ハッシュ生成

A hash function takes any input, a word or a whole document, and produces a fixed-size string of characters called a digest. SHA-256, for example, always returns 256 bits written as 64 hexadecimal characters, whether you feed it one letter or a megabyte of text.

Two properties make hashes useful. They are deterministic, so the same input always produces the same digest, and they show the avalanche effect, so changing a single character produces a completely different result. That makes a hash a compact fingerprint of the exact content.

This tool computes SHA-1, SHA-256, SHA-384 and SHA-512 digests of your text locally using the browser's Web Crypto API, then shows the hex result ready to copy. SHA-256 is the sensible default for most purposes.

Hashing is one-way: you cannot reverse a digest back into the original input. That is the point. It is used to verify integrity (has this file or message changed?), to build checksums, to deduplicate content, and as a building block inside signatures and version-control systems like Git.

SHA-1 is broken for security-critical uses because collisions can be engineered, though it is still fine as a non-security checksum. Prefer SHA-256 or stronger when security matters. MD5 is intentionally not offered because it is considered insecure.

Hashing is not encryption and is not, by itself, the right way to store passwords. Raw SHA functions are deliberately fast, which helps attackers guess passwords quickly. For passwords use a slow, salted scheme such as bcrypt, scrypt or Argon2; the bcrypt generator here is built for that.