setkey_r(3)

1ENCRYPT(3)                 Linux Programmer's Manual                ENCRYPT(3)
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NAME

6       encrypt, setkey, encrypt_r, setkey_r - encrypt 64-bit messages
7

SYNOPSIS

9       #define _XOPEN_SOURCE       /* See feature_test_macros(7) */
10       #include <unistd.h>
11
12       void encrypt(char block[64], int edflag);
13
14       #define _XOPEN_SOURCE       /* See feature_test_macros(7) */
15       #include <stdlib.h>
16
17       void setkey(const char *key);
18
19       #define _GNU_SOURCE         /* See feature_test_macros(7) */
20       #include <crypt.h>
21
22       void setkey_r(const char *key, struct crypt_data *data);
23       void encrypt_r(char *block, int edflag, struct crypt_data *data);
24
25       Each of these requires linking with -lcrypt.
26

DESCRIPTION

28       These  functions  encrypt  and  decrypt  64-bit messages.  The setkey()
29       function sets the key used by encrypt().  The key argument used here is
30       an  array  of  64 bytes, each of which has numerical value 1 or 0.  The
31       bytes key[n] where n=8*i-1 are  ignored,  so  that  the  effective  key
32       length is 56 bits.
33
34       The  encrypt()  function modifies the passed buffer, encoding if edflag
35       is 0, and decoding if 1 is being passed.  Like the key  argument,  also
36       block  is  a  bit vector representation of the actual value that is en‐
37       coded.  The result is returned in that same vector.
38
39       These two functions are not reentrant, that is, the key data is kept in
40       static storage.  The functions setkey_r() and encrypt_r() are the reen‐
41       trant versions.  They use the following structure to hold the key data:
42
43           struct crypt_data {
44               char keysched[16 * 8];
45               char sb0[32768];
46               char sb1[32768];
47               char sb2[32768];
48               char sb3[32768];
49               char crypt_3_buf[14];
50               char current_salt[2];
51               long current_saltbits;
52               int  direction;
53               int  initialized;
54           };
55
56       Before calling setkey_r() set data->initialized to zero.
57

RETURN VALUE

59       These functions do not return any value.
60

ERRORS

62       Set errno to zero before calling the above functions.  On  success,  it
63       is unchanged.
64
65       ENOSYS The  function  is  not provided.  (For example because of former
66              USA export restrictions.)
67

VERSIONS

69       Because they employ the DES block cipher, which is no longer considered
70       secure,  crypt(),  crypt_r(),  setkey(), and setkey_r() were removed in
71       glibc 2.28.  Applications should switch to a  modern  cryptography  li‐
72       brary, such as libgcrypt.
73

ATTRIBUTES

75       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
76       tributes(7).
77
78       ┌────────────────────────┬───────────────┬──────────────────────┐
79       │Interface               │ Attribute     │ Value                │
80       ├────────────────────────┼───────────────┼──────────────────────┤
81       │encrypt(), setkey()     │ Thread safety │ MT-Unsafe race:crypt │
82       ├────────────────────────┼───────────────┼──────────────────────┤
83       │encrypt_r(), setkey_r() │ Thread safety │ MT-Safe              │
84       └────────────────────────┴───────────────┴──────────────────────┘

CONFORMING TO

86       encrypt(), setkey(): POSIX.1-2001, POSIX.1-2008, SUS, SVr4.
87
88       The functions encrypt_r() and setkey_r() are GNU extensions.
89

NOTES

91   Availability in glibc
92       See crypt(3).
93
94   Features in glibc
95       In glibc 2.2, these functions use the DES algorithm.
96

EXAMPLES

98       #define _XOPEN_SOURCE
99       #include <stdio.h>
100       #include <stdlib.h>
101       #include <unistd.h>
102       #include <crypt.h>
103
104       int
105       main(void)
106       {
107           char key[64];
108           char orig[9] = "eggplant";
109           char buf[64];
110           char txt[9];
111
112           for (int i = 0; i < 64; i++) {
113               key[i] = rand() & 1;
114           }
115
116           for (int i = 0; i < 8; i++) {
117               for (int j = 0; j < 8; j++) {
118                   buf[i * 8 + j] = orig[i] >> j & 1;
119               }
120               setkey(key);
121           }
122           printf("Before encrypting: %s\n", orig);
123
124           encrypt(buf, 0);
125           for (int i = 0; i < 8; i++) {
126               for (int j = 0, txt[i] = '\0'; j < 8; j++) {
127                   txt[i] |= buf[i * 8 + j] << j;
128               }
129               txt[8] = '\0';
130           }
131           printf("After encrypting:  %s\n", txt);
132
133           encrypt(buf, 1);
134           for (int i = 0; i < 8; i++) {
135               for (int j = 0, txt[i] = '\0'; j < 8; j++) {
136                   txt[i] |= buf[i * 8 + j] << j;
137               }
138               txt[8] = '\0';
139           }
140           printf("After decrypting:  %s\n", txt);
141           exit(EXIT_SUCCESS);
142       }
143

COLOPHON

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150       latest    version    of    this    page,    can     be     found     at
151       https://www.kernel.org/doc/man-pages/.
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155                                  2020-11-01                        ENCRYPT(3)