TryHackMe — Cryptography Basics | Cyber Security 101 (THM)

Importance of Cryptography

Cryptography ensures secure communication, maintaining data confidentiality, integrity, and authenticity in the presence of adversaries. You rely on cryptography daily:

• Login: Your credentials are encrypted, preventing unauthorized access.
• SSH: Encrypted tunnels protect your session from eavesdropping.
• Online Banking: Cryptography verifies the server’s authenticity.
• Downloads: Hash functions check file integrity.

Cryptography is fundamental for standards like PCI DSS for credit card data and HIPAA/GDPR for medical records, establishing necessary security without direct user interaction.

Questions and Answers

1. What is the standard required for handling credit card information?

• PCI DSS

Plaintext to Ciphertext

Plaintext is readable data, like text or images, before encryption. Using a cipher (encryption algorithm) and a key, plaintext is transformed into ciphertext, the unreadable, scrambled output. To revert it back to plaintext, we pass the ciphertext and key through the decryption process.

Key terms:

• Plaintext: Original, readable data.
• Ciphertext: Encrypted, unreadable data.
• Cipher: Algorithm for encryption and decryption.
• Key: Secret bit sequence used with the cipher.
• Encryption: Turning plaintext into ciphertext.
• Decryption: Turning ciphertext back into plaintext.

Questions and Answers

1. What do you call the encrypted plaintext?

• ciphertext

1. What do you call the process that returns the plaintext?

• decryption

Historical Ciphers

Cryptography has ancient roots, with simple ciphers like the Caesar Cipher, which shifts each letter by a set number. For example, shifting TRYHACKME by a key of 3 results in WUBKDFNPH. To decrypt, reverse the shift by the same key. This simplicity, however, makes it vulnerable to brute-force attacks since there are only 25 possible keys in the English alphabet.

Other notable historical ciphers:

• Vigenère cipher (16th century)
• Enigma machine (WWII)
• One-time pad (Cold War)

Questions and Answers

1. Knowing that XRPCTCRGNEI was encrypted using Caesar Cipher, what is the original plaintext?

• ICANENCRYPT

Types of Encryption

There are two main encryption types: symmetric and asymmetric.

1. Symmetric Encryption: Uses the same key for both encryption and decryption. Keeping this key secure is crucial as it is shared with intended recipients. Examples include DES, 3DES, and AES.

• DES: A 56-bit key, now insecure as it was cracked in under 24 hours in 1999.
• 3DES: An extension of DES, using a 168-bit key (effective security of 112 bits); deprecated in 2019.
• AES: Adopted in 2001, with key sizes of 128, 192, or 256 bits; the current standard.

1. Asymmetric Encryption: Uses two keys — public for encryption and private for decryption. Asymmetric encryption includes RSA, Diffie-Hellman, and ECC, where ECC achieves strong security with shorter keys. This type is based on problems that are easy to compute in one direction but hard to reverse, ensuring long-term security.

Questions and Answers

1. Should you trust DES? (Yea/Nay)

• Nay

1. When was AES adopted as an encryption standard?

• 2001

Basic Math

Cryptography relies on math, especially XOR and modulo operations.

1. XOR Operation: XOR (exclusive OR) compares binary bits; it returns 1 if bits differ, 0 if they’re the same. XOR is useful in cryptography due to properties like A ⊕ A = 0 and A ⊕ 0 = A. For encryption, XOR can be applied to plaintext and a key to produce ciphertext, and the original text can be recovered by XORing the ciphertext with the key again.
2. Modulo Operation: The modulo (X%Y) gives the remainder of dividing X by Y. It’s commonly used in cryptographic algorithms. The result of X%Y is always between 0 and Y-1.

Questions and Answers

1. What’s 1001 ⊕ 1010?

• 0011

1. What’s 118613842%9091?

• 3565

1. What’s 60%12?

• 0