1.\" 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.\" ---------------------------------------------------------------------------- 8.\" 9.\" $FreeBSD$ 10.\" 11.Dd April 26, 2016 12.Dt MDX 3 13.Os 14.Sh NAME 15.Nm MDXInit , 16.Nm MDXUpdate , 17.Nm MDXPad , 18.Nm MDXFinal , 19.Nm MDXEnd , 20.Nm MDXFile , 21.Nm MDXFileChunk , 22.Nm MDXData 23.Nd calculate the RSA Data Security, Inc., ``MDX'' message digest 24.Sh LIBRARY 25.Lb libmd 26.Sh SYNOPSIS 27.In sys/types.h 28.In mdX.h 29.Ft void 30.Fn MDXInit "MDX_CTX *context" 31.Ft void 32.Fn MDXUpdate "MDX_CTX *context" "const void *data" "unsigned int len" 33.Ft void 34.Fn MDXPad "MDX_CTX *context" 35.Ft void 36.Fn MDXFinal "unsigned char digest[16]" "MDX_CTX *context" 37.Ft "char *" 38.Fn MDXEnd "MDX_CTX *context" "char *buf" 39.Ft "char *" 40.Fn MDXFile "const char *filename" "char *buf" 41.Ft "char *" 42.Fn MDXFileChunk "const char *filename" "char *buf" "off_t offset" "off_t length" 43.Ft "char *" 44.Fn MDXData "const void *data" "unsigned int len" "char *buf" 45.Sh DESCRIPTION 46The MDX functions calculate a 128-bit cryptographic checksum (digest) 47for any number of input bytes. 48A cryptographic checksum is a one-way 49hash-function, that is, you cannot find (except by exhaustive search) 50the input corresponding to a particular output. 51This net result is a 52.Dq fingerprint 53of the input-data, which does not disclose the actual input. 54.Pp 55MD4 is the fastest and MD5 is somewhat slower. 56MD4 has now been broken; it should only be used where necessary for 57backward compatibility. 58MD5 has not yet (1999-02-11) been broken, but sufficient attacks have been 59made that its security is in some doubt. 60The attacks on both MD4 and MD5 61are both in the nature of finding 62.Dq collisions 63\[en] 64that is, multiple 65inputs which hash to the same value; it is still unlikely for an attacker 66to be able to determine the exact original input given a hash value. 67.Pp 68The 69.Fn MDXInit , 70.Fn MDXUpdate , 71and 72.Fn MDXFinal 73functions are the core functions. 74Allocate an 75.Vt MDX_CTX , 76initialize it with 77.Fn MDXInit , 78run over the data with 79.Fn MDXUpdate , 80and finally extract the result using 81.Fn MDXFinal . 82.Pp 83The 84.Fn MDXPad 85function can be used to pad message data in same way 86as done by 87.Fn MDXFinal 88without terminating calculation. 89.Pp 90The 91.Fn MDXEnd 92function is a wrapper for 93.Fn MDXFinal 94which converts the return value to a 33-character 95(including the terminating '\e0') 96.Tn ASCII 97string which represents the 128 bits in hexadecimal. 98.Pp 99The 100.Fn MDXFile 101function calculates the digest of a file, and uses 102.Fn MDXEnd 103to return the result. 104If the file cannot be opened, a null pointer is returned. 105The 106.Fn MDXFileChunk 107function is similar to 108.Fn MDXFile , 109but it only calculates the digest over a byte-range of the file specified, 110starting at 111.Fa offset 112and spanning 113.Fa length 114bytes. 115If the 116.Fa length 117parameter is specified as 0, or more than the length of the remaining part 118of the file, 119.Fn MDXFileChunk 120calculates the digest from 121.Fa offset 122to the end of file. 123The 124.Fn MDXData 125function calculates the digest of a chunk of data in memory, and uses 126.Fn MDXEnd 127to return the result. 128.Pp 129When using 130.Fn MDXEnd , 131.Fn MDXFile , 132or 133.Fn MDXData , 134the 135.Fa buf 136argument can be a null pointer, in which case the returned string 137is allocated with 138.Xr malloc 3 139and subsequently must be explicitly deallocated using 140.Xr free 3 141after use. 142If the 143.Fa buf 144argument is non-null it must point to at least 33 characters of buffer space. 145.Sh SEE ALSO 146.Xr md4 3 , 147.Xr md5 3 , 148.Xr ripemd 3 , 149.Xr sha 3 , 150.Xr sha256 3 , 151.Xr sha512 3 , 152.Xr skein 3 153.Rs 154.%A R. Rivest 155.%T The MD4 Message-Digest Algorithm 156.%O RFC 1186 157.Re 158.Rs 159.%A R. Rivest 160.%T The MD5 Message-Digest Algorithm 161.%O RFC 1321 162.Re 163.Rs 164.%A H. Dobbertin 165.%T Alf Swindles Ann 166.%J CryptoBytes 167.%N 1(3):5 168.%D 1995 169.Re 170.Rs 171.%A MJ. B. Robshaw 172.%T On Recent Results for MD2, MD4 and MD5 173.%J RSA Laboratories Bulletin 174.%N 4 175.%D November 12, 1996 176.Re 177.Sh HISTORY 178These functions appeared in 179.Fx 2.0 . 180.Sh AUTHORS 181The original MDX routines were developed by 182.Tn RSA 183Data Security, Inc., and published in the above references. 184This code is derived directly from these implementations by 185.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org . 186.Pp 187Phk ristede runen. 188.Sh BUGS 189No method is known to exist which finds two files having the same hash value, 190nor to find a file with a specific hash value. 191There is on the other hand no guarantee that such a method does not exist. 192