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The scope of Digital Signature is not just limited to exchange of
messages. The handwritten signature is commonly used in all kinds of
applications to prove the identity of the signer. In the same way, a
digital signature can be used for all kinds of electronic records. Any
field in which the integrity and validity of the data is crucial, can
make use of a Digital Signature. Here we discuss a few of these
applications.

1. Electronic Mail.

When we send an e-mail to a mailbox, it is desired that the owner of
the mailbox should get the e-mail in its original form. If during
transport, the content changes either accidentally or due to intrusion
by a third party, then the receiving end should be able to recognize
this change in the content. Also no person should be able to send
e-mail in the disguise of another person. Both these factors are taken
care of by the Digital signature. Any change in the e-mail will affect
the message digest generated by the SHA and thus the digital signature
will be marked as unverified. So the recipient will reject that
message.

2. Data storage.

This is one more interesting application of Digital Signature.
Suppose a large amount of data is stored on a computer. Only
authorized people are allowed to make changes to the data. In such
case, along with the data, a signature can also be stored as an
attachment. This signature is generated from the data digest and the
private key. So if any changes are made in the data by some
unauthorized person, then they will get easily recognized at the time
of signature verification and thus that copy of data will be
discarded.

3. Electronic funds transfer.

Applications like online banking, e-commerce come under this
category. In these applications the information being exchanged by the
two sides is vital and thus extreme secrecy and authenticity must be
maintained. A digital signature can ensure the authentication of the
information but, the secrecy should be maintained by using some
encryption techniques. So before generating the message digest, the
message should be encrypted. Then the digital signature is generated
and attached to the message. At the receiving end after verification
of signature, the message is decrypted to recover the original
message.

5. Software Distribution.
Software developers often distribute their software using some
electronic media, for example, the internet. In this case, in order to
ensure that the software remains unmodified and its source is genuine,
Digital Signature can be used. The developer signs the software and
the users verify the signature before using it. If signature gets
verified, then only the users can be sure about the validity of that
software.