Keylime is a CNCF project, originating at MIT Lincoln Laboratory, that turns the raw cryptographic primitives of the TPM into an operable remote attestation system for fleets of Linux machines. Its mission is narrow but important: given that a TPM can produce a signed quote over PCR values, and that IMA can accumulate a runtime measurement log into PCR 10, Keylime provides the infrastructure to continuously collect those quotes from many machines, verify them against policy, react to failures, and gate secret delivery on attestation success — without requiring operators to understand TPM protocols directly.
fs-verity is a Linux kernel filesystem feature, merged in kernel 5.4, that provides read-only, content-addressable integrity verification at the individual file level. When fs-verity is enabled on a file (via the FS_IOC_ENABLE_VERITY ioctl), the kernel builds a Merkle tree of the file’s content blocks and stores it in a filesystem-specific location (in an ext4 or f2fs Merkle tree block range, or in a separate xattr-adjacent structure on btrfs). From that point, the file becomes immutable — writes are rejected — and every page read from the file is verified against the Merkle tree before being returned to userspace. The file’s fs-verity digest is the SHA-256 (or SHA-512) root hash of the Merkle tree, computable without reading the file at all once the tree is built: fsverity digest file returns this digest. A file’s fs-verity digest is a stable, content-derived identity: two files with the same content have the same digest, and any byte-level modification produces a different digest that verification will detect and reject with EIO. The kernel caches verified Merkle tree nodes in the page cache alongside file data, so the amortised verification overhead is low for sequentially-read files.
