IT 221: Introduction to Information Security Principles Lecture 9: Email Security For Educational Purposes Only Revised: October 27, 2002

IT 221:Introduction to Information Security Principles

Lecture 9: Email Security

For Educational Purposes Only

Revised: October 27, 2002

2October 30, 2002 IT 221: Introduction to Information Security Principles For Educational Purposes Only

•Outline:

Context and Overview

Email History

-Email History (1)

-Email History (2)

-Email History (3)

Security Concerns: Email Threats

Security Concerns: Countermeasures

PGP (Pretty Good Privacy)

-Operational Description

-Summary of PGP Services

- (1) Authentication

- (2) Confidentiality

- (3) Compression

- (4) Email Compatibility

- (5) Segmentation and Reassembly

-PGP Key Management

-Crypto Keys / Key Rings

Lecture Outline (1)


•Outline:S/MIME

-S/MIME Overview

-S/MIME Functions

-S/MIME Algorithms

Discussion Points

Resources

Lecture Outline (2)


Context and Overview

•Context [2]:

In today’s distributed computing environment:

-(1) Email is perhaps the most ubiquitous network-based activity.

-(2) It’s the only distributed app that is widely used across all architectures and vendor platforms.

-(3) Users expect to (and do) send mail to others who are connected to the Internet, regardless of host OS or communications suite.

•Issues [2]:

There is a growing need for authentication and confidentiality services.

Two dominant schemas will be examined: PGP and S/MIME.


Email History (1)

•Email History [4]:“One September evening in 1973, Len Kleinrock, a computer scientist at UCLA, had just come from a conference on computing and communications." [4]

“Upon realizing he had forgotten his razor, [Kleinrock] thought he might find someone still at the conference to retrieve it." [4]

“There was a handy bit of software on the network called the resource-sharing executive, or RSEXEC. If you typed in "where so-and-so," RSEXEC looked for so-and-so by searching the "who" list -- a roster of everyone logged on -- at each site." [4]

"I asked myself, What maniac would be logged in at 3 a.m.?" Kleinrock remembered. He went to his terminal and typed "where [Colleague]." [4]


Email History (2)

•Email History [4]:“Contrary to popular myth, the US Government’s ARPANET -- a multimillion-dollar network launched in 1969 by the Defense Department's Advanced Research Projects Agency (ARPA) with the aim of electronically linking dozens of major computer science labs throughout the country -- was never intended to serve as a means of communication built to survive nuclear war.” [4]

“The whole idea was simply to link the large (and expensive) computers that ARPA purchased for individual researchers in distant laboratories throughout the country so they could economize and share resources.” [4]

“By 1969, in Cambridge and Los Angeles, the inventions of a tight community of a few dozen computer scientists and engineers…were being wired up to form the ARPANET. And, as ARPA continued pouring on the funding, in the 1970s network growth exploded with the advent of e-mail.” [4]


Email History (3)

•Email History [4]:“ARPANET was not intended as a message system. In the minds of its inventors, the network was intended for resource-sharing, period. [email].” [4]

“Between 1972 and the early 1980s, e-mail…was discovered by thousands of early users. Those years gave rise to many of the enduring features of modern digital culture: flames, emoticons, the @ sign, debates on free speech and privacy, and a sleepless search for technical improvements and agreements about the technical underpinnings of it all.

At first, e-mail was difficult to use, but by the end of the 1970s the big problems…were [solved]. The big rise in message traffic was to become the largest early force in the network's growth and development.” [4]

“[Email] would become the long-playing record of cyberspace. Just as the LP was invented for connoisseurs and audiophiles but spawned an entire industry, electronic mail grew first among the elite community of computer scientists on the ARPANET, then later bloomed like plankton across the Internet.” [4]


Security Concerns: Email Threats

•Email Threats [1]:

There are specific problems associated with Confidentiality, Integrity and Authenticity in email.

Method is to use a combination of encryption, protocols and data integrity controls to protect email:

-Interception (Confidentiality)

-Interception (Blocked Delivery)

-Interception and subsequent Replay

-Content Modification

-Origin Modification

-Content Forgery by Outsider or Recipient

-Origin Forgery by Outsider of Recipient

-Denial of message Transmission


Security Concerns: Countermeasures

•Encryption[1]:

Often prevents Confidentiality breaches and content forgery.

Defends against replay – but this requires a protocol in which each message contains something unique (e.g. seq. number) that is encrypted.

Symmetric encryption cannot protect against forgery by a recipient because both Sender and Recipient share a common key.

Because lack of control over the middle points of a network, it is difficult for a Sender or Receiver to protect against blocked delivery.


PGP (Pretty Good Privacy): Overview

•Overview [3]:Created by Philip R. Zimmerman.Provides a Confidentiality and Authentication service that can be used for email and file storage applications.Agreement with Network Associates provides a fully compatible, low cost commercial version of PGP.

•Reason for Popularity [3]:Consolidates best practices of crypto systems:

-Public-Key Encryption: RSA, DSS and Diffie Hellman-Conventional Encryption: CAST-128, IDEA and 3xDES-Hash-Coding: SHA-

Availiable for free on a variety of platforms.Wide range of applicabilityNot developed or controlled by governmental or standards organizations


Operational Description

•Operational Description [2]:

The actual operation of PGP, as opposed to the management of its keys, consists of 5 services:

-(1) Authentication

-(2) Confidentiality

-(3) Compression

-(4) Email Compatibility

-(5) Segmentation and Reassemby


Summary of PGP Services

•Summary of PGP Services [2]:

FUNCTION ALGORITHMS USED

Digital Signature DSS/SHA or RSA/SHA

Message Encryption

CAST or IDEA or Triple-key DES with Diffie-Hellman or RSA

Compression ZIP

Email Compatibility

Radix 64-conversion

Segmentation -


(1) Authentication

•STEPS [2]:(1) Sender creates a message.

(2) SHA-1 is used to generate a 160-bit hash code of the message.

(3) Hash code is encrypted with RSA using the sender’s private key, and the result is attached to the message.

(4) Receiver uses RSA with the sender’s public key to decrypt and recover the hash code.

(5) Receiver generates a new hash code for the message and compares it with the decrypted hash code. If the two match, the message is accepted as authentic.


(2) Confidentiality

•STEPS [2]:(1) Sender generates a message and a random 128-bit number to be used as a session key.

(2) Message is encrypted, using CAST-128 (or IDEA of 3xDES) with the session key.

(3) Session key is encrypted with RSA, using the recipient’s public key, and is attached to the message.

(4) Receiver uses RSA with its private key to decrypt and recover the session key.

(5) Session key is used to decrypt the message.


(3) Compression

•Compression [2]:

PGP compresses the message after applying the signature but before encryption.

Benefit of this method is that saves space both for email transmissions and for file storage)

Message encryption is applied after compression to strengthen cryptographic security. Because the compressed message has less redundancy than the original plaintext, cryptanalysis is more difficult.


(4) Email Compatibility

•NOTES [2]:When PGP is used, at least part of the block to be transmitted is encrypted. Thus, part or all of the resulting block consists of arbitrary 8-bit octets.

However, many email systems only permit the use of blocks consisting of ASCII text. To accommodate, PGP provides the services of converting the raw 8-bit binary stream to a stream of printable ASCII characters (64-Radix).

Use of radix-64 expands the message by 33%.


(5) Segmentation and Reassembly

•Segmentation and Reassembly [2]:

Email facilities often are restricted to a maximum message length. Any message longer that that a certain length must be broken up into smaller segments, each of which is mailed separately.

To accommodate this restriction, PGP automatically subdivides a message that is too large into segments that are small enough to send via email.

Receiver is responsible for stripping all e-mail headers and reassembling the block.


PGP Key Management

•Key Management [1]:

PGP Key Management is Ad Hoc.

-Each user has a set of people s/he knows and trusts. User exchanges public keys with those contacts

-Some people accept not just the public keys of those contacts, but all the public keys that their contacts have.

-Assumption is that a friend of yours is a friend of mine.

-Chain of believability / creditability becomes strained.

Instead, a PGP user can build a key ring, which is a set of all public keys s/he possesses.

-In this way, when an encrypted message arrives, the person can decrypt it if the key is on that person’s key ring.

-PGP allows a user to sign a ‘confidence value’ to key providers.


Crypto Keys/ Key Rings

•Cryptographic Keys and Key Rings [2]:

PGP makes use of four types of keys:

-(1) One-time session conventional Keys

-(2) Public Keys

-(3) Private Keys

-(4) Passphrase-based conventional Keys


S/MIME Overview

•S/MIME Overview [3]:Secure/Multipurpose Internet Mail Extension – security enhancement to the MIME Internet e-mail format standard

Based on RSA Data Security.

Will probably emerge as the industry standard.


S/MIME Functions

•S/MIME Functionality [3]:In terms of general functionality, S/MIME is very similar to PGP. Both offer the ability to sign and/or encrypt messages.

-Enveloped Data: Encrypted content and encrypted session keys for recipients.

-Signed Data: Message Digest encrypted with private key of “signer.”

-Clear-Signed Data: Signed but not encrypted.

-Signed and Enveloped Data: Various orderings for encrypting and signing.


S/MIME Algorithms

•Algorithms Used [3]:Message Digesting: SHA-1 and MDS

Digital Signatures: DSS

Secret-Key Encryption: Triple-DES, RC2/40 (exportable)

Public-Private Key Encryption: RSA with key sizes of 512 and 1024 bits, and Diffie-Hellman (for session keys).


Discussion Points

•Discussion Points:‘Real-Life’ email Threats

Alternative Methods of Protection

Commercial Best Practices


•[1] Pfleeger, Charles. Security In Computing, Prentice Hall, 1997. Chapter 9.

•[2] Stallings, William. Cryptography and Network Security, Prentice Hall, 1999. Chapter 12.

•[3] Johnson, Hedric. ‘Email Security’. Blekinge Institute of Technology,Sweden. Lecture based on Stallings, William. Cryptography and Network Security, Prentice Hall, 1999. Chapter 12.

•[4] Hafner, Katie and Matthew Lyon. "Talking Headers." Washington Post Magazine, August 4, 1996. Edited by Bob Thompson and John Cotter.

Resources

Documents

IT 221: Introduction to Information Security Principles Lecture 9: Email Security For Educational Purposes Only Revised: October 27, 2002