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 May 21, 2019 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 , 82which will also erase the 83.Vt MDX_CTX . 84.Pp 85The 86.Fn MDXPad 87function can be used to pad message data in same way 88as done by 89.Fn MDXFinal 90without terminating calculation. 91.Pp 92The 93.Fn MDXEnd 94function is a wrapper for 95.Fn MDXFinal 96which converts the return value to a 33-character 97(including the terminating '\e0') 98ASCII string which represents the 128 bits in hexadecimal. 99.Pp 100The 101.Fn MDXFile 102function calculates the digest of a file, and uses 103.Fn MDXEnd 104to return the result. 105If the file cannot be opened, a null pointer is returned. 106The 107.Fn MDXFileChunk 108function is similar to 109.Fn MDXFile , 110but it only calculates the digest over a byte-range of the file specified, 111starting at 112.Fa offset 113and spanning 114.Fa length 115bytes. 116If the 117.Fa length 118parameter is specified as 0, or more than the length of the remaining part 119of the file, 120.Fn MDXFileChunk 121calculates the digest from 122.Fa offset 123to the end of file. 124The 125.Fn MDXData 126function calculates the digest of a chunk of data in memory, and uses 127.Fn MDXEnd 128to return the result. 129.Pp 130When using 131.Fn MDXEnd , 132.Fn MDXFile , 133or 134.Fn MDXData , 135the 136.Fa buf 137argument can be a null pointer, in which case the returned string 138is allocated with 139.Xr malloc 3 140and subsequently must be explicitly deallocated using 141.Xr free 3 142after use. 143If the 144.Fa buf 145argument is non-null it must point to at least 33 characters of buffer space. 146.Sh ERRORS 147The 148.Fn MDXEnd 149function called with a null buf argument may fail and return NULL if: 150.Bl -tag -width Er 151.It Bq Er ENOMEM 152Insufficient storage space is available. 153.El 154.Pp 155The 156.Fn MDXFile 157and 158.Fn MDXFileChunk 159may return NULL when underlying 160.Xr open 2 , 161.Xr fstat 2 , 162.Xr lseek 2 , 163or 164.Xr MDXEnd 3 165fail. 166.Sh SEE ALSO 167.Xr md4 3 , 168.Xr md5 3 , 169.Xr ripemd 3 , 170.Xr sha 3 , 171.Xr sha256 3 , 172.Xr sha512 3 , 173.Xr skein 3 174.Rs 175.%A R. Rivest 176.%T The MD4 Message-Digest Algorithm 177.%O RFC 1186 178.Re 179.Rs 180.%A R. Rivest 181.%T The MD5 Message-Digest Algorithm 182.%O RFC 1321 183.Re 184.Rs 185.%A H. Dobbertin 186.%T Alf Swindles Ann 187.%J CryptoBytes 188.%N 1(3):5 189.%D 1995 190.Re 191.Rs 192.%A MJ. B. Robshaw 193.%T On Recent Results for MD2, MD4 and MD5 194.%J RSA Laboratories Bulletin 195.%N 4 196.%D November 12, 1996 197.Re 198.Sh HISTORY 199These functions appeared in 200.Fx 2.0 . 201.Sh AUTHORS 202The original MDX routines were developed by 203RSA Data Security, Inc., and published in the above references. 204This code is derived directly from these implementations by 205.An Poul-Henning Kamp Aq Mt phk@FreeBSD.org . 206.Pp 207Phk ristede runen. 208.Sh BUGS 209The MD5 algorithm has been proven to be vulnerable to practical collision 210attacks and should not be relied upon to produce unique outputs, 211.Em nor should they be used as part of a cryptographic signature scheme. 212