What is a hash function?

A hash function takes input data of any size and produces a fixed-size string of characters (the hash). Good hash functions are one-way (can't reverse to original), deterministic (same input = same hash), and collision-resistant.

No, MD5 is cryptographically broken and should not be used for security purposes. Collision attacks are practical. However, MD5 is still useful for non-security checksums like verifying file downloads.

SHA-256 is a member of the SHA-2 family, producing 256-bit (32-byte) hashes. It's currently considered secure and is used in Bitcoin, SSL certificates, and many security applications.

Can you reverse a hash to get the original text?

No, cryptographic hash functions are designed to be one-way. You cannot mathematically reverse a hash. However, weak passwords can be found using rainbow tables or brute force attacks, which is why salting is important.

What's the difference between hashing and encryption?

Hashing is one-way and irreversible; encryption is two-way and reversible with a key. Hashing is for integrity verification and password storage; encryption is for protecting data confidentiality.

Hash Generator 2026 | MD5, SHA-1, SHA-256, SHA-512

What is a Cryptographic Hash Function?

A cryptographic hash function takes an input (message) and returns a fixed-size string of bytes, typically represented as a hexadecimal number. The output is called a hash, digest, or checksum.

Key properties of cryptographic hashes: deterministic (same input always produces same output), fast to compute, infeasible to reverse, small changes produce vastly different hashes (avalanche effect), and collision-resistant.

Hash Algorithm Comparison

Algorithm Properties:

MD5
• Output: 128 bits (32 hex characters)
• Status: BROKEN - collisions found in seconds
• Use for: Non-security checksums only

SHA-1
• Output: 160 bits (40 hex characters)
• Status: BROKEN - collision attack demonstrated
• Use for: Legacy systems only, being phased out

SHA-256
• Output: 256 bits (64 hex characters)
• Status: SECURE - recommended for most uses
• Use for: Digital signatures, certificates, Bitcoin

SHA-512
• Output: 512 bits (128 hex characters)
• Status: SECURE - highest security in SHA-2 family
• Use for: When maximum security is needed

Common Uses of Hash Functions

Password storage: Store hashes instead of plain passwords (with salt!).
File integrity: Verify downloads haven't been corrupted or tampered with.
Digital signatures: Sign the hash of a document rather than the document itself.
Blockchain: Bitcoin uses SHA-256 for mining and transaction verification.
Data deduplication: Identify duplicate files by comparing hashes.
Cache keys: Create unique identifiers for cached content.

Why MD5 and SHA-1 are Broken

MD5: In 2004, researchers demonstrated practical collision attacks. By 2008, researchers created a rogue CA certificate. Today, MD5 collisions can be generated in seconds on a laptop.

SHA-1: In 2017, Google and CWI Amsterdam published "SHAttered," demonstrating the first practical SHA-1 collision. While more expensive than MD5 attacks, SHA-1 is no longer considered secure for cryptographic purposes.

Hashing vs Encryption

Hashing: One-way function. Cannot recover original data. Used for verification.
Encryption: Two-way function. Can decrypt with correct key. Used for confidentiality.
Hash output: Fixed length regardless of input size.
Encryption output: Length depends on input size.

Password Hashing Best Practices

Never use plain SHA-256 for passwords. Instead, use specialized password hashing functions:

bcrypt: Built-in salt, adjustable work factor, widely supported.
scrypt: Memory-hard, resistant to GPU attacks.
Argon2: Winner of Password Hashing Competition, recommended for new projects.

Frequently Asked Questions

Can two different inputs produce the same hash?

Theoretically yes (called a collision), since hashes are fixed-length but inputs are unlimited. Secure algorithms make finding collisions computationally infeasible. MD5 and SHA-1 have known practical collisions; SHA-256 does not.

Why can't I reverse a hash to get the original text?

Hashes are one-way functions that lose information. Many different inputs can produce the same hash (collision), so there's no unique "original." The math is designed to make reversal computationally infeasible.

What is a "salt" in password hashing?

A salt is random data added to a password before hashing. It ensures identical passwords produce different hashes, defeating rainbow table attacks. Each user should have a unique salt stored alongside their hash.

How long does it take to crack a hash?

It depends on the algorithm and password complexity. A weak password like "123456" can be found instantly using rainbow tables. A strong random password with SHA-256 would take longer than the age of the universe to brute force.

Is SHA-256 the same as SHA-2?

SHA-2 is a family of algorithms including SHA-224, SHA-256, SHA-384, and SHA-512. SHA-256 is the most commonly used member. They all share the same underlying design but differ in output length.

Should I use SHA-512 instead of SHA-256?

For most applications, SHA-256 is sufficient and often faster on 32-bit systems. SHA-512 can be faster on 64-bit systems and offers a larger security margin. Both are currently considered secure.