1

• He, who wants to defend everything, defends
  nothing.
• --- Frederick, the Great

2
Security planning (contd)

• Components of security planning
•  Step 1 assessing the threat,
•  Step 2 writing a security policy a statement
  of what is allowed and what is not allowed
  assigning security responsibilities.
• Step 3 Choosing
• the mechanism,
• tools and
• methodologies
• to implement the policy

3
Focus of a PlanReference Thomas
Calabrese,Information Security Intelligence,
Thomson Delmar learning, 2004, pp 4

• Scope restricting the scope as much as possible
• reduce size of target
• disable unneeded services
• Prioritization and Continuous vigilance by
  monitoring and analysis
• Access Control limit access of attacker to
  target systems
• Multi-layer security security in depth
• hardening the OS and applications
• Use technologies, which cannot be hacked easily

4
Names of Security Technologies

• Confidentiality encrypting sensitive data
• Integrity (no tampering of data) Hashing,
  Digital Signatures
• Authentication (not an impostor) Digital
  certificates
• Non-repudiation Trusted Digital 3rd party
  signatures
• The basis of the above technologies
• 
  CRYPTOGRAPHY.

5
Authentication

• Privacy is the best-known benefit of
  cryptography Cryptography also provides
  authenticity, which enables communicators to be
  sure of the identities of the people with whom
  they are communicating. In a business
  transaction, authentication verifies that the
  person acting in one instance is the same person
  who acted in another -- that the person who is
  writing a check, for example, is the same person
  who opened the account and put the money in it.
  - Whitfield Diffie and Susan Landau, Privacy on
  the Line The Politics of Wiretapping and
  Encryption, MIT Press, May 2007

6

• Using encryption on the Internet is the
  equivalent of using an armored car to deliver
  credit card information from someone living in a
  cardboard box to someone living on a park bench.
• --- Professor Eugene Spafford
• Purdue
  University

7
CRYPTOGRAPHY

• Cryptography (from two words in Greek) means
  secret writing.
• CRYPTOGRAPHY used to process data (cleartext)
  into unintelligible form (ciphertext),
• reversibly/irreversibly
• without data loss
• usually one-to-one in size /compression
• Encryption vs Decryption
• Cryptoanalysis obtaining cleartext from
  ciphertext through breaking of a cryptographic
  code

8
Cryptography

• Services, provided by cryptographic tools
• Encryption or Enciphering

Encryption Algorithm
Ciphertext
Plaintext
Key
9
Decryption

• Decryption or Deciphering

Decryption Algorithm
Plaintext
Ciphertext
Key
10
Why encrypt?

• A few valid reasons for (reversibly) encrypting
  data are
• To prevent casual browsers from viewing sensitive
  data files
• To prevent accidental disclosure of sensitive
  data
• To prevent privileged users (e.g., system
  administrators) from viewing private data files
• To complicate matters for intruders who attempt
  to search through a system's files

11
Kerckhoffs principle

• The security of an encryption scheme should
  depend upon only the secrecy of the key, and NOT
  on the secrecy of the algorithm.

12
Classification

• Two types of Encryption Algorithms
• Reversible
• Irreversible
• Two types of Keys
• Symmetric
• Asymmetric

13
Types of Cryptographic Algorithms

• Reversible with Symmetric key
• Secret Key
• Example DES, AES (Rijndael)
• Reversible with Asymmetric key
• Public Key
• Example RSA
• Irreversible without any key
• Message Digest (Hash or cryptographic checksum)
  Example SHA 256
• Irreversible with a symmetric key
• Message Authentication Codes

14
Reversible Encryption

• Reversible ENCRYPTION
• cleartext ENCRYPTION DEVICE
• 
  encryption key
• cleartext
• can be used only when the same type of encryption
  software/equipment is available at both the ends

ciphertext
Decryption key
Decryption Device
15
Cryptanalysis continued

• Cryptanalysis It tries to locate the structures
  and patterns of the plaintext in the ciphertext.
• None of the cryptological methods can completely
• eliminate the patterns and structures of the
  plaintext in the ciphertext.
• Polyalphabetic cipher where the substitution
• differs from character to character in response
• to a key, which is
• as long as the message, and which is,
• truly random
• can eliminate such patterns. But the key?

16

• CRYPTANALYSIS
• Consider the case of
• Reversible Symmetric Key encryption.

17
Cryptanalysis Methods
Finding the Key

• Assumption The hacker always knows the
  ciphertext and the encryption algorithm.
• More is the information available to a hacker
• ? Easier is the analysis for finding the Key
• TYPES OF ATTACKS The type is dependent on the
  amount of INFORMATION available to a Hacker
• 1.ciphertext only Analysis for key Most
  difficult
• 2.Known plaintext-ciphertext pairs
• 3.Chosen plaintext-ciphertext pairs
• 4.Chosen ciphertext-plaintext pairs
• 5.Chosen text (both 3 and 4) Analysis for key
  Easiest

18
Two Definitions

• UNCONDITIONALLY SECURE An encryption algorithm
  for which no amount of ciphertext can make it
  possible for one to determine uniquely the
  corresponding plaintext.
• There is no such algorithm available.
• COMPUTATIONALLY SECURE An encryption algorithm
  is said to be computationally secure if
• The cost of breaking the cipher is more than the
  intrinsic value of the information, or,
• the time required to break the cipher is more
  than the time over which the information is
  required to be confidential.

19
Exhaustive Key Search

• Key Size No. of Average
  Time
• Possible keys at 1
  decryption
• 
  per
• 
  microsecond
• 32 232 4.3x109 231
  35.8m
• 56 256 7.2x1016
  1142 y
• 128 2128 3.4 x1038
  5.4x1024 y
• 26P 26!4x1026 4x1026 6.4x1012y

20
Large numbers and computational security --
as worked out by Dr
Lawrie Brown

• It can be shown from energy consumption
  considerations that the maximum number of
  possible elementary operations in 1000 years is
  about
• 3 x 1048.
• Similarly if 10 atoms are needed to store a bit
  of information, the greatest possible number of
  bits storable in a volume of say the moon is
  1045.
• If for deciphering a cipher requires more
  operations than 3 x 1048, or needs more storage
  than 1045, it is pretty reasonable to say it is
  computationally secure.
• Reference Notes of Dr Lawrie Brown, Australian
  Defence Force
• Academy available at http//www.williamstallings.c
  om/Crypto3e.html

21
Some Large Numbers

• DES 56 bits 7.2x1016 keys
• Time to next ice age 14,000 yrs
• Age of planet 109 yrs
• Age of universe 1010 yrs
• Time until sun goes nova 1014 yrs
• Number of atoms in universe 1077
• DES is a symmetric key standard for encryption.
• Ref (for cryptography) Professor Schulzrinne,
  Columbia Univ

22
Exhaustive Key Search (continued)

• A calculation in 1995 showed that
• 56-bit key broken in 1 week with 120,000
  processors
• (6.7M)
• 56-bit key broken in 1 month with 28,000
  processors (1.6M)
• 64-bit key broken in 1 week with 3.1x 107
  processors (1.7B)
• 128-bit key broken in 1week with 5.6x 1026
  processors

23
Brute Force Cryptoanalysis

• 1999 56-bit key broken in 22.5 h with 1,800
  chips (250,000) (245 109 keys/s, or 4.08
  microsecond for one key -- see eff.org) helped
  by distributed.net
• 1998 56-bit key broken, on dedicated h/w, in a
  few days
• 1997 56-bit key broken, by using a large number
  of machines in parallel on the Internet, in a few
  months

24
Birthday paradox

• A result from probability theory Consider an
  element that has an equal probability of assuming
  any one of the N values. The probability of a
  collision is more than 50 after choosing 1.2vN
  values.

Function
Random input
One of k equally likely values
The same output can be expected after 1.2k1/2
inputs. Thus in a group of 23, two or more
persons are likely to share the same birthday.
(Put k 365) Birthday attacks are used to find
collisions of Hash functions
25
Birthday Bound

• A 64 bit key has 264 18x1018 different key
  values.
• A Key is selected at random.
• So after seeing 1.2x 232 5.16x109 transactions,
  a hacker can expect the same key to be used.
• For an n-bit case, 2n/2 is called the Birthday
  Bound

26
Example of a Birthday Attack
Replacing part of the message attack

• Assume
• A 64 bit key
• The first statement in a message is always the
  same.
• A hacker
• listens to and stores all encrypted messages.
• When the FIRST encrypted sentence turns out to be
  the same, he replaces the rest of the new message
  by the old message, that he has in his memory.
• By Birthday Paradox, this is likely to happen
  after 232 transactions.

27
Example of a Meet in the Middle attack

• Generate 232 keys.
• Store encrypted messages of the first sentence.
• Compare the first sentence of every encrypted
  message on the net with each of the stored
  messages.
• On getting a match, the Hacker knows the key. So
  he can now replace the remaining message by
  whatever he wants.

28

• Message Digests/ Checksum
• Used for confirming Integrity of data
• CRC not sufficient
• Cyclic Redundancy Check

29
Irreversible Encryption
Fingerprinting Data

• Hash Functions

Encryption Algorithm
Hash
Plaintext
Collisions in the output?
30
Cryptographic Hash Functions (H)

• H A transformation
• m variable size input
• h hash value a fixed size string,
• also known as message digest or fingerprint or
  compression function.

H(m)
m
h
31
Message Digest

Variable Length Message
Fixed Length Digest
Hashing Algorithm
32
Uses of Hash Functions

• Integrity check
• for getting a document time- stamped without
  revealing its contents to the time stamp service
• Authentication through Digital Signatures
• For generation of pseudo-random numbers to
  generate several keys from a single shared secret
• Typical output of a Hash 128 to 512 bits

33
A Cryptographic Hash function

• Properties of Cryptographic Hash functions
• One-way functions
• Hard to invert Computationally infeasible
  to find some input m such that H(m) h.
• Collision-resistant a very large number of
  collisions exist. But these cannot be found.
• Should be a random mapping from all possible
  input values to the set of possible output values
  

34
Message Digest

• Consider an algorithm that generates outputs
  which are randomly distributed.
• Let the MD (output) be of n bits
• 2n No of possible outputs.
• Since these are randomly distributed, the
  probability is that after 1.2 (2n )1/2 digests
  are computed, we may find the same value.
• ( Remember Birthday Paradox)
• Thus for n 128, it would be (1.2)264 .

35
Definitions

• WEAKLY COLLISION FREE HASH FUNCTION
• Given a message m1.
• It is computationally infeasible to find m2
  
• such that
• m1 is not equal to m2, and,
• H(m1) H(m2).
• STRONGLY COLLISION FREE HASH FUNCTION
• No message is given.
• It is computationally infeasible to find any two
  messages m1 and m2 such that
• H(m1) H(m2).
  

36
Hash Functions Collision-free Example

• Example Consider a Hash of 128 bits.
• Weak The probability of finding a message m2
  corresponding to a given hash value H(m1) is
• 2-128.
• StrongThe probability of finding two messages
  with the same hash value (with no constraint on
  any of the two messages) is 2-64.

37
Properties of Cryptographic Hash functions
(continued)

• H(m) is easy to compute.
• The input can be of any length.
• The output has a fixed length.
• Notes 1 Consider a transformation of a sequence
  of length n1 to a sequence of length n2, where n1
  gt n2.
• In such a case, there must exist multiple input
  sequences that map to the same fixed-length hash
  value.

38
Notes on hash functions (continued)

• 1. In the definitions of hash functions, it is
  only
• required that to find x should be
  computationally infeasible, even though we know
  that x exists.
• 2. Computationally Infeasible (CI) means that the
  time complexity of the algorithm should grow
  faster than any polynomial.
• So CI means that it may take an extremely long
  time to compute x on even the fastest machine of
  the day.

39
Popular Hash Functions

• Iterative functions
• Split the message to equal sized blocks m1, m2,
  mk (Use padding for the last block.)
• Hi h(Hi-1, mi), with H0 as a fixed value
• MD2 , MD4 and MD5 developed by Rivest.
• MD2 (1989 ) Optimized for 8 bit machine
• MD4 (1990) , MD5 (1991) Optimized for 32-bit
  machines .
• MD2, MD4 and MD5 produce a 128-bit hash value.
• 2004 Muller showed that MD2 is vulnerable to
  PRE-IMAGE attack ( Attempt to find a message,
  that has a specific hash value) So not a one-way
  function

40
Popular Hash Function MD5

• MD4
• Den Boer and Bosselaers ( in a paper in 1991)
  discovered weaknesses.
• was cracked by Dobbertin. He devised a method to
  generate collisions in MD4.
• MD5 (Ref RFC 1321) was supposed to be more
  secure. probability of MD5 collision
  1/3x1038
• 1994 A non-fatal flaw discovered.
• SHA1 (Secure Hash Algorithm) Produces a 160
  bit hash value from a message of less than 264
  bits

41
Popular Hash Function SHA 1

• SHA 1 designed by NSA and standardized by NIST
  as a part of the Capstone project. (based on MD5
  and 2 to 3 times slower than MD5) (Ref RFC
  3174 and FIPS 180-1)
• Aug 2004 reported generating collisions in MD4
  using "hand calculation", and in the family of
  MD4/MD5/SHA/RIPEMD. So its usage is now not
  recommended.
• Reference Xiaoyun Wang and Dengguo Feng and
  Xuejia Lai and Hongbo Yu, Collisions for Hash
  Functions MD4, MD5, HAVAL-128 and RIPEMD,
  Cryptology ePrint Archive Report 2004/199,
  http//eprint.iacr.org/2004/199.pdf

42
Popular Hash Functions To be used today

• SHA 256, SHA 384 and SHA 512 (Ref FIPS 180-2)
• designed for use with AES with 128, 196 and 256
  bits. Slower than SHA1 may take nearly as much
  time as encryption by AES.
• SHA384 uses SHA 512 method and discards the
  remaining bits. So though it takes the same time
  as SHA 512, it is less secure.
• Others Snerfu generates 128 bit or 256 bit
  hash
• Haval produces 128, 160, 192, 224 or 256 bit
  hash.

43

• Reversible Symmetric-Key Encryption
• Used for confidentiality of data

44
Secret Key/ Symmetric Cryptography

• Also called Private/Secret key Encryption
• Simpler and faster (than asymmetric)

45
Symmetric Key Encryption

• Sender-end

Message by sender
Encrypted Message
Pr-key
Internet
Message at receiver
Pr-key
Encrypted Message
Receiver-end
46

• Public-key cryptography was not only "the most
  revolutionary new concept in the field since. .
  .the Renaissance but it was generated totally
  outside of the government's domain -- by a
  privacy fanatic, no less! -- David
  Kahn
• quoted by Steven Levy in Crypto
  Rebels,
• Wired News,
  May/June 1993

47

• Reversible Asymmetric-Key Encryption
• Used for digital signatures

48
Public Key/ Asymmetric Cryptography

• invented in 1976 by Whitfield Diffie and Martin
  Hellman
• two keys private (d), public (e)
• Both are mathematically related.
• REQUIREMENTS Computationally infeasible
• to derive one key from the other
• to find out the private key from a chosen
  plaintext attack
• much slower (about 1000 times) than secret key
  cryptography
• Vice president and Sun fellow chief security
  officer, Sun Microsystems Inc.

49
public-key cryptography (continued)

• public-key cryptography system requires
• a trusted system for distributing public keys
• RSA (Rivest, Shamir and Adelman) Algorithm is
  well known for the public key system.
• APPLICATIONS
• a digital signature system to authenticate
  that a message is really from whom it purports to
  be from
• Pretty Good Privacy system, an e-mail system,
  uses the public key system for security.

50
History again Who was
Diffie?

• Mid-sixties Whitfield Diffie son of a historian
  became a member of hackers Community at MIT
  passionate about privacy
• The user's privacy depended on the degree to
  which the administrators were willing to protect
  the password file. You may have protected files,
  but if a subpoena was served to the system
  manager, it wouldn't do you any good," Diffie
  notes with withering accuracy. "The
  administrators would sell you out, because they'd
  have no interest in going to jail."

51
Who was Diffie? 2

• 1965 Diffie got wrong information that National
  security Agency was encrypting phone
  conversations in their own building. Diffie
  started thinking about the problem.
• 1967 The Codebreakers by David Kahn.
• The book a history of cryptography,
  focussing on US Military work of 20th century
• Diffie became enthralled by the book.
• His interest in complex mathematical algorithms
  to help protect privacy

52
What did Diffie do?

• Not much of published literature on cryptography.
  
• So Diffie, with wife Mary, started touring
  Universities in USA to talk to any one,
  interested in cryptography.
• Sept 74 Diffie got a 30 minute appointment with
  Prof Hellman at Stanford
• Hellman took Diffie as his doctoral student and
  made him responsible for weekly seminars

53
Others contribute

• Ralph Merkle, another doctoral student of
  Hellman developed Knapsack, a public key
  system. But Adi Shamir soon showed that it could
  be broken.
• Peter Blattman, a Berkeley grad student told
  Diffie that Ralph Merkle was trying to solve the
  problem of communicating securely with someone
  you had never had any contact with before. "I
  persuaded him it couldn't be done. But then
  ., -- Diffie
• Hellman started asking colleagues for
  mathematical equations that were easy to compute,
  but hard to work backward.
• John Gill, a mathematics professor at the
  University of California at Berkeley, told
  Hellman about computing exponents in finite
  fields.

54
The P-K systems

• May 1975 Martin Hellman and Whitfield Diffies
  seminal paper on public key cryptography
• 1977 Three professors at MIT Ron Rivest, Adi
  Shamir and Len Adleman followed with another
  similar approach known by their initials, RSA
• Unannounced Systems
• 1974British government's eavesdropping
  organization known as the Government
  Communications Headquarters, or GCHQ Malcolm
  Williamson, discovered an algorithm very similar
  to the work of Diffie and Hellman. (published
  1997)
• David Kahn NSA had also discovered the public
  key system. But both GCHQ and NSA did not
  announce it.

55
Patents

• 1983 Jim Bidzos took up reins of RSA and kept
  it alive for 12 years, waiting for Internet to
  create the demand for digital signatures
• Stanford held Diffie-Hellman patent Diffie made
  10,000 by royalty
• MIT held RSA patent. MIT made 10 Million dollars

56
Diffie-Hellman algorithm

• To find a key, Alice chooses a random number "a"
  and Bob chooses a random number "b." They also
  agree on some value of "g" in advance.
• Alice ships ga that is, g raised to the power
  a, as in238 to Bob and Bob ships gb to Alice.
  
• Alice computes (gb)a and Bob computes (ga)b.
  These serve as the key.
• The system can't be broken because the arithmetic
  occurs in a "finite field" with some prime number
  "p. This is indicated by appending "mod p" to
  the equation.
• No one knows an efficient way to find a from g
  and ga. This is known as taking the "discrete
  log, making the link secure from the
  eavesdroppers.

57
Diffie-Hellman algorithm

• To find a key, Alice chooses a random number "a"
  and Bob chooses a random number "b." They also
  agree on some value of "g" in advance.
• Alice ships ga that is, g raised to the power
  a, as in238 to Bob and Bob ships gb to Alice.
  
• Alice computes (gb)a and Bob computes (ga)b.
  These serve as the key.
• The system can't be broken because the arithmetic
  occurs in a "finite field" with some prime number
  "p. This is indicated by appending "mod p" to
  the equation.
• No one knows an efficient way to find a from g
  and ga. This is known as taking the "discrete
  log, making the link secure from the
  eavesdroppers.

58
public-key cryptography (continued)
59
Asymmetric Key Encryption Example to ensure
that no one else the recipient reads the message

• Also called Public key Encryption

A
Bs public
Encrypted Message
Message
key
Internet
Bs private
Encrypted Message
Message
key
B
60
public-key cryptography (continued)

• Data transmission private key(d), public key (e)

61
public-key cryptography (continued)

• Applications and Advantages
• Storage for safety use public key of trusted
  person
• Secret vs. Public Key system
• secret key system needs secret key for every
  pair of persons, that wish to communicate
• n users ? n(n-1)/2 keys
• public key system needs two keys for every
  person, who wants to communicate.
• n users ? 2n keys

62
Public Key of Alice

• Send through e-mail (A hacker, say Eve could
  pretend to be Alice.)
• A trusted authority maintains a public directory
  mapping names to public key
• Publish hard copy using water-marked paper
• Secure electronic access by locking through
  private key of trusted party
• (If Trusted Authoritys private key is
  compromised, the whole system becomes suspect.)

63
Digital certificate for getting
Public Key reliably

• A digital certificate from a trusted party may
  contain
• The name of a person
• His e-mail address
• His public key
• The recipient of the encrypted certificate uses
  the public key of the Certification Authority to
  decode the certificate.
• Standard for certificate X.509

64
Certifying Authorities

• Examples of CAs www.verisign.com or
  www.thawte.com
• Verisigns Certificate Classes
• Individual ( without identity check) certifies
  that this is an individual, who has paid the
  Verisign fee for getting a Certificate
  Verisigns liability limited to 100 only!
• Individuals and Organizations (with physical
  verification by a notary) Cost of certificate
  much higher Verisigns liability limited to
  100,000.
• Revoking the Certificate (CRL)

65
Digital Certificate

• private key(d), public key (e)
• Alice wants to send a non-repudiable message to
  Bob.
• Alice gets a certificate from the trusted
  authority
• CA EdTAlice, e-mail address of
  Alice, eA.
• Alice encrypts the message (m) with her private
  key. Ci EdTm
• Alice sends (Ci CA) to Bob.
• Bob uses eT to find public key of Alice from CA
• Bob obtains m by decrypting Ci by using the
  public key of Alice.

66
Digital signatures

• Digital Signatures A is to sign a Msg and send
  it to B

B
Decode digest using Public key of A
Msg
Msg Encoded Digest
Msg Encoded Digest
A
Digest Algorithm
Digest
Digest Algorithm
Msg
Encoding using Private key of A
Digest
Compare
67
Secure Socket Layer

• A user sends a Hello message to the Server
• The server sends its Certificate.
• The user checks the certificate by using the
  public key of the trusted authority
• The user picks a random number K, encrypts it by
  using the public key of the server and sends it
  to the server.
• The server decrypts using its private key.
• Thus both the user and the server share the
  secret key K for the session. K may be used for
  exchanging encrypted messages.

68
Pretty Good Privacy

• private key(d), public key (e)
• Key-ring List of public keys, signed by the
  owners private key
• Example Alice knows Bob and Rita.
• Alices Key-ring EdA(Bob, e-mail address of
  Bob, eB)(Rita, e-mail address of Rita, eR)
• Web of trust

69

• Confidentiality of data

70
Message/data Encryption
Combines conventional and public-key encryption
Recipients Public key
Session key
Encrypted session key
Encrypt
Encrypt
data
Encrypted data
71
Message/data Encryption
Combines conventional and public-key encryption
Recipients Private key
Session key
Encrypted session key
Decrypt
Decrypt
data
Encrypted data
Public-key encryption provides a secure channel
to exchange symmetric encryption keys
72

• Message Authentication Code

73
Message Authentication Codes

• m message (can be of any size)
• K fixed-size symmetric key
• known to both the sender and receiver only
• MAC of fixed size

m
MAC
MAC Function
Key
74
MACs for integrity
Message Authentication code, adds a password/key
to a hash
data
data
Mac
Message MAC
Password/key
Only the password holder(s) can generate the MAC
75
MAC continued

• A MAC function (also called a cryptographic
  checksum)
• Need not be reversible.
• Many-to-one function
• MAC provides
• Authentication and
• integrity
• If one more symmetric key is used,
  confidentiality can be provided.
• This separates authentication and
  confidentiality functionalities.

76
MAC continued

• This may be required in a system wherein
  authentication may be at the application layer,
  whereas confidentiality may be required at a
  lower layer (like at transport layer.)
• Separation of Authentication and Confidentiality
• Or the recipient organisation may check for
  authentication at the entry system. The
  confidentiality may be required up to the final
  host within the recipient organization.
• Does not provide signatures
• The recipient can forge the message.
• The sender can repudiate it.

77
HMAC keyed Hashing for Message
Authentication

• HMAC An algorithm which uses a keyless hash
  function and a cryptographic key to develop a MAC
• Advantages Hash functions are faster
• no export controls on keyless hash functions.
• H a keyless hash function
• Input a block of b bytes
• Output a hash of l bytes
• K key no longer than b bytes (If larger than b,
  take a hash of K and use it as the key)
• Kpad K, with zeros on the left - if required,
  so that K becomes b bytes long
• Reference RFC 2104

78
HMAC (continued)

• ipad a sequence of b bytes obtained by repeating
  the byte 0011 0110
• opad a sequence of b bytes obtained by repeating
  the byte 0101 1100
• Definition of a HMAC-H function with a key K and
  message m
• H(K,m)
• H( (K XOR opad) ll H( (K XOR
  ipad) ll m) )
• Reference 1. M. Bellare, R. Kaneti and
  H.Krawczyk, Keyed Hash Functions and Message
  Authentication, Advances in Cryptology-
  Proceedings of CRYPTO 96, PP. 1-15 (1996)
  2.H.Krawczyk, M. Bellare and R. Kaneti, RFC
  2104, Feb 1997

79
Function for MAC

• HMAC
• MD5 or an SHA function may be used.
• Recommendation for a 128 bit security SHA-256
• MAC may also be obtained by using a block cipher
  and by throwing away all the blocks except the
  last block. This is called CBC-MAC.
• CBC cipher block chaining method
• However if it is used, the key for encryption
  and the key for message authentication must be
  different.
• Slower than HMAC

80
Authentication issues

• If only the message between Alice and Bob is
  authenticated,
• Eve could store the message and send it later
  again. Or
• Eve could send the message from Alice -- back to
  Alice at some later time, spoofing it as a
  message from Bob.
• To avoid it, m2 information like message
  number, sender address and receiver address etc
  may be concatenated with m before creating a MAC.
• Further problem Version problem, which may
  increase the size of fields.
• Example Alice sends the older version. Eve
  adds data to make it look to Bob as if Alice sent
  the new version. So version number has also to be
  added to m2. RULE Authentication at a higher
  layer only.

81
Laws for security before
the networking age

• Privacy Act of 1974, passed by the United States
  Congress following revelations of the abuse of
  privacy during the administration of President
  Richard Nixon mandates that each United States
  Government agency have in place an administrative
  and physical security system to prevent the
  unauthorized release of personal records
• Computer Matching and Privacy Protection Act of
  1988, amended the Privacy Act of 1974 by adding
  certain protections for the subjects of Privacy
  Act records whose records are used in automated
  matching programs mandates the establishment of
  Data Integrity Boards at each agency engaging in
  matching to monitor the agency's matching
  activity for oversight of matching programs

82
Laws for security after
the networking age

• Health Insurance Portability and Accountability
  Act of 1996 (HIPAA) for convenience, privacy and
  security of electronic health transactions
• Federal Information Security Management Act of
  2002 (FISMA) mandates yearly audits of computer
  and network security of federal government and
  affiliated parties (like government contractors)
  requires that processes used by all these
  entities must follow a combination of
• Federal Information Processing standards (FIPS)
  documents,
• the special publications SP-800 series issued by
  National Institute of Standards and Technology
  (NIST), and
• other legislation pertinent to federal
  information systems, such as the Privacy Act of
  1974 and HIPAA
• Also called E-government Act

83
Laws for security after the
networking age.2

• Sarbanes-Oxley Act of 2002 (also known as the
  Public Company Accounting Reform and Investor
  Protection Act and commonly called SOX or
  Sarbox), named after Senator Paul Sarbanes and
  Representative Michael G. Oxley)
• establishes a new quasi-public agency, the Public
  Company Accounting Oversight Board (PCAOB), which
  is charged with
• overseeing,
• regulating,
• inspecting, and
• disciplining accounting firms working as as
  auditors of public companies.
• covers issues such as
• auditor independence,
• corporate governance,
• internal control assessment, and
• enhanced financial disclosure.
• SOX ? additional audit/reporting costs of 45 B

84
Laws for security after the
networking age.3

• SB 1386, a California law 2003, introduced by
  State Senator Peace regulating the privacy of
  personal information mandates the necessity of
  informing individuals, whose personal information
  may have been disclosed to unauthorized persons,
  due to a security breach
• Personal Information Protection and Electronic
  Documents Act (PIPEDA or PIPED Act), a Canadian
  law relating to data privacy makes mandatory
  provisions of the Canadian Standards
  Association's Model Code for the Protection of
  Personal Information 1995

85
International Laws

• 1980 OECD Guidelines for the Protection of
  Privacy and Transborder Flows of Personal Data
• 1981 Council of Europe Convention for the
  Protection of Individuals with Regard to
  Automatic Processing of Personal Data
• Both the above adopted by 50 countries.
• Privacy as a fundamental human right accepted by
  many European countries
• Privacy as a constitutional guarantee accepted
  by Brazil

86
International Laws 2

• 1992 The OECD Guidelines for the Security of
  Information Systems consist of Democracy
  Principle and Ethics Principle
• eviscerated in 2002
• 1992Democracy Principle The security of
  information systems should be compatible with the
  legitimate use and flow of data and information
  in a democratic society.
• 2002 The security of information systems and
  networks should be compatible with essential
  values of a democratic society

87
International Laws 3

• 1992 Ethics Principles Information systems and
  the security of information systems should be
  provided and used in such a manner that the
  rights and legitimate interests of others are
  respected.
• 2002 Participants should respect the legitimate
  interests of others.

88
IP and the Internet Architecture
OSI Model
Internet Architecture
Application/data
Application
Presentation/data
Session/data
Transport/segment
Internet addressing, routing
Network/packet
IP
Data Link/frame
Network
Ethernet, Token Ring, etc.Bridging and switching
Physical/bit
89
FTP
SMTP
TELNET
DNS
BGP
RIP
OSPF
UDP
TCP
ICMP
IP
RARP
ARP
Data Link Layer
Physical Layer
90

• Ethernet Type
• ARP 080616
• RARP 803516
• IP 080016
• IP Protocol
• OSPF 89
• UDP 17
• TCP 6
• ICMP 1

• UDP Ports
• RIP 520
• DNS 53
• TCP Ports
• BGP 179
• DNS 53
• SMTP 25
• TELNET 23
• FTP 21
• HTTP 80
• HTTP PROXY 8080

91
TCP/IP STACK
92
Stream Control Transmission Protocol
(SCTP)

• SCTP
• a reliable transport protocol operating on top of
  IP.
• It offers acknowledged error-free non-duplicated
  transfer of datagrams (messages).
• Detection of
• data corruption,
• loss of data and
• duplication of data
• is achieved by using checksums and sequence
  numbers. A selective retransmission mechanism is
  applied to correct loss or corruption of data.

93
Difference between SCTP and TCP

• difference with to TCP multihoming and the
  concept of several streams within a connection.
  Where in TCP a stream is referred to as a
  sequence of bytes, an SCTP stream represents a
  sequence of messages (and these may be very short
  or long).
• References 1. SCTP for beginners
  http//tdrwww.exp-math.uni-essen.de/inhalt/forschu
  ng/sctp_fb/index.html as of Oct 12/2006
• 2. http//www.sctp.org/ 3. RFC2960

94
Session Initiation Protocol (SIP)

• a signalling protocol used for establishing
  sessions in an IP network.
• A session may be
• a simple two-way telephone call or
• a collaborative multi-media conference session.

95
Uses of SIP

• VoIP telephony
• voice-enriched e-commerce,
• web page click-to-dial,
• Instant Messaging with buddy lists
• References 1. RFC 3261
• 2.http//www.sipcenter.com/sip.nsf/html/WhatIsSI
  PIntroduction

96
Session Initiation Protocol

• VoIP uses the following standards and protocols
• to ensure transport (RTP),
• to authenticate users (RADIUS, DIAMETER),
• to provide directories (LDAP),
• to be able to guarantee voice quality (RSVP,
  YESSIR) and
• to inter-work with today's telephone network,
  many ITU standards

97
H.323 and H.248

• H.323 (ITU standard to allow telephones, on the
  public telephone network, to talk to computers,
  connected to Internet)
• used for local area networks (LANs), but was not
  capable of scaling to larger public networks.
• H.248 also called MEGACO
• Media Gateway Control Protocol (Megaco) --- the
  name used by IETF
• H.248 the name used by ITU-T Study Group 16

98
H.248/MEGACO

• MEGACO a standard protocol for handling the
  signaling and session management needed during a
  multimedia conference.
• defines a means of communication between a media
  gateway, which converts data from the format
  required for a circuit-switched network to that
  required for a packet-switched network, and the
  media gateway controller.
• References 1.RFC 3015
• 2. http// searchnetworking.techtarget.com/
  sDefinition/0,,sid7_ gci817224,00.html as of 12th
  Oct 2006

99
IEEE 802.3 Standard
Dest add
Src add
data
preamble
type
crc
8
6
6
2
46B 1500B
4
bits 368-12,000 FRAME
16 bits
CRC Cyclic Redundancy Check