Provided by: libcrypt2-dev_4.1.1-1_amd64 bug

NAME

       crypt, crypt_r, crypt_rn, crypt_ra - passphrase hashing

SYNOPSIS

       #include <crypt.h>

       char *crypt(const char *phrase, const char *setting);
       char *crypt_r(const char *phrase, const char *setting, struct crypt_data *data);
       char *crypt_rn(const char *phrase, const char *setting, void *data, int size);
       char *crypt_ra(const char *phrase, const char *setting, void **data, int *size);

       Link with -lcrypt.

DESCRIPTION

       The  crypt,  crypt_r,  crypt_rn,  and  crypt_ra  functions  irreversibly “hash” phrase for
       storage in the  system  password  database  (shadow(5))  using  a  cryptographic  “hashing
       method.”   The  result of this operation is called a “hashed passphrase” or just a “hash.”
       Hashing methods are described in crypt(5).

       setting controls which hashing method to use, and also supplies various parameters to  the
       chosen  method,  most  importantly a random “salt” which ensures that no two stored hashes
       are the same, even if the phrase strings are the same.  The hashing methods are  explained
       below.

       The crypt_data structure passed to crypt_r has at least these fields:

           struct crypt_data {
               char output[CRYPT_OUTPUT_SIZE];
               char setting[CRYPT_OUTPUT_SIZE];
               char phrase[CRYPT_MAX_PASSPHRASE_SIZE];
               char initialized;
           };

       Upon  a  successful  return  from crypt_r, the hashed passphrase will be stored in output.
       Applications are encouraged, but not required, to use the setting  and  phrase  fields  to
       store the strings that they will pass as phrase and setting to crypt_r.  This will make it
       easier to erase all sensitive data after it is no longer needed.

       The initialized field must be set to zero before the first time  a  crypt_data  object  is
       first  used  in a call to crypt_r.  We recommend zeroing the entire crypt_data object, not
       just initialized and not just the documented fields, before the first use.  (Of course, do
       this before storing anything in setting and phrase.)

       The data argument to crypt_rn should also point to a crypt_data object, and size should be
       the size of that object, cast to int.  When used  with  crypt_rn,  the  entire  crypt_data
       object  must  be  zeroed before its first use; this is not just a recommendation, as it is
       for crypt_r.  (setting and phrase are still allowed to be used.)  Otherwise, the fields of
       the object have the same uses that they do for crypt_r.

       On  the  first  call  to  crypt_ra, data should be the address of a void * variable set to
       NULL, and size should be the address of an  int  variable  set  to  zero.   crypt_ra  will
       allocate  and  initialize  a crypt_data object, using malloc(3), and write its address and
       size into *data  and  *size.   These  can  be  reused  in  subsequent  calls.   After  the
       application is done hashing passphrases, it should deallocate *data using free(3).

RETURN VALUE

       Upon  successful  completion, crypt, crypt_r, crypt_rn, and crypt_ra return a pointer to a
       string which encodes both the hashed passphrase, and the settings that were used to encode
       it.   This  string  is  directly  usable  as  setting  with other calls to crypt, crypt_r,
       crypt_rn, and crypt_ra, and as prefix with calls to crypt_gensalt,  crypt_gensalt_rn,  and
       crypt_gensalt_ra.  It will be entirely printable ASCII, and will not contain whitespace or
       the characters ‘:’, ‘;’, ‘*’, ‘!’, or ‘\’.  See crypt(5) for more detail on the format  of
       hashed passphrases.

       crypt  places its result in a static storage area, which will be overwritten by subsequent
       calls to crypt.  It is not safe to call crypt from multiple threads simultaneously.

       crypt_r, crypt_rn, and crypt_ra place their result in the output field of  the  crypt_data
       object  that  they  are  supplied  with;  it  is  safe  to call them from multiple threads
       simultaneously, as long as a separate crypt_data object is used for each thread.

       Upon error, crypt and crypt_r return a pointer to  an  invalid  hashed  passphrase.   This
       string  will  be  shorter  than 13 characters, will begin with a ‘*’, and will not compare
       equal to setting.  (This peculiar behavior is for compatibility with old applications that
       assume that crypt cannot return a null pointer.  See PORTABILITY NOTES below.)

       crypt_rn and crypt_ra also write an invalid hashed passphrase to the output field of their
       crypt_data object when they fail, but they return a null pointer.

       All four functions set errno when they fail.

ERRORS

       EINVAL setting is invalid, or requests a hashing method that is not supported.

       ERANGE crypt_rn only: size is too small for the hashing method requested by setting.

       ENOMEM Failed to allocate internal scratch memory.
              crypt_ra only: failed to allocate memory for *data.

       ENOSYS or EOPNOTSUPP
              Hashing passphrases is not supported at all on this installation,  or  the  hashing
              method  requested  by  setting is not supported.  These error codes are not used by
              this version of libcrypt, but may be encountered on other systems.

PORTABILITY NOTES

       crypt is included in POSIX, but crypt_r, crypt_rn,  and  crypt_ra  are  not  part  of  any
       standard.

       POSIX  does not specify any hashing methods, and does not require hashed passphrases to be
       portable between systems.  In practice, hashed passphrases are portable as  long  as  both
       systems  support  the hashing method that was used.  However, the set of supported hashing
       methods varies considerably from system to system.

       The behavior of crypt on errors isn't  well  standardized.   Some  implementations  simply
       can't  fail  (except  by  crashing  the  program), others return a null pointer or a fixed
       string.  Most implementations don't set errno, but some do.  POSIX specifies  returning  a
       null  pointer  and  setting  errno, but it defines only one possible error, ENOSYS, in the
       case where crypt is not supported at all.  Many existing applications are not prepared  to
       handle   null  pointers  returned  by  crypt.   The  behavior  described  above  for  this
       implementation, setting errno and returning an invalid hashed  passphrase  different  from
       setting, is chosen to make these applications fail closed when an error occurs.

       Due to historical restrictions on the export of cryptographic software from the USA, crypt
       is an optional POSIX component.  Applications should therefore be prepared for  crypt  not
       to be available, or to always fail (setting errno to ENOSYS) at runtime.

       POSIX  specifies that crypt is declared in unistd.h, but only if the macro _XOPEN_CRYPT is
       defined and has a value greater than or equal to zero.  Since libcrypt  does  not  provide
       unistd.h, it declares crypt, crypt_r, crypt_rn, and crypt_ra in crypt.h instead.

       On  a  minority  of  systems  (notably  recent  versions of Solaris), crypt uses a thread-
       specific static storage buffer,  which  makes  it  safe  to  call  from  multiple  threads
       simultaneously,  but  does  not  prevent  each  call  within a thread from overwriting the
       results of the previous one.

BUGS

       Some implementations of crypt, upon error, return an invalid hash  that  is  stored  in  a
       read-only location or only initialized once, which means that it is only safe to erase the
       buffer pointed to by the crypt return value if an error did not occur.

       struct crypt_data may be quite large (32kB in this implementation of libcrypt; over  128kB
       in some other implementations).  This is large enough that it may be unwise to allocate it
       on the stack.

       Some recently designed hashing methods need even more  scratch  memory,  but  the  crypt_r
       interface  makes  it  impossible  to change the size of crypt_data without breaking binary
       compatibility.  The crypt_rn interface could accommodate larger allocations  for  specific
       hashing  methods,  but  the  caller  of  crypt_rn has no way of knowing how much memory to
       allocate.  crypt_ra does the allocation itself,  but  can  only  make  a  single  call  to
       malloc(3).

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────────────┬───────────────┬──────────────────────┐
       │InterfaceAttributeValue                │
       ├───────────────────┼───────────────┼──────────────────────┤
       │crypt              │ Thread safety │ MT-Unsafe race:crypt │
       ├───────────────────┼───────────────┼──────────────────────┤
       │crypt_r, crypt_rn, │ Thread safety │ MT-Safe              │
       │crypt_ra           │               │                      │
       └───────────────────┴───────────────┴──────────────────────┘

HISTORY

       A rotor-based crypt function appeared in Version 6 AT&T UNIX.  The "traditional" DES-based
       crypt first appeared in Version 7 AT&T UNIX.

       crypt_r  originates  with the GNU C Library.  There's also a crypt_r function on HP-UX and
       MKS Toolkit, but the prototypes and semantics differ.

       crypt_rn and crypt_ra originate with the Openwall project.

SEE ALSO

       crypt_gensalt(3), getpass(3), getpwent(3), shadow(3), login(1), passwd(1), crypt(5),
       passwd(5), shadow(5), pam(8)