# Hashing

## Overview
Cryptographic hash functions transform data of any size into a fixed-length message digest or checksum, with SHA256 producing a 256-bit (64 hexadecimal digit) output regardless of input size. These functions are deterministic and demonstrate the avalanche effect—even a single-bit change in input produces a completely different hash value. Hash functions serve critical security purposes including secure password storage and detecting file modifications or tampering. Older algorithms like MD5 and SHA-1 are now cryptographically broken and vulnerable to collision attacks.

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## Key Information
- Fixed Output Size: Hash functions always produce the same length output regardless of input file size (e.g., SHA256 always produces 256 bits or 64 hex digits)
- Avalanche Effect: A single-bit change in input data produces a drastically different hash value, enabling reliable tamper detection
- Primary Applications: Password storage (with salting), file integrity verification, and detecting both intentional tampering and transfer errors
- Secure vs. Broken Algorithms: SHA224, SHA256, SHA384, SHA512, and RIPEMD160 are currently secure; MD5 and SHA-1 are cryptographically broken and susceptible to hash collisions
- HMAC Authentication: HMAC combines a hash function with a secret key using inner/outer padding (ipad/opad) to provide message authentication.
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## Notes
`sha256sum file`

`hmac256 key file`


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## Task
1. What is the SHA256 checksum of the file `order.json`?
    1. `sha256sum order.json`
    2. `2c34b68669427d15f76a1c06ab941e3e6038dacdfb9209455c87519a3ef2c660`
3. Open the file `order.json` and change the amount from `1000` to `9000`. What is the new SHA256 checksum?
    1. `sha256sum order.json`
    2. `11faeec5edc2a2bad82ab116bbe4df0f4bc6edd96adac7150bb4e6364a238466` 
4. Using SHA256 and the key `3RfDFz82`, what is the HMAC of `order.txt`?
    1. `hmac256 3RfDFz82 order.json`
    2. `c7e4de386a09ef970300243a70a444ee2a4ca62413aeaeb7097d43d2c5fac89f`


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## Conclusion
Cryptographic hash functions are fundamental security tools that provide both data integrity verification and secure password storage mechanisms. Understanding the difference between secure algorithms (SHA-256 family) and broken ones (MD5, SHA-1) is essential for implementing modern cybersecurity solutions. HMAC extends basic hashing by incorporating secret keys, making it suitable for message authentication in scenarios requiring both integrity and authenticity verification.

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## Resources

- **TryHackMe**: [Intro to Cryptography](https://www.tryhackme.com)

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