1. Chapter 12 Advanced Cryptography
Security+
Chapter 12
Advanced Cryptography
Modified 10/06/ jw

2. Objectives Define digital certificates
List the various types of digital certificates and how they are used
Describe the components of Public Key Infrastructure (PKI)
List the tasks associated with key management
Describe the different transport encryption algorithms

3. Stuxnet
Stuxnet Virus used four different Zero Day exploits on Windows platforms.
In addition to the Zero Day attacks, the ‘payload’ included a stolen digital certificate that was issued by Verisign.
The certificate allowed the malware to act as a trusted application and communicate with other devices.

4. Digital Certificates Common application of cryptography
Aspects of using digital certificates
Understanding their purpose
Knowing how they are managed
Determining which type of digital certificate is appropriate for different situations

5. Defining Digital Certificates
Digital signature
Used to prove a document originated from a valid sender

7. Defining Digital Certificates (cont’d)
Weakness of using digital signatures
Digital signatures require a reliable way to get public keys
A forged public key could be used to forge a digital signature
Imposter could post a public key under a sender’s name
Do not definitively prove who the sender
Do not confirm true identity of the sender

8. Imposter public key

9. Defining Digital Certificates (cont’d.)
Can be used to associate or “bind” a user’s identity to a public key
The user’s public key that has itself been “digitally signed” by a reputable source entrusted to sign it
Digital certificates make it possible for Alice to verify Bob’s claim that the key belongs to him
When Bob sends a message to Alice he does not ask her to retrieve his public key from a central site
Instead, Bob attaches the digital certificate to the message

10. Defining Digital Certificates (cont’d.)
SOLUTION is to use Trusted third party
Used to help solve the problem of verifying identity
Verifies the owner and that the public key belongs to that owner
Helps prevent man-in-the-middle attack that impersonates owner of public key
NOTE: Self Signed Certificates do not use a trusted third party

11. Defining Digital Certificates (cont’d.)
Information contained in a digital certificate
Owner’s name or alias
Owner’s public key
Name of the issuer
Digital signature of the issuer
Serial number of the digital certificate
Expiration date of the public key

12. Managing Digital Certificates
Technologies used for managing digital certificates
Certificate Authority (CA)
Registration Authority (RA)
Certificate Revocation List (CRL)
Certificate Repository (CR)
Web browser

13. Managing Digital Certificates (cont’d)
Certificate Authority (CA)
Trusted third-party agency responsible for issuing digital certificates
A user provides information to a CA that verifies her identity
The user generates public and private keys and sends the public key to the CA
The CA inserts this public key into the certificate
Trusted third party
Can be internal or external to an organization

14. Managing Digital Certificates (cont’d.)
Duties of a CA
Generate, issue, an distribute public key certificates
Distribute CA certificates
Generate and publish certificate status information
Provide a means for subscribers to request revocation
Revoke public-key certificates
Maintain security, availability, and continuity of certificate issuance signing functions

15. Managing Digital Certificates (cont’d.)
Subscriber requesting a digital certificate
Generate public and private keys
Generate Certificate Signing Request (CSR) - Specially formatted encrypted message that validates information CA requires
CA receives and verifies the CSR
Inserts the public key into certificate
Certificates digitally signed with private key of the issuing CA

16. Managing Digital Certificates (cont’d.)
Registration Authority (RA)
Subordinate entity designed to handle specific CA tasks
Offloading registration functions creates improved workflow for CA
General duties of an RA
Receive, authenticate, and process certificate revocation requests
Identify and authenticate subscribers

17. Managing Digital Certificates (cont’d.)
General duties of an RA (cont’d.)
Obtain a public key from the subscriber
Verify that the subscriber possesses the asymmetric private key corresponding to the public key submitted for certification
Primary function of an RA
Verify identity of an individual

18. Managing Digital Certificates (cont’d.)
Means for a digital certificate requestor to identify themselves to an RA
Insufficient for activities that must be very secure
Documents
Birth certificate, employee badge
In person
Providing government-issued passport or driver’s license

19. Managing Digital Certificates (cont’d.)
Certificate Revocation List (CRL)
Lists digital certificates that have been revoked
Can be accessed to check the certificate status of other users
Most CRLs can either be viewed or downloaded directly into the user’s Web browser

20. Managing Digital Certificates (cont’d.)
Certificate Revocation List (CRL)
Reasons a certificate would be revoked
Certificate is no longer used
Details of the certificate have changed, such as user’s address
Private key has been lost or exposed (or suspected lost or exposed)
Digital certificates stolen from CA

21. Certificate Revocation List (CRL)

22. Managing Digital Certificates (cont’d.)
Certificate Repository (CR)
Publicly accessible centralized directory of digital certificates and CRLs published by a CA
Used to view certificate status
Can be managed locally as a storage area connected to the CA server
CRs are often available to all users through a Web browser interface

23. Certificate Repository (CR)

24. Managing Digital Certificates (cont’d.)
Web browser management
Modern Web browsers preconfigured with default list of CAs
Advantages
Users can take advantage of digital certificates without need to manually load information
Users do not need to install a CRL manually
Automatic updates feature will install them automatically if feature is enabled

25. Trusted Root Certification Authorities
In MS Windows:
Start
Internet Options
Content Tab
Publishers

26. Online Certificate Status Protocol (OCSP)
Online Certificate Status Protocol (OCSP) - Performs real-time lookup of a certificate’s status
OCSP is called “request-response protocol”
Browser sends certificate's information to a trusted entity like the CA, known as an OCSP Responder
OCSP Responder then provides immediate revocation information on that one specific certificate
Online Certificate Status Protocol (OCSP)
Online Certificate Status Protocol (OCSP) - Performs real-time lookup of a certificate’s status
OCSP is called “request-response protocol”
Browser sends certificate's information to a trusted entity like the CA, known as an OCSP Responder
OCSP Responder then provides immediate revocation information on that one specific certificate

27. OCSP Stapling OCSP stapling - Variation of OCSP
OCSP requires OCSP Responder provide responses to every web client of certificate in real time; generates high volume of traffic
OCSP stapling - Web servers send queries to Responder OCSP server at regular intervals to receive a signed time-stamped OCSP response
When Web browser attempts to connect to web server the server can include (staple) in handshake previously received OCSP response
OCSP Stapling
OCSP stapling - Variation of OCSP
OCSP requires OCSP Responder provide responses to every web client of certificate in real time; generates high volume of traffic
OCSP stapling - Web servers send queries to Responder OCSP server at regular intervals to receive a signed time-stamped OCSP response
When Web browser attempts to connect to web server the server can include (staple) in handshake previously received OCSP response

28. OCSP Stapling OCSP Stapling (Figure 6-4)
A figure of OCSP Stapling. The Web server connects by a line to the OCSP Responder with the line labeled “Step 1: is this certificate valid?” A line from the Responder back to the Web server is labeled “Step 2: Yes here is a signed approval.” A line from the Web server connects to the Web browser and is labeled “Step 3: I want to connect.” A line from the Web server to the Web browser says “Step 4: Here is the approval.”

29. Uses of Digital Certificates
Bind a user's identity to a public key
Encrypt channels to provide secure communication between clients and servers
Encrypt messages for secure Internet communication
Verify the identity of clients and servers on the Web
Verify the source and integrity of signed executable code

30. Types of Digital Certificates
Different categories of digital certificates
Class 1 through Class 5
Dual-key sided
Dual sided

31. Common Categories of Digital Certificates
Personal digital certificates
Used to send from one person to another
Server digital certificates
Used by Web servers to make HTTPS connections
$200 to $300 / year from Thawte & Verisign
$30 / year GoDaddy
Software publisher digital certificates
$300 / year from Thawte

32. Types of Digital Certificates (cont’d.)
Class 1: personal digital certificates
Issued by an RA directly to individuals
Frequently used to secure transmissions
Typically only require user’s name and address to receive
Users can create Microsoft Word or Adobe Portable Document Format (PDF) document and then use digital certificate to create digital signature

33. Types of Digital Certificates (cont’d.)
Class 2: Server Digital certificates
Issued from a server (Web, , etc) to a client
Ensure authenticity of a Server
Ensure authenticity of the cryptographic connection to a Server

34. Figure 12-5 Server digital certificate
© Cengage Learning 2012

35. Cryptographic Handshake: Steps 1-2
Web servers set up secure cryptographic “handshake” connections so that all transmitted data is encrypted by providing server’s public key with digital certificate to client
Browser sends message ("ClientHello") to server that contains information, including list of cryptographic algorithms that client supports
Web server responds ("ServerHello") by indicating which cryptographic algorithm will be used, and then sends the server digital certificate to browser
Cryptographic Handshake: Steps 1-2
Web servers set up secure cryptographic “handshake” connections so that all transmitted data is encrypted by providing server’s public key with digital certificate to client
Browser sends message ("ClientHello") to server that contains information, including list of cryptographic algorithms that client supports
Web server responds ("ServerHello") by indicating which cryptographic algorithm will be used, and then sends the server digital certificate to browser

36. Cryptographic Handshake: Steps 3-4
Browser verifies server certificate (not expired) and extracts server’s public key; browser generates random value (pre-master secret), encrypts it with server’s public key and sends back to server ("ClientKeyExchange").
Server decrypts message and obtains browser’s pre-master secret; both browser and server can each create the same master secret that used to create session keys (symmetric keys to encrypt/decrypt information exchanged during session and to verify integrity)
Cryptographic Handshake: Steps 3-4
Browser verifies server certificate (not expired) and extracts server’s public key; browser generates random value (pre-master secret), encrypts it with server’s public key and sends back to server ("ClientKeyExchange").
Server decrypts message and obtains browser’s pre-master secret; both browser and server can each create the same master secret that used to create session keys (symmetric keys to encrypt/decrypt information exchanged during session and to verify integrity)

37. Server Digital Certificate Handshake
Server Digital Certificate Handshake (Figure 6-5)
A figure with a Web browser on the left and a Web server on the right. A line from the browser to the server says “1. ClientHello Cryptographic Information.” A line from the server to the browser says “2. ServerHello Algorithms supported Server digital certificate.” The web browser says, “3. Verifies certificate and creates pre-master secret.” The web browser and web server says, “4. Creates master secret and session keys.”

38. Types of Digital Certificates (cont’d.)
Class 2: server digital certificates (cont’d.)
Server authentication and secure communication can be combined into one certificate
Displays padlock icon in the browser
Click padlock icon to display information about the digital certificate

39. Padlock icon and certificate information

40. Extended Validation SSL Certificate (EV SSL)
Enhanced type of server digital certificate that requires more extensive verification of legitimacy of the business
CA must pass an independent audit verifying that it follows the EV standards.
Existence and identity of the website owner, including its legal existence, physical address, and operational presence, must be verified by the CA.
CA must verify that the website is registered holder and has exclusive control of domain name
Extended Validation SSL Certificate (EV SSL)
Extended Validation SSL Certificate (EV SSL) - Enhanced type of server digital certificate that requires more extensive verification of legitimacy of the business
CA must pass an independent audit verifying that it follows the EV standards.
Existence and identity of the website owner, including its legal existence, physical address, and operational presence, must be verified by the CA.
CA must verify that the website is registered holder and has exclusive control of domain name

41. Extended Validation SSL
Company must be audited and follow EV standards
Company can't be "located in a country or be part of an industry identified on a government prohibited list"
$400 / year

42. Types of Digital Certificates (cont’d.)
Class 3: software publisher digital certificates
Provided by software publishers
Purpose: verify programs are secure and have not been tampered with

43. Types of Digital Certificates (cont’d.)
Class 3: software publisher digital certificates

44. Types of Digital Certificates (cont’d.)
Specialized classes of digital certificates:
Class 4
Online business transactions between companies
Class 5
Private organizations or governmental security

45. Managing Digital Certificates
For Alice and Bob to use asymmetric cryptography:
Alice and Bob must generate public and private keys
A Certificate Authority (CA) or Registration Authority (RA) must verify the identities of Alice and Bob
The certificates must be placed in a Certificate Repository (CR)
When they expire, they must be placed on a Certificate Revocation List (CRL)
All these things are done by Public key infrastructure (PKI)

46. Public Key Infrastructure (PKI)
Important management tool for the use of:
Digital certificates:
Asymmetric cryptography
Aspects of PKI
Public-key cryptography standards
Trust models
Key management

47. What is Public Key Infrastructure (PKI)?
Need for consistent means to manage digital certificates
PKI is digital certificate management
PKI: framework for all entities involved in digital certificates
Includes hardware, software, people, policies and procedures
Certificate management actions facilitated by PKI
Create
Store
Distribute
Revoke

48. Public-Key Cryptographic Standards (PKCS)
Numbered set of PKI standards defined by the RSA Corporation
Widely accepted in industry
Based on the RSA public-key algorithm
Composed of 15 standards

49. Trust Models
Trust may be defined as confidence in or reliance on another person or entity
Trust model
Refers to the type of trusting relationship that can exist between individuals or entities
Direct trust
A relationship exists between two individuals because one person knows the other person
Third party trust
Refers to a situation in which two individuals trust each other because each trusts a third party

50. Web of Trust
Direct trust is not easily scaled to multiple users who each have digital certificates
PGP uses a "Web of Trust" in which people trust "friends of friends"
Not very secure or scalable
(comic from xkcd.org)

51. Trust Models (cont’d) Four PKI trust models that use a CA
Hierarchical trust model
Distributed trust model
Bridge trust model
Hybrid trust model

52. Trust Models (cont’d) Hierarchical trust model
also known as a tree—a root CA at the top provides all the information
Bridge trust model
a peer-to-peer relationship exists between the root CAs
Mesh trust model
expands the concepts of the bridge model by supporting multiple paths and multiple root CAs
Hybrid trust model
can use the capabilities of any or all of the structures discussed in the previous sections

53. Trust Models (cont’d.) Hierarchical trust model
Assigns single hierarchy with one master CA called the root
Root signs all digital certificate authorities with a single key
Can be used in an organization where one CA is responsible for only that organization’s digital certificates
Hierarchical trust model has several limitations
Single CA private key may be compromised rendering all certificates worthless

54. One master "root" CA signs all digital certificates with a single key
Figure 12-8 Hierarchical trust model
© Cengage Learning 2012
One master "root" CA signs all digital certificates with a single key
Single point of failure

55. Trust Models (cont’d.) Distributed trust model
Multiple CAs sign digital certificates
Eliminates limitations of hierarchical trust model
Used on the Internet

56. Distributed Trust Model

57. Trust Models (cont’d.) Bridge trust model
One CA acts as facilitator to connect all other CAs
Facilitator CA does not issue digital certificates
Acts as hub between hierarchical and distributed trust model
Allows the different models to be linked

58. Trust Models (cont’d.) Bridge trust application examples
Federal and state governments
Pharmaceutical industry
Aerospace industry

59. Bridge Trust Model Bridge Trust Model
Used to link federal and state governments
Links military and civilian ID cards

60. Managing PKI Certificate Policy (CP)
Published set of rules that govern operation of a PKI
Provides recommended baseline security requirements for use and operation of CA, RA, and other PKI components
Certificate Practice Statement (CPS)
Describes in detail how the CA uses and manages certificates
A more technical document than a CP

61. Managing PKI (cont’d.) Certificate life cycle Creation Suspension
Occurs after user is positively identified
Suspension
Certificate cannot be used while suspended
May occur when employee on leave of absence
Revocation
Certificate goes on Certificate Revocation List (CRL)
When a private key is lost
Certificate no longer valid
Expiration
Key can no longer be used

62. Key Management

63. Key Storage Means of public key storage Means of private key storage
Embedding within digital certificates
Means of private key storage
Stored on user’s local system
The drawback to software-based storage is that it may leave keys open to attacks
Alternative: storing private keys in hardware
Tokens
Smart-cards

64. Key Usage Multiple pairs of dual keys
Created if more security needed than single set of public/private keys
One pair used to encrypt information
Public key backed up in another location
Second pair used only for digital signatures
Public key in that pair never backed up

65. Key-Handling Procedures
Key escrow
Keys managed by a third party
Private key is split and each half is encrypted
Two halves sent to third party, which stores each half in separate location
User can retrieve and combine two halves and use this new copy of private key for decryption
Expiration
Keys expire after a set period of time

66. Key-Handling Procedures (cont’d.)
Renewal
Existing key can be renewed
Revocation
Key may be revoked prior to its expiration date
Revoked keys may not be reinstated

67. Key-Handling Procedures (cont’d.)
Recovery
Need to recover keys of an employee hospitalized for extended period
Key recovery agent (KRA) may be used
A highly trusted person authorized to recover others' keys
Group of people may be used (M-of-N control)
A certain number of people need to agree to recover a key

68. Figure 12-11 M-of-N control
© Cengage Learning 2012

69. Key-Handling Procedures (cont’d.)
Suspension
Suspended for a set period of time and then reinstated
Destruction
Removes all public and private keys and user’s identification from the CA

70. Cryptographic Transport Protocols

71. Transport Encryption Algorithms
Secure Sockets Layer (SSL)
A protocol developed by Netscape for securely transmitting documents over the Internet
Uses a public key to encrypt data that is transferred over the SSL connection
Transport Layer Security (TLS)
A protocol that guarantees privacy and data integrity between applications communicating over the Internet
An extension of SSL
Are often referred to as SSL/TLS or TLS/SSL
Both provide server and client authentication, and data encryption

72. Secure Shell (SSH)
Secure encrypted alternative to Telnet protocol used to access remote computers
Linux/UNIX-based command interface and protocol
Suite of three utilities: slogin, ssh, and scp
Client and server ends of connection are authenticated using a digital certificate
Passwords and traffic are encrypted
Can be used as a tool for secure network backups
TCP Port 22

73. Table 12-3 SSH commands

74. Hypertext Transport Protocol over Secure Sockets Layer (HTTPS)
Another use of SSL is to secure Web HTTP communications between a browser and a Web server
Secure Web Hypertext Transport Protocol (HTTPS) communications between browser and Web server
Users must enter URLs with
“Plain” HTTP sent over SSL/TLS
Secure Hypertext Transport Protocol (SHTTP)
Cryptographic transport protocol released as a public specification
Supports a variety of encryption types, including 3DES
Not as widely used as HTTPS
Security+ Guide to Network Security Fundamentals, Fourth Edition

75. HTTPS continued Are you safe with your Web Browser using SSL / TLS?

76. IP Security (IPsec) Open System Interconnection (OSI) model
Security tools function at different layers
Operating at higher levels such as Application layer
Advantage: tools designed to protect specific applications
Disadvantage: multiple security tools may be needed

77. IP Security (IPsec) (cont’d)
A set of protocols developed to support the secure exchange of packets
Because it operates at a low level in the OSI model IPsec is considered to be a transparent security protocol for applications, users, and software
IPsec provides three areas of protection:
Authentication, confidentiality, and key management

78. Security tools and the OSI model

79. IP Security (cont’d.) IPsec considered transparent to:
Applications
Users
Software
Located in the operating system or communication hardware
Supports two encryption modes: transport and tunnel

80. Figure 12-13 New IPsec packet using transport or tunnel mode
© Cengage Learning 2012

81. Summary
Digital certificate provides third party verification of public key owner’s identity
A Certificate Authority issues digital certificates for others
Personal digital certificates are issued by an RA to individuals
Server digital certificates ensure authenticity of a Web server and its cryptographic connection

82. Summary (cont’d.)
PKI is a framework for all entities involved in digital certificates
Three basic PKI trust models exist
Cryptography can protect data as it is being transported across a network
SSL/TLS is a widely used algorithm
IPsec supports a secure exchange of packets
Considered to be a transparent security protocol