--- a/handouts/ho01.tex	Wed Nov 26 10:15:43 2014 +0000
+++ b/handouts/ho01.tex	Thu Nov 27 17:52:17 2014 +0000
@@ -286,14 +286,25 @@
 problem). So encryption seems to not solve the problem we face
 with the integrity of our counter.
 
-Fortunately, \emph{hash functions} seem to be more suitable
-for our purpose. Like encryption, hash functions scramble data
-in such a way that it is easy to calculate the output of a
-hash function from the input. But it is hard (i.e.~practically
-impossible) to calculate the input from knowing the output.
-Therefore hash functions are often called \emph{one-way
-functions}\ldots you cannot go back from the output to the
-input (without some tricks, see below). There are several such
+Fortunately, \emph{cryptographic hash functions} seem to be
+more suitable for our purpose. Like encryption, hash functions
+scramble data in such a way that it is easy to calculate the
+output of a hash function from the input. But it is hard
+(i.e.~practically impossible) to calculate the input from
+knowing the output. This is often called \emph{preimage
+resistance}. Cryptographic hash functions also ensure that
+given a message and a hash, it is computationally infeasible to
+find another message with the same hash. This is called
+\emph{collusion resistance}. Because of these properties hash
+functions are often called \emph{one-way functions}\ldots you
+cannot go back from the output to the input (without some
+tricks, see below). 
+
+
+
+
+
+There are several such
 hashing function. For example SHA-1 would hash the string
 \pcode{"hello world"} to produce the hash-value