Question 1

Can I reverse a SHA-256 hash back to the original text?

Accepted Answer

No, SHA-256 is a one-way cryptographic function; there is no way to recover the original input from the hash alone.

Question 2

Why does my hash differ from the one my server produced?

Accepted Answer

Almost always because the input is not identical, even though it looks it. A trailing newline, Windows line endings instead of Unix ones, or a stray space all change the bytes and therefore the digest. That is why the byte count sits under the input: if you expected 40 bytes and it says 41, you have found your culprit. This tool hashes the UTF-8 bytes of exactly what is in the box.

Question 3

What is per-line mode for?

Accepted Answer

Hashing a list without doing it one at a time: user identifiers to pseudonymise, a set of URLs to key a cache by, test fixtures that need stable IDs. Each line is hashed on its own, blank lines are skipped, and carriage returns from Windows text are stripped so a pasted list hashes the same as a typed one. The copy button at the top takes the entire column.

Question 4

When would I want base64 instead of hex?

Accepted Answer

When whatever consumes the digest expects it packed rather than spelled out. Base64 encodes the same 32 bytes in 44 characters instead of 64, which is why HTTP headers, JSON payloads and subresource integrity attributes use it. Hex is the convention for checksums and command-line tools. Neither is more correct; they are two spellings of the same number.

Question 5

Is SHA-256 the same algorithm used in Bitcoin?

Accepted Answer

Yes, SHA-256 is the hashing algorithm behind Bitcoin's proof-of-work, and it's also widely used for TLS certificates and file integrity checks.

Question 6

Why would two different inputs never produce the same hash?

Accepted Answer

In theory they could (a "collision"), but SHA-256's output space is so large that no collision has ever been found in practice, making it safe for integrity verification.

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SHA256 Hash Generator

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