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Diffstat (limited to 'manual/crypt.texi')
| -rw-r--r-- | manual/crypt.texi | 147 |
1 files changed, 28 insertions, 119 deletions
diff --git a/manual/crypt.texi b/manual/crypt.texi index 6bbe2bfdc5..0f04ee9899 100644 --- a/manual/crypt.texi +++ b/manual/crypt.texi @@ -1,8 +1,14 @@ -@c This node must have no pointers. -@node Cryptographic Functions -@c @node Cryptographic Functions, Debugging Support, System Configuration, Top -@chapter DES Encryption and Password Handling -@c %MENU% DES encryption and password handling +@node Cryptographic Functions, Debugging Support, System Configuration, Top +@chapter Cryptographic Functions +@c %MENU% Password storage and strongly unpredictable bytes + +@menu +* crypt:: A one-way function for passwords. +* Unpredictable Bytes:: Randomness for cryptography purposes. +@end menu + +@node crypt +@section Encrypting Passwords On many systems, it is unnecessary to have any kind of user authentication; for instance, a workstation which is not connected to a @@ -30,103 +36,6 @@ message-digest algorithm that is compatible with modern BSD systems, and the other based on the Data Encryption Standard (DES) that is compatible with Unix systems. -@menu -* Legal Problems:: This software can get you locked up, or worse. -* getpass:: Prompting the user for a password. -* crypt:: A one-way function for passwords. -* Unpredictable Bytes:: Randomness for cryptography purposes. -@end menu - -@node Legal Problems -@section Legal Problems - -Because of the continuously changing state of the law, it's not possible -to provide a definitive survey of the laws affecting cryptography. -Instead, this section warns you of some of the known trouble spots; this -may help you when you try to find out what the laws of your country are. - -Some countries require that you have a license to use, possess, or import -cryptography. These countries are believed to include Byelorussia, -Burma, India, Indonesia, Israel, Kazakhstan, Pakistan, Russia, and Saudi -Arabia. - -Some countries restrict the transmission of encrypted messages by radio; -some telecommunications carriers restrict the transmission of encrypted -messages over their network. - -Many countries have some form of export control for encryption software. -The Wassenaar Arrangement is a multilateral agreement between 33 -countries (Argentina, Australia, Austria, Belgium, Bulgaria, Canada, the -Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, -Ireland, Italy, Japan, Luxembourg, the Netherlands, New Zealand, Norway, -Poland, Portugal, the Republic of Korea, Romania, the Russian -Federation, the Slovak Republic, Spain, Sweden, Switzerland, Turkey, -Ukraine, the United Kingdom and the United States) which restricts some -kinds of encryption exports. Different countries apply the arrangement -in different ways; some do not allow the exception for certain kinds of -``public domain'' software (which would include this library), some -only restrict the export of software in tangible form, and others impose -significant additional restrictions. - -The United States has additional rules. This software would generally -be exportable under 15 CFR 740.13(e), which permits exports of -``encryption source code'' which is ``publicly available'' and which is -``not subject to an express agreement for the payment of a licensing fee or -royalty for commercial production or sale of any product developed with -the source code'' to most countries. - -The rules in this area are continuously changing. If you know of any -information in this manual that is out-of-date, please report it to -the bug database. @xref{Reporting Bugs}. - -@node getpass -@section Reading Passwords - -When reading in a password, it is desirable to avoid displaying it on -the screen, to help keep it secret. The following function handles this -in a convenient way. - -@deftypefun {char *} getpass (const char *@var{prompt}) -@standards{BSD, unistd.h} -@safety{@prelim{}@mtunsafe{@mtasuterm{}}@asunsafe{@ascuheap{} @asulock{} @asucorrupt{}}@acunsafe{@acuterm{} @aculock{} @acucorrupt{}}} -@c This function will attempt to create a stream for terminal I/O, but -@c will fallback to stdio/stderr. It attempts to change the terminal -@c mode in a thread-unsafe way, write out the prompt, read the password, -@c then restore the terminal mode. It has a cleanup to close the stream -@c in case of (synchronous) cancellation, but not to restore the -@c terminal mode. - -@code{getpass} outputs @var{prompt}, then reads a string in from the -terminal without echoing it. It tries to connect to the real terminal, -@file{/dev/tty}, if possible, to encourage users not to put plaintext -passwords in files; otherwise, it uses @code{stdin} and @code{stderr}. -@code{getpass} also disables the INTR, QUIT, and SUSP characters on the -terminal using the @code{ISIG} terminal attribute (@pxref{Local Modes}). -The terminal is flushed before and after @code{getpass}, so that -characters of a mistyped password are not accidentally visible. - -In other C libraries, @code{getpass} may only return the first -@code{PASS_MAX} bytes of a password. @Theglibc{} has no limit, so -@code{PASS_MAX} is undefined. - -The prototype for this function is in @file{unistd.h}. @code{PASS_MAX} -would be defined in @file{limits.h}. -@end deftypefun - -This precise set of operations may not suit all possible situations. In -this case, it is recommended that users write their own @code{getpass} -substitute. For instance, a very simple substitute is as follows: - -@smallexample -@include mygetpass.c.texi -@end smallexample - -The substitute takes the same parameters as @code{getline} -(@pxref{Line Input}); the user must print any prompt desired. - -@node crypt -@section Encrypting Passwords - @deftypefun {char *} crypt (const char *@var{key}, const char *@var{salt}) @standards{BSD, crypt.h} @standards{SVID, crypt.h} @@ -177,6 +86,23 @@ password against the result of a previous call to @code{crypt}, pass the result of the previous call as the @var{salt}. @end deftypefun +@deftypefun {char *} crypt_r (const char *@var{key}, const char *@var{salt}, {struct crypt_data *} @var{data}) +@standards{GNU, crypt.h} +@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @asulock{} @ascuheap{} @ascudlopen{}}@acunsafe{@aculock{} @acsmem{}}} +@c Compared with crypt, this function fixes the @mtasurace:crypt +@c problem, but nothing else. + +The @code{crypt_r} function does the same thing as @code{crypt}, but +takes an extra parameter which includes space for its result (among +other things), so it can be reentrant. @code{data@w{->}initialized} must be +cleared to zero before the first time @code{crypt_r} is called. + +The @code{crypt_r} function is a GNU extension. +@end deftypefun + +The @code{crypt} and @code{crypt_r} functions are prototyped in the +header @file{crypt.h}. + The following short program is an example of how to use @code{crypt} the first time a password is entered. Note that the @var{salt} generation is just barely acceptable; in particular, it is not unique between @@ -195,23 +121,6 @@ for a password and prints ``Access granted.'' if the user types @include testpass.c.texi @end smallexample -@deftypefun {char *} crypt_r (const char *@var{key}, const char *@var{salt}, {struct crypt_data *} @var{data}) -@standards{GNU, crypt.h} -@safety{@prelim{}@mtsafe{}@asunsafe{@asucorrupt{} @asulock{} @ascuheap{} @ascudlopen{}}@acunsafe{@aculock{} @acsmem{}}} -@c Compared with crypt, this function fixes the @mtasurace:crypt -@c problem, but nothing else. - -The @code{crypt_r} function does the same thing as @code{crypt}, but -takes an extra parameter which includes space for its result (among -other things), so it can be reentrant. @code{data@w{->}initialized} must be -cleared to zero before the first time @code{crypt_r} is called. - -The @code{crypt_r} function is a GNU extension. -@end deftypefun - -The @code{crypt} and @code{crypt_r} functions are prototyped in the -header @file{crypt.h}. - @node Unpredictable Bytes @section Generating Unpredictable Bytes |