Understanding Hash Functions: SHA-256 and Beyond

What Is a Hash Function?

A hash function converts input data of any size into a fixed-size output called a hash or digest. The same input always produces the same output, but even a tiny change in input produces a completely different hash.

Properties of Good Hash Functions

Deterministic

Same input always produces same output

Fast Computation

Hashes are quick to compute

Irreversible

Cannot reverse a hash to get original input

Collision Resistant

Extremely unlikely for two different inputs to produce same hash

Avalanche Effect

Small input changes cause drastically different outputs

Common Hash Algorithms

MD5

• Output: 128 bits (32 hex characters)
• Status: BROKEN - Do not use for security
• Still used for checksums

SHA-1

• Output: 160 bits (40 hex characters)
• Status: BROKEN - Deprecated for security
• Previously used for file integrity

SHA-256

• Output: 256 bits (64 hex characters)
• Status: SECURE - Widely used
• Part of SHA-2 family

SHA-384, SHA-512

• Output: 384/512 bits
• Status: SECURE - Even stronger
• Better for long-term security

Common Use Cases

1. Password Storage

Store password hashes, not plaintext:

```

Password123 → 3c9909afe21...

```

2. File Integrity

Verify files haven't been tampered:

```bash

sha256sum file.iso

```

3. Digital Signatures

Hash documents before signing

4. Blockchain

Blocks are linked using hashes

5. Data Deduplication

Identify duplicate data by hash

Hash vs. Encryption

| Hash | Encryption |

| --- | --- |

| One-way | Two-way |

| Fixed output | Variable output |

| For verification | For confidentiality |

| Cannot decrypt | Can decrypt |

Security Best Practices

• Use SHA-256 or stronger for security
• Add "salt" to passwords before hashing
• Use key derivation functions (bcrypt, scrypt, Argon2)
• Never store plaintext passwords

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