Cryptography

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🌐 Resources 🔗

• Cryptography Basics - TryHackMe

  • Public Key Cryptography Basics - TryHackMe

  • Hashing Basics - TryHackMe

  • Introduction to Cryptography

• CryptoBook

  • CryptoHack – A fun, free platform for learning cryptography

• What is encryption? - Cloudflare

• Wolfram|Alpha

• Modular arithmetic - Britannica

• RSA Encryption - Brilliant

• Diffie-Hellman - Brilliant

• What is SSH? - Cloudflare

• Digital signature

• CA/Included Certificates - MozillaWiki

• net/data/ssl/chrome_root_store/root_store.md

• The GNU Privacy Guard

  • Email Self-Defense

• SHA - Brilliant

• Peter Selinger: MD5 Collision Demo

• SHAttered - Collision attack

• Common Password List - rockyou.txt - Kaggle

  • Understanding RockYou.txt: A Tool for Security and a Weapon for Hackers - Keeper

• What is a rainbow table attack and how to prevent it? - Proton

• HMAC (Hash-Based Message Authentication Codes) Definition - Okta

  • HMAC

• pyca/cryptography

Tools

• dCode - Online Ciphers, Solvers, Decoders, Calculators

• RsaCtfTool

• rsatool

• CyberChef

• gpg

• CrackStation - Online Password Hash Cracking

• Hashes.com - hash decryptor

  • Hashes.com - hash identifier

• Free Online Encoding Tools For Developers - FreeFormatter.com

• hashID

• hashcat

• John the Ripper

  • John the Ripper jumbo

  • John the Ripper - wordlist rules syntax

• hash-identifier

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Theory

• Hashing is a process that transforms input data into a unique hash value, a fixed-length string of characters, also known as a digest. This hash value serves as a unique representation of the original data, and even a minor modification in the data will result in a different hash value. Unlike encryption or encoding, hashing is a one-way process, meaning the original data cannot be recovered from the hash.

  • Computer science - Polynomial Time (e.g. hashing algorithm = reasonable time) vs Non-deterministic Polynomial Time (e.g. un-hashing algorithm = long time)

  • Some hashing algorithms: MD4, MD5, SHA1, NTLM, etc

Word: "white"

MD4		76b737528246b908e6817dd81bd41e5d
MD5		d508fe45cecaf653904a0e774084bb5c
SHA1	528cef87d0bfb947548ab94679d1e5765f19089a
SHA256	018fa96a44715c90bf93be148069cb28dd45d398f2cc75aa1565311f6e55d174

• Encoding is used to convert data into a different format to ensure compatibility with a particular system. Common encoding methods for the English language include ASCII, UTF-8, UTF-16, UTF-32, ISO-8859-1, and Windows-1252. UTF-8, UTF-16, and UTF-32 are Unicode encodings capable of representing characters from various languages, such as Arabic and Japanese.

• Encryption is the only method that safeguards data confidentiality by using a cryptographic cipher and a key. This process is reversible, as long as the cipher is known and the key is accessible.

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Commands

ssh-keygen

gpg --import <yourkey>.key
gpg --decrypt <message>.gpg

hexdump -C <file.txt>
md5sum <file.txt>
sha1sum <file.txt>
sha256sum <file.txt>
sha512sum <file.txt>

cat /etc/shadow
# Encrypted password:
# $prefix$options$salt$hash
man 5 crypt

echo "Text" | base64
echo "EncodedText" | base64 -d

Hash cracking

john

# John the Ripper
john <options> <file with hashes>
john --list=formats
cat /usr/share/john/john.conf | grep -i rules

john --wordlist=<path to wordlist> <path to file>
john --format=<format> --wordlist=<path to wordlist> <path to file>
# e.g.
john --wordlist=/usr/share/wordlists/rockyou.txt hash_to_crack.txt
john --format=raw-md5 --wordlist=/usr/share/wordlists/rockyou.txt hash_to_crack.txt

# Crack Windows authentication hashes
# e.g.
john --format=NT --wordlist=/usr/share/wordlists/rockyou.txt ntlm_to_crack.txt

# Crack /etc/shadow hashes
unshadow <path to passwd> <path to shadow>
# e.g.
unshadow local_passwd local_shadow > unshadowed.txt
john --format=sha512crypt --wordlist=/usr/share/wordlists/rockyou.txt unshadowed.txt

# Single crack mode & mangling rules
john --single --format=<format> <path to file>

# Crack password-protected Zip/RAR files
zip2john <options> <zip file> > <output file>
rar2john <rar file> > <output file>
# e.g.
zip2john zipfile.zip > zip_hash.txt
rar2john rarfile.rar > rar_hash.txt
john --wordlist=/usr/share/wordlists/rockyou.txt zip_hash.txt

# Crack SSH keys
ssh2john <id_rsa private key file> > <output file>
# e.g.
ssh2john id_rsa > id_rsa_hash.txt
john --wordlist=/usr/share/wordlists/rockyou.txt id_rsa_hash.txt

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