We develop a new methodology for verifying cryptographic software. We target production code written in Rust for performance and system integration, rather than verification convenience. Rust's ownership discipline enables Aeneas to extract a pure model of this code in Lean, relieving us from low-level reasoning about pointer liveness and aliasing. Lean's extensibility lets us develop tactics and libraries that greatly simplify reasoning about extracted Rust code. We design and tune our toolchain to facilitate the use of AI. Agents autonomously write formal proofs, which are independently verified by the Lean kernel. Agents also assist in the formalization of cryptographic standards and platform-specific intrinsics, which still requires expert design and review. We apply our methodology to SymCrypt, Microsoft's cryptographic provider. We verify its implementations of algorithms such as SHA-3 and ML-KEM, which were ported from C to Rust. We also extend SymCrypt with experimental optimizations and implementations of algorithms such as FrodoKEM, ML-DSA, and HPKE to explore the scalability of writing, adapting, and verifying cryptographic code. Our 237~KLOC Lean development establishes safety, panic-freedom, and functional correctness of 16.7~KLOC of Rust code supporting post-quantum cipher suites for x86-64 and ARM platforms. Our evaluation shows that verified Rust can meet SymCrypt's performance, portability, deployment, and maintainability requirements.
Ho Son, C. Fournet, Jonathan Protzenko et al.· 0 citations
Confidential computing protects applications inside Trusted Execution Environments (TEEs), but it leaves storage vulnerable. Even with disk encryption, a malicious cloud provider can roll back, replay, fork, or tamper with disk state, breaking the integrity and freshness guarantees required by stateful applications. Existing solutions either assume trusted storage, incur high overheads, or push integrity logic into applications. We present ShieldFS, a POSIX-compliant filesystem that provides end-to-end integrity and freshness for persistent storage in the confidential-computing threat model without requiring application changes. ShieldFS represents permissible filesystem states using succinct cryptographic commitments, maintained inside TEEs and replicated in a lightweight trusted registry. On-disk data structures, including a write-ahead log and a storage pool, are authenticated using hash chains and an embedded Merkle tree. ShieldFS utilizes transactions and copy-on-write to update persistent filesystem state and commitments atomically. The commitments are verified during reads, ensuring that rollback, replay, and equivocation attacks are detected even when the entire I/O stack is untrusted. We implement the design by extending ZFS, yielding ShieldZFS. Evaluation with standard filesystem benchmarks and real-world workloads shows that ShieldZFS provides strong integrity and freshness guarantees with performance comparable to state-of-the-art filesystems.
Dimitra Giantsidi, A. Delignat-Lavaud, C. Fournet et al.· 0 citations
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