Appropriate use if IDisposable

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C#

C#4.0

cryptography

Is there any need to use IDisposable in the block of code below. I am availing of using and hash contains the SHA1 of text taken in from the user and inputData is a byte array. I assume the second block of code is correct.

Example 1:

using (SHA1 hash = SHA1.Create())
{
    txtSHA1.Text = GetBytesToString(hash.ComputeHash(inputData));
    ((IDisposable)hash).Dispose();
}

Example 2:

using (SHA1 hash = SHA1.Create())
{
    txtSHA1.Text = GetBytesToString(hash.ComputeHash(inputData));
}