLPrivateKey(String instr)
  {
  const  String pemprivheader = "-----BEGIN RSA PRIVATE KEY-----" ;
  const  String pemprivfooter   = "-----END RSA PRIVATE KEY-----" ;
  String pemstr = instr.Trim() ;
  byte[] binkey;
       if(!pemstr.StartsWith(pemprivheader) || !pemstr.EndsWith(pemprivfooter))
    return null;

       StringBuilder sb = new StringBuilder(pemstr) ;
        sb.Replace(pemprivheader, "") ;  //remove headers/footers, if present
        sb.Replace(pemprivfooter, "") ;

String pvkstr = sb.ToString().Trim();   //get string after removing leading/trailing whitespace

   try{        // if there are no PEM encryption info lines, this is an UNencrypted PEM private key
    binkey = Convert.FromBase64String(pvkstr) ;
    return binkey;
    }
   catch(System.FormatException) {      //if can't b64 decode, it must be an encrypted private key
    //Console.WriteLine("Not an unencrypted OpenSSL PEM private key");
    }

 StringReader str = new StringReader(pvkstr);

//-------- read PEM encryption info. lines and extract salt -----
 if(!str.ReadLine().StartsWith("Proc-Type: 4,ENCRYPTED"))
    return null;
 String saltline = str.ReadLine();
 if(!saltline.StartsWith("DEK-Info: DES-EDE3-CBC,") )
    return null;
 String saltstr =  saltline.Substring(saltline.IndexOf(",") + 1).Trim() ;
 byte[] salt = new byte[saltstr.Length/2];
 for (int i=0; i <salt.Length; i++)
    salt[i] = Convert.ToByte(saltstr.Substring (i*2, 2), 16);
 if(! (str.ReadLine() == ""))
    return null;

//------ remaining b64 data is encrypted RSA key ----
String encryptedstr =  str.ReadToEnd() ;

 try{   //should have b64 encrypted RSA key now
    binkey = Convert.FromBase64String(encryptedstr) ;
 }
   catch(System.FormatException) {  // bad b64 data.
    return null;
    }

//------ Get the 3DES 24 byte key using PDK used by OpenSSL ----

    SecureString  despswd = GetSecPswd("Enter password to derive 3DES key==>") ;
   //Console.Write("\nEnter password to derive 3DES key: ");
   //String pswd = Console.ReadLine();
  byte[] deskey = GetOpenSSL3deskey(salt, despswd, 1, 2);    // count=1 (for OpenSSL implementation); 2 iterations to get at least 24 bytes
  if(deskey == null)
    return null;
  //showBytes("3DES key", deskey) ;

//------ Decrypt the encrypted 3des-encrypted RSA private key ------
 byte[] rsakey = DecryptKey(binkey, deskey, salt);  //OpenSSL uses salt value in PEM header also as 3DES IV
if(rsakey !=null)
    return rsakey;  //we have a decrypted RSA private key
else {
    Console.WriteLine("Failed to decrypt RSA private key; probably wrong password.");
    return null;
   }
 }