C# Catching an exception by message

Question

I need to change specific system exception message with my custom one.

Is it bad practice to catch an exception and inside the catch block check if the system exception message matches a specific string and if so, throw my custom exception?

try
{
    ...
}
catch (System.Security.Cryptography.CryptographicException ex)
{
    if (ex.Message.Equals("The specified network password is not correct.\r\n", StringComparison.InvariantCultureIgnoreCase))
        throw new Exception("Wrong Password");
    else
        throw ex;
}

Or is there a better way to achieve this.

Answer 1

There's nothing inherently wrong with throwing an exception within a catch statement. However there are a couple of things to bear in mind:

Rethrow the exception using "throw" not "throw ex", otherwise you will loose the stack trace.

From [Creating and Throwing Exceptions] 1.

Do not throw System.Exception, System.SystemException, System.NullReferenceException, or System.IndexOutOfRangeException intentionally from your own source code.

If the CrytographicException is really not suitable for you, you could create a specific exception class to represent an invalid password:

try
{
    ...
}
catch (System.Security.Cryptography.CryptographicException ex)
{
    if (ex.Message.Equals("The specified network password is not correct.\r\n",
            StringComparison.InvariantCultureIgnoreCase))
        throw new InvalidPasswordException("Wrong Password", ex);
    else
        throw;
}

Note how the original exception is preserved in the new InvalidPasswordException.