summaryrefslogtreecommitdiffstats
path: root/lib/libmd/sha.3
blob: a319dbcdab89b18ddad0648f67633dd19e4c2ae7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
.\"
.\" ----------------------------------------------------------------------------
.\" "THE BEER-WARE LICENSE" (Revision 42):
.\" <phk@FreeBSD.org> wrote this file.  As long as you retain this notice you
.\" can do whatever you want with this stuff. If we meet some day, and you think
.\" this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
.\" ----------------------------------------------------------------------------
.\"
.\" 	From: Id: mdX.3,v 1.14 1999/02/11 20:31:49 wollman Exp
.\" $FreeBSD$
.\"
.Dd February 25, 1999
.Dt SHA 3
.Os
.Sh NAME
.Nm SHA_Init ,
.Nm SHA_Update ,
.Nm SHA_Final ,
.Nm SHA_End ,
.Nm SHA_File ,
.Nm SHA_FileChunk ,
.Nm SHA_Data ,
.Nm SHA1_Init ,
.Nm SHA1_Update ,
.Nm SHA1_Final ,
.Nm SHA1_End ,
.Nm SHA1_File ,
.Nm SHA1_FileChunk ,
.Nm SHA1_Data
.Nd calculate the FIPS 160 and 160-1 ``SHA'' message digests
.Sh LIBRARY
.Lb libmd
.Sh SYNOPSIS
.In sys/types.h
.In sha.h
.Ft void
.Fn SHA_Init "SHA_CTX *context"
.Ft void
.Fn SHA_Update "SHA_CTX *context" "const unsigned char *data" "unsigned int len"
.Ft void
.Fn SHA_Final "unsigned char digest[20]" "SHA_CTX *context"
.Ft "char *"
.Fn SHA_End "SHA_CTX *context" "char *buf"
.Ft "char *"
.Fn SHA_File "const char *filename" "char *buf"
.Ft "char *"
.Fn SHA_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SHA_Data "const unsigned char *data" "unsigned int len" "char *buf"
.Ft void
.Fn SHA1_Init "SHA_CTX *context"
.Ft void
.Fn SHA1_Update "SHA_CTX *context" "const unsigned char *data" "unsigned int len"
.Ft void
.Fn SHA1_Final "unsigned char digest[20]" "SHA_CTX *context"
.Ft "char *"
.Fn SHA1_End "SHA_CTX *context" "char *buf"
.Ft "char *"
.Fn SHA1_File "const char *filename" "char *buf"
.Ft "char *"
.Fn SHA1_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
.Ft "char *"
.Fn SHA1_Data "const unsigned char *data" "unsigned int len" "char *buf"
.Sh DESCRIPTION
The
.Li SHA_
and
.Li SHA1_
functions calculate a 160-bit cryptographic checksum (digest)
for any number of input bytes.  A cryptographic checksum is a one-way
hash function; that is, it is computationally impractical to find
the input corresponding to a particular output.  This net result is
a ``fingerprint'' of the input-data, which doesn't disclose the actual
input.
.Pp
.Tn SHA
(or
.Tn SHA-0 )
is the original Secure Hash Algorithm specified in
.Tn FIPS
160.  It was quickly proven insecure, and has been superseded by
.Tn SHA-1 .
.Tn SHA-0
is included for compatibility purposes only.
.Pp
The
.Fn SHA1_Init  ,
.Fn SHA1_Update ,
and
.Fn SHA1_Final
functions are the core functions.  Allocate an SHA_CTX, initialize it with
.Fn SHA1_Init ,
run over the data with
.Fn SHA1_Update ,
and finally extract the result using
.Fn SHA1_Final .
.Pp
.Fn SHA1_End
is a wrapper for
.Fn SHA1_Final
which converts the return value to a 41-character
(including the terminating '\e0')
.Tn ASCII
string which represents the 160 bits in hexadecimal.
.Pp
.Fn SHA1_File
calculates the digest of a file, and uses
.Fn SHA1_End
to return the result.
If the file cannot be opened, a null pointer is returned.
.Fn SHA1_FileChunk
is similar to
.Fn SHA1_File ,
but it only calculates the digest over a byte-range of the file specified,
starting at
.Fa offset
and spanning
.Fa length
bytes.
If the
.Fa length
parameter is specified as 0, or more than the length of the remaining part
of the file,
.Fn SHA1_FileChunk
calculates the digest from
.Fa offset
to the end of file.
.Fn SHA1_Data
calculates the digest of a chunk of data in memory, and uses
.Fn SHA1_End
to return the result.
.Pp
When using
.Fn SHA1_End ,
.Fn SHA1_File ,
or
.Fn SHA1_Data ,
the
.Fa buf
argument can be a null pointer, in which case the returned string
is allocated with
.Xr malloc 3
and subsequently must be explicitly deallocated using
.Xr free 3
after use.
If the
.Fa buf
argument is non-null it must point to at least 41 characters of buffer space.
.Sh SEE ALSO
.Xr md2 3 ,
.Xr md4 3 ,
.Xr md5 3 ,
.Xr ripemd 3
.Sh AUTHORS
The core hash routines were implemented by Eric Young based on the
published
.Tn FIPS
standards.
.Sh HISTORY
These functions appeared in
.Fx 4.0 .
.Sh BUGS
No method is known to exist which finds two files having the same hash value,
nor to find a file with a specific hash value.
There is on the other hand no guarantee that such a method doesn't exist.
.Pp
The
.Tn IA32
(Intel) implementation of
.Tn SHA-1
makes heavy use of the
.Ql bswapl
instruction, which is not present on the original 80386.  Attempts
to use
.Tn SHA-1
on those processors will cause an illegal instruction trap.
(Arguably, the kernel should simply emulate this instruction.)
OpenPOWER on IntegriCloud