SHA256Transform(3)

1SHA2(3)                  BSD Library Functions Manual                  SHA2(3)
2

NAME

4     SHA256Init, SHA256Update, SHA256Pad, SHA256Final, SHA256Transform,
5     SHA256End, SHA256File, SHA256FileChunk, SHA256Data — calculate the NIST
6     Secure Hash Standard (version 2)
7

LIBRARY

9     Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)
10

SYNOPSIS

12     #include <sys/types.h>
13     #include <sha2.h>
14
15     void
16     SHA256Init(SHA2_CTX *context);
17
18     void
19     SHA256Update(SHA2_CTX *context, const uint8_t *data, size_t len);
20
21     void
22     SHA256Pad(SHA2_CTX *context);
23
24     void
25     SHA256Final(uint8_t digest[SHA256_DIGEST_LENGTH], SHA2_CTX *context);
26
27     void
28     SHA256Transform(uint32_t state[8],
29         const uint8_t buffer[SHA256_BLOCK_LENGTH]);
30
31     char *
32     SHA256End(SHA2_CTX *context, char *buf);
33
34     char *
35     SHA256File(const char *filename, char *buf);
36
37     char *
38     SHA256FileChunk(const char *filename, char *buf, off_t offset,
39         off_t length);
40
41     char *
42     SHA256Data(uint8_t *data, size_t len, char *buf);
43
44     void
45     SHA384Init(SHA2_CTX *context);
46
47     void
48     SHA384Update(SHA2_CTX *context, const uint8_t *data, size_t len);
49
50     void
51     SHA384Pad(SHA2_CTX *context);
52
53     void
54     SHA384Final(uint8_t digest[SHA384_DIGEST_LENGTH], SHA2_CTX *context);
55
56     void
57     SHA384Transform(uint64_t state[8],
58         const uint8_t buffer[SHA384_BLOCK_LENGTH]);
59
60     char *
61     SHA384End(SHA2_CTX *context, char *buf);
62
63     char *
64     SHA384File(char *filename, char *buf);
65
66     char *
67     SHA384FileChunk(char *filename, char *buf, off_t offset, off_t length);
68
69     char *
70     SHA384Data(uint8_t *data, size_t len, char *buf);
71
72     void
73     SHA512Init(SHA2_CTX *context);
74
75     void
76     SHA512Update(SHA2_CTX *context, const uint8_t *data, size_t len);
77
78     void
79     SHA512Pad(SHA2_CTX *context);
80
81     void
82     SHA512Final(uint8_t digest[SHA512_DIGEST_LENGTH], SHA2_CTX *context);
83
84     void
85     SHA512Transform(uint64_t state[8],
86         const uint8_t buffer[SHA512_BLOCK_LENGTH]);
87
88     char *
89     SHA512End(SHA2_CTX *context, char *buf);
90
91     char *
92     SHA512File(char *filename, char *buf);
93
94     char *
95     SHA512FileChunk(char *filename, char *buf, off_t offset, off_t length);
96
97     char *
98     SHA512Data(uint8_t *data, size_t len, char *buf);
99

DESCRIPTION

101     The SHA2 functions implement the NIST Secure Hash Standard, FIPS PUB
102     180-2.  The SHA2 functions are used to generate a condensed representa‐
103     tion of a message called a message digest, suitable for use as a digital
104     signature.  There are three families of functions, with names correspond‐
105     ing to the number of bits in the resulting message digest.  The SHA-256
106     functions are limited to processing a message of less than 2^64 bits as
107     input.  The SHA-384 and SHA-512 functions can process a message of at
108     most 2^128 - 1 bits as input.
109
110     The SHA2 functions are considered to be more secure than the sha1(3)
111     functions with which they share a similar interface.  The 256, 384, and
112     512-bit versions of SHA2 share the same interface.  For brevity, only the
113     256-bit variants are described below.
114
115     The SHA256Init() function initializes a SHA2_CTX context for use with
116     SHA256Update() and SHA256Final().  The SHA256Update() function adds data
117     of length len to the SHA2_CTX specified by context.  SHA256Final() is
118     called when all data has been added via SHA256Update() and stores a mes‐
119     sage digest in the digest parameter.
120
121     The SHA256Pad() function can be used to apply padding to the message di‐
122     gest as in SHA256Final(), but the current context can still be used with
123     SHA256Update().
124
125     The SHA256Transform() function is used by SHA256Update() to hash 512-bit
126     blocks and forms the core of the algorithm.  Most programs should use the
127     interface provided by SHA256Init(), SHA256Update(), and SHA256Final() in‐
128     stead of calling SHA256Transform() directly.
129
130     The SHA256End() function is a front end for SHA256Final() which converts
131     the digest into an ASCII representation of the digest in hexadecimal.
132
133     The SHA256File() function calculates the digest for a file and returns
134     the result via SHA256End().  If SHA256File() is unable to open the file,
135     a NULL pointer is returned.
136
137     SHA256FileChunk() behaves like SHA256File() but calculates the digest
138     only for that portion of the file starting at offset and continuing for
139     length bytes or until end of file is reached, whichever comes first.  A
140     zero length can be specified to read until end of file.  A negative
141     length or offset will be ignored.
142
143     The SHA256Data() function calculates the digest of an arbitrary string
144     and returns the result via SHA256End().
145
146     For each of the SHA256End(), SHA256File(), SHA256FileChunk(), and
147     SHA256Data() functions the buf parameter should either be a string large
148     enough to hold the resulting digest (e.g. SHA256_DIGEST_STRING_LENGTH,
149     SHA384_DIGEST_STRING_LENGTH, or SHA512_DIGEST_STRING_LENGTH, depending on
150     the function being used) or a NULL pointer.  In the latter case, space
151     will be dynamically allocated via malloc(3) and should be freed using
152     free(3) when it is no longer needed.
153

EXAMPLES

155     The following code fragment will calculate the SHA-256 digest for the
156     string "abc", which is
157     “0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad”.
158
159           SHA2_CTX ctx;
160           uint8_t results[SHA256_DIGEST_LENGTH];
161           char *buf;
162           int n;
163
164           buf = "abc";
165           n = strlen(buf);
166           SHA256Init(&ctx);
167           SHA256Update(&ctx, (uint8_t *)buf, n);
168           SHA256Final(results, &ctx);
169
170           /* Print the digest as one long hex value */
171           printf("0x");
172           for (n = 0; n < SHA256_DIGEST_LENGTH; n++)
173                   printf("%02x", results[n]);
174           putchar('\n');
175
176     Alternately, the helper functions could be used in the following way:
177
178           uint8_t output[SHA256_DIGEST_STRING_LENGTH];
179           char *buf = "abc";
180
181           printf("0x%s\n", SHA256Data(buf, strlen(buf), output));
182

HISTORY

189     The SHA2 functions appeared in OpenBSD 3.4.
190

AUTHORS

192     This implementation of the SHA functions was written by Aaron D. Gifford.
193
194     The SHA256End(), SHA256File(), SHA256FileChunk(), and SHA256Data() helper
195     functions are derived from code written by Poul-Henning Kamp.
196

CAVEATS

198     This implementation of the Secure Hash Standard has not been validated by
199     NIST and as such is not in official compliance with the standard.
200
201     If a message digest is to be copied to a multi-byte type (i.e. an array
202     of 32-bit integers) it will be necessary to perform byte swapping on lit‐
203     tle endian machines such as the i386, alpha, and vax.
204
205BSD                           September 12, 2008                           BSD