A high level view, without using maths of the development in cryptography since World War 2. Professor Piper covers the changing attitudes of governments, the significance of Public key cryptography in modern society and the potential impact on information security professionals. This was a presentation for the Institute of Information Security Professionals NW branch meeting in Manchester on 11th June 2013. The copyright is held by the author - Prof. Fred Piper

1. Manchester 2013 1
Fred Piper
Information Security Group

2. Cryptography
From Black Art
to
Popular Science
Fred Piper
Codes & Ciphers Ltd
12 Duncan Road, Richmond
Surrey, TW9 2JD
Royal Holloway, University of London
Egham Hill, Egham
Surrey TW20 0EX
f.piper@rhul.ac.uk
www.isg.rhul.ac.uk

3. Aims of Lecture
• To enjoy ourselves
• To look at some implementation issues for
cryptographic systems
• To see how cryptography has changed in the
last 40 years
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4. Industry’s Problems with Implementing
Cryptography
• No real problems with algorithms – it’s the wraparounds
• Serious concerns about some recent events – DigiNotar, RSA
• Not sure how they should be regarding possibility of quantum
computers
• Cryptography needs standards (change slowly), but we need
flexibility
• Need for early warning about necessary changes (e.g. key
lengths)
• Concerns about timeliness of hardware (cryptographers
recommend changes faster than hardware can be replaced)
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5. A Little History
• Pre-1975: Hush hush!
– Practised mainly by Governments and military
• Early 1980s: Courses start
– Customers start to know what they require
• Early 1990s: Qualifications start
– The role of security manager is no longer a
punishment
• Early 2000s: Popular science
– Everyone knows about it
• Today: Fundamental to e-commerce, e-Government
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6. Popular Does Not Mean Easy
• Golf is a popular sport
• Anyone can swing a golf club
• Occasionally a complete novice will hit a good
tee short
• Being a professional is hard work
– Training
– practice
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7. Royal Holloway: Our Most Famous Ex-Student?
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8. Manchester 2013
Why is the Profile of Encryption Growing?
• Increase in volume of communications over
insecure channels
• Increased requirement for remote access to
information
• Regulatory requirements for ‘adequate’
protection of data
• Need for electronic ‘equivalent’ to handwritten
signatures and other forms of identification
• It can be fun!
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9. Bletchley Park
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10. Some Important Changes since 1945
• Advent of software
• Advent of fast computers
• Advent of new communications media
• Advent of binary codes
• Increase in general awareness
• Many applications other than provision of
confidentiality
• Public key cryptography
• Seen as part of a wider discipline: Information
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What is Information Security?
Information Security includes the following three
aspects:
• Confidentiality
– Protecting information from unauthorised disclosure, perhaps to
a competitor or to the press
• Integrity
– Protecting information from unauthorised modification, and
ensuring that information, such as a customer list, can be relied
upon and is accurate and complete
• Availability
– Ensuring information is available when you need it
NOTE: Impersonating an authorised user is ofter a more effective form
of attack than ‘breaking’ the technology

12. Authentication
• It is important to authenticate people and
devices
• Man-in-the-Middle Attacks
• How to beat a Grand Master at chess
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13. Manchester 2013
Early Definition of a Cipher System
Cryptogram
c
Key
Encryption
Algorithm
Message
m Decryption
Algorithm
Key
Message
m
Interceptor
Key establishment channel
(secure)
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14. Confidentiality
How do you keep a secret?
• Don’t let anyone have access to the information
• Disguise it so that ‘unauthorised’ people cannot
understand it
– Shared secrets rely on trust
– Trust in people, processes, technology
• If you use cryptography to protect your
information then there will be a key to which
you must deny access
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15. Warnings
• If that key is lost and the algorithm is strong then
your data is lost ‘forever’
• If someone else gains access to that key then
they almost certainly have access to your
information
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16. Breaking an Algorithm
• Being able to determine plaintext from ciphertext
without being given key
• Exhaustive key search is always (theoretically)
possible
Well Designed (Symmetric) Algorithm
• ‘Easiest’ attack is exhaustive key search
Strong Algorithm
• Well designed with a large number of keys
Note: History is full of instances where algorithms were
assumed to be well designed but ……
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17. Breaking a Security System
• ‘Broken’ is an emotive term
• Attacks often work only in unrealistic conditions
chosen by attacker
• Always understand assumptions associated with the
term
• For algorithms:
– Ciphertext only
– Known plaintext attack
– Chosen plaintext attack
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18. The ‘Secure Channel’ Concept
AIM: To send information securely over an insecure
network
•We achieve this by building a “secure channel”
between two end points on the network
•Typically offering:
–Data origin authentication
–Data integrity
–Confidentiality
•Cryptography is an important tool
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19. Attacking Cryptographic Systems
•Passive interceptor attempts to break algorithm
•Active interceptor has more options
•Interception not necessarily the ‘best’ form of attack
– Attack protocols
– Attack key management
– Attack the hardware
– Impersonate genuine users
– Espionage
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20. Manchester 2013
Is PK Cryptography built on a ‘sound’
basis?
“Many cryptographic systems rely on the inability
of mathematicians to do mathematics”.
(Donald Davies: LMS Lecture)
Tongue in cheek?
Existence proofs do not provide solutions
Algorithms should be implementable
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21. Are Today’s Algorithms ‘Future Proof’?
• Symmetric algorithms
–if well designed then key searches are ‘best’ attacks
–Main concern is advances in technology
–Moore’s Law
• Asymmetric algorithm
–Always concerned about mathematical advances
–Quantum computing
• Hash functions
–Confidence shaken
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22. A Never Ending Debate
• What gives us confidence in an algorithm?
–Standards?
–Ask the opinions of experts?
• Early debate
–Publicly known or proprietary algorithms?
–Less of an issue now than in the 1980s
WARNING
The fact that an algorithm is published and unbroken
says nothing about its strength
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23. Kerchoff’s Principle
• The security of a cryptographic system should not depend on
keeping the encryption algorithm secret
It does not say
• The encryption algorithm should be made public
However
• Anyone assessing the security of a cryptographic system needs
to have confidence that the algorithm is strong
So:
• Financial institutions should use public algorithms where
appropriate
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24. It is NOT just about Algorithms
Early 1980s:
• Thorn EMI conference
“Security is People”
Early 1990s:
• Ross Anderson’s paper
“Why crypto systems fail”
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25. A Fact of Life !
• In theory there is no difference between
theory and practice. In practice there is.
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26. RSA: The Theory
• The published modulus is the product of 2 secret
primes
• Knowledge of the secret primes makes it easy to
find the private key
• In general, determining the private key appears
to require knowledge of the primes
• Factorisation is difficult
• So, for large moduli, RSA is secure
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27. Attacks on RSA
The theory assumes that the attacker will need to
factor n using a mathematical factorisation
algorithm
In practice this may not be so
EARLY ATTACKS
Attack prime generator rather than try to factor n
mathematically
(1) Exhaustive prime search
(2) Exploit bias in generation process
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28. Progress?
• So have we learnt from these early mistakes?
In theory: YES
In practice: NO
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29. ‘Shared’ Primes
• Factoring RSA moduli is very difficult
• Finding g.c.d. of two RSA moduli is easy
• Factoring two RSA moduli which share a prime
factor is easy
• Recent research showed that, for a sample 6.6
million RSA keys, over 4% either have a
common modulus or gave moduli sharing a
common prime factor
• Suspect prime generators?
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30. “Ron was wrong, Whit is right”
“When exploited it could affect the expectation that
the public key infrastructure is intended to achieve”
(Arjen K Lenstra, James P Hughes et al)
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31. Cryptographic Systems
• The use of strong algorithms prevents attackers
from calculating or guessing keys
• Keys need to be stored and/or distributed
throughout the system
• Keys need protection
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32. Protecting Keys (Storage or Distribution)
• Physical security
– Tamper Resistant Security Module (TRSM)
– Tokens (Smart Cards)
• Components
– Secret Sharing Scheme
• Key hierarchies
– Keys encrypted using other keys
– Lower level keys derived from higher level ones
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33. Side Channel Attacks (1)
To find a cryptographic key
• Exhaustive key search attacks try to find the
secret key by random trial and error
• Side channel attacks try to use additional
information drawn from the physical
implementation of the cryptographic algorithm at
hand so as to be substantially better than trial
and error
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34. Side Channel Attacks (2)
• Changed the way cryptographers think about
security
– Properties of digital circuits are far more important for
security than was previously believed
• Many previous design approaches recognised as inadequate
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35. Some Recent ‘Changes’
• More attacks concentrate on the implementation of
the algorithm and the accompanying protocols
• Some exploit error messages
• Academic research is becoming less ‘blue skies’ and
focussing on real systems/problems
• Theory and practice are getting closer to each other
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36. Error Messages
ATM transaction
• Incorrect PIN
• Insufficient funds in account
• Exceeded daily limit
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37. Disclaimer: Cryptography ≠ Security
• Crypto is only a tiny piece of the security puzzle
– but an important one
• Most systems break elsewhere
– incorrect requirements or specifications
– implementation errors
– application level
– social engineering
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38. Security Breaches
Many Reasons:
• Badly designed systems
• Inappropriate policies
• Human error
• Clever, innovative (technical) attacks
• Misplaced trust (e.g. In employees or trusted
third party)
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39. Public Key Infrastructures
• Certification Authorities
• Sign certificates to bind user’s ID to their public
key
• Hierarchy of CAs
• Root CA at top of hierarchy
NOTE: If root CA’s private key is compromised
then the entire PKI is affected
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40. DigiNotar
• Netherlands based CA
• Host many other CAs
– SSL certificates
– Qualified certificates
– Government accredited
• Hackers gained unauthorised access to their CA servers
• Issued series of rogue certificates
SERIOUS BREACH: DigiNotar root certificate was trusted
by most widely used web browsers and email clients
Hacker set up spoof websites (e.g. Googlemail)
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41. Problem
• Who, or what, can we trust?
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42. Protocol Security (1)
In recent work analysing Internet protocols:
• A design flaw in SSH leading to a plaintext recovery
attack against OpenSSH
– Recovering 32 bits of plaintext with probability 2-14
• Plaintext recovery attacks against all MAC-then-
encrypt configurations of IPsec
– Recovering all protected IP traffic
• A (minor) flaw in SSL/TLS leading to a distinguishing
attack which breaks the design goals of the protocol
– Can tell whether ‘yes’ or ‘no’ is encrypted in the channel!
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43. Protocol Security (2)
• In all cases the cryptographic algorithms are secure
but the protocols are insecure
• The attacks illustrate the gap between theory and
practice in cryptography and protocol design
• More details at www.isg.rhul.ac.uk/~kp
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44. Some Things Never Change
• The widespread use of encryption for confidentiality
has always been a cause of concern for Governments
• Simplified version of Government’s position
– They are happy to support the use of strong encryption for
‘good’ purposes
– Unhappy about the use of strong encryption for ‘bad’
purposes
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45. Manchester 2013 45
Saints or Sinners ?
Receiver
Interceptor
Sender
Who are the ‘good’ guys ?

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Law Enforcement’s Dilemmas
• Do not want to intrude into people’s private
lives
• Do not want to hinder e-commerce
• Want to have their own secure communications
• Occasionally use interception to obtain
information
• Occasionally need to read confiscated,
encrypted information

47. Loss of Control of Encryption
•Academic papers
–Attacks on DES
–New algorithms
•Text books
•Need for international systems
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48. Newton Minow, Speech to the Association of
American Law Schools, 1985
•After 35 years, I have finished a comprehensive study of
European comparative law
•In Germany, under the law, everything is prohibited, except
that which is permitted
•In France, under the law, everything is permitted, except that
which is prohibited
•In the Soviet Union, under the law, everything is prohibited,
including that which is permitted
•And in Italy, under the law, everything is permitted, especially
that which is prohibited
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49. Manchester 2013
Future Developments ?
• Steganography
– You hide information rather than distort it
– Harder to detect?
• Quantum
– Quantum key establishment
– Quantum cryptography
– Quantum computing
• Provable security
– Academic ‘dream’ or reality?
• Default encryption
– Who looks after keys? (liability issues)
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