Provided by: libcrypt-dev_4.4.27-1_amd64 bug

NAME

       crypt, crypt_r, crypt_rn, crypt_ra — passphrase hashing

LIBRARY

       Crypt Library (libcrypt, -lcrypt)

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, struct crypt_data *data, int size);

       char *
       crypt_ra(const char *phrase, const char *setting, void **data, int *size);

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 data argument to crypt_r is a structure of type struct crypt_data.  It 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 phrase and setting 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 struct crypt_data object is first  used
       in  a  call  to crypt_r().  We recommend zeroing the entire 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 struct crypt_data object, and size should be the
       size of that object, cast to int.  When used with crypt_rn, the entire data object (except for the phrase
       and setting fields) must be zeroed before its first use; this is not just a recommendation, as it is  for
       crypt_r.  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  struct
       crypt_data  object, using malloc(3), and write its address and size into the variables pointed to by data
       and size.  These can be reused in subsequent calls.  After the application is done  hashing  passphrases,
       it should deallocate the struct crypt_data object using free(3).

RETURN VALUES

       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  in other calls to crypt, crypt_r, crypt_rn, and crypt_ra, and as prefix in
       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 their data argument.  It is
       safe to call them from multiple threads simultaneously, as long as a separate data  object  is  used  for
       each thread.

       Upon  error,  crypt_r,  crypt_rn,  and crypt_ra write an invalid hashed passphrase to the output field of
       their data argument, and crypt writes an invalid hash to its static storage area.  This  string  will  be
       shorter than 13 characters, will begin with a ‘*’, and will not compare equal to setting.

       Upon  error,  crypt_rn  and  crypt_ra  return  a  null pointer.  crypt_r and crypt may also return a null
       pointer, or they may return a pointer to the invalid hash, depending  on  how  libcrypt  was  configured.
       (The  option to return the invalid hash is for compatibility with old applications that assume that crypt
       cannot return a null pointer.  See “PORTABILITY NOTES” below.)

       All four functions set errno when they fail.

ERRORS

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

       ERANGE             phrase is too long  (more  than  CRYPT_MAX_PASSPHRASE_SIZE  characters;  some  hashing
                          methods may have lower limits).
                          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.  Some older 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 struct 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, crypt_ra │ Thread safety │ MT-Safe              │
       └─────────────────────────────┴───────────────┴──────────────────────┘

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)

Openwall Project                                October 11, 2017                                        CRYPT(3)