Secure Web Applications via Automatic Partitioning Stephen Chong, Jed Liu, Andrew C. Meyers, Xin Qi, K. Vikram, Lantian Zheng, Xin Zheng. Cornell University

Outline Introduction Swift Architecture Writing Swift Applications WebIL Swift Runtime Evaluation Conclusion

Introduction Web applications are a critical part of today’s infrastructure

Introduction Web applications account for 69% of internet vulnerabilities Developer dilemma Performance vs security

Introduction Guess a number game Confidentiality requirement Client cannot see number Integrity requirement Client cannot affect number of guesses Only server can decide if guess is correct Client side only implementation Best performance Client can cheat

Swift Building web applications that are secure by construction Automatic partitioning of code and data Security critical code/data placed on server side only Code/data placed on client side for performance

Swift Architecture Jif Source Code WebIL WebIL Optimization Splitting Code JavaScript and Java Output Partitioning and Replication

Swift Architecture

Writing Swift Applications Extensions of Jif programming language Security policies expressed using labels Confidentiality and Integrity policies Labels refer to principals *(server) and client principals Compiler statically checks that information flow is consistent with policies Trust model Un trusted client Trusted server

Sample Policies

Guess a number Application

WebIL Concerned with placement of code and data Replace Jif labels with placement annotations Placements chosen to optimize responsiveness without sacrificing security Partitioning solved as Integer programming problem

Placement Annotations 9 placement annotations

Guess-a-Number in WebIL

Partitioning Algorithm Represent control flow as weighted directed graph Graph nodes are statements Edge weights are exec. frequencies Integer programming problem Reduce to instance of max flow problem Solution is placements of code/data

Partioning of Guess-a-Number

Swift Runtime Controls synchronization and communication JavaScript runs on Client Java code runs on server Asymmetric trust model Execution blocks Closures Activation Records

Execution Block Methods divided into execution blocks Single entry Multiple exits Unique ids Control transfer message Branch to block executing on different host

Execution Blocks of Guess-a-Number

Activation Records Execution blocks run in context of activation records Client/server have different views of same activation record Activation record updates forwarding between hosts Security restrictions of forwarding

Closures Next execution block id and activation record id Stack of closures Correct simulation of method calls/exceptions Integrity of control flow Clients invoke high integrity closures in controlled way

Evaluation Swift Compiler Jif compiler + 20K LOC Runtime system = 2.6K LOC Six web applications implemented

Generated code size

Network messages

Conclusion Constructing secure web applications Automatic partitioning of functionality Enforcement of information security policies Programmer effort to add annotations