Rewriting x86 binaries without code producer cooperation

Binary code from untrusted sources remains one of the primary vehicles for software propagation and malicious software attacks. All previous work to mitigate such attacks requires code-producer cooperation, has signicant deployment issues, or incurs a high performance penalty. The problem of accurate static x86 disassembly without metadata is provably undecidable, and is regarded by many as uncircumventable. This dissertation presents a framework for x86 binary rewriting that requires no cooperation from code-producers in the form of source code or debugging symbols, requires no client-side support infrastructure (e.g., a virtual machine or hypervisor), and preserves the behavior of even complex, event-driven, x86 native COTS binaries generated by aggressively optimizing compilers. This makes it exceptionally easy to deploy. The framework is instantiated as two software security systems: Stir, a runtime basic block randomization rewriter for Return-oriented programming (ROP) attack mitigation, and Reins, a machine veriable Software Fault Isolation (SFI) and security policy specication rewriter. Both systems exhibit extremely low performance overheads in experiments on real-world COTS software| 1.6% and 2.4% respectively. The foundation of the system includes three novel approaches to static x86 disassembly, along with a method of statically proving transparency for rewriting systems.