SHA-1 Hash Generator
Generate a SHA-1 hash from any text instantly in your browser. Fast, private, and free.
Private ● Runs entirely in your browser Your text never leaves your device.No account required.No data uploaded.Nothing stored unless you choose to save it.What is SHA-1?
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.
What does a SHA-1 hash look like?
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.
Is SHA-1 still safe to use?
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.
What was the SHAttered attack?
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.
What should I use instead of SHA-1?
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.
Does Git use SHA-1? Is that a problem?
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.
Can you reverse a SHA-1 hash?
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.
What's the difference between SHA-1 and SHA-256?
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.
Is HMAC-SHA1 still secure?
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.