CRIME Attack

Scott Johnson
Cryptography II
Spring 2013
CRIME Attack
Compression Ratio Infoleak
Made Easy

What is CRIME?
Exploit for SSL/TSL
Takes Advantage of Compression in
SSL/TSL
Allows Attacker To Obtain Control

Who and When of CRIME?
security researchers
Juliano Rizzo
Thai Duong
Also created the BEAST exploit
Browser Exploit Against SSL/TLS
Introduced at the 2012 Ekoparty
Security Conference

Background Information
What is SSL/TSL
Security Protocols to assist in transferring
data securely via the Internet
Built-in Compression Option
Requires a Session Cookie Containing a
Key to Validate Messages
Used by Many Websites that Require
Security

How Does CRIME Work?
The attacker creates a special
JavaScript
Script will append data to attackee’s
transmissions
This data is very specific and created to
obtain patterns
The attacker introduces the JavaScript
into the attackee’s system

How Does CRIME Work? (con’t)
Once in the system JavaScript executes
Finds active SSL/TSL Connections
Appends Specific Patterns to Outgoing SSL
Messages
Repeats the Appending Process to Output
Various Predefined Patterns
Done Before Encryption/Compression
Attacker Obtains Encrypted Message via
Man-in-the-Middle method

How Does CRIME Work? (con’t)
Attacker Compares Messages to
Achieve Patterns Created By JavaScript
Attacker Acquires Compression and
Encryption Methods via Patterns
Attacker Obtains Session Cookie
Information from Header via
Compression and Encryption Method
Attacker Uses Cookie Information to
Hijack Session

How Are The Patterns Obtained?
Attacker Uses SSL’s Compression to
Create Patterns
Attacker Introduces a Three Character
Pattern to Same Attackee Message
Multiple Times
Three characters must all be the same

The Pattern
Example of Pattern
Attackee’s data: [unknown]
Attacker Appends Various Three Characters
AAA[unknown]
BBB[unknown]
Etc.
SSL Compresses and Encrypts
Attacker Obtains Compressed and Encrypted
Message

The Pattern (con’t)
Attacker Compares Message Lengths
AAA[unknown] = 1df4h6a
BBB[unknown] = 23fdhd234
Etc.
AAA[unknown] has a smaller message length
Due to compression the first character in the
unknown data must be an A.
Attacker Repeats To Obtain A
Compression/Encryption Pattern

Compression/Encryption Pattern
With Pattern In Hand
Attacker obtains session header
Uses Compression/Encryption Pattern to
decode header
From header the attacker obtains all cookie
information
With Cookie Information Attacker Can
Act As The Attacked System and Send
Messages To Host

How To Prevent CRIME?
Simple Solutions
Turn off compression at either end of the
connection
Use another form of secure connection
CRIME is still relatively new
More in-depth solution are being researched
Exact details of attack a not published
CRIME creators are working with NIST to
create a solution

Browsers and CRIME
Microsoft Internet Explorer is not
vulnerable to CRIME
Crome added patch to latest version to
mitigate CRIME attack
FireFiox also added patch to latest
version to mitigate CRIME attack
Many Websites have added protection
on their end to thwart CRIME attacks

Conclusion
CRIME is a very specific attack
Can be easily avoided
This avoidance comes with transmission speed
decrease
Users must determine if compression or
security is top priority
Compression increases speed but allows for
CRIME
Security Defeats CRIME but disables
Compression.

Conclusion (con’t)
CRIME was easily defeated, but….
Will its knick in the armor of SSL/TSL put
doubts in the minds of the computer security
world?