# Cryptography

![](https://1099202751-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FEhofjMfYbx3gOUSReXD7%2Fuploads%2Fgit-blob-e908ad76817db14116409aab03ee90043a1f65cd%2F9118859.png?alt=media)

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## 🌐 Resources 🔗

> * [Cryptography Basics - TryHackMe](https://tryhackme.com/r/room/cryptographybasics)
>   * [Public Key Cryptography Basics - TryHackMe](https://tryhackme.com/r/room/publickeycrypto)
>   * [Hashing Basics - TryHackMe](https://tryhackme.com/r/room/hashingbasics)
>   * [Introduction to Cryptography](https://tryhackme.com/r/room/cryptographyintro)
> * [CryptoBook](https://cryptohack.gitbook.io/cryptobook)
>   * [CryptoHack – A fun, free platform for learning cryptography](https://cryptohack.org/)
> * [What is encryption? - Cloudflare](https://www.cloudflare.com/learning/ssl/what-is-encryption/)
> * [Wolfram|Alpha](https://www.wolframalpha.com/)
> * [Modular arithmetic - Britannica](https://www.britannica.com/science/modular-arithmetic)
> * [RSA Encryption - Brilliant](https://brilliant.org/wiki/rsa-encryption/)
> * [Diffie-Hellman - Brilliant](https://brilliant.org/wiki/diffie-hellman-protocol/)
> * [What is SSH? - Cloudflare](https://www.cloudflare.com/learning/access-management/what-is-ssh/)
> * [Digital signature](https://www.docusign.com/how-it-works/electronic-signature/digital-signature/digital-signature-faq)
> * [CA/Included Certificates - MozillaWiki](https://wiki.mozilla.org/CA/Included_Certificates)
> * [net/data/ssl/chrome\_root\_store/root\_store.md](https://chromium.googlesource.com/chromium/src/+/main/net/data/ssl/chrome_root_store/root_store.md)
> * [The GNU Privacy Guard](https://gnupg.org/)
>   * [Email Self-Defense](https://emailselfdefense.fsf.org/en/)
> * [SHA - Brilliant](https://brilliant.org/wiki/secure-hashing-algorithms/)
> * [Peter Selinger: MD5 Collision Demo](https://www.mscs.dal.ca/~selinger/md5collision/)
> * [SHAttered - Collision attack](https://shattered.io/)
> * [Common Password List - rockyou.txt - Kaggle](https://www.kaggle.com/datasets/wjburns/common-password-list-rockyoutxt)
>   * [Understanding RockYou.txt: A Tool for Security and a Weapon for Hackers - Keeper](https://www.keepersecurity.com/blog/2023/08/04/understanding-rockyou-txt-a-tool-for-security-and-a-weapon-for-hackers/)
> * [What is a rainbow table attack and how to prevent it? - Proton](https://proton.me/blog/what-is-rainbow-table-attack)
> * [HMAC (Hash-Based Message Authentication Codes) Definition - Okta](https://www.okta.com/identity-101/hmac/)
>   * [HMAC](https://cryptography.io/en/latest/hazmat/primitives/mac/hmac/)
> * [pyca/cryptography](https://cryptography.io/en/stable/)

### Tools

> * [dCode - Online Ciphers, Solvers, Decoders, Calculators](https://www.dcode.fr/cipher-identifier)
> * [RsaCtfTool](https://github.com/RsaCtfTool/RsaCtfTool)
> * [rsatool](https://github.com/ius/rsatool)
> * [CyberChef](https://gchq.github.io/CyberChef/)
> * [gpg](https://www.gnupg.org/gph/de/manual/r1023.html)
> * [CrackStation - Online Password Hash Cracking](https://crackstation.net/)
> * [Hashes.com - hash decryptor](https://hashes.com/en/decrypt/hash)
>   * [Hashes.com - hash identifier](https://hashes.com/en/tools/hash_identifier)
> * [Free Online Encoding Tools For Developers - FreeFormatter.com](https://www.freeformatter.com/encoders-cryptography.html)
> * [hashID](https://pypi.org/project/hashID/)
> * [hashcat](https://hashcat.net/wiki/doku.php?id=example_hashes)
> * [John the Ripper](https://www.openwall.com/john/)
>   * [John the Ripper jumbo](https://github.com/openwall/john)
>   * [John the Ripper - wordlist rules syntax](https://www.openwall.com/john/doc/RULES.shtml)
> * [hash-identifier](https://gitlab.com/kalilinux/packages/hash-identifier/-/tree/kali/master)

***

## 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

```bash
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.

***

## Commands

```bash
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

```bash
# 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
```

***