Internet Security Revised

Front 1

STEGANOGRAPHY?

Back 1

The practice of communicating secret data
that has been concealed in an innocuous
cover-medium

Front 2

Encryption aims

Back 2

protect data by making it
unintelligible

Front 3

Steganography aims

Back 3

protect data by making
it undetectable

Front 4

Steganography by cover selection

Back 4

Sender selects a cover from a large set of available covers so
that the required message is communicated (e.g. Book titles,
newspaper headlines).

Front 5

Steganography by cover synthesis

Back 5

Sender creates the cover that communicates the desired
message (e.g. mimic functions, crafted photographs)

Front 6

Steganography by cover modification

Back 6

Sender modifies an existing cover in order to convey the
required message (e.g. modify LSBs in images)

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Secret

Back 7

E.g. image, document, audio, video file

Front 8

Cover-medium

Back 8

E.g. File, Data Packet, file slack,
volume slack etc

Front 9

Carrier-medium

Back 9

i.e. Cover-medium + Secret =
Carrier-medium

Front 10

Stego-key

Back 10

Method or key required to access the
Secret from the carrier-medium (e.g. instructions, key,
password)

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Steganalysis

Back 11

Study, detection and recovery of carrier medium
payloads (i.e. secrets)

Front 12

Secrecy

Back 12

Considers the effectiveness of concealment.
For example:
– What is the probability of the secret data being
detected by casual observation?

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Capacity

Back 13

Considers the limitations of storage space for
Secret data within a cover-medium.
– What happens to the cover-medium if a capacity
threshold is exceeded.

Front 14

Robustness

Back 14

Considers the limitations, thresholds and
vulnerabilities of a carrier-medium. For
example:
– Does secret data survive when the carrier-medium
is converted, cropped or scaled?

Front 15

Steganographic Techniques

Back 15

• Substitution
• Transform domain
• Spread spectrum
• Statistical
• Cover generation
• Distortion

Front 16

LSB Embedding

Back 16

A method of steganography that embeds the
binary digits of secret data, into the least
significant bit positions of cover-medium
bytes.

Front 17

LSB Embedding
BENEFITS

Back 17

Exploits deficiencies in HVS
• Easy implementation
• Good capacity
• Good secrecy for general use (Cannot be
casually browsed when used with 24 bit images)

Front 18

LSB Embedding
LIMITATIONS

Back 18

Robustness performance is poor (although
alternate LSB methods have improved this)
• Can easily be detected by Steganalysis

Front 19

Secret Sharing Overview

Back 19

Terminology: given some secret s, a dealer will divide it into shares amongst n shareholders/players

Front 20

(t,n)-threshold scheme

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–Individual shares do not reveal s
–If at least users combine their shares, they can reconstruct s

If t=n: Secret Splitting, otherwise: Secret Sharing

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Shamir’s Secret Sharing Scheme

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Idea: a polynomial f of degree t-1 is uniquely determined by t different points
•We share n such distinct points (xi, f(xi)) amongst players
The secret will be f(0)

Front 22

Lagrange Interpolation

Back 22

Goal: given (x1, y1), ..., (xt, yt), explicitly construct polynomial f of degree t-1, satisfying f(xi) = yi for all i

Front 23

Dealer-Free (Distributed/Random) Secret Sharing (RSS)

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Goal: create and distribute shares without the need for centralised dealer
Ideal in peer-to-peer scenario.
Principle: each player Pi creates random value and distributes its shares to all other players

Front 24

Proactive Secret Sharing (PSS)

Back 24

Goal: prevent leakage of information in long-term secret sharing
Important application: key distribution in (wireless) sensor networks, MANETs
Classic scheme: Herzberg

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Herzberg’s Scheme

Back 25

Each player Pi creates a random polynomial with constant term 0

Robust and secret in the presence of passive adversaries

Front 26

Dynamic Secret Sharing (DSS)

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Goal: adapt to dynamic environment
–Change of number of players
–Change threshold value t

Front 27

Secret Sharing Applications

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•Cloud computing
•Virtual private social networks
•Peer-to-peer networking,
MANET (Mobile Ad-hoc Network)

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Ramp Secret Sharing Schemes

Back 28

current active research

This would allow for a larger secret (shorter shares), useful in applications

Front 29

Anonymity
Security Goals
•Privacy:

Back 29

protect individuals against harm caused by leakage of their (personal) information

Front 30

Anonymity
Impact of Privacy Loss without Identification

Back 30

Damage arises due to data aggregation and the potential of linking together user actions

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Anonymity
Security Goals
•Privacy:

Back 31

protect individuals against harm caused by leakage of their (personal) information

Front 32

Anonymity Goals
•Sender anonymity:

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Remove identifying information from user requests
–Is a difficult task, whether or not servers require authentication

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Receiver anonymity:

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–Impossibility of identifying the recipient of a message

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Unlinkability = Sender and Receiver Anonymity:

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–Ensure that attacker is unable to trace the server(s) a given user is talking to
–Cannot distinguish between single user running multiple sessions with single server OR multiple users, each running a single session

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Anonymous Routing

Back 35

mechanism for establishing unlinkability

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Anonymity
Mixed Nets

Back 36

•First method published for anonymous routing
•Idea: network packets are sent through a special service (“mix”)
•This permute the output order of packets
•Encryption prevents tracing back the packets

Front 37

Onion Routing

Back 37

Popular technique for implementing anonymous routing
Routing path is unpredictable
•Encryption works in layers
•To some extent, resistant to compromise

Front 38

Crowds

Back 38

achieve anonymity by blending in with a crowd
all users form a crowd
send message to random crowd member
randomly forwards to another member, or the server

Front 39

Anonymous Authentication Protocols
Secure authentication

Back 39

no unauthorised user should get access by the server, except with a very small probability

Front 40

Anonymous Authentication Protocols
Anonymity:

Back 40

the server should not know which of the user it is interacting with

Front 41

Verifiable Anonymity

Back 41

if a malicious server can reveal user identity, this will always be detected by the user

Front 42

Ring Signatures

Back 42

–Guaranteed that signer belongs to a specific set of users
–However, impossible to detect which particular user signed

Front 43

Anonymous Authentication Using Ring Signatures

Back 43

1.Server sends a random challenge w to user
2.User then returns a ring signature on w
3.Server grants access if the signature is valid

Front 44

Confidentiality:

Back 44

to prevent unauthorised
disclosure of the information

Front 45

Integrity:

Back 45

to prevent unauthorised modification of
the information

Front 46

Availability:

Back 46

to guarantee access to information

Front 47

Authentication:

Back 47

to prove the claimed identity can
be Data or Entity authentication

Front 48

Non repudiation

Back 48

to prevent false denial of
performed actions

Front 49

Authorisation:

Back 49

What Alice can do”

Front 50

• Auditing:

Back 50

to securely record evidence of
performed actions

Front 51

Attack-tolerance

Back 51

ability to provide some degree
of service after failures or attacks

Front 52

Disaster Recovery

Back 52

ability to recover a safe state

Front 53

Types of attack
• Passive

Back 53

the attacker can only read any information
– Tempest (signal intelligence)
– Packet Sniffing

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Types of attack
• Active:

Back 54

the attacker can read, modify,
generate, destroy any information

Front 55

Virtual Private Social Networks

Back 55

A VPSN, in analogy with VPN, leverages an already existing host social network.
Nodes of a VPSN are users that share information (profile) confidential with regard to other users not part of the VPSN.

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VSPN
OSN

Back 56

Much of this data is shared via Online Social Networks (OSNs) : Facebook, LinkedIn, Twitter, and Google+.

Host vast quantities of user generated content (UGC)

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VSPN
Dichotomy of Security Goals – OSN Host

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Mitigate risks of false account registrations, identity masquerading, account compromising (e.g. hacking), and threats from malware.

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VSPN
Dichotomy of Security Goals - Users

Back 58

Ideally, users want to use trusted OSNs that implement the security goals of confidentiality, integrity, and availability to UGC.

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VSPN
UGC Data Threats
Data Exploitation

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An OSN host may impose the right to use UGC for commercial or marketing purposes, without the need to consult, or compensate the user

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VSPN
UGC Data Threats
Data Censorship

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An OSN host may impose the right to modify or remove UGC for reasons of censorship or violation of terms and conditions.

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VSPN
UGC Data Threats
Data Sanitisation

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OSN hosts may sanitise user data prior to publication, in order to protect themselves and other users from malware.

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VPSN Characteristics

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hidden to users that are not part of it, as well as the OSN provider.
VPSN inherits security mechanisms from the OSN.
User profile information can be hidden from any non-intended audience

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VPSN Confidentiality

Back 63

Our approach is based on combining two fundamental cryptographic techniques:
- information distribution (secret sharing)
- information hiding (steganography).

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Mobile Ad-hoc Networks (MANETs)

Back 64

•Peer-to-peer, decentralised network architecture
•Nodes are self-organising and (highly) mobile
•They can send, receive or route data
•No fixed infrastructure
•Communication uses wireless links

Front 65

MANET Routing Protocols

Back 65

–Proactive (table-driven)
–Reactive (On-Demand)
–Hybrid
–Flow-oriented –Hierarchical
–Power-aware –Multicast

Front 66

Cryptographic Tools

Back 66

•Information Protection (Encryption/Decryption)
•Information Fingerprinting (Hash Functions)
•Information Distribution (Secret Sharing)
•Information Hiding (Steganography)

Front 67

Key exchange and management protocols

Back 67

SSL,
TLS,
HTTPS,
IPSec

Front 68

Secret Sharing
• A (t, n) perfect threshold scheme

Back 68

–The secret s can be divided into n parts (shares)
–Less than t shares to not reveal any information about s
–Equal to or more than t shares allow reconstructing s

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CIA

Back 69

•Confidentiality
•Integrity
–Data Integrity, Origin Integrity (Authentication)
–Non-Repudiation
•Availability

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Aspects of MANET Security

Back 70

•Secure Routing
•(Specific) Attack Prevention
•Intrusion Detection
•Key Management

Front 71

Aspects of MANET Security
Secure Routing

Back 71

MANETs do not have any pre-deployed infrastructure
•Nodes cooperatively form the network by agreeing to certain routing messages
•Thus, intermediate nodes must route the packets

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Specification-based Intrusion Detection

Back 72

Hand-made model of states and transitions. Detect:
–A node moves to an illegal state
–A node makes an illegal transition (input missing)
–A node transitions without proper output
–Messages sent don’t follow expected model

Front 73

Statistical-based IDS

Back 73

Can find attacks where state is not violated
–Flooding
–Dropping
–Partitioning

Front 74

MANET - Joining the Network
–A new node can join the network by securely contacting t member nodes and receiving all required information

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•Its share of the network-wide private key
•Its own private key
•The network-wide public key
•Capability to compute public keys
•Capability to compute shared symmetric keys

Front 75

MANET
Saxena Approach

Back 75

–A verifiable secret sharing scheme is used in order to distribute the security parameters
–Each node has a share of the network-wide private key