Network systems security by mort anvari lecture12

Countering Clever Smurf Attack  When R3 receives a message, R3 needs to determine whether message was indeed sent by R2, or was modified or replayed by an adversary between R3 and R2 

Denial-of-Service (DoS) Attacks Network Systems

Security

Mort Anvari

 These inserted, modified, and replayed

messages can go undetected until they cause severe damage to network

 The physical location of the adversary in

network may never be determined

 Example: denial-of-service attacks

Denial-of-Service (DoS)

Attacks

 Aimed to deny normal service

provided by the target computer

Ping Protocol

 Allow any computer to check whether any other computer in the Internet is up

 Any computer x can send a “ping” message to any computer y

which replies by sending back a “pong” message (thus x knows y is up)

 In ping message: src = xand dst = y

 In pong message: src = yand dst = x

ping(x, y)

Broadcast Ping Protocol

 If in ping message dst = “all”, a copy of ping is broadcast to every computer

 Each computer replies by sending back a pong, and x is

flooded with pong messages

 In ping message: src = xand dst = “all”

 In pong message: src = yand dst = x

ping(x,all)

y´

pong(y´,x)

Countering Smurf Attack

 Make each router check the src of each

received message and discard the message

Clever Smurf Attack

 An adversary inserts a ping(x, all) message between routers R2 and R3

 R3 thinks the message was forwarded by R2 and so accepts the message

R1

Countering Clever Smurf

Attack

 When R3 receives a message, R3 needs to determine whether message was indeed sent by R2, or was modified or replayed

by an adversary between R3 and R2

 If use IPSec, will need to set up SA’s

between each pair of adjacent routers: too expensive

 Our solution: use hop integrity protocol

between each pair of adjacent routers

Hop Integrity

subnetwork

 Detection of Message Modification:

from p, q can check that m was not modified after sent

 Detection of Message Replay:

from p, q can check that m was not a replay

of an old message

Adversary vs Routers

actions to disrupt communication between two routers

 Message loss

 Message modification

 Message replay

cannot be compromised by the adversary

 The routers will execute hop integrity

protocols that can detect and defeat the adversary actions

Hop Integrity Protocol

 Each pair of adjacent routers need to share a secret S, which is updated periodically by the two routers using a secret exchange protocol

 To each IP message sent between two adjacent routers, add a sequence number sq, and an integrity check d

Component of

Hop Integrity Protocols

 Three protocols between each pair

of adjacent routers

How to Exchange Secret

for computing the digest of every msg

sent to an adjacent router q

to q periodically?

to q periodically and q sends an ack to p?

layer and integrity check layer

Secret Exchange Protocol

a secret update message to p every T

hours

from q, p updates secret and sends an ack to q

seconds, q retransmits the secret

update message

Secret Exchange Protocol

S[0] old S[1] new

Recovery in

Secret Exchange Protocol

S[0] old S[1] new

if S[1] = S then S[0] :=S[1]

t seconds

t seconds

if S = S[0] S = S[1] then S :=S[1]

BpS[0], S[1]

S[1] = S  S[0]

 To detect insertion and modification

 Each sent msg from p to q is as follows

(hd | d | txt)where p computes d as

d = MD(S | hd | txt)

 On receiving a msg, q checks

if d = MD(S[0] | hd | txt) 

d = MD(S[1] | hd | txt) then q forwards msg

else q discards msg

Weak Integrity Protocol

Weak Integrity Protocol

.

(hd | d | txt) S[0]

Strong Integrity

numbers are attached to all sent msgs from p to q

 If p is reset, unbounded number of fresh messages are discarded by q

 If q is reset, it can accept unbounded

number of replayed messages

 Soft sequence numbers

 Successive sequence numbers are attached to all sent msgs from p to q:

(hd | sq | txt)

 q maintains two variables

expsequence number of next msg

fi; q updates exp, c, cmax

Soft Sequence Numbers

Soft Sequence Numbers

sq

.

 Each sent msg from p to q is as follows

(hd | sq | d | txt)where p computes d as

d = MD(S | hd | sq | txt)

 On receiving a msg, q checks

if (d = MD(S[0] | hd | sq | txt) 

d = MD(S[1] | hd | sq | txt) ) (exp  sq  c = random value cmax)then q forwards msg

else q discards msgfi; q updates exp, c, cmax

Strong Integrity Protocol

Using Soft Sequence Numbers

Hard Sequence Numbers

SAVE and FETCH

sequence number will be stored in

persistent memory

stored sequence number will be loaded from persistent memory into memory

Strong Integrity Protocol

Using Hard Sequence Numbers

 Each sent msg from p to q is as follows

(hd | sq | d | txt) where p computes d as

d = MD(S | hd | sq | txt)

 On receiving a msg, q checks

if (d = MD(S[0] | hd | sq | txt) 

d = MD(S[1] | hd | sq | txt) )  (exp  sq) then q forwards msg

else q discards msg fi; q updates exp

 p and q executes SAVE periodically

 When waking up from a reset, p (or q) executes FETCH to fetch last stored seq#, executes SAVE to store next seq#, and

continues after SAVE finishes

Other Applications of Hop Integrity

 Mobile IP

 Secure multicast

 Security of routing protocols

Mobile IP

other than its home network H

agent (HA) and forwarded to its foreign agent (FA)

Internet

home agent (HA)

Problem with Mobile IP

 Mobile computer c can send a msg thru FA

 However, this msg may be filtered out by next router q because its source address is

“strange”

Internet

home agent (HA)

foreign agent

(FA)

H F

q

m

m

Mobile IP with Hop Integrity

 With integrity check d added to msg m, q can check that m was indeed forwarded by FA

 Thus, q ignores strange source of msg m and forwards m toward its ultimate destination

Internet

home agent (HA)

foreign agent

(FA)

H F

 Multicast msgs are forwarded through a spanning tree from root to every multicast destination

 If a destination receives a multicast msg, then each

destination receives a copy of same msg with high probability

 Multicast msgs are forwarded through a spanning tree from root to every multicast destination

 If a destination receives a multicast msg, then each

destination receives a copy of same msg with high probability

 Multicast msgs are forwarded through a spanning tree from root to every multicast destination

 If a destination receives a multicast msg, then each

destination receives a copy of same msg with high probability

 Multicast msgs are forwarded through a spanning tree from root to every multicast destination

 If a destination receives a multicast msg, then each

destination receives a copy of same msg with high probability

Security Problem with

Multicast with Hop Integrity

 With hop integrity, an inserted or modified multicast message will be detected and

discarded at its first hop in the spanning tree

Routing Information Protocol

(RIP)

 Every 30 seconds, RIP process in router R’ sends its routing table in a response msg to RIP process in each adjacent R

 R updates its routing table when it receives a response

msg from any adjacent R’

RIP with Hop Integrity

 With hop integrity, the response msgs are protected against message modification, insertion, and replay

Security of Routing Protocols

protection (against message

modification, insertion, and replay) for other routing protocols

 OSPF protocols (Hello, Exchange, Flood)

mechanisms that have been proposed for some protocols

Implementation of Hop

Integrity

 Implementation of hop integrity

protocols in Linux kernel

 Add integrity check digest and soft sequence number to IP options in

IP header

 Compatible with legacy routers

 Flexibility of deployment

Related Works

 Completes hop integrity

 Not needed if hop integrity is installed

denial-of-Next Class

 Security in transport layer

 SSL and TLS

 Application of SSL/TLS in Web security