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offline-finding

offline device-finding network

Apple Find My, AirTag

SystemTechniques · 1Primitives · 10 offline-finding LSM-treestorage · medium: Buffer writes in memory, flush them as immutable sorted files and merge in the background; turns random writes into sequential I/O.›Ble advertisingembedded · low: Bluetooth LE advertising packets, scanning and rotating identifiersUwb rangingembedded · low: UWB two-way ranging and angle of arrival for precise device findingAEAD (AES-GCM, ChaCha20-Poly1305)security · low: Authenticated encryption that encrypts and detects tampering in one call; the only kind of symmetric encryption you should use.›Cryptographic hashes (SHA-2, BLAKE3)security · low: Collision-resistant fingerprints of data; SHA-256 for interoperability, BLAKE3 for speed, HMAC/HKDF for keyed uses.›ECDH key exchange (X25519, P-256)security · low: Each side multiplies the other's public curve point by its own scalar and both get the same point; always validate the peer key and run the result through a KDF.›Hardware backed keystoresecurity · low: Non-exportable keys in Secure Enclave, StrongBox, TPM: generation, use policies, biometric gatingHKDF key derivation (extract-and-ex…security · low: HMAC-based two-step key derivation: extract a uniform pseudorandom key from any secret, then expand it into as many context-bound keys as you need.›Token bucketsystems · low: A bucket of up to b tokens refilled at rate r; requests spend tokens, enforcing an average rate while allowing bursts of b.›Constant time codesecurity · low: Writing secret-dependent code without branches or memory lookups on secrets; constant-time compare and selectCsprngsecurity · low: OS-backed cryptographically secure random numbers (getrandom), and when a fast PRNG is not enough

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