Chapter 1 – Introduction Part 4 1. Message Authentication Codes Allows for Alice and Bob to have data integrity, if they share a secret key. Given a message.

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Presentation transcript:

Chapter 1 – Introduction Part 4 1

Message Authentication Codes Allows for Alice and Bob to have data integrity, if they share a secret key. Given a message M, Alice computes H(K||M) and sends M and this hash to Bob. 2 (attack detected) =? MAC h h shared secret key Communication channel SenderRecipient Attacker (modifying) MAC 6B C66809 message M’ h h shared secret key 87F9024 received MAC computed MAC message M

Public Key Problem Alice wants to send Bob a secret key K so they can communicate securely. Alice sends X = E PB (K) to Bob. Bob decrypts K = D SB (X) How does Alice know that PB is Bob’s public key and not evil Eve’s?

Digital Certificates certificate authority (CA) digitally signs a binding between an identity and the public key for that identity. 4

Firefox CA Options | Advanced | Encryption | View Certificates

Passwords A short sequence of characters used as a means to authenticate someone via a secret that they know. Userid: _________________ Password: ______________ 6

How a password is stored? Password file User Butch:ASDSA 21QW3R50E ERWWER323 … hash function Dog124

8 Strong Passwords What is a strong password – UPPER/lower case characters – Special characters – Numbers When is a password strong? – Seattle1 – M1ke03 – – TD2k5secV

Password Complexity A fixed 6 symbols password: – Numbers 10 6 = 1,000,000 – UPPER or lower case characters 26 6 = 308,915,776 – UPPER and lower case characters 52 6 = 19,770,609,664 – 32 special characters (&, %, $, £, “, |, ^, §, etc.) 32 6 = 1,073,741, practical symbols available – 94 6 = 689,869,781,056 ASCII standard 7 bit 2 7 =128 symbols – = 4,398,046,511,104 9

10 Password Length 26 UPPER/lower case characters = 52 characters 10 numbers 32 special characters => 94 characters available 5 characters: 94 5 = 7,339,040,224 6 characters: 94 6 = 689,869,781,056 7 characters: 94 7 = 64,847,759,419,264 8 characters: 94 8 = 6,095,689,385,410,816 9 characters: 94 9 = 572,994,802,228,616,704

11 Password Validity: Brute Force Test Password does not change for 60 days how many passwords should I try for each second? – 5 characters: 1,415 PW /sec – 6 characters: 133,076 PW /sec – 7 characters: 12,509,214 PW /sec – 8 characters: 1,175,866,008 PW /sec – 9 characters: 110,531,404,750 PW /sec

Secure Passwords A strong password includes characters from at least three of the following groups: Use pass phrases eg. "I want to buy 11 Dogs!" 12

Password Generators generator.en generator.en

Social Engineering Pretexting: creating a story that convinces an administrator or operator into revealing secret information. Baiting: offering a kind of “gift” to get a user or agent to perform an insecure action. Quid pro quo: offering an action or service and then expecting something in return. 14