• What is cryptography? • Why it’s helpful in a network and how hackers broke security? • Different methods of encryption and decryption?

1. ASSIGNMENT # 4
SUBMITTED TO:
MISS AYESHA RASHID
SUBMITTED BY:
RABIA ZAFAR
17581556-045
BS (IT)4TH
‘A’
TOPIC:
 What is cryptography?
 Why it’s helpful in a network and how
hackers broke security?

2.  Different methods of encryption and
decryption?
Cryptography:
The term cryptography is a Greek word which means "secret writing".
 It is an art and science of transforming messages so as to make them secure and
immune to attacks.
 Cryptography involves the process of encryption and decryption.
 Convert plain text to cipher text and cipher text into plain text.
Cryptography is helpful in networking:
The role ofcryptography in network security can be understand with the help of following
points:
 Transmission channel encryption: When data is confidential and needed security
in term of readability, then data should encrypt from the sender and it should by
only decrypted by intended person.
 For authenticity and authorization cryptography should be used.
 Cryptography is useful in network security by providing security services.
Encryption and decryption:
Encryption is a process of transforming information so it is unintelligible to anyone but
the intended recipient.
Decryption is the process of transforming encrypted information so that it is intelligible
again.
Different methods of encryption and decryption:
Encryption Algorithms:
Cryptography is broadly classified into two categories: Symmetric key Cryptography
and Asymmetric key Cryptography (popularly known as public key cryptography).

3. Asymmetric-Key Cryptography
In asymmetric or public-key cryptography, there are two keys: a private key and a public
key. The private key is kept by the receiver. The public key is announced to the public.
Imagine Aqsa wants to send a message to sana. Aqsa uses the public key to encrypt
message. When the message is received by sana, the private key is used to decrypt the
message.
Symmetric Key Cryptography:
An encryption system in which the sender and receiver of a message share a single,
common key that is used to encrypt and decrypt the message. The most
popular symmetric–key system is the Data Encryption Standard (DES).
Transposition Ciphers:
In Cryptography, a transposition cipher is a method of encryption by which the positions
held by units of plaintext (which are commonly characters or groups of characters) are
shifted according to a regular system, so that the cipher text constitutes a permutation of
the plaintext.
That is, the order of the units is changed (the plaintext is reordered). Mathematically, a
bijective function is used on the characters’ positions to encrypt and an inverse function
to decrypt.

4. Substitution Cipher:
Method of encryption by which units of plaintext are replaced with ciphertext, according
to a fixed system; the “units” may be single letters (the most common), pairs of letters,
triplets of letters, mixtures of the above, and so forth.
Stream Cipher:
Symmetric or secret-key encryption algorithm that encrypts a single bit at a time. With a
Stream Cipher, the same plaintext bit or byte will encrypt to a different bit or byte every
time it is encrypted.
Block Cipher:
An encryption method that applies a deterministic algorithm along with a symmetric key
to encrypt a block of text, rather than encrypting one bit at a time as in stream ciphers.

5. Example:
Let’s say there’s a person named Aqsa. Now suppose Aqsa sends a message to his
friend Sana who is on the other side of the world. Now obviously he wants this message
to be private and nobody else should have access to the message. He uses a public
forum, for example, WhatsApp for sending this message. The main goal is to secure this
communication.
Let’s say there is a smart girl called Amna. Who secretly got access to your
communication channel. Since this girl has access to your communication, she can do
much more than just eavesdropping, for example, she can try to change the
message. Now, this is just a small example. Let’s see how cryptography can help secure
the connection between Aqsa and Sana.
So, to protect his message, Aqsa first convert his readable message to unreadable form.
Here, he converts the message to some random numbers. After that, she uses a key to
encrypt his message, in Cryptography, known as ciphertext.
Aqsa sends this ciphertext or encrypted message over the communication channel, she
won’t have to worry about somebody in the middle of discovering his private messages.
Suppose, Amna here discover the message and she somehow manages to alter it before it
reaches Sana.
Now, Sana would need a key to decrypt the message to recover the original plaintext. In
order to convert the ciphertext into plain text, Sana would need to use the decryption key.
Using the key he would convert the ciphertext or the numerical value to the
corresponding plain text.

6. After using the key for decryption what will come out is the original plaintext message,
is an error. Now, this error is very important. It is the way Sana knows that message sent
by Aqsa is not the same as the message that he received. Thus, we can say that encryption
is important to communicate or share information over the network.
Main Reasons for Broken Cryptography
Broken cryptography in Android apps can be introduced due to various reasons.
 Using a weak algorithm for encryption/decryption
 Using a strong encryption algorithm but implementing it in an insecure way
Key theft
The easiest way for a hacker to bypass encryption scheme is simply to steal the key. If the
hacker manages to plant a key logger on your system, he can record your activities
including the generation or use ofcryptographic keys. In additionsome forms ofmalware
enable the controller to browse the contents of your hard drive, so if you store
cryptographic key and passwords in plain text, they could be vulnerable. Keeping your
operating system, firewall and anti-malware programs up to date can help prevent this
type of attack.