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.Dd October 12, 2021
.Dt PW_GENSALT 3
.Os
.Sh NAME
.Nm pw_gensalt
.Nd passwd salt generation function
.Sh LIBRARY
.Lb libcrypt
.Sh SYNOPSIS
.In pwd.h
.Ft int
.Fn pw_gensalt "char *salt" "size_t saltlen" "const char *type" "const char *option"
.Sh DESCRIPTION
The
.Fn pw_gensalt
function generates a
.Dq salt
to be added to a password hashing function to guarantee uniqueness and
slow down dictionary and brute force attacks.
The function places a random array of
.Ar saltlen
bytes in
.Ar salt
using the hash function specified in
.Ar type
with the function-specific
.Ar option .
.Pp
The new salt types follow the
.Dq Modular Crypt Format
(MCF) standard and are of the form:
.Bd -literal -offset indent
.Li $<id>[$<param>=<value>(,<param>=<value>)*][$<salt>[$<hash>]]
.Ed
.Pp
The characters allowed in the password salt are alphanumeric and
include a forward slash and a period (are in the regular expression
format
.Li [A-Za-z0-9/.] ) .
.Pp
The following types are available:
.Bl -tag -width blowfish -offset indent
.It old
The original Unix implementation.
This is of the form
.Li _Gl/.???? ,
where
.Li \&?
denotes a random alphanumeric character.
The minimum salt size is
.Dv 3 .
.It new
The Seventh Edition Unix 12 bit salt.
This has the same form as the
.Sq old .
The minimum salt size is
.Dv 10 .
The number of rounds can be specified in
.Ar option
and is enforced to be between
.Dv 7250
and
.Dv 16777215 .
.It newsalt
An alias for
.Sq new .
.It md5
A salt generated using the
.Xr md5 1
algorithm.
This is of the form
.Li $1$????????$ .
The minimum salt size is
.Dv 13 .
.It sha1
A salt generated using the
.Xr sha1 1
algorithm.
This is of the form
.Li $sha1$nrounds$????????$ ,
where
.Ar nrounds
is the number of rounds to be used.
The number of rounds can be specified in
.Ar option ,
and defaults to random if
.Dv NULL .
The minimum salt size is
.Dv 8
and the maximum is
.Dv 64 .
.It blowfish
A salt generated using the
.Sq blowfish
algorithm.
The minimum salt size is
.Dv 30
and the number of rounds needs to be specified in
.Ar option .
This is of the form:
.Li $2a$nrounds$?????????????????????? .
The
.Li 2
in the salt string indicates the current blowfish version.
.It argon2d
This is of the form:
.Li $argon2d$v=19$m=MEMORY,t=TIME,p=THREADS$????????????????$
.It argon2i
This is of the form:
.Li $argon2i$v=19$m=MEMORY,t=TIME,p=THREADS$????????????????$
.It argon2id
This is of the form:
.Li $argon2id$v=19$m=MEMORY,t=TIME,p=THREADS$????????????????$
.It argon2
An alias for
.Dq argon2id .
.Pp
See
.Xr crypt 3
for details on the Argon2 parameters.
.El
.Sh RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn pw_gensalt
will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
If the
.Ar option
is not specified or has an illegal value.
.It Bq Er ENOSPC
The
.Ar saltlen
was not large enough to fit the salt for the specified
.Ar type .
.El
.Sh SEE ALSO
.Xr passwd 1 ,
.Xr pwhash 1
.Sh HISTORY
The
.Fn pw_gensalt
function was written in 1997 by
.An Niels Provos Aq Mt provos@physnet.uni-hamburg.de .
.Pp
The
.Lk https://passlib.readthedocs.io/en/stable/modular_crypt_format.html "Modular Crypt Format (MCF)" .
.Pp
The
.Lk https://github.com/P-H-C/phc-string-format/blob/master/phc-sf-spec.md "Password Hashing Competition (PHC) format" .