2. Encrypting a DocumentEncrypting a Document
To use a digital signature or encryption youTo use a digital signature or encryption you
must have a digital id also known as a digitalmust have a digital id also known as a digital
certificate. A digital id/digital certificate used tocertificate. A digital id/digital certificate used to
do two things. First, it can be used to do emaildo two things. First, it can be used to do email
encryption or encrypt files so that they can onlyencryption or encrypt files so that they can only
be read by the person they are intended for.be read by the person they are intended for.
Second, it can be used to “sign” or place aSecond, it can be used to “sign” or place a
digital signature on a document to guaranteedigital signature on a document to guarantee
that it arrives in the same state it was originallythat it arrives in the same state it was originally
sent and no one has added or changed things.sent and no one has added or changed things.
3. A digital id or digital certificate consists ofA digital id or digital certificate consists of
aa publicpublic andand privateprivate key. Your public key is sharedkey. Your public key is shared
with everyone. Your private key is kept private.with everyone. Your private key is kept private.
These keys are text documents full of what appearsThese keys are text documents full of what appears
to be random numbers and letters, but with the properto be random numbers and letters, but with the proper
algorithm, these numbers and letters have a veryalgorithm, these numbers and letters have a very
unique property.unique property.
If you take a document and run it through an algorithmIf you take a document and run it through an algorithm
with your public key, you get back an encryptedwith your public key, you get back an encrypted
document or an encrypted email.document or an encrypted email.
4. Once it is encrypted, the public key can’t be used toOnce it is encrypted, the public key can’t be used to
decrypt the document. The process is one way so itdecrypt the document. The process is one way so it
doesn’t matter if other people have the public key,doesn’t matter if other people have the public key,
they can’t read the document.they can’t read the document.
To decrypt the document you must have the privateTo decrypt the document you must have the private
key. If you give the encrypted document to ankey. If you give the encrypted document to an
algorithm with the private key, you will get back thealgorithm with the private key, you will get back the
original document.original document.
5. An encrypted document does three things.An encrypted document does three things.
It guarantees that the document was actually sentIt guarantees that the document was actually sent
by the sender.by the sender.
It guarantees that the document wasn’t modifiedIt guarantees that the document wasn’t modified
in route.in route.
It guarantees that no one else can read theIt guarantees that no one else can read the
document.document.
Digital signature on it guarantees who sent it andDigital signature on it guarantees who sent it and
that it wasn’t modified.that it wasn’t modified.
6. Basic Concepts Related to Digital SignaturesBasic Concepts Related to Digital Signatures
When transferring important documentsWhen transferring important documents
electronically, it is often necessary to certify inelectronically, it is often necessary to certify in
a reliable way who is actually the sendera reliable way who is actually the sender
(author) of a given document. One approach for(author) of a given document. One approach for
certifying the origin of documents and files iscertifying the origin of documents and files is
by using the so-called digital signatureby using the so-called digital signature
(electronic signature).(electronic signature).
The digital signing of documents uses publicThe digital signing of documents uses public
key cryptography as a mathematical base.key cryptography as a mathematical base.
