1MD5(3)                   BSD Library Functions Manual                   MD5(3)
2

NAME

4     MD5Init, MD5Update, MD5Pad, MD5Final, MD5Transform, MD5End, MD5File,
5     MD5FileChunk, MD5Data — calculate the RSA Data Security, Inc., ``MD5''
6     message digest
7

LIBRARY

9     Utility functions from BSD systems (libbsd, -lbsd)
10

SYNOPSIS

12     #include <sys/types.h>
13     #include <md5.h>
14
15     void
16     MD5Init(MD5_CTX *context);
17
18     void
19     MD5Update(MD5_CTX *context, const u_int8_t *data, size_t len);
20
21     void
22     MD5Pad(MD5_CTX *context);
23
24     void
25     MD5Final(u_int8_t digest[MD5_DIGEST_LENGTH], MD5_CTX *context);
26
27     void
28     MD5Transform(u_int32_t state[4], u_int8_t block[MD5_BLOCK_LENGTH]);
29
30     char *
31     MD5End(MD5_CTX *context, char *buf);
32
33     char *
34     MD5File(const char *filename, char *buf);
35
36     char *
37     MD5FileChunk(const char *filename, char *buf, off_t offset,
38         off_t length);
39
40     char *
41     MD5Data(const u_int8_t *data, size_t len, char *buf);
42

DESCRIPTION

44     The MD5 functions calculate a 128-bit cryptographic checksum (digest) for
45     any number of input bytes.  A cryptographic checksum is a one-way hash-
46     function, that is, you cannot find (except by exhaustive search) the
47     input corresponding to a particular output.  This net result is a
48     “fingerprint” of the input-data, which doesn't disclose the actual input.
49
50     MD4 has been broken; it should only be used where necessary for backward
51     compatibility.  MD5 has not yet (1999-02-11) been broken, but recent
52     attacks have cast some doubt on its security properties.  The attacks on
53     both MD4 and MD5 are both in the nature of finding “collisions” - that
54     is, multiple inputs which hash to the same value; it is still unlikely
55     for an attacker to be able to determine the exact original input given a
56     hash value.
57
58     The MD5Init(), MD5Update(), and MD5Final() functions are the core func‐
59     tions.  Allocate an MD5_CTX, initialize it with MD5Init(), run over the
60     data with MD5Update(), and finally extract the result using MD5Final().
61
62     The MD5Pad() function can be used to apply padding to the message digest
63     as in MD5Final(), but the current context can still be used with
64     MD5Update().
65
66     The MD5Transform() function is used by MD5Update() to hash 512-bit blocks
67     and forms the core of the algorithm.  Most programs should use the inter‐
68     face provided by MD5Init(), MD5Update() and MD5Final() instead of calling
69     MD5Transform() directly.
70
71     MD5End() is a wrapper for MD5Final() which converts the return value to
72     an MD5_DIGEST_STRING_LENGTH-character (including the terminating '\0')
73     ASCII string which represents the 128 bits in hexadecimal.
74
75     MD5File() calculates the digest of a file, and uses MD5End() to return
76     the result.  If the file cannot be opened, a null pointer is returned.
77
78     MD5FileChunk() behaves like MD5File() but calculates the digest only for
79     that portion of the file starting at offset and continuing for length
80     bytes or until end of file is reached, whichever comes first.  A zero
81     length can be specified to read until end of file.  A negative length or
82     offset will be ignored.  MD5Data() calculates the digest of a chunk of
83     data in memory, and uses MD5End() to return the result.
84
85     When using MD5End(), MD5File(), MD5FileChunk(), or MD5Data(), the buf
86     argument can be a null pointer, in which case the returned string is
87     allocated with malloc(3) and subsequently must be explicitly deallocated
88     using free(3) after use.  If the buf argument is non-null it must point
89     to at least MD5_DIGEST_STRING_LENGTH characters of buffer space.
90

SEE ALSO

92     cksum(1), md5(1), adler32(3), md4(3), rmd160(3), sfv(3), sha1(3),
93     sha2(3), suma(3), tiger(3), whirlpool(3)
94
95     R. Rivest, The MD4 Message-Digest Algorithm, RFC 1186.
96
97     R. Rivest, The MD5 Message-Digest Algorithm, RFC 1321.
98
99     RSA Laboratories, Frequently Asked Questions About today's Cryptography,
100     <http://www.rsa.com/rsalabs/faq/>.
101
102     H. Dobbertin, "Alf Swindles Ann", CryptoBytes, 1(3):5, 1995.
103
104     MJ. B. Robshaw, "On Recent Results for MD4 and MD5", RSA Laboratories
105     Bulletin, 4, November 12, 1996.
106
107     Hans Dobbertin, Cryptanalysis of MD5 Compress.
108

HISTORY

110     These functions appeared in OpenBSD 2.0.
111

AUTHORS

113     The original MD5 routines were developed by RSA Data Security, Inc., and
114     published in the above references.  This code is derived from a public
115     domain implementation written by Colin Plumb.
116
117     The MD5End(), MD5File(), MD5FileChunk(), and MD5Data() helper functions
118     are derived from code written by Poul-Henning Kamp.
119

BUGS

121     Collisions have been found for the full versions of both MD4 and MD5 as
122     well as strong attacks against the SHA-0 and SHA-1 family.  The use of
123     sha2(3), or rmd160(3) is recommended instead.
124
125BSD                             April 29, 2004                             BSD