1.
Cryptography
João Paulo Barraca <jpbarraca@ua.pt>
ENEI 2014 - Aveiro

2.
Privacy
Restrict information to a limited number of entities
Privacy
State of
being free
from being
observed
Flickr, valpearl/5103209989

3.
Security
• The state of being free from danger or threat
Security
The state
of being
free from
danger or
threat
Flickr, juanktru/3503494338

4.
Cryptography
Write something in a covert way
Greek: Kryptós (Hidden),
graphein (Write)
!
Similar to Steganography
Cryptography
Flickr, delgrossodotcom/3211643440

5.
Cryptography
key = ‘qwerty’
text = ‘Meet with Alex at 13:05’
Base64( AES-128-ECB(key, text) )
U2FsdGVkX1/
Q7MhqgxAWF5YU57uZRzDfCDuJa6k0u
QW9CZvB22svyiE/WdxKXid3

6.
Cryptography
key = ‘qwerty’
text = ‘Meet with Alex at 13:05’
Base64( AES-128-ECB(key, text) )
U2FsdGVkX1/
Q7MhqgxAWF5YU57uZRzDfCDuJa6k0u
QW9CZvB22svyiE/WdxKXid3
Output seems to be
random

7.
Steganography
!
text = ‘Meet with Alex at 13:05’
method = encode Least Significant Bit (00000001)

8.
Steganography
!
text = ‘Meet with Alex at 13:05’
method = encode Least Significant Bit (00000001)
Covert Channel

9.
Steganography
!
text = ‘Meet with Alex at 13:05’
method = encode Least Significant Bit (00000001)
Output seems to be
unmodified

10.
Cryptography Uses
Increase Security
2 - Assure origin of information (Authentication)
1 - Condition access to information (Privacy)

11.
Ancient Times
• Simple ciphers
• Transposition: change symbol order
• Substitution: replace symbols
• Transmit encoded messages
• Military, Political partners, Private
conversations
Flickr, stuckincustoms/189321498

12.
Scytale
Flickr, templar-revenged/12468322164
!
Transposition Cipher
!
Used by Greeks and Spartans

13.
Caesar Cipher
!
!
E -> B
N -> K
E -> B
I -> F
Substitution Cipher

14.
Stallings, W. Cryptography and Internet Security: Principles and Practices. Upper Saddle River: Prentice, 1999.

15.
XIX, XX centuries
More complex ciphers
Using electro-
mechanical devices
Integration with
communication lines
(telegraph)
Flickr, elsie/3916831047

16.
Enigma
Transposition Cipher
Flickr, timg_vancouver/200625463

17.
Flickr, brewbooks/3317243295

18.
Lorenz
Vernan Cipher (substitution)

19.
Modern Times: > 1970
• Even more complex ciphers
!
• Based on mathematical models
• Applied by computers
• Impossible to solve by hand!
!
• Mostly use substitution algorithms

20.
Symmetric Crypto
• Single key to cipher and decipher
• Key sets state of cipher algorithm
Text
Cipher
Algorithm Cryptogram
Key
Cipher
Algorithm Text
Key
???

21.
Stream Ciphers
• Key sets cipher state
• Cipher produces random sequence
• Sequence is XORed with data

22.
Stream Ciphers
Text
Cipher
Algorithm
Key
Cipher
Algorithm
Key
???
++ Cryptogram Text
Key Stream Key Stream

23.
Stream Ciphers
• 1 byte encoded (XOR) at a time
• Very fast!
• Good for communications!
• Size of input equals size of output
• Typical Key Sizes: >128 bits

24.
Stream Ciphers
• A5 - Mobile Phone Communications
• RC4 - Wifi WEP, Internet HTTPS

25.
• O
Original Text

26.
Cryptogram seems to be random

27.
Block Ciphers
• Input processed in blocks
• Block size related to key size
!
• Output is multiple of block size
• Typical sizes: 64bits, 128bits, 192bits, 256bits

28.
Block Ciphers
• Cipher algorithm does substitutions and
permutations
• Key defines how
• Typical algorithms: AES, Blowfish, 3DES…

29.
Block Ciphers
CipherKey Decipher Key
???
Cryptogram
Cryptogram

30.
Cryptogram doesn’t seems to be random

31.
Block Ciphers
• Blocks with same content will result in same
output
• … because blocks are ciphered individually
• …. no feedback mechanism

32.
Cipher Modes
• Aditional Cipher Modes destroy patterns
• eg, Cipher-block chaining (CBC)
CipherKey
Block 1
Cryptogram
CipherKey
Cryptogram
Block 2
+ +IV

33.
Asymmetric Crypto
• Uses a pair of keys:
• Public Key: every one may have it
• Private Key: never should be disclosed
• One key can do the oposite of the other

34.
Confidentiality
CipherPublic
Key
Decipher
???
Cryptogram
Cryptogram
Private
Key

35.
Authentication
CipherPrivate
Key
Decipher
???
Cryptogram
Cryptogram
Public
Key

36.
Who uses
cryptography?
Should I (You) use?
Flickr, icedsoul/3194511482

37.
Spies
Flickr, dunechaser/2630433944

38.
Military
Flickr, lord_dane/4809995767

39.
… and every one else

40.
Cryptography
It’s a building block of
our society
Flickr, nickobec/359440072

41.
Enforces Security
• Cipher: Restricts access to Information
• Only holder of KEY can decipher cryptogram
!
• Authentication: Restricts access to Actions
• KEY asserts identity of its holder
Flickr, adulau/7712545428

42.
In other words…
• You really know with whom you are sharing
information
• Entities are Authenticated
• Mechanisms really restrict who accesses
information
• Data is private
Flickr, adulau/7712545428

43.
Wifi
• Restrict Access to authorised users
• eg, Your friends
• Make traffic confidential
• Wireless signals travel a long distance
Flickr, _miki/3425273296

44.
Wifi
• Shared key (Password) provided by user is
converted into key
• All traffic is ciphered
• Only key holders are authorised to associate
• Prevents eavesdropping and usage

45.
Wifi
• WEP: RC4 (Stream Cipher, weak)
• Uses 24bits IV (‘random’) + 104bit Key
• WPA/WPA2: AES/CCMP (Block Ciphers)
• 128bit, per packet key
• 802.1x: Extensible Authentication Protocol
(EAP)

46.
Mobile Phones
Identify user
Identify sim card (client)
Identify terminal
Make all traffic confidencial
Flickr, 26311710@N02/3235380837

47.
Mobile Phones
• SIM card is protected by PIN
• Contains algorithms for authentication
• Contains Keys shared with Service Provider
• Terminal contains identifier (IMEI)
• Traffic is ciphered

48.
Secure Sockets Layer (SSL)
• Protect traffic over communication networks
• Authenticate endpoints
• Make traffic confidential

49.
Secure Sockets Layer (SSL)
• Extensively used in the Internet
• HTTPS, IMAPS, POP3S, XMPP, etc..
• Based on Certificates and Asymmetric
Cryptography
• Established tunnel before actual data

50.
Secure Sockets Layer (SSL)
• Server has Certificated issued by Trusted CA
• Client has temporary keys or trusted certificate
• Single (Server) or Mutual authentication
• All traffic is confidential

51.
Identification
• Identify citizen / user
• Stronger method than visual ones
• Enable authentication over the Internet
• eg, web pages, emails, digital documents

52.
Identification
• Smart Card protected by PIN codes
• Certificate issued by State
• Private Key that can be used for signing
• Card is secure against tampering
• Private Key never leaves Smart Card

53.
Identification
I'm Maria
Prove It! Random_number
Sure! Sign(Random_number), CertVerify
Certificate
Verify
Signature
Request
Card to Sign
Hello Maria!

54.
Information Confidentiality
• Most systems provide
Software ciphered
storage
• FileVault, BitLocker,
TrueCrypt
• Devices also support
ciphered storage
• Self Encrypting Drives
Seagate

55.
Attacking
Cryptographic
Systems

56.
Direct Attacks
• Analyse cryptographic algorithms
• Find weaknesses in its components
• Require serious mathematical skills
!
• Frequent contests to elect the best algorithm
• ex: 3DES, AES, SHA

57.
Direct Attacks
• Brute force
• Try every possible combination
• Example: RSA 2048
• Time required: ~6.4 quadrillion years
• Universe age: 13.2 billion years
http://www.digicert.com/TimeTravel/math.htm
ECRYPT II

58.
Direct Attacks
• Brute force
• Try every possible combination
• Example: RSA 2048
• Time required: ~6.4 quadrillion years
• Universe age: 13.2 billion years
http://www.digicert.com/TimeTravel/math.htm
Considering evolution in computer capacity
RSA 2048 secure until 2030
!
Source, ECRYPT II

59.
Direct Attacks
• Brute force
• Try every possible combination
• Example: RSA 2048
• Time required: ~6.4 quadrillion years
• Universe age: 13.2 billion years
http://www.digicert.com/TimeTravel/math.htm
If aiming at a user created password,
results should be ready soon

60.
Indirect Attacks
• Obtain information indirectly
• Algorithm is not broken
• Implementation is broken
• Implementation leaks information
• User is the frequent target

61.
Human Behaviour

62.
Human Behaviour

63.
Power Leakage
Consumption
when Key bit is 0
Consumption
when Key bit is 1
Wikimedia Foundation

64.
Sound Leakage
Daniel et al

65.
Implementation Errors
• Heartbleed bug in openssl 1.0.1-1.0.1f
• Allows extracting 64Kbytes from server
memory
• Affects all systems using SSL

66.
Implementation Errors
...
if ((err = SSLHashSHA1.update(&hashCtx, &serverRandom)) != 0)
goto fail;
if ((err = SSLHashSHA1.update(&hashCtx, &signedParams)) != 0)
goto fail;
goto fail;
if ((err = SSLHashSHA1.final(&hashCtx, &hashOut)) != 0)
goto fail;
…
Apple “GOTO” bug, 2014

67.
Thanks