Module 18 Network Security I Cryptography

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Module 18Network Security ICryptography
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• Textbook sections
• LG 11.1 Security and Cryptographic Algorithms
• LG 11.3 Cryptographic Algorithms
• Topics
• Security Attacks
• Security Requirements
• Conventional Encryption
• Model of Conventional Cryptography
• Simplified DES
• Mathematical Operations
• Example S-DES
• Public-key Cryptography
• Overview
• RSA Algorithm
• Encryption
• Digital Signature
• Message Digest

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LG Figure 11.1Network security threats- Part 1
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LG Figure 11.1 Network security threats- Part 2
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1. Security Attacks

• Threats
• Eavesdropping
• Information transmitted over the network is not
  secure and can be observed and recorded by
  eavesdroppers. This information can be replayed
  I attempts to access the server
• Client imposter
• Imposters can attempt to gain unauthorized access
  to a server, for example, a bank account or a
  database of personal records
• Denial of service
• An attacker can also flood a server with
  requests, overloading the server resources and
  resulting in a denial of service to legitimate
  clients
• Server imposter
• An imposter can impersonate a legitimate server
  and gain sensitive information from a client, for
  example, a bank account number and associated
  user password
• Man in the middle
• An imposter managers to place itself as the man
  in the middle, convincing the server that it is
  the legitimate client and the legitimate client
  that it is the legitimate server

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1. Security Attacks

• Most networks have been designed to prevent
  external attacks firewalls, intrusion detection,
  system and access controls
• Trusted insider threats
• Who
• Disgruntled employee
• Financially distressed employee
• Emotionally distressed employee
• Threats
• Intend to cause damage
• Know where valued resources are located
• Know how to enter the system
• Damage
• Statistics show that more than 2/3 of computer
  security incidents (both government and
  commercial) resulted from the activities of
  authorized users.
• Monitoring
• History logs of network connections including web
  addresses visited.
• Traffic logs of connection types such as
  e-mail,web, FTP, etc.
• Keystroke monitoring (Usually used only when
  hostile activities or inappropriate behavior is
  suspected.)

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1. Security Attacks

• Malicious code
• Worm
• A worm is an independent program that spreads
  through network connections and may consume
  computing resources but does not attach itself to
  other programs.
• Bomb
• A logic bomb detonates (executes) when a certain
  condition is met. A time bomb detonates
  (executes) at a pre-determined time.
• Virus
• A virus is a hidden self-replicating section of
  software that spreads by infecting (that is,
  attaching itself to ) and becoming part of
  another program. They can spread via the
  Internet or through removable media such as
  floppy disks or CDs.
• Trojan Horse
• An application that performs one function but
  contains a hidden malicious function.
• Back doors/Trapdoor
• They permit access to system resources without
  using required security mechanisms such as user
  logon.

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2. Security Requirements
Information Protection Requirements The A-I-C
Triad
Availability
Integrity
Confidentiality
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2. Security Requirements

• Availability
• Availability means that information is there when
  you need it. A system, or information contained
  in a system is usable by an authorized user
  according to the systems designed performance
  specifications.
• Integrity
• Integrity assumes that information has not been
  changed, altered, or destroyed in an unauthorized
  manner.
• Confidentiality
• Confidentiality ensures that only authorized
  people or processes are able to access the
  information

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2. Security Requirements

• Authenticity
• It is possible to verity that the sender or
  receiver is who he or she claims to be
• Example Bank ability to prove that it is in
  fact you requesting the transfer
• Non-repudiation
• The sender cannot deny having sent a given
  message
• Example If you request that 100 be transferred
  to pay a bill, you cannot, at later date, deny
  having authorized the transfer
• Control Access
• Need a method of granting access to private or
  secret data to those who require it.

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2. Security Requirements - IT Security Domains

• Ten domains of information technology (IT)
  security
• Security architecture and models
• Physical security
• Access control systems and methodology
• Cryptography
• Telecommunications and network security
• Applications and systems development security
• Operations security
• Security management practices
• Business continuity planning and disaster
  recovery planning
• Law, investigation, and ethics.

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2. Security Requirements - IT Security Domains

• 1. Security Architecture and Models
• This domain contains the concepts, principles,
  structures, and standards used to design,
  implement, monitor, and secure operating systems,
  equipment, networks, applications, and those
  controls used to enforce various levels of
  confidentiality, integrity, and availability.
• 2. Physical Security
• This domain addresses the threats,
  vulnerabilities, and countermeasures utilized to
  physically protected an enterprises resources
  and sensitive information. These resources
  include people, the facility in which they work,
  and the data equipment, support systems, media,
  and supplies they utilize.

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2. Security Requirements - IT Security Domains

• 3. Access Control Systems and Methodology
• Access control is the collection of mechanisms
  for limiting, controlling, and monitoring system
  access to certain items of information or to
  certain features based on a users identity and
  membership in various predefined group. It
  permits the managers of a system to exercise a
  directing or restraining influence on the
  behavior use, and content of the system for
  availability, integrity, and confidentiality.
• 4. Cryptography
• This domain addresses the principles, means, and
  methods of securing information to ensure its
  integrity, confidentiality, and authenticity.

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2. Security Requirements - IT Security Domains

• 5. Telecommunications and network security
• This domain includes the structures,
  transmission methods, transport formats, and
  security measures used to provide integrity,
  availability, and authentication, as well as
  confidentiality for transmissions over private
  and public communications networks.
• 6. Applications and systems development security
• This domain refers to controls included with
  system software and applications software and the
  steps used in their development. Applications
  include agents, applets, software, databases,
  data warehouses, and knowledge-based systems.
  These application may be used in distributed or
  centralized environments.

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2. Security Requirements - IT Security Domains

• 7. Operations security
• Operation security is used to identify the
  controls over hardware, media, and operators with
  access privileges to any of these resources.
  Audit and monitoring are the mechanism, tools,
  and facilities that permit the identification of
  security events and subsequent actions to
  identify key elements and reports the pertinent
  information to the appropriate individuals,
  group, or process.
• 8. Security management practices
• Security management entails the identification
  of an organizations information assets and the
  development, documentation, and implementation of
  policies, standards, procedures, and guidelines
  that ensure confidentiality, integrity, and
  availability. Management tools such as data
  classification, risk assessment, and risk
  analysis are used to identify threats, classify
  assets, and to rate vulnerabilities so that
  effective security controls can be implemented.

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2. Security Requirements - IT Security Domains

• 9. Business continuity planning and disaster
  recovery planning
• This domain addresses the preservation of the
  business in the face of major disruptions to
  normal business operations. BCP and DRP involves
  the preparation, testing, and updating of
  specific actions to protect critical business
  processes from the effect of major systems and
  network failures.
• 10.Law, investigation, and ethics
• This domain addresses computer crime laws and
  regulations, the investigative measures and
  techniques used to determine if a crime has been
  committed and methods to gather evidence if it
  has and the ethical constraints that provide a
  code of conduct for the security professional.

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2. Security Requirements - Key Terms

• Cryptology
• The study of secure communications, which
  encompasses both cryptography and cryptanalysis
• Cryptography
• The branch of cryptology dealing with the design
  of algorithms for encryption and decryption,
  intended to ensure the secrecy and/or
  authenticity of messages
• Cryptanalysis
• The branch of cryptology dealing with the
  breaking of a cipher to recover information, or
  forging encrypted information that will be
  accepted as authentic
• Encryption
• The conversion of plaintext or data into
  unintelligible form by means of a reversible
  translation, based on a translation table or
  algorithm. Also called enciphering.

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2. Security Requirements - Key Terms

• Decryption
• The translation of encrypted text or data (called
  ciphertext) into original text or data (called
  plaintext). Also called deciphering.
• Cipher
• An algorithm for encryption and decryption. A
  cipher replaces a piece of information (an
  element in plaintext) with another object, with
  the intent to conceal meaning. Typically, the
  replacement rule is governed by a secret key.
• Plaintext
• The input to an encryption function or the output
  of a decryption function
• Ciphertext
• The output of an encryption algorithm the
  encrypted form of a message or data.

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2. Security Requirements - Key Terms

• Symmetric encryption
• A form of cryptosystem in which encryption and
  decryption are performed using the same key
  (secret key). Also known as conventional
  encryption.
• Asymmetric encryption
• A form of cryptosystem in which encryption and
  decryption are performed using two different
  keys, one of which is referred to as the public
  key and one of which is referred to as the
  private key. Also known as public-key
  encryption.
• Private Key
• One of the two keys used in an asymmetric
  encryption system. For secure communication, the
  private key should only be known to its creator.
• Public Key
• One of the two keys used in an asymmetric
  encryption system. The public key is made
  public, to be used in conjunction with a
  corresponding private key.

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3. Conventional Encryption - Model of
Conventional Cryptography

• Encryption
• Y EK(X)
• Y is produced by using encryption algorithm E as
  a function of the plaintext X, with the specific
  function determined by the value of the key K
• Plaintext X X1,X2,...,XN. Typically, each
  element of X belongs to the space 0,1
• Ciphertext Y Y1,Y2,...,YN. Typically, each
  element of Y belongs to the space 0,1
• Decryption
• X DK(Y)

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3. Conventional Encryption - Simplified DES

• Data Encryption Standard (DES)
• Designed by IBM and adopted by the U.S.
  government as the standard encryption method for
  nonmilitary and non-classified use.
• Standardized by ANSI in 1981 as ANSI X.3.92
• Was a widely used method of providing secure
  connections through data encryption until it was
  broken in July 1998.
• Encrypts a 64-bit plaintext using a 56-bit key.
  The text is put through 19 different and very
  complex procedures to create a 64-bit ciphertext.
• Simplified DES
• Simplified version of DES to enhance
  understanding of DES
• A teaching tool
• Major components
• Plaintext
• Ciphertext
• Key
• Encryption algorithm
• Decryption algorithm

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Encryption (ciphertext generation)
ciphertext IP-1(fk(SW(fk(IP(plaintext)))))
Subkey 1 generation K1 P8(Shift(P10(key)))
Subkey 2 generation K2 P8(Shift(Shift(P10(key))
))
Decryption (plaintext generation) plaintext
IP-1(fk(SW(fk(IP(ciphertext)))))
Note fk is a complex function which
involves Both permutation, substitution, and key
input.
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3. Conventional Encryption - Mathematical
Operations

• Exclusive OR
• Switch function
• Shift operation
• Example
• Circular left shift (LS-1)
• Define LS-1(k1,k2,k3,k4,k5,k6,k7,k8,k9,k10)
  (k2,k3,k4,k5,k6,k7,k8,k9,k10,k1) then
• LS-1(1,0,0,0,0,0,1,1,0,0) (0,0,0,0,0,1,1,0,0,1)
• Permutation (P-Box)
• Can be viewed as an mapping or transportation
• Example
• Define P10(k1,k2,k3,k4,k5,k6,k7,k8,k9,k10)
  (k3,k5,k2,k7,k4,k10,k1,k9,k8,k6)
• then P10(1,0,1,00,0,0,0,0,1,0)
  (1,0,0,0,0,0,1,1,0,0)
• Define P8(k1,k2,k3,k4,k5,k6,k7,k8,k9,k10)
  (k6,k3,k7,k4,k8,k5,k10,k9)
• then P8(0,0,0,0,1,1,1,0,0,0) (1,0,1,0,0,1,0,0)

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3. Conventional Encryption - Mathematical
Operations

• Substitution S-boxes
• An S-box is simply a substitution a mapping of
  m-bits inputs to n-bit outputs.
• An S-box with an m-bit inputs and n-bit outputs
  is called a mn-bit S-box
• S-boxes are generally the only nonlinear step in
  an algorithm. They are what give a block cipher
  its security. In general, the bigger they are,
  the better.
• DES has eight different 64-bit S-boxes. Blowfish
  has 832-bit S-boxes.

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3. Conventional Encryption - Example S-DES Key
Generation

• Step1 P10 operation
• Given 10-bit key (10100 00010)
• Given P10(k1,k2,k3,k4,k5,k6,k7,k8,k9,k10)
  (k3,k5,k2,k7,k4,k10,k1,k9,k8,k6)
• The result is P10(10100 00010) (10000 01100)
• Step 2 LS-1 (circular left shift one bit)
• Perform LS-1 on the first five bits, and then
  perform LS-1 on the second five bits of the
  result of step1
• The result is (00001 11000)
• Step3 P8 operation
• Given P8(k1,k2,k3,k4,k5,k6,k7,k8,k9,k10)
  (k6,k3,k7,k4,k8,k5,k10,k9)
• The result is K1 P8(00001 11000) (1010 0100)
• Step 4 LS-2 (circular left shift two bits)
• Use the result of Step 2, which is (00001 11000)
• Perform LS-2 on the first five bits, and then
  perform LS-2 on the second five bits of the
  result of step 2
• The result is (00100 00011)
• Step 5 P8 operation
• Given P8(k1,k2,k3,k4,k5,k6,k7,k8,k9,k10)
  (k6,k3,k7,k4,k8,k5,k10,k9)
• The result is K2 P8(00100 00011) (0100 0011)

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3. Conventional Encryption - Example S-DES
Encryption Algorithm

• Step1 Initial Permutation (IP) operation
• Given IP(n1,n2,n3,n4,n5,n6,n7,n8)
  (n2,n6,n3,n1,n4,n8,n5,n7)
• The result is IP(1111 0011) (1011 1101)
• Step 2 Expansion /permutation (E/P) operation
• Given E/P(n1,n2,n3,n4) (n4,n1,n2,n3,n2,n3,n4,n1)
  
• The result is (1101 0111)
• Step3 The usage of subkey K1
• Given 8-bit subkey K1 (k11,k12,k13,k14,k15,k16,k
  17,k18)
• (1010 0100) from previous page
• Rearrange the result of E/P as
• n4 n1 n2 n3
• n2 n3 n4 n1
• XOR the above result and K1 as follows
• n4 XOR k11 n1 XOR k12 n2 XOR k13 n3 XOR k14
• n2 XOR k15 n3 XOR k16 n4 XOR k17 n1 XOR k18
• Plug in numerical values
• 1 XOR 1 1 XOR 0 0 XOR 1 1 XOR 0
• 0 XOR 0 1 XOR 1 1 XOR 0 1 XOR 0
• The result is

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3. Conventional Encryption - Example S-DES
Encryption Algorithm

• Step 4 The usage of S-box
• Given
• 0 1 2 3 0 1 2 3
• 0 1 0 3 2 0
  0 1 2 3
• S0 1 3 2 1 0 S1
  1 2 0 1 3
• 2 0 2 1 3
  2 3 0 1 0
• 3 3 1 3 2
  3 2 1 0 3
• The S-boxes operates as follows The first and
  fourth inputs bits of p are treated as 2-bit
  numbers that specify a row of the S-box, and the
  second and third input bits of p specify a column
  of the S-box.
• For example, if (p00p03) (00) and (p01p02)
  (10), then the output is from row 0, column 2 of
  S0, which is 3, or (11) in binary.
• The first four bits of p are fed into S0 to
  produce a 2-bit output, s1 and s2, and the
  remaining 4 bits (second row) are fed into S1 to
  produce another 2-bit output s3 and s4.
  Therefore, (s1,s2,s3,s4) (0,0,0,0)

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3. Conventional Encryption - Example S-DES
Encryption Algorithm

• Step 5P4 operation
• A P4 operation will be performed on the four
  bits,(s1,s2,s3,s4), calculated from step 4
• P4(s1,s2,s3,s4) (s2,s4,s3,s1)
• Switch operation
• The function fk only alter the leftmost bits of
  the plaintext. The switch operation interchanges
  the left and right 4 bits so that the second
  instance of fk operates on a different 4 bits.
  In this second instance, the E/P, S0,S1, and P4
  functions are the same However, the subkey used
  is K2
• Step 6 Final IP-1 operation
• Given IP-1(k1,k2,k3,k4,k5,k6,k7,k8)
  (k4,k1,k3,k5,k7,k2,k8,k6)
• Note IP-1is the inverse of IP specified in Step 1

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4. Public-key Cryptography - Overview

• Public key encryption An encryption technique
  that generate encryption keys in pairs. One of
  the pair must be kept secret, and one is
  published.
• Publicly revealing an encryption key does not
  thereby reveal the corresponding decryption key.
• Couriers or other secure means are not needed to
  transmit keys, since a message can be enciphered
  using an encryption key publicly revealed by the
  intended recipient. Only the intended recipient
  can decipher the message, since only he knows the
  corresponding decryption key.

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4. Public-key Cryptography
The use of public-key cryptography in encryption
Corresponding keys
The use of public-key cryptography in digital
signatures
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4. Public-key Cryptography - Overview

• The security of Public Key Cryptography is based
  on the difficulty of solving hard problems.
• For example, many public key algorithms base
  their security of the difficulty of factoring the
  product of very large prime numbers (a number
  whos only factors are one and itself). Although
  these algorithms present many interesting
  possibilities, they are quite slow when compared
  to symmetric algorithms.
• Not all public key algorithms are designed to
  perform the same functions
• Some algorithms are designed to do encryption
• Some algorithms are designed to perform key
  exchange
• Some algorithms are designed to perform digital
  signature
• Some algorithms are designed to perform all three
  functions

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4. Public-key Cryptography - RSA Algorithm

• RSA algorithm
• Named after its inventors, Rivest, Shamir, and
  Adleman
• A widely accepted scheme for public cryptography
• It involves different keys for encryption (public
  key) and decryption (private key).
• A public/private pair is required when two
  participants want to encrypt data they are
  sending to each other using a public key
  algorithms like RSA.
• It does not work to encrypt with your private key
  and let the other side decrypt with the public
  key because everyone has access to the public key
  and so could decrypt the message.
• Participant A encrypts data it sends to
  participant B using Bs public key and B uses its
  private key to decrypt this data.
• Similarly, Participant B encrypts data it sends
  to participant A using As public key and A uses
  its private key to decrypt this data.
• RSA security is based on the premise that
  factoring large numbers is a computationally
  expensive proposition.

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4. Public-key Cryptography - RSA Algorithm

• Algorithm to generate public and private keys
• Choose two large prime numbers p and q (larger
  than 512 bits)
• n is set equal to the product of p and q
• The plaintext P that is represented by a number
  must be less than n
• Find a number e that is relatively prime to (p-1)
  (q-1)
• Two numbers are said to be relatively prime if
  they have no common factors except 1
• The public key consists of e, n.
• Find a number d such that de (mod((p-1)
  (q-1))) 1
• The private key consists of d,n.

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4. Public-key Cryptography - RSA Algorithm

• Algorithm to perform RSA encryption
• Suppose that P is an integer that corresponds to
  a block of plaintext, then the corresponding
  ciphertext is generated as follows
• C Pe(mod(n))
• Algorithm to perform RSA decryption
• P Cd(mod(n))

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4. Public-key Cryptography - RSA Algorithm

• Example Using RSA
• Keys generation
• Choose p 5 and q 11.
• Therefore, n 55
• Since (p-1)(q-1) 40, a value of e 7 is valid
• The public key consists of 7,55
• To satisfy 7d(mod 40) 1, choose d 23.
• The public key consists of 23,55
• Encryption of a message represented numerically
  as 18
• C 187 mod 55 17
• Decryption of the ciphertext
• P 1723 mod 55 18

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4. Public-key Cryptography - RSA Algorithm

• The security of RSA
• The number n and e are given publicly. If the
  recipient can calculate d, why not the snooper?
• RSA algorithm starts with p and q to calculate n,
  e, and d. The snooper does not know p and q.
  The snooper needs to use n to first find p and q,
  and then guess d.
• If p and q are large, it is extremely difficult
  to find its prime factors (p and q).

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4. Public-key Cryptography - RSA Algorithm

• There are two possible approaches to defeat the
  RSA algorithm
• The first is the brute-force approach
• Try all possible private keys.
• Thus, the larger the number of bits in e and d,
  the more secure the algorithm.
• However, because complex calculations are
  involved in key generation and in
  encryption/decryption, larger size of the key
  means the system will run slower.
• Factoring n into its two prime factors
• For a large n with large prime factors, factoring
  is a hard problem, but not as hard as it used to
  be

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4. Public-key Cryptography - RSA Algorithm

• Digital signature
• An authentication mechanism that enables the
  creator of a message to attach a code that acts
  as a signature. The signature guarantees the
  source and integrity of the message.
• Digital signature must be message-dependent and
  signer-dependent.
• In network transaction, one can not presumably
  sign the request for withdrawal. One can ,
  however, create the equivalence of an electronic
  or digital signature by the way one send data.
• Reciprocity of RSA algorithm
• Section II of the RSA paper
• DE(M) M . (1)
• ED(M) M .. (2)
• Where E stands for encryption which uses public
  key and D stands for decryption which uses
  private key

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4. Public-key Cryptography - RSA Algorithm

• Section VI signature of the RSA paper
• How can a sender, say Bob, send a signed
  message M to a receiver, say Alice, using
  public-key cryptography?
• The sender, Bob, has the following keys
  DB(private), EA (Public key)
• The receiver, Alice, has the following keys
  DA(private key), EB (Public key)

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4. Public-key Cryptography
The use of public-key cryptography in encryption
Corresponding keys
The use of public-key cryptography in digital
signatures
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4. Public-key Cryptography

• Point for Discussion Performance of RSA
  Algorithm
• DES and MD5 are several orders of magnitude
  faster than RSA when implemented in software. For
  example, when run on an Alpha workstation, DES
  processes data at 36 Mbps, MD5 at 85 Mbps, and
  RSA at only 1 Kbps.
• When implemented in hardware, by custom VLSI
  chips, it has been reported that DES and MD5 can
  achieve rate measured in the hundreds of Mbps,
  whereas RSA achieve a 64 Kbps.
• Even when implemented in hardware, RSA is still
  too slow to be of any practical use in encrypting
  data message. Instead, RSA is typically used to
  encrypt very small amounts of data, such as a
  secret key or a secret number. Security
  protocols then used these RSA-protected secrets
  in conjunction with DES and MD5, to provide
  message privacy and integrity.

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5. Message Digest (MD)

• Methodology
• The public key technology can be used to create a
  digital signature. However the main concern in
  signing data by encryption is that encryption and
  decryption are computationally expensive.
• The message digest (MD) algorithm can be used if
  the needs are to ensure that
• Requirement 1 The sender of the data is as
  claimed, that is, that the sender has signed the
  data and this signature can be checked.
• Requirements 2 The transmitted data has not been
  changed since the sender created and signed the
  data.

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5. Message Digest (MD)

• Message digest algorithm
• Take a message, m, of arbitrary length and
  computer a fixed-length fingerprint of the data
  known as a message digest, H(m). (The message
  digest protects the data in the sense that if m
  is changed to m, either maliciously or by
  accident, then H(m) computed for the original
  data and transmitted with that data, will not
  match the H(m) computer over the changed data,
  m. Thus, the second requirement is met by the
  message digest.
• While the message digest provides for data
  integrity, the first requirement can be met by
  digitally signing the message digest.

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5. Message Digest (MD)

• Hash function
• A message digest algorithm must have the
  following property
• It is computationally infeasible to find any two
  different message x and y such that H(x) H(y).

Bobs long message, m, to Alice
Fixed-length message digest H(m)
Dear Alice This is a very long letter since
there is so much to say ... ... ... Bob
Opgmdvboijrtnsdgghppdogmlcbkb
Many-to-one hash function
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Sending a digitally signed message
Bobs original long message to Alice
Many-to-one hash function
Fixed-length message digest
Encrypt the fixed-length message digest
Bobs private key
encrypted message digest
Combine the long message and the encrypted
message digest
Bobs digitally signed message to Alice
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Verifying the integrity of a signed message
Message received by Alice
Extract Long message
Extract encrypted message digest
Long message, m
Signed message digest
Many-to-one hash function
decrypt the encrypted message digest
Bobs public key
Fixed-length message digest
Fixed-length message digest
Compare