Modular Crypt Format
Unix系のパスワードの標準書式
https://passlib.readthedocs.io/en/stable/modular_crypt_format.html
$1$ md5_crypt
$2$ $2a$ bcrypt
$5$ sha256_crypt
$6$ sha512_crypt
https://www.akkadia.org/drepper/SHA-crypt.txt
一部ライブラリ
$bcrypt_sha256$ bcrypt sha-256
$pbkdf2$ PBKDF2
$pbkdf2_sha256$ PBKDF2 SHA-256