SHA-256 (Secure Hash Algorithm 256-bit) is a cryptographic hash function from the SHA-2 family, standardized by NIST. It converts any input into a fixed 256-bit (64 hex character) digest. It is used in TLS certificates, Bitcoin, JWT signing, and password hashing.

Is SHA-256 one-way? Can I reverse it?

SHA-256 is mathematically one-way. There is no algorithm that can recover the original input from a SHA-256 hash. It is computationally infeasible to reverse by brute force given the 2^256 possible output space.

What is the difference between SHA-256 and MD5?

MD5 produces 128-bit (32 hex chars) output and has known collision vulnerabilities — two different inputs can produce the same hash. SHA-256 produces 256-bit (64 hex chars) output and has no known collisions. For security purposes, always prefer SHA-256 or SHA-512.

Can I use SHA-256 to store passwords?

Not recommended without salting. SHA-256 is fast, making it vulnerable to GPU brute-force and rainbow table attacks. For passwords, use bcrypt, Argon2, or scrypt — algorithms designed to be slow and include built-in salting.

How is SHA-256 used in blockchain?

Bitcoin uses double SHA-256 for block hashing and proof-of-work. Each block contains the hash of the previous block, forming a chain. Changing any block alters its hash, invalidating all subsequent blocks and making tampering evident.

Is my input text sent to a server?

No. All SHA-256 computation uses the browser's Web Crypto API (crypto.subtle.digest). Nothing leaves your device. Even file hashes are computed locally without uploading the file.

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