Wiretapping and Encryption
Chapter 3

Early Forms of Wiretapping
? Party Lines
? Human Operators


Wiretapping Today
? Federal and state law enforcement
? Businesses
? Private Detectives
? Political Candidates
? ......

Cellular Phones
? Can be tapped with over-the-counter 
devices


Standard Phones
? Easily tapped if signal travels by 
microwave or satellite
? Government has secured phones


Legal Mandates
? 1937 - Supreme Court rules that wiretapping is 
illegal
? 1968 - Congress explicitly allowed it by law 
enforcement agencies
? needs court order
? Electronic Communications Privacy Act include new 
technologies


Cryptography - Making and breaking 
of secret codes
? Translation of the original message into a new 
incomprehensible one by a mathematical algorithm 
using a specific KEY
? Plaintext - a message or data
? Ciphertext - coded text
? Decryption - decoding back to plaintext


Encryption Includes:
? Coding scheme or cryptographic 
algorithm
? Specific sequence of characters key 
used by the algorithm


Examples
? Cereal box codes
? Substitute cipher
? Cryptoquip in newspaper


Variations - Symmetric
? Use the same key to encrypt and 
decrypt (secret key)
? Requires a more secure system to send 
the key than the system itself


Variation - Asymmetric
? Use a key (public key) to encrypt a 
message
? Another  (private key) to decrypt it
? Requires both keys


Who Uses Encryption?
? Banks
? Industry
? Professionals
? National ID cards
? Criminals
? .....


Industrial Espionage
? Knowledge of a company’s cost and 
price structure
? Market research
? Strategic plans
? Order and customer lists
? Insider information


Professionals
? Cellular telephones and electronic mail
? unencrypted data on machines


National ID Cards
? Strong encryption can be used to authenticate data 
- unforgeable
? Users would have to have a reader with the 
government’s public key to decrypt
? Fearful of key “leakage”
? Accessibility to law enforcement agencies


Criminals
? Cryptography allows criminals to keep their 
identities a secret
? Provides security to law breakers
? Allows anonymity
? Don’t use systems that leave trails


Reliability
? The longer the key has remained unbroken, the 
stronger it is likely to be
? The longer the key is in use, the more likely 
someone will be able to discover it
? larger amount of info will be compromised
? change key frequently


Algorithms available
? DES - Data Encryption Standard 
? Developed by IBM
? Adopted as a Federal Information Processing Standard
? Uses a 56 bit key
? Has been broken
? To extend life - extend key to 128 bits
? or triple DES


RSA algorithm
? Used in public key cryptography 
? Patented in US
? Based on multiplication of large prime 
numbers


PGP - Pretty Good Privacy
? Based on RSA
? Used for protecting E-Mail

IDEA - International Data Encryption 
Algorithm
? 1991 in Switzerland
? Uses 128 - bit key
? More mathematical theory than DES


New Controversies
? 1991 - Senate Bill - Government wants to be 
able to intercept any message and be able to 
decode it as well - not passed
? FBI and wiretapping - Telephony bills
? FBI and Clipper Chip


Benefits of Government Intervention
? Aid law enforcement in protecting us 
from criminals and terrorists

Problems
? Threats to 
? privacy
? global competitiveness
? civil liberties


Communications Assistance for Law 
Enforcement Act 1994
? to and from Requires that telecommunications equipment be 
designed so govt. can:
? intercept all wire and electronic communic.
? Intercept commun. from mobile users
? Obtain call-identifying info
? phone numbers 
? Have info transmitted to a specific location
? Government will help foot the bill


Arguments for...
? Protection from terrorists and criminals
? FBI wants no new privileges
? BUT
? Necessity has not been justified
? Expense and other problems outweigh the benefits
? There has never been a guarantee of interception of 
private messages before


NEED?
? Wiretaps are less useful than informants, witnesses, etc.
? BUT
? 90% of terrorist cases used wiretaps
? Industry claims full compliance with FBI
? BUT
? Continued cooperation is not guaranteed


COST?
? A lot more than government is giving
? Will save money in
? fines, forfeitures, prevented economic loss
? Used only in a subset of investigations
? Could use the money on other technologies


Innovation and global 
competitiveness
? Stifle or delay new technologies
? economic costs
? prevent new technologies’ implementation
? Damage to US competitiveness in global 
markets due to reduced security and privacy


Public Key Cryptography
? Public Keys
? Secret key for each pair of parties who wish to 
communicate privately
? key is passed between the parties in a method 
more secure than the method used for sending 
the messages


HISTORY
? 1970 - Developed by Diffie & Hellman
? Two mathematically related keys
? to encrypt
? to decrypt
? Knowing the key to encrypt does not help decrypt 
? Each person has their own key pair

History
? The encrypting key can become public
? Public key - encrypt
? Private key - decrypt
? Senders can ID the recipients public key to encrypt 
yet only the recipient can decrypt it.
? No need to transfer secret keys


PGP - Pretty Good Privacy
? Free
? Distributed on Internet
? Developed by Zimmerman for use with 
E-Mail


Digital Signature
? Add a statement of acceptance to the electronic document
? encrypted with private key
? cyphertext is decrypted with public key
? providing any other key produced gibberish
? Others can decrypt and read but only the one with the right 
key is signed


Protection from Dossier Society
? Digital cash made possible by public key 
encryption
? Secure financial transactions without a 
credit card or checking account number

E-Cash
? No link between payer and recipient
? Convenience of credit card
? Anonymity of cash
? Use on Internet for ordinary shopping
? Can transfer credentials
? Can prevent duplicate cash files
? Back up at home incase card is lost or stolen


E-Cash continued
? Not easy to form a consumer profile or 
dossier
? Prevent fraud and forgery
? Protect privacy from mailing lists
? More control over personal information


History of Encryption
? Secret - NSA
? National Security Agency
? can do anything
? has powerful computers - break codes
? monitors all communications between US and 
other countries and within
? Designs codes and breaks codes


Government Interception
? NSA censored research
? controlled researchers
? DES thought to have back door
? Export restrictions
? munitions
? can’t export secure systems


Clipper Chip
? Why?
? need for strong encryption for business
? Desire for privacy of many Americans
? Provide a government back door
? What?
? Skipjack algorithm
? Telephones and computer
? field ID to tell government the key


Key Escrow Scheme
? Key split into two parts
? both needed to decrypt
? key kept by two different parties
? held by escrow agents
? hardware to decrypt sold only to law 
enforcement agencies


Arguments
? Needs to be secret
? to keep foreign government from using it
? so no one can use it without providing the key to the NSA
? BUT
? Computer experts can’t test it or evaluate security
? Is there a secret door??
? How secure are the agents??


Arguments - government side
? Protect us from bad guys
? provide better encryption for everyone
? ensure needs of law enforcement and 
national security are met
? improve privacy


Other Side
? Criminals can encrypt themselves before putting 
through NSA chips
? Global trade opportunities reduced
? Free market will develop better products than the 
government
? Security risks of government key escrow