203 lines
4.9 KiB
Groff
203 lines
4.9 KiB
Groff
.\"
|
|
.\" ----------------------------------------------------------------------------
|
|
.\" "THE BEER-WARE LICENSE" (Revision 42):
|
|
.\" <phk@FreeBSD.org> wrote this file. As long as you retain this notice you
|
|
.\" can do whatever you want with this stuff. If we meet some day, and you think
|
|
.\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
|
|
.\" ----------------------------------------------------------------------------
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd February 11, 1999
|
|
.Dt MDX 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm MDXInit ,
|
|
.Nm MDXUpdate ,
|
|
.Nm MDXPad ,
|
|
.Nm MDXFinal ,
|
|
.Nm MDXEnd ,
|
|
.Nm MDXFile ,
|
|
.Nm MDXFileChunk ,
|
|
.Nm MDXData
|
|
.Nd calculate the RSA Data Security, Inc., ``MDX'' message digest
|
|
.Sh LIBRARY
|
|
.Lb libmd
|
|
.Sh SYNOPSIS
|
|
.In sys/types.h
|
|
.In mdX.h
|
|
.Ft void
|
|
.Fn MDXInit "MDX_CTX *context"
|
|
.Ft void
|
|
.Fn MDXUpdate "MDX_CTX *context" "const unsigned char *data" "unsigned int len"
|
|
.Ft void
|
|
.Fn MDXPad "MDX_CTX *context"
|
|
.Ft void
|
|
.Fn MDXFinal "unsigned char digest[16]" "MDX_CTX *context"
|
|
.Ft "char *"
|
|
.Fn MDXEnd "MDX_CTX *context" "char *buf"
|
|
.Ft "char *"
|
|
.Fn MDXFile "const char *filename" "char *buf"
|
|
.Ft "char *"
|
|
.Fn MDXFileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
|
|
.Ft "char *"
|
|
.Fn MDXData "const unsigned char *data" "unsigned int len" "char *buf"
|
|
.Sh DESCRIPTION
|
|
The MDX functions calculate a 128-bit cryptographic checksum (digest)
|
|
for any number of input bytes.
|
|
A cryptographic checksum is a one-way
|
|
hash-function, that is, you cannot find (except by exhaustive search)
|
|
the input corresponding to a particular output.
|
|
This net result is a
|
|
.Dq fingerprint
|
|
of the input-data, which does not disclose the actual input.
|
|
.Pp
|
|
MD2 is the slowest, MD4 is the fastest and MD5 is somewhere in the middle.
|
|
MD2 can only be used for Privacy-Enhanced Mail.
|
|
MD4 has now been broken; it should only be used where necessary for
|
|
backward compatibility.
|
|
MD5 has not yet (1999-02-11) been broken, but sufficient attacks have been
|
|
made that its security is in some doubt.
|
|
The attacks on both MD4 and MD5
|
|
are both in the nature of finding
|
|
.Dq collisions
|
|
\[en]
|
|
that is, multiple
|
|
inputs which hash to the same value; it is still unlikely for an attacker
|
|
to be able to determine the exact original input given a hash value.
|
|
.Pp
|
|
The
|
|
.Fn MDXInit ,
|
|
.Fn MDXUpdate ,
|
|
and
|
|
.Fn MDXFinal
|
|
functions are the core functions.
|
|
Allocate an
|
|
.Vt MDX_CTX ,
|
|
initialize it with
|
|
.Fn MDXInit ,
|
|
run over the data with
|
|
.Fn MDXUpdate ,
|
|
and finally extract the result using
|
|
.Fn MDXFinal .
|
|
.Pp
|
|
The
|
|
.Fn MDXPad
|
|
function can be used to pad message data in same way
|
|
as done by
|
|
.Fn MDXFinal
|
|
without terminating calculation.
|
|
.Pp
|
|
The
|
|
.Fn MDXEnd
|
|
function is a wrapper for
|
|
.Fn MDXFinal
|
|
which converts the return value to a 33-character
|
|
(including the terminating '\e0')
|
|
.Tn ASCII
|
|
string which represents the 128 bits in hexadecimal.
|
|
.Pp
|
|
The
|
|
.Fn MDXFile
|
|
function calculates the digest of a file, and uses
|
|
.Fn MDXEnd
|
|
to return the result.
|
|
If the file cannot be opened, a null pointer is returned.
|
|
The
|
|
.Fn MDXFileChunk
|
|
function is similar to
|
|
.Fn MDXFile ,
|
|
but it only calculates the digest over a byte-range of the file specified,
|
|
starting at
|
|
.Fa offset
|
|
and spanning
|
|
.Fa length
|
|
bytes.
|
|
If the
|
|
.Fa length
|
|
parameter is specified as 0, or more than the length of the remaining part
|
|
of the file,
|
|
.Fn MDXFileChunk
|
|
calculates the digest from
|
|
.Fa offset
|
|
to the end of file.
|
|
The
|
|
.Fn MDXData
|
|
function calculates the digest of a chunk of data in memory, and uses
|
|
.Fn MDXEnd
|
|
to return the result.
|
|
.Pp
|
|
When using
|
|
.Fn MDXEnd ,
|
|
.Fn MDXFile ,
|
|
or
|
|
.Fn MDXData ,
|
|
the
|
|
.Fa buf
|
|
argument can be a null pointer, in which case the returned string
|
|
is allocated with
|
|
.Xr malloc 3
|
|
and subsequently must be explicitly deallocated using
|
|
.Xr free 3
|
|
after use.
|
|
If the
|
|
.Fa buf
|
|
argument is non-null it must point to at least 33 characters of buffer space.
|
|
.Sh SEE ALSO
|
|
.Xr md2 3 ,
|
|
.Xr md4 3 ,
|
|
.Xr md5 3 ,
|
|
.Xr sha 3
|
|
.Rs
|
|
.%A B. Kaliski
|
|
.%T The MD2 Message-Digest Algorithm
|
|
.%O RFC 1319
|
|
.Re
|
|
.Rs
|
|
.%A R. Rivest
|
|
.%T The MD4 Message-Digest Algorithm
|
|
.%O RFC 1186
|
|
.Re
|
|
.Rs
|
|
.%A R. Rivest
|
|
.%T The MD5 Message-Digest Algorithm
|
|
.%O RFC 1321
|
|
.Re
|
|
.Rs
|
|
.%A RSA Laboratories
|
|
.%T Frequently Asked Questions About today's Cryptography
|
|
.%O \&<http://www.rsa.com/rsalabs/faq/>
|
|
.Re
|
|
.Rs
|
|
.%A H. Dobbertin
|
|
.%T Alf Swindles Ann
|
|
.%J CryptoBytes
|
|
.%N 1(3):5
|
|
.%D 1995
|
|
.Re
|
|
.Rs
|
|
.%A MJ. B. Robshaw
|
|
.%T On Recent Results for MD2, MD4 and MD5
|
|
.%J RSA Laboratories Bulletin
|
|
.%N 4
|
|
.%D November 12, 1996
|
|
.Re
|
|
.Sh HISTORY
|
|
These functions appeared in
|
|
.Fx 2.0 .
|
|
.Sh AUTHORS
|
|
The original MDX routines were developed by
|
|
.Tn RSA
|
|
Data Security, Inc., and published in the above references.
|
|
This code is derived directly from these implementations by
|
|
.An Poul-Henning Kamp Aq phk@FreeBSD.org
|
|
.Pp
|
|
Phk ristede runen.
|
|
.Sh BUGS
|
|
No method is known to exist which finds two files having the same hash value,
|
|
nor to find a file with a specific hash value.
|
|
There is on the other hand no guarantee that such a method does not exist.
|
|
.Pp
|
|
MD2 has only been licensed for use in Privacy Enhanced Mail.
|
|
Use MD4 or MD5 if that is not what you are doing.
|