1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
138 lines
3.7 KiB
Groff
138 lines
3.7 KiB
Groff
.\"
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.\" ----------------------------------------------------------------------------
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.\" "THE BEER-WARE LICENSE" (Revision 42):
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.\" <phk@login.dkuug.dk> wrote this file. As long as you retain this notice you
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.\" can do whatever you want with this stuff. If we meet some day, and you think
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.\" this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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.\" ----------------------------------------------------------------------------
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.\"
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.\" $FreeBSD$
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.\"
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.Dd October 9, 1996
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.Dt MDX 3
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.Os FreeBSD 2
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.Sh NAME
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.Nm MDXInit ,
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.Nm MDXUpdate ,
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.Nm MDXFinal ,
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.Nm MDXEnd ,
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.Nm MDXFile ,
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.Nm MDXData
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.Nd calculate the RSA Data Security, Inc., ``MDX'' message digest
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <mdX.h>
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.Ft void
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.Fn MDXInit "MDX_CTX *context"
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.Ft void
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.Fn MDXUpdate "MDX_CTX *context" "unsigned char *data" "unsigned int len"
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.Ft void
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.Fn MDXFinal "unsigned char digest[16]" "MDX_CTX *context"
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.Ft "char *"
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.Fn MDXEnd "MDX_CTX *context" "char *buf"
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.Ft "char *"
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.Fn MDXFile "char *filename" "char *buf"
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.Ft "char *"
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.Fn MDXData "unsigned char *data" "unsigned int len" "char *buf"
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.Sh DESCRIPTION
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The MDX functions calculate a 128-bit cryptographic checksum (digest)
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for any number of input bytes. A cryptographic checksum is a one-way
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hash-function, that is, you cannot find (except by exhaustive search)
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the input corresponding to a particular output. This net result is
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a ``fingerprint'' of the input-data, which doesn't disclose the actual
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input.
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.Pp
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MD2 is the slowest, MD4 is the fastest and MD5 is somewhere in the middle.
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MD2 can only be used for Privacy-Enhanced Mail.
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MD4 has been criticized for being too weak, so MD5 was developed in
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response as ``MD4 with safety-belts''. When in doubt, use MD5.
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.Pp
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The
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.Fn MDXInit ,
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.Fn MDXUpdate ,
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and
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.Fn MDXFinal
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functions are the core functions. Allocate an MDX_CTX, initialize it with
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.Fn MDXInit ,
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run over the data with
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.Fn MDXUpdate ,
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and finally extract the result using
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.Fn MDXFinal .
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.Pp
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.Fn MDXEnd
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is a wrapper for
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.Fn MDXFinal
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which converts the return value to a 33-character
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(including the terminating '\e0')
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.Tn ASCII
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string which represents the 128 bits in hexadecimal.
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.Pp
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.Fn MDXFile
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calculates the digest of a file, and uses
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.Fn MDXEnd
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to return the result.
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If the file cannot be opened, a null pointer is returned.
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.Fn MDXData
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calculates the digest of a chunk of data in memory, and uses
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.Fn MDXEnd
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to return the result.
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.Pp
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When using
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.Fn MDXEnd ,
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.Fn MDXFile ,
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or
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.Fn MDXData ,
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the
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.Ar buf
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argument can be a null pointer, in which case the returned string
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is allocated with
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.Xr malloc 3
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and subsequently must be explicitly deallocated using
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.Xr free 3
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after use.
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If the
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.Ar buf
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argument is non-null it must point to at least 33 characters of buffer space.
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.Sh SEE ALSO
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.Xr md2 3 ,
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.Xr md4 3 ,
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.Xr md5 3
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.Rs
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.%A B. Kaliski
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.%T The MD2 Message-Digest Algorithm
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.%O RFC 1319
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.Re
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.Rs
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.%A R. Rivest
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.%T The MD4 Message-Digest Algorithm
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.%O RFC 1186
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.Re
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.Rs
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.%A R. Rivest
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.%T The MD5 Message-Digest Algorithm
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.%O RFC 1321
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.Re
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.Rs
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.%A RSA Laboratories
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.%T Frequently Asked Questions About today's Cryptography
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.Re
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.Sh AUTHOR
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The original MDX routines were developed by
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.Tn RSA
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Data Security, Inc., and published in the above references.
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This code is derived directly from these implementations by Poul-Henning Kamp
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.Aq Li phk@login.dkuug.dk
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.Pp
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Phk ristede runen.
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.Sh HISTORY
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These functions appeared in
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.Fx 2.0 .
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.Sh BUGS
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No method is known to exist which finds two files having the same hash value,
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nor to find a file with a specific hash value.
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There is on the other hand no guarantee that such a method doesn't exist.
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.Pp
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MD2 has only been licensed for use in Privacy Enhanced Mail.
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Use MD4 or MD5 if that isn't what you're doing.
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.Sh COPYRIGHT
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