2 .\" ----------------------------------------------------------------------------
3 .\" "THE BEER-WARE LICENSE" (Revision 42):
4 .\" <phk@FreeBSD.org> wrote this file. As long as you retain this notice you
5 .\" can do whatever you want with this stuff. If we meet some day, and you think
6 .\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
7 .\" ----------------------------------------------------------------------------
23 .Nd calculate the RSA Data Security, Inc., ``MDX'' message digest
30 .Fn MDXInit "MDX_CTX *context"
32 .Fn MDXUpdate "MDX_CTX *context" "const void *data" "unsigned int len"
34 .Fn MDXPad "MDX_CTX *context"
36 .Fn MDXFinal "unsigned char digest[16]" "MDX_CTX *context"
38 .Fn MDXEnd "MDX_CTX *context" "char *buf"
40 .Fn MDXFile "const char *filename" "char *buf"
42 .Fn MDXFileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
44 .Fn MDXData "const void *data" "unsigned int len" "char *buf"
46 The MDX functions calculate a 128-bit cryptographic checksum (digest)
47 for any number of input bytes.
48 A cryptographic checksum is a one-way
49 hash-function, that is, you cannot find (except by exhaustive search)
50 the input corresponding to a particular output.
53 of the input-data, which does not disclose the actual input.
55 MD4 is the fastest and MD5 is somewhat slower.
56 MD4 has now been broken; it should only be used where necessary for
57 backward compatibility.
58 MD5 has not yet (1999-02-11) been broken, but sufficient attacks have been
59 made that its security is in some doubt.
60 The attacks on both MD4 and MD5
61 are both in the nature of finding
65 inputs which hash to the same value; it is still unlikely for an attacker
66 to be able to determine the exact original input given a hash value.
73 functions are the core functions.
78 run over the data with
80 and finally extract the result using
82 which will also erase the
87 function can be used to pad message data in same way
90 without terminating calculation.
94 function is a wrapper for
96 which converts the return value to a 33-character
97 (including the terminating '\e0')
99 string which represents the 128 bits in hexadecimal.
103 function calculates the digest of a file, and uses
105 to return the result.
106 If the file cannot be opened, a null pointer is returned.
109 function is similar to
111 but it only calculates the digest over a byte-range of the file specified,
119 parameter is specified as 0, or more than the length of the remaining part
122 calculates the digest from
127 function calculates the digest of a chunk of data in memory, and uses
129 to return the result.
138 argument can be a null pointer, in which case the returned string
141 and subsequently must be explicitly deallocated using
146 argument is non-null it must point to at least 33 characters of buffer space.
157 .%T The MD4 Message-Digest Algorithm
162 .%T The MD5 Message-Digest Algorithm
174 .%T On Recent Results for MD2, MD4 and MD5
175 .%J RSA Laboratories Bulletin
177 .%D November 12, 1996
180 These functions appeared in
183 The original MDX routines were developed by
185 Data Security, Inc., and published in the above references.
186 This code is derived directly from these implementations by
187 .An Poul-Henning Kamp Aq Mt phk@FreeBSD.org .
191 No method is known to exist which finds two files having the same hash value,
192 nor to find a file with a specific hash value.
193 There is on the other hand no guarantee that such a method does not exist.