# HG changeset patch
# User cu
# Date 1508715394 -3600
# Node ID 490079e1615747ad45c6dd123234a09d05c4176d
# Parent  9fe160a13539aefe440e8cd7449a971586e9eb54
updated

diff -r 9fe160a13539 -r 490079e16157 handouts/ho05.pdf
Binary file handouts/ho05.pdf has changed
diff -r 9fe160a13539 -r 490079e16157 handouts/ho05.tex
--- a/handouts/ho05.tex	Wed Oct 18 22:31:20 2017 +0100
+++ b/handouts/ho05.tex	Mon Oct 23 00:36:34 2017 +0100
@@ -201,9 +201,9 @@
 \{\{msg\}_{K_1}\}_{K_2}
 \] 
 
-\noindent This protocol is called lockstep protocol.
+\noindent 
 The idea is that even if attacker Eve has the
-key $K_2$ she could decrypt the outer envelop, but
+key $K_2$, she could decrypt the outer envelop, but
 still does not get to the message, because it is still
 encrypted with the key $K_1$. Note, however,
 while an attacker cannot obtain the content of the message
@@ -416,7 +416,7 @@
 course that it requires a pre-shared secret key. That is
 something that needs to be established beforehand. Not all
 situations allow such an assumption. For example if I am a
-whistleblower (say Snowden) and want to talk to a journalist
+whistle-blower (say Snowden) and want to talk to a journalist
 (say Greenwald) then I might not have a secret pre-shared key.
 
 Another limitation is that such mutual challenge-response
@@ -467,7 +467,7 @@
 risk to be shot. So we add our own challenge $N'_A$ and
 encrypt it under the secret key $K_{AB}$ (step 3). Now $E$
 does not need to know this key in order to form the correct
-answer for the first protocol. It will just replays this
+answer for the first protocol. It will just replay this
 message back to us in the challenge mode (step 4). I happily
 accept this message---after all it is encrypted under the
 secret key $K_{AB}$ and it contains the correct challenge from
@@ -477,7 +477,7 @@
 might suspect, erroneously, that an idiot must have leaked the
 secret key. Because I followed in both cases the protocol to
 the letter, but somehow $E$, unknowingly to me with my help,
-managed to disguise as a friend. As a pilot, I would be a bit
+managed to disguise as a friend. As a fighter-pilot, I would be a bit
 peeved at that moment and would have preferred the designer of
 this challenge-response protocol had been a tad smarter. For
 one thing they violated the best practice in protocol design
@@ -807,7 +807,7 @@
 
 \noindent
 I hope you have thought about all these questions. $E$ cannot modify
-the received messages---$A$ and $B$ woudl find this out. To stay
+the received messages---$A$ and $B$ would find this out. To stay
 undetected, $E$ can only forward the messages (unmodified) and this is
 all what $A$ and $B$ need in order to establish a shared secret.  For
 example they can use the Hellman-Diffie key exchange protocol (see
@@ -886,7 +886,7 @@
 \end{center}
 
 \noindent
-With this $E$ is in the possesion of both halves from $A$. 
+With this $E$ is in the possession of both halves from $A$. 
 In order to get the reply from $B$, $E$ can send the message
 
 \begin{center}
@@ -916,7 +916,7 @@
 \noindent
 $A$ and $B$ receive expected messages and were able to verify
 their first halves. That means they do not suspect anything dodgy
-going on: $E$ has sucessfully managed a man-in-the middle attack.
+going on: $E$ has successfully managed a man-in-the middle attack.
 In case $A$ and $B$ are computers, there is not much that can 
 prevent this attack. In case they are humans, there are a few
 things they can do. For example $A$ and $B$ can craft their