
diff -r 2492b771122e -r 47e06cb75837 handouts/ho05.tex
--- a/handouts/ho05.tex	Thu Nov 06 00:23:45 2014 +0000
+++ b/handouts/ho05.tex	Thu Nov 06 12:32:05 2014 +0000
@@ -534,16 +534,17 @@
 \subsubsection*{Averting Person-in-the-Middle Attacks}
 
 The idea of public-private key encryption is that one can make
-public the key $K^{pub}$ which people can use to encrypt
-messages for me. and I can use my key $K^{priv}$ to be the
-only one that can decrypt them. While this sounds all good, it
-relies that people can associate me, for example, with my
-public key. That i snot so trivial as it sounds. For example,
-if I would be the government, say Cameron, and try to find out
-who are the trouble makers in the country, I would publish an
-innocent looking webpage and say I am The Guardian newspaper
-(or alternatively The Sun for all the juicy stories), publish
-a public key on it, and then just wait for incoming messages. 
+publish the key $K^{pub}$ which people can use to encrypt
+messages for me and I can use my private key $K^{priv}$ to be
+the only one that can decrypt them. While this sounds all
+good, it relies on the ability that people can associate me
+with my public key. That is not as trivial as it sounds. For
+example, if I would be the government, say Cameron, and try to
+find out who are the trouble makers in the country, I would
+publish an innocent looking webpage and say I am The Guardian
+newspaper (or alternatively The Sun for all the juicy
+stories), publish a public key on it, and then just wait for
+incoming messages. 
 
 This problem is supposed to be solved by using certificates.
 The purpose of certification organisations is that they verify
@@ -654,13 +655,13 @@
 public key. Finally $B$ checks whether the received $M_1$
 matches with its first half, and if yes sends $A$ its
 second half $M_2$. Now $A$ and $B$ are in the possession 
-of $H_1$ and $H_2$, respectively $M_1$ and $M_2$ and can
+of $H_1$ and $H_2$, respectively $M_1$ and $M_2$, and can
 decrypt the corresponding messages.
 
 Now the big question is, why on earth does this splitting
 of messages in half and additional message exchange help
 with defending against person-in-the-middle attacks? Well,
-lets try to be such an attacker. As before we intercept
+let's try to be such an attacker. As before we intercept
 the messages where public keys are exchanged and inject
 our own.
 
@@ -725,7 +726,7 @@
 \noindent Now $E$ is in the possession of $H_1$ and $H_2$,
 which it can join together in order to obtain
 $\{A,m\}_{K^{pub}_E}$ which it can decrypt. It seems
-like from now on all is lost, but lets see: in order to
+like from now on all is lost, but let's see: in order to
 stay undetected it must send a message to $B$. It now has two
 options: one is to use the newly obtained knowledge and
 modify $A$'s message to be 
@@ -770,9 +771,9 @@
 
 With this the protocol has ended. $E$ was able to decrypt all
 messages, but what messages did $A$ and $B$ receive and from
-whom? Do you notice that they will find out that something
-strange has happened and probably not talk on this channel
-anymore? I leave you to think about it.
+whom? Do you notice that $A$ and $B$ will find out that
+something strange has happened and probably not talk on this
+channel anymore? I leave you to think about it.
 
 Recall from the beginning that a person-in-the middle
 attack can easily be mounted at the key fob and car
@@ -825,10 +826,10 @@
 that you sit in the ``middle'' of the communication of two people.
 You just have to route their traffic through a node you own.
 
-An article in The Guardien from 2013 reveals how GCHG and the NSA at a
+An article in The Guardian from 2013 reveals how GCHG and the NSA at a
 G20 Summit in 2009 sniffed emails from Internet cafes, monitored phone
 calls from delegates and attempted to listen on phone calls which were made
-by Russions and which were transmitted via satelite links:
+by Russians and which were transmitted via satellite links:
 
 \begin{center}
 \url{http://www.theguardian.com/uk/2013/jun/16/gchq-intercepted-communications-g20-summits}




