CRYPT(3) | Library Functions Manual | CRYPT(3)

# NAME

`crypt`, `bcrypt_gensalt`, `bcrypt` — password hashing

# SYNOPSIS

`#include <stdlib.h>`

`#include <unistd.h>`

char *
`crypt`(const char *key, const char *setting);

`#include <pwd.h>`

char *
`bcrypt_gensalt`(u_int8_t log_rounds);

char *
`bcrypt`(const char *key, const char *salt);

# DESCRIPTION

These functions are deprecated in favor of crypt_checkpass(3) and crypt_newhash(3).

The `crypt`() function performs password hashing. Additional code has been added to deter key search attempts and to use stronger hashing algorithms.

The first argument to `crypt`() is a NUL-terminated string key, typically a user's typed password. The second, setting, currently supports a single form. If it begins with a string character (‘`$`’) and a number then a different algorithm is used depending on the number. At the moment ‘`$2`’ chooses Blowfish hashing; see below for more information.

## Blowfish crypt

The Blowfish version of crypt has 128 bits of salt in order to make building dictionaries of common passwords space consuming. The initial state of the Blowfish cipher is expanded using the salt and the password repeating the process a variable number of rounds, which is encoded in the password string. The maximum password length is 72. The final Blowfish password entry is created by encrypting the string

“OrpheanBeholderScryDoubt”

with the Blowfish state 64 times.

The version number, the logarithm of the number of rounds and the concatenation of salt and hashed password are separated by the ‘`$`’ character. An encoded ‘8’ would specify 256 rounds. A valid Blowfish password looks like this:

“$2b$12$FPWWO2RJ3CK4FINTw0Hi8OiPKJcX653gzSS.jqltHFMxyDmmQ0Hqq”.

The whole Blowfish password string is passed as setting for interpretation.

# RETURN VALUES

The function `crypt`() returns a pointer to the encrypted value on success, and `NULL` on failure.

# SEE ALSO

encrypt(1), login(1), passwd(1), blowfish(3), crypt_checkpass(3), getpass(3), passwd(5)

# HISTORY

An M-209 based `crypt`() function appeared in Version 3 AT&T UNIX. A DES-based `crypt`() first appeared in Version 7 AT&T UNIX. `bcrypt`() first appeared in OpenBSD 2.1.

# BUGS

The `crypt`() function returns a pointer to static data, and subsequent calls to `crypt`() will modify the same object.

January 9, 2025 | Debian