A digital signature is a mathematical scheme for demonstrating the authenticity of a message stored in electronic form. A valid digital signature gives a recipient reason to believe that the message was created by a known sender. Digital signatures are commonly used in everyday situations such as writing a letter, software distribution and financial transactions, etc. The first practical public-key cryptosystem is the RSA. One of the primary applications of RSA is in the use of digital signature. In this paper we describe the RSA digital signature sheme.