How long is a SHA-1 hash?

A SHA-1 digest is 160-bit, written as 40 hexadecimal characters. 40 hexadecimal characters. Unambiguous: no other common password hash is exactly 40 hex characters.

SHA-1 Decrypt & Reverse Lookup

Q: Can SHA-1 be decrypted?

No. SHA-1 is a one-way hash function and cannot be mathematically reversed. What lookup tools do is search a precomputed index of previously hashed passwords for one that produces the same digest.

Q: Is SHA-1 safe for storing passwords?

No. Collision resistance and password security are different problems. Even a SHA-1 with no known collisions would still be a poor password hash, because it is fast and unsalted. A lookup table does not care whether the algorithm is mathematically sound — it only needs the password to have been hashed before. Use bcrypt, scrypt or Argon2, which are deliberately slow and salted.

SHA-1 produces a 40-character hexadecimal digest. It replaced MD5 in a great deal of software during the 2000s and is still present in older authentication systems, Git object IDs and legacy TLS certificates.

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What a SHA-1 hash looks like

plaintext	123456
SHA-1 digest	7c4a8d09ca3762af61e59520943dc26494f8941b
digest size	160-bit — 40 hex characters
published	1995, by the NSA
identify it by	40 hexadecimal characters. Unambiguous: no other common password hash is exactly 40 hex characters.

Can SHA-1 be decrypted?

Strictly, no — and any tool claiming to "decrypt" it is describing the wrong operation. SHA-1 is a one-way function: it destroys information, so there is no key and no inverse. What actually happens is a lookup. Enormous numbers of candidate passwords are hashed in advance and stored sorted by digest. Recovering a password means finding the digest in that index, not reversing anything.

The practical consequence: a password that has never appeared in any wordlist or breach will not be found here, no matter how weak it looks. A password that has appeared will be found almost instantly.

Why SHA-1 hashes fall to lookup

Collision resistance and password security are different problems. Even a SHA-1 with no known collisions would still be a poor password hash, because it is fast and unsalted. A lookup table does not care whether the algorithm is mathematically sound — it only needs the password to have been hashed before.

Do not use SHA-1 for passwords. Broken in 2017. Use bcrypt, scrypt or Argon2 instead.

History

SHA-1 was published by the NSA in 1995. Theoretical weaknesses were known from 2005, but the decisive moment came in February 2017 when Google and CWI Amsterdam published SHAttered, the first practical collision, costing roughly 6,500 CPU-years. In 2020 a chosen-prefix collision brought the cost within reach of a well-funded attacker. Browsers stopped trusting SHA-1 certificates in 2017.

What to use instead

If you are storing passwords, use bcrypt, scrypt or Argon2id. All three are deliberately slow and salted: the salt makes every stored hash unique, so a precomputed index cannot exist, and the cost factor means an attacker gets thousands of guesses per second instead of billions. That is why this tool is useless against them — by design, and that is the point.

Look up a SHA-1 hash

The lookup runs against a corpus of over a billion real passwords, covering MD5, SHA-1, SHA-256 and NTLM. It is free, needs no account, and no hashes are retained.

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