man3/encrypt.3

   1 .\" Copyright 2000 Nicolás Lichtmaier <nick@debian.org>
   2 .\" Created 2000-07-22 00:52-0300
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  25 .\" Modified 2002-07-23 19:21:35 CEST 2002 Walter Harms
  26 .\" <walter.harms@informatik.uni-oldenburg.de>
  27 .\"
  28 .\" Modified 2003-04-04, aeb
  29 .\"
  30 .TH ENCRYPT 3 2017-09-15 "" "Linux Programmer's Manual"
  31 .SH NAME
  32 encrypt, setkey, encrypt_r, setkey_r \- encrypt 64-bit messages
  33 .SH SYNOPSIS
  34 .nf
  35 .BR "#define _XOPEN_SOURCE" "       /* See feature_test_macros(7) */"
  36 .B #include <unistd.h>
  37 .PP
  38 .BI "void encrypt(char " block "[64], int " edflag );
  39
  40 .BR "#define _XOPEN_SOURCE" "       /* See feature_test_macros(7) */"
  41 .B #include <stdlib.h>
  42 .PP
  43 .BI "void setkey(const char *" key );
  44
  45 .BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
  46 .B "#include <crypt.h>"
  47 .PP
  48 .BI "void setkey_r(const char *" key ", struct crypt_data *" data );
  49 .BI "void encrypt_r(char *" block ", int " edflag \
  50 ", struct crypt_data *" data );
  51 .fi
  52 .PP
  53 Each of these requires linking with \fI\-lcrypt\fP.
  54 .SH DESCRIPTION
  55 These functions encrypt and decrypt 64-bit messages.
  56 The
  57 .BR setkey ()
  58 function sets the key used by
  59 .BR encrypt ().
  60 The
  61 .I key
  62 argument used here is an array of 64 bytes, each of which has
  63 numerical value 1 or 0.
  64 The bytes key[n] where n=8*i-1 are ignored,
  65 so that the effective key length is 56 bits.
  66 .PP
  67 The
  68 .BR encrypt ()
  69 function modifies the passed buffer, encoding if
  70 .I edflag
  71 is 0, and decoding if 1 is being passed.
  72 Like the
  73 .I key
  74 argument, also
  75 .I block
  76 is a bit vector representation of the actual value that is encoded.
  77 The result is returned in that same vector.
  78 .PP
  79 These two functions are not reentrant, that is, the key data is
  80 kept in static storage.
  81 The functions
  82 .BR setkey_r ()
  83 and
  84 .BR encrypt_r ()
  85 are the reentrant versions.
  86 They use the following
  87 structure to hold the key data:
  88 .PP
  89 .in +4n
  90 .EX
  91 struct crypt_data {
  92     char     keysched[16 * 8];
  93     char     sb0[32768];
  94     char     sb1[32768];
  95     char     sb2[32768];
  96     char     sb3[32768];
  97     char     crypt_3_buf[14];
  98     char     current_salt[2];
  99     long int current_saltbits;
 100     int      direction;
 101     int      initialized;
 102 };
 103 .EE
 104 .in
 105 .PP
 106 Before calling
 107 .BR setkey_r ()
 108 set
 109 .I data\->initialized
 110 to zero.
 111 .SH RETURN VALUE
 112 These functions do not return any value.
 113 .SH ERRORS
 114 Set
 115 .I errno
 116 to zero before calling the above functions.
 117 On success, it is unchanged.
 118 .TP
 119 .B ENOSYS
 120 The function is not provided.
 121 (For example because of former USA export restrictions.)
 122 .SH ATTRIBUTES
 123 For an explanation of the terms used in this section, see
 124 .BR attributes (7).
 125 .TS
 126 allbox;
 127 lbw23 lb lb
 128 l l l.
 129 Interface       Attribute       Value
 130 T{
 131 .BR encrypt (),
 132 .BR setkey ()
 133 T}      Thread safety   MT-Unsafe race:crypt
 134 T{
 135 .BR encrypt_r (),
 136 .BR setkey_r ()
 137 T}      Thread safety   MT-Safe
 138 .TE
 139 .SH CONFORMING TO
 140 .BR encrypt (),
 141 .BR setkey ():
 142 POSIX.1-2001, POSIX.1-2008, SUS, SVr4.
 143 .PP
 144 The functions
 145 .BR encrypt_r ()
 146 and
 147 .BR setkey_r ()
 148 are GNU extensions.
 149 .SH NOTES
 150 .SS Availability in glibc
 151 The
 152 .BR crypt (),
 153 .BR encrypt (),
 154 and
 155 .BR setkey ()
 156 functions are part of the POSIX.1-2008 XSI Options Group for Encryption
 157 and are optional. If the interfaces are not available then the symbolic
 158 constant
 159 .BR _XOPEN_CRYPT
 160 is either not defined or defined to -1, and can be checked at runtime with
 161 .BR sysconf ().
 162 This may be the case if the downstream distribution has switched from glibc
 163 crypt to libxcrypt.  When recompiling applications in such distributions the
 164 user must detect if
 165 .BR _XOPEN_CRPYT
 166 is not available and include crypt.h for the function prototypes; otherwise
 167 libxcrypt is a ABI compatible drop-in replacement.
 168 .SS Features in glibc
 169 In glibc 2.2, these functions use the DES algorithm.
 170 .SH EXAMPLE
 171 .EX
 172 #define _XOPEN_SOURCE
 173 #include <stdio.h>
 174 #include <stdlib.h>
 175 #include <unistd.h>
 176 #include <crypt.h>
 177
 178 int
 179 main(void)
 180 {
 181     char key[64];
 182     char orig[9] = "eggplant";
 183     char buf[64];
 184     char txt[9];
 185     int i, j;
 186
 187     for (i = 0; i < 64; i++) {
 188         key[i] = rand() & 1;
 189     }
 190
 191     for (i = 0; i < 8; i++) {
 192         for (j = 0; j < 8; j++) {
 193             buf[i * 8 + j] = orig[i] >> j & 1;
 194         }
 195         setkey(key);
 196     }
 197     printf("Before encrypting: %s\\n", orig);
 198
 199     encrypt(buf, 0);
 200     for (i = 0; i < 8; i++) {
 201         for (j = 0, txt[i] = \(aq\\0\(aq; j < 8; j++) {
 202             txt[i] |= buf[i * 8 + j] << j;
 203         }
 204         txt[8] = \(aq\\0\(aq;
 205     }
 206     printf("After encrypting:  %s\\n", txt);
 207
 208     encrypt(buf, 1);
 209     for (i = 0; i < 8; i++) {
 210         for (j = 0, txt[i] = \(aq\\0\(aq; j < 8; j++) {
 211             txt[i] |= buf[i * 8 + j] << j;
 212         }
 213         txt[8] = \(aq\\0\(aq;
 214     }
 215     printf("After decrypting:  %s\\n", txt);
 216     exit(EXIT_SUCCESS);
 217 }
 218 .EE
 219 .SH SEE ALSO
 220 .BR cbc_crypt (3),
 221 .BR crypt (3),
 222 .BR ecb_crypt (3),
 223 .\" .BR fcrypt (3)