🐸 CIPHERS 🐸

🔑 ROT13 CIPHER 🔑

The ROT13 cipher is a substitution cipher where each letter is replaced by the letter 13 places down the alphabet. It is a special case of the Caesar cipher with a shift of 13.

How It Works

• Replace each letter with the letter 13 positions down the alphabet.
• Wrap around to the beginning of the alphabet if necessary.
• Applying ROT13 twice returns the original text.
• USE YOUR CIPHER WHEEL!

Decrypting ROT13 Ciphers

Cipher 1

Qvq lbh xabj... Cvenpl jnf na rkgerzryl pbzcrgvgvir ohfvarff. Cvengrf jbhyq bsgra wbva sbeprf jvgu bar nabgure, sbezvat nyyvnaprf naq syrrgf, va beqre gb vapernfr gurve punaprf bs fhpprff naq znkvzvfr gurve cebsvgf.

Cipher 2

Va gur pnaqyryvg unyyf bs Ubtjnegf, frpergf geniry snfgre guna bjyf, naq rirel juvfcre pneevrf gur jrvtug bs zntvp naq zvfpuvrs.

🔒 CAESAR CIPHER 🔒

The Caesar cipher is a substitution cipher where each letter in the plaintext is shifted by a fixed number of places down the alphabet.

How It Works

• Choose a shift value (e.g., 3).
• Replace each letter with the letter that is shift positions down the alphabet.
• Wrap around to the beginning of the alphabet if necessary.
• USE YOUR CIPHER WHEEL!

Decrypting Caesar Ciphers

Cipher 1

Y qcapcr kcqqyec uyq upgrrcl ml rfc uyjjq md rfc aytcpl, uygrgle dmp qmkcmlc ajctcp clmsef rm qmjtc gr.

Cipher 2

Oek adem jxqj vuubydw oek wuj mxud oekhu ijqdtydw yd q xywx fbqsu... ikttud khwu je zkcf?... Y tedj xqlu yj. - Sqfjqyd Zqsa Ifqhhem.

Cipher 3

Liztqvo, pwtl ug pivl. Vwbpqvo jmiba i Rmb bew pwtqlig, ivl zqopb vwe gwc kiv aidm nqnbg xwcvla xmz xmzawv. Bpiba bew pcvlzml xwcvla wnn nwz i niuqtg wn nwcz.

🕵️ SUBSTITUTION CIPHERS 🕵️

Substitution ciphers are where one character is replaced by another character.

Frequency & Word Analysis

Decryption helper website Decryption helper website from the lecture

Frequency analysis website

Decrypting Substitution Ciphers

Cipher 1

VJIF RPF GJPY XPFRE, VJIF RKDAFLF XPFREYFVV, RYH VJIF DRLF XPFREYFVV EDPUVE UNJY EDFI.

Cipher 2

HM'S V UZRRI MKHRW, VQCHMHJR. HM NVR MVPT JRT MJ SZCOHQT KTHWKMS JG KVGGJLHRW YTXMKS. VRY SJQTMHQTS MKTI VGT JRT VRY MKT SVQT.

Cipher 3

DST HTEIFL YEEC TEIC WNOCE WE'TE OK VNEF. OV'L DKCP WNEK WE WIBE WE TEICOLE VNOKML WETE LVTIKME.

🧩 Vigenere Ciphers 🧩

A Vigenere Cipher is like a substitution cipher, except that we use a different rotation for every letter.

Usually these are based off a phrase or word.

Try encrypting/decrypting

Vigenere Cipher encryption/decryption

Examples

Attempt if you dare!

1. G xuzc fa vm fa rmybrjgn lmdwhfabh yzp wyhq usz! Fwge ytqemvc ue hsbqg jazv ra majai icotcgcgtq.
2. O pir ibcrz gw xka! Wrk ges zuzik swyx sqzk fqb yrdit rqkng vmtr bit.

ASYMMETRIC ENCRYPTION & RSA

What Makes It Asymmetric?

• In symmetric encryption, the same key is used to both encrypt and decrypt.
  • For instance, in the Ceaser Ciphers covered earlier, we use the same key to encrypt (shift forwards) and decrypt (shift backwards).
• In asymmetric encryption, there are two different keys:
  • Public key: used to lock (encrypt) the message 🔓
  • Private key: used to unlock (decrypt) the message 🔑

We call it asymmetric since the keys are not the same for encrypting and decrypting.

This means you can safely share your public key with the world, while keeping your private key secret.

Why Do We Need RSA?

• Symmetric ciphers (like Substitution or Caesar) need both people to share the same secret key.
• But how do we share that key securely over the internet?
• This is a big problem for symmetric encryption schemes.
• RSA solves this by letting you publish your public key so anyone can encrypt messages to you.
• Only your secret private key can decrypt it.

How Does RSA Work? (Simplified)

1. Pick two prime numbers (For this example we will use 5 and 11)
2. Multiply them together (n = 5 × 11 = 55).
3. Choose a public exponent (we will choose e = 3).
4. Work out a private exponent (this is quite difficult to do but in this case, d = 27 will work).
5. We will chose 9, as our message.
6. To encrypt: Raise message to the public exponent, then mod by 55. c = (9^3 mod 55) = 14
7. To decrypt: Raise ciphertext to the private exponent, mod by 55. m = (14^27 mod 55) = 9 which was our message!

Practice Task

Task 1: Encryption

Bob’s RSA public key, n = 55 and public exponent, e = 3. Alice wants to send him the message, m = 4. What is the ciphertext? (encrypted message)

Try to solve before opening the answer!

Task 2: Decryption

Bob’s private key, d = 27 and public exponent, n = 55. He receives ciphertext, c = 9. What is the hidden message, m? Hint (use this calculator for large values: https://www.wolframalpha.com)

Try to solve before opening the answer!

This is the first page of the section about Breaking Game Saves

1: Locating Save Files

In this section you will learn to:

• Use the inspect element to find save files
• Use the export and import features in games

1.2: Using Import and Export

Some games make it super easy to locate a save file, as they want people to be able to use different saves. This will typically work by having a way to "Export" and "Import" the current save file.

To check for this, look in the settings of the game for an option that looks like:

Pressing the "export" button here will typically copy something to our clipboard, or download a file that we can use later with cyberchef.

To use a save file, try pressing the "import" option, which should prompt us to upload a file, or paste something into a box.

2: Decoding & Encoding Save Files

In this section you will learn to:

• Decode save files into an editable format
• Use cyberchef
• Encode decoded save files

Part 2.1: Using Cyberchef

Cyberchef (https://gchq.github.io/CyberChef/) is a great tool for simple decoding/encoding tasks.

It comes with a list of "Operations" we can combine into a "Recipe" to decode or encode text.

For example, to encode "Hello, world!" using Base64, we can:

1. Type our text into the "Input" box:

2. We can then use the search box on the left-hand side to find the "To Base64" operation.

3. We can then drag the operation into the "Recipe" section to make the recipe.

This will then run the recipe on our text, and we can see the encoded/decoded text in the "Output" section

Part 2.2: Decoding With CyberChef

When given a save file, if it is not in a readable format, we can try decoding with cyberchef!

1. To do this, first paste your save file into the input box.

If your save file is a file on your computer, press "Open file as input": Next, find the save file and double click it (or press open). This will place the file into input for you.

2. Now, we can guess the operation that will decode our text. Some typical encodings are "Base64" and "Zlib". "Decoding" operations typically have some word like "From" or "Inflate" in the operations.

If you are struggling, you can try the "Magic" operation, which will give you a hint for what encoding may be used.

3. Repeat step 2, adding more operations to the recipe until we can read the text in the "Output" section!

2.3: Encoding with Cyberchef

After decoding and modifying our save file, we will need to encode the save file before the game we were playing can use it.

For example, if a game's save file was originally encoded in base64, the game will only accept new saves that use base64.

In cyberchef, this means we will need to encode our modified save file using the opposite recipe of how we decoded it.

We can do this like:

1. For every operation in our recipe, find the opposite operation using the search feature, and replace it using the opposite operation.

Some common examples may be:

• From Base64 becomes To Base64
• Zlib inflate becomes Zlib deflate
• Unzip becomes Zip

2. Then reverse the order of the operations - if your recipe was:

1. From Base64
2. Zlib inflate

After reversing each operation and their order, we should have the recipe

1. Zlib deflate
2. To Base64

The encoded save file should now be in the "Output" section, ready for use!

Data Compression

Why Compress Save Files?

Data compression is simply the process of shrinking a file to make it smaller. Game developers do this for a few reasons:

• Saving Disk Space: A smaller save file takes up less storage.
• Faster Loading and Saving: Smaller files can be read and written much faster, leading to quicker save and load times in the game.
• Hiding Data: Compressed data is not readable. This stops users from opening the save file in a text editor and easily changing the file content.

How to Identify Compressed Files

A computer needs a way to know what kind of file it's reading. It doesn't look at the file extension (like .zip). Instead, it reads the first few bytes of the file itself, called the header. The most important part of the header is the first 2 to 4 bytes, called the File Signature (or Magic Number).

Common Compression Formats

Guide

🕸️ DAY 3 - Web Attacks

Cookies

Cookies can sometimes store a special kind of token (JWT tokens), like a special id that is used for authentication. If you could somehow trick the computer to think you are someone else, then you could gain access to their account.

There are 3 main parts of a JWT.

Each JWT can be split into 3 main parts.

1. Header
   • Contains metadata.
   • The type of the JWT token.
2. Payload
   • The main user data that is being sent.
   • Contains certain key-value pairs, like 'isadmin': true
3. Signature
   • The 'password' that is being sent with the token, that is used to verify that the token hasn't been modified.

1. First, paste the token into the token field in this decoding tool
2. Modify the payload. Notice how the entire token changes even with a very small change.
3. Copy the changed token and paste it back into the browser. (Right click, Inspect, Storage, Cookies, and click on the value field of the token. )

IDOR

How IDOR Works

IDOR vulnerabilities typically occur when an application does not check the user has access to a certain thing before giving them access. This can be very dangerous.

LocalStorage

Local storage stores data in the form of key - value pairs. You can think of this like a name tag associated with each value. Whenever you are trying to look for something, all you need to know is the name tag!

SQL Injection

What is SQL?

SQL stands for Structured Query Language, and you can think of it as another programming language that allows us to get information out of a 'database'.

Think of a database like a giant dictionary. You can look things up, and pull information. Say you wanted to look up 'all the words that began with the letter K'. This is something that you could do with SQL.

The issue begins when we perform queries like 'Give me all the users that ...' and the user is able to inject their custom phrases into that sentence. For example, the attacker might say 'have a username of 'bob''. Then, without checking, the computer would execute the query 'Give me all the users that have a username of bob'.

' OR '1'='1'