Omit outdated cryptographic claims as noted in PR 44160.

Interested readers can follow the references or read Wikipedia; this
is the wrong place to explain cryptographic hash functions and give
security advice.

usr.bin/cksum/cksum.1

@@ -1,4 +1,4 @@
-.\"	$NetBSD: cksum.1,v 1.43 2010/05/14 01:57:21 joerg Exp $
+.\"	$NetBSD: cksum.1,v 1.44 2012/06/25 02:32:12 riastradh Exp $
 .\"
 .\" Copyright (c) 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -32,7 +32,7 @@
 .\"
 .\"	@(#)cksum.1	8.2 (Berkeley) 4/28/95
 .\"
-.Dd January 2, 2009
+.Dd June 24, 2012
 .Dt CKSUM 1
 .Os
 .Sh NAME
@@ -95,38 +95,14 @@ described below.
 It is provided for compatibility only.
 .Pp
 The
-.Nm md5
-utility takes as input a message of arbitrary length and produces
-as output a 128-bit
-.Dq fingerprint
-or
-.Dq message digest
-of the input.
-It is conjectured that it is computationally infeasible
-to product two messages having the same message digest, or to produce
-any message having a given prespecified target message digest.
-The
-MD5 algorithm is intended for digital signature applications, where
-a large file must be
-.Dq compressed
-in a secure manner before being encrypted with a private (secret)
-key under a public-key encryption system such as
-.Pa RSA .
-.Pp
-The
-.Nm md2
+.Nm md2 ,
+.Nm md4 ,
+.Nm md5 ,
+.Nm sha1 ,
 and
-.Nm md4
-utilities behave in exactly the same manner as
-.Nm md5
-but use different algorithms.
-.Pp
-The
 .Nm rmd160
-and
-.Nm sha1
-utilities also produce message digests, however the output from these
-two programs is 160 bits in length, as opposed to 128.
+utilities compute cryptographic hash functions, and write to standard
+output the hexadecimal representation of the hash of their input.
 .Pp
 The options are as follows:
 .Bl -tag -width indent