1 .TH DES 3
2 .SH NAME
3 setupDESstate, des_key_setup, block_cipher, desCBCencrypt, desCBCdecrypt, desECBencrypt, desECBdecrypt, des3CBCencrypt, des3CBCdecrypt, des3ECBencrypt, des3ECBdecrypt, key_setup, des56to64, des64to56, setupDES3state, triple_block_cipher,  - single and triple digital encryption standard
4 .SH SYNOPSIS
5 .B #include <u.h>
6 .br
7 .B #include <libc.h>
8 .br
9 .B #include <mp.h>
10 .br
11 .B #include <libsec.h>
12 .PP
13 .B
14 void	des_key_setup(uchar key[8], ulong schedule[32])
15 .PP
16 .B
17 void	block_cipher(ulong *schedule, uchar *data,
18 .B
19 		int decrypting)
20 .PP
21 .B
22 void	setupDESstate(DESstate *s, uchar key[8], uchar *ivec)
23 .PP
24 .B
25 void	desCBCencrypt(uchar*, int, DESstate*)
26 .PP
27 .B
28 void	desCBCdecrypt(uchar*, int, DESstate*)
29 .PP
30 .B
31 void	desECBencrypt(uchar*, int, DESstate*)
32 .PP
33 .B
34 void	desECBdecrypt(uchar*, int, DESstate*)
35 .PP
36 .B
37 void	triple_block_cipher(ulong keys[3][32], uchar*, int)
38 .PP
39 .B
40 void	setupDES3state(DES3state *s, uchar key[3][8],
41 .B
42 			 uchar *ivec)
43 .PP
44 .B
45 void	des3CBCencrypt(uchar*, int, DES3state*)
46 .PP
47 .B
48 void	des3CBCdecrypt(uchar*, int, DES3state*)
49 .PP
50 .B
51 void	des3ECBencrypt(uchar*, int, DES3state*)
52 .PP
53 .B
54 void	des3ECBdecrypt(uchar*, int, DES3state*)
55 .PP
56 .B
57 void	key_setup(uchar[7], ulong[32])
58 .PP
59 .B
60 void	des56to64(uchar *k56, uchar *k64)
61 .PP
62 .B
63 void	des64to56(uchar *k64, uchar *k56)
64 .SH DESCRIPTION
65 .PP
66 The Digital Encryption Standard (DES)
67 is a shared key or symmetric encryption using either
68 a 56 bit key for single DES or three 56 bit keys for triple des.
69 The keys are encoded into 64 bits where every eight bit
70 is parity. 
71 .PP
72 The basic DES function,
73 .IR block_cipher ,
74 works on a block of 8 bytes, converting them in place.
75 It takes a key schedule, a pointer to the block, and
76 a flag indicating encrypting (0) or decrypting (1).
77 The key schedule is created from the key using
78 .IR des_key_setup .
79 .PP
80 Since it is a bit awkward,
81 .I block_cipher
82 is rarely called directly.  Instead, one normally uses
83 routines that encrypt larger buffers of data and
84 which may chain the encryption state from one buffer
85 to the next.
86 These routines keep track of the state of the
87 encryption using a
88 .B DESstate
89 structure that contains the key schedule and any chained
90 state.
91 .I SetupDESstate
92 sets up the
93 .B DESstate
94 structure using the key and an 8 byte initialization vector.
95 .PP
96 Electronic code book, using
97 .I desECBencrypt
98 and 
99 .IR desECBdecrypt , 
100 is the less secure mode.  The encryption of each 8 bytes
101 does not depend on the encryption of any other.
102 Hence the encryption is a substitution
103 cipher using 64 bit characters.
104 .PP
105 Cipher block chaining mode, using
106 .I desCBCencrypt
107 and
108 .IR desCBCdecrypt ,
109 is more secure.  Every block encrypted depends on the initialization
110 vector and all blocks encrypted before it.
111 .PP
112 For both CBC and ECB modes, a stream of data can be encrypted as
113 multiple buffers.  However, all buffers except the last must
114 be a multiple of 8 bytes to ensure successful decryption of
115 the stream.
116 .PP
117 There are equivalent triple DES functions for each of the
118 DES functions.
119 .PP
120 In the past Plan 9 used a 56 bit or 7 byte
121 format for DES keys.  To be compatible with the rest
122 of the world, we've abandoned this format.
123 There are two functions:
124 .I des56to64
125 and
126 .I des64to56
127 to convert back and forth between the two formats.
128 Also a key schedule can be set up from the 7 byte format
129 using
130 .IR key_setup .
131 .PP
132 .SH SOURCE
133 .B \*9/src/libsec
134 .SH SEE ALSO
135 .MR mp (3) ,
136 .MR aes (3) ,
137 .MR blowfish (3) ,
138 .MR dsa (3) ,
139 .MR elgamal (3) ,
140 .MR rc4 (3) ,
141 .MR rsa (3) ,
142 .MR sechash (3) ,
143 .MR prime (3) ,
144 .MR rand (3)