Lesson 24 Encryption Methods 1

​Lesson 24 Encryption Methods 1

By Ryan Mordey

Big Picture

Discussed how network functionality is divided into layers.

Past

Explain basic encryption methods some of which pre-date

Assess the effectiveness of a range of encryption methods..

Present

Future

Careers: Network Security Specialist, Cryptographer, Cryptanalyst

When data is encrypted, it passed through a process that combines data with a key, which is used to encrypt data then at the receiving end it is used to decrypt the data.

This is known as symmetric key encryption, with applications such as whole disk encryption the key is kept safe by the user and applied every time the computer is booted.

Symmetric Encryption

Data being transmitted needs a different process, as sending the same key used to encrypt to decrypt data, could be more vulnerable to data interception.

Asymmetric keys use different keys to encrypt and decrypt the data but are mathematically related to each other. For example a encrypt key might be a calculation but the decrypt key is the matching answer.

Asymmetric Encryption

​ Comparison

Here is an comparison on the use of encryption methods:

Categorize

Options (10)

Same key is used

User keeps the key private

Used for whole disk encryption

Applied each time computer boots up

One key to encrypt

Another key to decrypt

Keys are mathematically linked

Best used for data transmission

Less Processing time needed

More processing time needed

Drag the correct characteristic to the encryption technique

Symmetric Encryption

Asymmetric Encryption

Pre-computing Cyphers

Substitution Cypher also known as a shift cypher, involves substituting one letter of the alphabet with another.

This is an outdated method that is easy to develop but can be easily cracked, providing little security:

As a written algorithm:
1. Select Shift Value
2. Input Message
3. Loop through characters of message
a) Encrypted character = current character + shift value
b) Save encrypted character
c) Next character in message
4. Output encrypted message

Pre-computing Cyphers

Transposition Cypher moves around the position of the letters in a message. This is different to substitution where the letters change but the position does not.

Here is a columnar transposition where each letter is placed into a table but we choose to transpose through the column to make a new word.

As a written algorithm:
1. Create a table to hold message
2. Loop through characters of message
a) insert character in table index
b)Move to next index on row
c)Next character in the message
3. Return to first index
4. Loop through index of table
a) Save character from index to encrypted message
b)Move to next index in column
5.Output encrypted message.

Fill in the Blanks

Fill in the Blanks

XOR Cyphers

This technique uses a binary operator called XOR. Applying an XOR operation to two binary numbers produces a new result which is the encrypted message.

To decrypt the message all you need to do is XOR the message with the same key. XOR is used in modern encryption methods

This encryption method is relatively simple and inexpensive to perform, however if you know the XOR cipher stream you can reverse engineer to decrypt the ciphertext.

Steganographic Cyphers

This method involves hiding a message within some other kind of data. For example binary data could be hidden in an image file, this method does not attract attention so is hard to spot.

Most hackers will see what just appears to be an image, so might not think anything of the additional binary data. Once discovered it is not difficult to crack the code.

Draw

Using the XOR cypher technique what would the result of comparing A and B be? Write your answer for each comparison in column C. 2 Marks.

Multiple Choice

How does a steganographic cypher work?

• A steganographic cypher replaces text with random characters.
• A steganographic cypher hides secret data within a non-secret medium.
• A steganographic cypher transmits data over secure channels.
• A steganographic cypher encrypts data using complex algorithms.

Main Task

Computer Task:

Use the written algorithm to try and create your own substitution encryption program in Python.

You should input a message and see if the person can try and crack your encryption technique.

Complete all the questions on the work sheet.