NAME
crypt_gensalt, crypt_gensalt_rn, crypt_gensalt_ra — encode settings for passphrase hashingLIBRARY
Crypt Library (libcrypt, -lcrypt)SYNOPSIS
#include <crypt.h> char *crypt_gensalt(const char *prefix, unsigned long count, const char *rbytes, int nrbytes); char *
crypt_gensalt_rn(const char * prefix, unsigned long count, const char *rbytes, int nrbytes, char * output, int output_size); char *
crypt_gensalt_ra(const char *prefix, unsigned long count, const char *rbytes, int nrbytes);
DESCRIPTION
The crypt_gensalt, crypt_gensalt_rn, and crypt_gensalt_ra functions compile a string for use as the setting argument to crypt, crypt_r, crypt_rn, and crypt_ra. prefix selects the hashing method to use. count controls the CPU time cost of the hash; the valid range for count and the exact meaning of “CPU time cost” depends on the hashing method, but larger numbers correspond to more costly hashes. rbytes should point to nrbytes cryptographically random bytes for use as “salt.” If prefix is a null pointer, the best available hashing method will be selected. (CAUTION: if prefix is an empty string, the “traditional” DES-based hashing method will be selected; this method is unacceptably weak by modern standards.) If count is 0, a low default cost will be selected. If rbytes is a null pointer, an appropriate number of random bytes will be obtained from the operating system, and nrbytes is ignored. See crypt(5) for other strings that can be used as prefix, and valid values of count for each.RETURN VALUES
crypt_gensalt, crypt_gensalt_rn, and crypt_gensalt_ra return a pointer to an encoded setting string. This string will be entirely printable ASCII, and will not contain whitespace or the characters ‘:
’,
‘;
’,
‘*
’,
‘!
’, or
‘\
’. See
crypt(5) for more detail on the format of this
string. Upon error, they return a null pointer and set
errno to an appropriate error code.
crypt_gensalt places its result in a static storage
area, which will be overwritten by subsequent calls to
crypt_gensalt. It is not safe to call
crypt_gensalt from multiple threads
simultaneously. However, it is safe to pass the
string returned by crypt_gensalt directly to
crypt without copying it; each function has its
own static storage area.
crypt_gensalt_rn places its result in the supplied
output buffer, which has
output_size bytes of storage available.
output_size should be greater than or equal
to CRYPT_GENSALT_OUTPUT_SIZE
.
crypt_gensalt_ra allocates memory for its result
using malloc(3). It should be freed with
free(3) after use.
Upon error, in addition to returning a null pointer,
crypt_gensalt and
crypt_gensalt_rn will write an invalid setting
string to their output buffer, if there is enough space; this string will
begin with a ‘*
’ and will not be equal
to prefix.
ERRORS
EINVAL
- prefix is invalid or not supported by this implementation; count is invalid for the requested prefix; the input nrbytes is insufficient for the smallest valid salt with the requested prefix.
ERANGE
- crypt_gensalt_rn only: output_size is too small to hold the compiled setting string.
ENOMEM
- Failed to allocate internal scratch memory.
-
ENOSYS
,EACCES
,EIO
, etc. - Obtaining random bytes from the operating system failed. This can only happen when rbytes is a null pointer.
FEATURE TEST MACROS
The following macros are defined by <crypt.h>:CRYPT_GENSALT_IMPLEMENTS_DEFAULT_PREFIX
- A null pointer can be specified as the prefix argument.
CRYPT_GENSALT_IMPLEMENTS_AUTO_ENTROPY
- A null pointer can be specified as the rbytes argument.
PORTABILITY NOTES
The functions crypt_gensalt, crypt_gensalt_rn, and crypt_gensalt_ra are not part of any standard. They originate with the Openwall project. A function with the name crypt_gensalt also exists on Solaris 10 and newer, but its prototype and semantics differ. The default prefix and auto entropy features are available since libxcrypt version 4.0.0. Portable software can use feature test macros to find out whether null pointers can be used for the prefix and rbytes arguments. The set of supported hashing methods varies considerably from system to system.ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).Interface | Attribute | Value |
crypt_gensalt | Thread safety | MT-Unsafe race:crypt_gensalt |
crypt_gensalt_rn , crypt_gensalt_ra | Thread safety | MT-Safe |
SEE ALSO
crypt(3), getpass(3), getpwent(3), shadow(3), login(1), passwd(1), crypt(5), passwd(5), shadow(5), pam(8)October 11, 2017 | Openwall Project |