Whitebox Cryptography

Whitebox Cryptography

1. Attack Model: White Box Model

   • other models
     • Black Box
       • Traditional Cryptography (until 90's)
       • Assumes sender/receiver are trusted
         • Attackers have access only to inputs and outputs
       • Most conservative
       • Bounded attack
         • practicality often determined by the amount and type of data (i.e., the number of known or (adaptively) chosen plaintexts/ciphertexts) required for the attack, for example 
     • Grey Box
       • more realistic than Black box
       • unstrusted users have access to additional info
         • such as HW temperature, processing time, etc..
       • Side-channel attacks
       • Severe for HW-based crypto systems
       • Bounded Attack
         • practicality often determined by the amount and type of data (i.e., the number of known or (adaptively) chosen plaintexts/ciphertexts) required for the attack, for example 
   • Assumes cryptographic algorithms are deployed in "hostile env"
     • such as open platforms
     • sender/receiver not assumed as trusted users
     • Attackers with stronger capabilities
       • Full control of execution platform.
       • can debug application (breakpoints, etc)
       • can inspect the memory
         • and search in memory for cryptographic keys, for example.
       • can inspect the binary
       • dynamic internal details of crypto algorithms are visible and aterable
       • static analysis (disassembly, decompile, etc)
     • introduced in 2002 by Chow et al.
     • Unbounded
       • white-box attacks tend to have negligible memory complexities. As a result, the overall complexity of a white-box attack is determined by its time complexity (work factor).

2. The challenge that white-box cryptography aims to address is to implement a cryptographic algorithm in software in such a way that cryptographic assets remain secure even when subject to white-box attacks.

   • Goal: Effort of analysis >= Black Box Attack

3. Implementations

   • Kerckhoffs’ Principle: A cryptosystem should be secure even if everything about the system, except for the key, is public knowledge
     • Stands in contrast to the “security through obscurity”
       • ...approach that is often conceived with code obfuscation, where one aims to prevent reverse engineering of an application’s code such that an attacker cannot disclose secret algorithms or IP sensitive code.

4. validated by "Security Notion"

   • is formal descrition of the security of a "Encryption Scheme"
     • https://crypto.stackexchange.com/questions/26689/easy-explanation-of-ind-security-notions
     • IND-CPA
     • IND-CCA2