Encyption and Cryptography 101 | TryHackMe Encryption – Crypto 101

We covered basics of Encryption and Cryptography by answering the questions in TryHackMe Encryption – Crypto 101 under complete beginner pathway.

OSCP Study Notes

The Complete Practical Web Application Penetration Testing Course

Cryptography & Encryption Basics

Cryptography is used to protect confidentiality, ensure integrity, ensure authenticity. You use cryptography every day most likely, and you’re almost certainly reading this now over an encrypted connection.

When logging into TryHackMe, your credentials were sent to the server. These were encrypted, otherwise someone would be able to capture them by snooping on your connection.

When you connect to SSH, your client and the server establish an encrypted tunnel so that no one can snoop on your session.

When you connect to your bank, there’s a certificate that uses cryptography to prove that it is actually your bank rather than a hacker.

When you download a file, how do you check if it downloaded right? You can use cryptography here to verify a checksum of the data.

You rarely have to interact directly with cryptography, but it silently protects almost everything you do digitally.

Whenever sensitive user data needs to be stored, it should be encrypted. Standards like PCI-DSS state that the data should be encrypted both at rest (in storage) AND while being transmitted. If you’re handling payment card details, you need to comply with these PCI regulations. Medical data has similar standards. With legislation like GDPR and California’s data protection, data breaches are extremely costly and dangerous to you as either a consumer or a business.

Ciphertext – The result of encrypting a plaintext, encrypted data

Cipher – A method of encrypting or decrypting data. Modern ciphers are cryptographic, but there are many non cryptographic ciphers like Caesar.

Plaintext – Data before encryption, often text but not always. Could be a photograph or other file

Encryption – Transforming data into ciphertext, using a cipher.

Encoding – NOT a form of encryption, just a form of data representation like base64. Immediately reversible.

Key – Some information that is needed to correctly decrypt the ciphertext and obtain the plaintext.

Passphrase – Separate to the key, a passphrase is similar to a password and used to protect a key.

Asymmetric encryption – Uses different keys to encrypt and decrypt.

Symmetric encryption – Uses the same key to encrypt and decrypt

Brute force – Attacking cryptography by trying every different password or every different key

Cryptanalysis – Attacking cryptography by finding a weakness in the underlying maths

Alice and Bob – Used to represent 2 people who generally want to communicate. They’re named Alice and Bob because this gives them the initials A and B. https://en.wikipedia.org/wiki/Alice_and_Bob for more information, as these extend through the alphabet to represent many different people involved in communication.

The two main categories of Encryption are symmetric and asymmetric.

Symmetric encryption uses the same key to encrypt and decrypt the data. Examples of Symmetric encryption are DES (Broken) and AES. These algorithms tend to be faster than asymmetric cryptography, and use smaller keys (128 or 256 bit keys are common for AES, DES keys are 56 bits long).

Asymmetric encryption uses a pair of keys, one to encrypt and the other in the pair to decrypt. Examples are RSA and Elliptic Curve Cryptography. Normally these keys are referred to as a public key and a private key. Data encrypted with the private key can be decrypted with the public key, and vice versa. Your private key needs to be kept private, hence the name. Asymmetric encryption tends to be slower and uses larger keys, for example RSA typically uses 2048 to 4096 bit keys.

RSA and Elliptic Curve cryptography are based around different mathematically difficult (intractable) problems, which give them their strength. More about RSA later.

What’s a Digital Signature?

Digital signatures are a way to prove the authenticity of files, to prove who created or modified them. Using asymmetric cryptography, you produce a signature with your private key and it can be verified using your public key. As only you should have access to your private key, this proves you signed the file. Digital signatures and physical signatures have the same value in the UK, legally.

The simplest form of digital signature would be encrypting the document with your private key, and then if someone wanted to verify this signature they would decrypt it with your public key and check if the files match.

Highlights

• SSH Key Protection: SSH keys are protected by a passphrase, not a password, adding a layer of security.
• Web Server Identification: Secure connections use certificates, as seen with HTTPS, which verifies the website’s identity.
• Math in Cryptography: Modulo operations are covered, such as calculating remainders, a foundational math concept in cryptography.
• Encryption Types: The video highlights encryption types like DES (considered outdated) and the improvement with Triple DES for greater security.
• RSA: RSA encryption uses key variables (p, q, n) to create public and private keys. In a task, these variables are multiplied to determine n, an essential RSA variable.
• Decrypting SSH Private Key: A provided SSH private key is cracked with John the Ripper to retrieve the passphrase.
• GPG Decryption: Using the gpg tool, a private key is imported, and an encrypted message file is decrypted to reveal the secret word.
• Diffie-Hellman Key Exchange: The room briefly introduces Diffie-Hellman without additional questions, followed by a practical GPG decryption task.

Room Answers

Video Walkthrough