1. Lecture No. 5: Data Encryption
Lecturer: Dr. Mazin Alkathiri
Department of Information Tecnology,
College of Applied Science,
Seiyun University
2023

2.  Encryption is a security method in which information is encoded in such a
way that only authorized user can read it.
 It uses encryption algorithm to generate ciphertext that can only be read if
decrypted.

3. plaintext
encryption
ciphertext
decryption
plaintext
• Plaintext: a message in its original form
• Ciphertext: a message in the transformed, unrecognized form
• Encryption: the process for producing ciphertext from plaintext
• Decryption: the reverse of encryption
• Key: a secret value used to control encryption/decryption

4.  There are two types of encryptions schemes as listed below:
 Symmetric Key encryption
 Public Key encryption

5.  Symmetric key encryption algorithm uses same cryptographic keys for both encryption and decryption
of cipher text.
plaintext
encryption
ciphertext
decryption
plaintext
key key
same key

6.  Public key encryption algorithm uses pair of keys, one of which is a secret key and one of which is
public. These two keys are mathematically linked with each other.
plaintext
encryption
ciphertext
decryption
plaintext
public key private key

7. In terms of security, hashing is a technique used to encrypt data and
generate unpredictable hash values. It is the hash function that
generates the hash code, which helps to protect the security of
transmission from unauthorized users.

8.  provides a way to verify that the message received is the same as
the message sent. It can take a plain text message as input and
then computes a value based on that message.
• Key Points
• The length of computed value is much shorter than the original message.
• It is possible that different plain text messages could generate the same value.

9.  is an electronic, encrypted, stamp of authentication on digital information such
as email messages, or electronic documents. A signature confirms that the
information originated from the signer and has not been altered.
 Signing certificate To create a digital signature, you need a signing certificate,
which proves identity.
◦ When you send a digitally-signed macro or document, you also send your certificate and
public key.
◦ Certificates are issued by a certification authority, and like a driver’s license, can be
revoked.
◦ A certificate is usually valid for a year, after which, the signer must renew, or get a new,
signing certificate to establish identity.

11.  There are several reasons to implement digital signatures to
communications:
 Authentication: Digital signatures help to authenticate the
sources of messages.
 Integrity: Once the message is signed, any change in the message
would invalidate the signature.
 Non-repudiation: By this property, any entity that has signed some
information cannot at a later time deny having signed it.

12.  is a barrier between Local Area Network (LAN) and the Internet. It
allows keeping private resources confidential and minimizes the
security risks. It controls network traffic, in both directions.
 The following diagram depicts a sample firewall between LAN and
the internet. The connection between the two is the point of
vulnerability. Both hardware and the software can be used at this
point to filter network traffic.

14. • Firewall management must be addressed by both system managers
and the network managers.
• The amount of filtering a firewall varies. For the same firewall, in
different directions.