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Security potpourri

INF 123 – Software architecturetdebeauv@uci.edu

(Slides from Dick Taylor and Crista Lopes)

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Potpourri

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Outline

• Definitions• Common security design decisions• Trust between users• Practical guidelines

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DEFINITIONS

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Security

• Non-functional property• Protection aimed at preserving the system’s:

– integrity, – availability, – and confidentiality.

• (Definition from the National Institute of Standards and Technology)

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Confidentiality

• Only authorized parties can access the information

• Breach

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Integrity

• Authorized parties can manipulate information only in the authorized ways

• Corruption

Denethor is only a steward, but he acts like a king.(He should not.)

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Availability

• Authorized parties can access resources on all appropriate occasions

• Denial of service

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SECURITY DESIGN DECISIONS

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Common security design decisions

• Principle Of Least Authority – POLA• Separation of privilege• Complete mediation• Fail-safe defaults• Access control• …

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POLA

• AKA Principle of Least Privilege• Do not give to a component more privilege

(data, visibility, CPU time, bandwidth, …) than it needs

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POLA

Something shiny!Don’t touch it!

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POLAWhat do you think of Sauron?

He’s a good guy!

I shouldn’t say more…

That’s not in the script …

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Separation of privilege

• Goal: avoid exploitation of privilege• Run different actions in different modes• Example:

– network.py needs to go through the firewall– view.py does not– Open port only for network.py

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Complete mediation

• Make sure every access is permitted

Accesscontrol

data

Frodo’s path

Mordor checkpoints

So easy …

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Fail-safe defaults

• Deny access if explicit permission is absent• Be paranoiac

I don’t trust him, Mr Frodo.

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Access control

• Decide whether access to a protected resource should be granted or denied

• Discretionary access control– Based on the identity of the requestor, the

resource, and whether the requestor has permission to access

• Mandatory access control– Policy based

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Discretionary Access ControlDatabase A Component Q Interface F

Alice Read-Write; Always

Bend Yes

Bob Read-Write;Between 9 and 5

Fold No

Charles No access Spindle No

Dave No access Mutilate Yes

Eve Read-only; Always

None No

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Mandatory Access Control

• Bob: Secret• Alice: Confidential• Tom: Top Secret

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TRUST BETWEEN USERS

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Example: Ebay

• Open decentralized application

• Independent buyers/sellers

• Potentially malicious participants

• Need to counter threats Marvin

(malicious)

Carol

Bob

Alice

Mallory(malicious)

DecentralizedAuctioning

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Trust and security

• Trust is not binary– You trust some people– About some topics– For some time

• Many security threats exploit human nature– Social engineering

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Security and trust

No trust Blind trust

Computermeasures

Socialmeasures

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ImpersonationBob

Alice

Mallory(malicious)

“I am Bob”

Bob is reliable and everyonehas a good opinion about Bob

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Fraudulent Actions

Alice “buyer”

Alice paysfor the items

Marvin “seller”(malicious)

Marvin doesnot ship the items

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MisrepresentationBob

Alice

Mallory(malicious)

“Bob is unreliable”

Bob is reliable and everyonehas a good opinion about Bob

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Collusion (!= collision)Bob

Alice

Mallory(malicious)

“Bob is unreliable”

Bob is reliable and everyonehas a good opinion about Bob

Marvin(malicious)

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Addition of UnknownsCarol

(new entrant in the system)

Bob Alice

Bob has no informationabout Carol; he is not sure

whether to interact with Carol

Carol is new and does notknow Alice; she is not sure

whether to interact with Alice

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PRACTICAL GUIDELINES

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In practice

• Never-ending game of:– Find vulnerability– Attack– Fix– Repeat

• No system is 100% secure• Least common denominator: A system is as

secure as its least secure component

Intermezzo: MD5

• Message Digest algorithm 5• Transforms an arbitrary-length message into a

128-bit value– One way function

• MD5("The quick brown fox jumps over ") = 9e107d9d372bb6826bd81d3542a419d6

• MD5("The quick brown fox jumps over.") = e4d909c290d0fb1ca068ffaddf22cbd0

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Intermezzo: MD5 dictionary attack

• Goal: recover passwords from their encryption• Brute-force

– Given 9e107d9d372bb6826bd81d3542a419d6– Iterate over MD5(words) and compare the hash

• Dictionary attack– Rainbow tables: map MD5 to common passwords

• { 9e107d9d: ‘password’, 6826bd85: ‘qwerty’, … }– http://www.cbsnews.com/news/the-25-most-com

mon-passwords-of-2013/

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Least common denominator: example

• MD5 encryption for passwords• Hash of passwords stored in DB• But root DB password is ‘password’ • Dictionary attack• Attacker knows all passwords

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Solutions

• MD5 with salt – MD5(password + salt) instead of MD5(password)– Prevent rainbow attack– But need to keep the salt around

• How do you protect the salt?

• Better password• MD5 has collisions: use SHA1 instead of MD5

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HTTPS = HTTP + SSL

• Send HTTP request to server• Problem: Eavesdropping• Problem: Man-in-the-middle

– Malicious server pretends to be your server• Solution: encrypt transmitted data

POST /home/login HTTP/1.1Hostname: …Content-Type: jsonContent-Length: 26{ name:foo, password:OMG }

1d5fs#d3R6[5wgfr48rs&g=24fg+3t2fgfdC5.3gdf*453gdfg241df3%2gdDf1we&4w*e348sf48q6xwBas2Aa213dJE

SSL

Encrypt headers and payload, but not (IP, port) (the attacker already knows my IP and that of the server to do a MITM attack)

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Practicality

• Sometimes the human is the least common denominator

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Password reuse

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Password vs passphrase

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Sanitize inputs

Solution: escape dangerous characters (replace ‘ by \’ or by space)PHP: mysql_real_escape_string

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Think about the problem first …

Voting machines download executables from the Internet???Yes, because they run on normal computers, with Windows OS, not as purpose-built embedded systems like ATMs.