SHA256 Hash
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Frequently Asked Questions
Is SHA256 safe to use in 2025? +
Yes. SHA256 (part of the SHA-2 family) has no known practical attacks and remains the standard for file verification, digital signatures, TLS, and blockchain. No collision has ever been found.
What's the difference between SHA256 and MD5? +
MD5 produces a 128-bit hash and is broken — collision attacks are practical. SHA256 produces a 256-bit hash and is cryptographically secure. Always prefer SHA256 over MD5 for any security purpose.
How is SHA256 used in blockchain? +
Bitcoin uses SHA256 twice (SHA256d) to hash block headers in its proof-of-work mining process. Each block's hash must start with a certain number of zeros, making the blockchain tamper-evident.
What is HMAC-SHA256 and how is it used? +
HMAC-SHA256 combines a secret key with SHA256 to create a message authentication code. It's used to sign API requests (AWS Signature, Stripe webhooks) and verify data integrity with authentication.
Can SHA256 be reversed or decrypted? +
No. SHA256 is a one-way function — reversing it is computationally infeasible. Common short strings may appear in rainbow tables, but a properly salted SHA256 (or better, bcrypt/Argon2) is secure for password storage.