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crypt.3p (4555B)

    

  1. '\" et
  2. .TH CRYPT "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
  3. .\"
  4. .SH PROLOG
  5. This manual page is part of the POSIX Programmer's Manual.
  6. The Linux implementation of this interface may differ (consult
  7. the corresponding Linux manual page for details of Linux behavior),
  8. or the interface may not be implemented on Linux.
  9. .\"
  10. .SH NAME
  11. crypt
  12. \(em string encoding function
  13. (\fBCRYPT\fP)
  14. .SH SYNOPSIS
  15. .LP
  16. .nf
  17. #include <unistd.h>
  18. .P
  19. char *crypt(const char *\fIkey\fP, const char *\fIsalt\fP);
  20. .fi
  21. .SH DESCRIPTION
  22. The
  23. \fIcrypt\fR()
  24. function is a string encoding function. The algorithm is
  25. implementation-defined.
  26. .P
  27. The
  28. .IR key
  29. argument points to a string to be encoded. The
  30. .IR salt
  31. argument shall be a string of at least two bytes in length not
  32. including the null character chosen from the set:
  33. .sp
  34. .RS 4
  35. .nf
  37. a b c d e f g h i j k l m n o p q r s t u v w x y z
  38. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
  39. 0 1 2 3 4 5 6 7 8 9 . /
  40. .fi
  41. .P
  42. .RE
  43. .P
  44. The first two bytes of this string may be used to perturb the
  45. encoding algorithm.
  46. .P
  47. The return value of
  48. \fIcrypt\fR()
  49. points to static data that is overwritten by each call.
  50. .P
  51. The
  52. \fIcrypt\fR()
  53. function need not be thread-safe.
  54. .SH "RETURN VALUE"
  55. Upon successful completion,
  56. \fIcrypt\fR()
  57. shall return a pointer to the encoded string. The first two bytes
  58. of the returned value shall be those of the
  59. .IR salt
  60. argument. Otherwise, it shall return a null pointer and set
  61. .IR errno
  62. to indicate the error.
  63. .SH ERRORS
  64. The
  65. \fIcrypt\fR()
  66. function shall fail if:
  67. .TP
  68. .BR ENOSYS
  69. The functionality is not supported on this implementation.
  70. .LP
  71. .IR "The following sections are informative."
  72. .SH EXAMPLES
  73. .SS "Encoding Passwords"
  74. .P
  75. The following example finds a user database entry matching a particular
  76. user name and changes the current password to a new password. The
  77. \fIcrypt\fR()
  78. function generates an encoded version of each password. The
  79. first call to
  80. \fIcrypt\fR()
  81. produces an encoded version of the old password; that encoded password
  82. is then compared to the password stored in the user database. The
  83. second call to
  84. \fIcrypt\fR()
  85. encodes the new password before it is stored.
  86. .P
  87. The
  88. \fIputpwent\fR()
  89. function, used in the following example, is not part of POSIX.1\(hy2008.
  90. .sp
  91. .RS 4
  92. .nf
  94. #include <unistd.h>
  95. #include <pwd.h>
  96. #include <string.h>
  97. #include <stdio.h>
  98. \&...
  99. int valid_change;
  100. int pfd;  /* Integer for file descriptor returned by open(). */
  101. FILE *fpfd;  /* File pointer for use in putpwent(). */
  102. struct passwd *p;
  103. char user[100];
  104. char oldpasswd[100];
  105. char newpasswd[100];
  106. char savepasswd[100];
  107. \&...
  108. valid_change = 0;
  109. while ((p = getpwent()) != NULL) {
  110.     /* Change entry if found. */
  111.     if (strcmp(p->pw_name, user) == 0) {
  112.         if (strcmp(p->pw_passwd, crypt(oldpasswd, p->pw_passwd)) == 0) {
  113.             strcpy(savepasswd, crypt(newpasswd, user));
  114.             p->pw_passwd = savepasswd;
  115.             valid_change = 1;
  116.         }
  117.         else {
  118.             fprintf(stderr, "Old password is not valid\en");
  119.         }
  120.     }
  121.     /* Put passwd entry into ptmp. */
  122.     putpwent(p, fpfd);
  123. }
  124. .fi
  125. .P
  126. .RE
  127. .SH "APPLICATION USAGE"
  128. The values returned by this function need not be portable among
  129. XSI-conformant systems.
  130. .P
  131. Several implementations offer extensions via characters outside
  132. of the set specified for the
  133. .IR salt
  134. argument for specifying alternative algorithms; while not portable, these
  135. extensions may offer better security. The use of
  136. \fIcrypt\fR()
  137. for anything other than password hashing is not recommended.
  138. .SH RATIONALE
  139. None.
  140. .SH "FUTURE DIRECTIONS"
  141. None.
  142. .SH "SEE ALSO"
  143. .IR "\fIencrypt\fR\^(\|)",
  144. .IR "\fIsetkey\fR\^(\|)"
  145. .P
  146. The Base Definitions volume of POSIX.1\(hy2017,
  147. .IR "\fB<unistd.h>\fP"
  148. .\"
  149. .SH COPYRIGHT
  150. Portions of this text are reprinted and reproduced in electronic form
  151. from IEEE Std 1003.1-2017, Standard for Information Technology
  152. -- Portable Operating System Interface (POSIX), The Open Group Base
  153. Specifications Issue 7, 2018 Edition,
  154. Copyright (C) 2018 by the Institute of
  155. Electrical and Electronics Engineers, Inc and The Open Group.
  156. In the event of any discrepancy between this version and the original IEEE and
  157. The Open Group Standard, the original IEEE and The Open Group Standard
  158. is the referee document. The original Standard can be obtained online at
  159. http://www.opengroup.org/unix/online.html .
  160. .PP
  161. Any typographical or formatting errors that appear
  162. in this page are most likely
  163. to have been introduced during the conversion of the source files to
  164. man page format. To report such errors, see
  165. https://www.kernel.org/doc/man-pages/reporting_bugs.html .