Validy Technology: a Short Introduction

Validy SA

The Problem

• when users run a software application on their PC, they can observe, understand, and change both its code and its data
• if the user is a cracker, this can lead to unlicensed use, altered behavior, or hijacking by malware

Secure Tokens

• secure and tamper resistant processors have progressed and can now be used to hide a part of the application from crackers
• but checking that a token is present, even in a roundabout way, or challenging it, even using cryptography, is not truly secure

Subtractive Protection

• an effective protection scheme must subtract a part of the application to execute it inside the token
• the challenge is to pick a part that is essential, hard to guess, and whose execution in the token does not ruin performance

Protection Time: Hiding Data

• chosen fields or variables are relocated to the secure token
• their value remain in the memory of the token at all time
• host data structures keep pointers to locations in the token

Protection Time: Hiding Code

• starting from loads and stores of relocated values, host instructions are selected and translated to the token instruction set
• operations to exchange values with the token are inserted to ensure each host or token instruction can access its operands

Protection Time: Hiding Code cont'd

• token instructions are combined with def-use chains derived from data flow analysis, ciphered, and embedded in place of the original host instructions
• the token is generic except for the cryptographic key that must match the one used when protecting the application

At Runtime

• values and ciphered instructions are forwarded to the token
• instructions are unciphered, checked for consistency/correct data flow, then executed
• computed values are returned when necessary

Reversing

• to remove the protection, a cracker must infer the incoming flow of data from the outgoing flow of data and instructions
• incoming values are the result of several kilo instructions operating each second on data accumulated over the lifetime of the application
• all the exchanges with the token can be observed, but because they embed data flow information and are ciphered, token instructions are extremely difficult to change or remove without the token detecting it

Advantages

• strong protection against software piracy without undue control of the user's machine or breach of privacy
• low impact on the development and distribution of the software: protection is mostly automated, application updates can be produced after the tokens are in the field
• integrity checks or accesses to token cryptographic resources (for authentication or signature) can be added and securely tied to other token instructions

Thank You

Validy SoftNaos for Java implements this protection scheme for applications running on the Java Virtual Machine.