SHA-1 Hash Generator

SHA-1 (Secure Hash Algorithm 1) is a cryptographic hash function that produces a 160-bit digest, displayed as 40 hexadecimal characters. It was designed by the NSA and published as a U.S. federal standard in 1995. It's been deprecated for security use since 2017, when a practical collision attack (SHAttered) was demonstrated.

Always 40 lowercase hexadecimal characters. The string "hello" hashes to `aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d`. It's always the same length regardless of input size: that's the point of a fixed-output hash function.

Not for security. NIST deprecated SHA-1 in 2011 and all major browsers dropped SHA-1 SSL certificates in 2017. The SHAttered attack generated two different PDF files with the same SHA-1 hash: a practical collision. For checksums in internal systems where tamper resistance isn't required, SHA-1 still works. For any security-critical use, switch to SHA-256.

In February 2017, researchers from CWI Amsterdam and Google produced two PDF files with identical SHA-1 hashes, the first practical SHA-1 collision. They named it SHAttered. The attack required roughly 9.2 × 10¹⁸ SHA-1 computations and 6.5 × 10²⁰ SHA-1 compressions. That's expensive, but within reach of well-resourced attackers, which is why it ended SHA-1's use in certificates and code signing.

SHA-256 for general cryptographic hashing. It's part of the SHA-2 family, produces a 256-bit output, and has no known collision attacks. If you need HMAC, HMAC-SHA256 is the current standard recommendation. For password hashing specifically, use bcrypt, scrypt, or Argon2: none of the SHA family is designed for that.

Git historically used SHA-1 to identify commits, trees, and blobs. For data integrity inside a repository, this is acceptable because Git's collision detection (added after SHAttered) flags if two different objects produce the same hash. Git is also transitioning to SHA-256 as its default. The exposure is limited: an attacker would need write access to your repository to exploit a crafted collision.

No. SHA-1 is a one-way function. You can't derive the original input from the hash. What's possible is a lookup: if the input is short or common, it might appear in a precomputed rainbow table. That's why password storage with any bare hash (SHA-1, SHA-256, or otherwise) is wrong. Use a slow hashing algorithm with a salt.

Output size and security. SHA-1 produces 160 bits (40 hex characters); SHA-256 produces 256 bits (64 hex characters). SHA-1 has known collision attacks; SHA-256 does not. SHA-256 is slower, which matters in high-throughput contexts but is rarely significant for individual operations. Use SHA-256 for anything new.

HMAC constructions are more resilient to collision attacks than bare hashing, because HMAC depends on a secret key, not just the hash function's collision resistance. HMAC-SHA1 is still considered secure for many use cases: for example, it's used in TOTP (one-time passwords, RFC 6238). That said, new protocols should use HMAC-SHA256 for margin and clarity.

Yes. The digest is computed in your browser. The text is not sent to a server to be hashed.

No. It computes a SHA-1 digest. It does not call a model, and it cannot turn a digest back into the original text.