The Quiet Divide Escrowed keylogs, QUIC and a sealed case

forensics
flag hiCTF{c8c46fdbd6e5e4eacabfba53a156ff9ab10567f2}

Category: Network · the-quiet-divide.zip → the-quiet-divide.pcap (110 248 pkts / 152 MB / ~98.8 s; pcap sha256 20745719…)

Chain

  1. Triage - http + quic + a little dns. The real payload is an "archive vault" HTTP API plus two QUIC v1 sessions (udp/4433, udp/4434).

  2. Keylogs from escrow shares - POST /v3/escrow bodies carry two diagnostic shares (slot A / slot B, 760 B each). shareA XOR shareB == the escrowed TLS keylog (sha256 matches keylog_sha256) → two keylog files.

  3. Decrypt the QUIC sessions with tshark -o tls.keylog_file:…. Payloads are mb-quic-observation/3 objects (signed by ARCH-14 resp. REC-14).

  4. Reference implementation - GET /v10/sdk returns text/x-python: the interop lib (evidence_components, archive_key, decrypt_archive, unmask_fragment, transaction_material_commit, final_key, seal_aad, decrypt_seal).

  5. Reassemble the codec - ranged GETs rebuild the pulse-codec_7.7.0 ELF (sha matches /v2/manifest). A PLS2 frame = the udp/9002 payload from ARCH-14; decode_pls2() → seq 10450910 / queue 23 / load 71.

  6. Archive key -

    output 
    evidence = sha256(canon(custody_records))
         || hmac(chain, "MB10/FULL/ELF||fw")
         || sig(attestation) || sig(quic_observation)
         || sha256("MB10/CODEC/STATE" || canon(state) || frame)
custody_records = /v8/audit FULL events (event_sha256 + signatures)
archive_key = HKDF(evidence, salt=archive_salt_hex, b"MIRRORBREAK/10/RECORD-VAULT")

    decrypts all three AVLT10 candidates to SQLite (mb-corpus/10, AAD commit = terminal event).

  7. Pick the winner - transfer.release_checkpoint == witnessed checkpoint_sha256 and case_commit == terminal_event_sha256; material = concat(unmask_fragment(codec, tx_id, ord, payload)); transaction_material_commit(material,…) == receipts.fragment_commit. All three archives had a structurally-valid candidate; only one material opens the independent witness (AES-256-GCM committee seal):

    output 
    archive 5a2c8adef3c0846a2d0fb62d00844c64 , tx 6dd9ec588c9914ca95df44b2

  8. Final key -

    output 
    final_key = HKDF(material || evidence || W0-checkpoint-signature,
                 salt=salt_hex, b"MIRRORBREAK/10/PRODUCTION-CASE")
decrypt_seal(b64_ciphertext, final_key, nonce_hex, body) -> hiCTF{…}

Repro

bash 
1python3 solve_quiet_divide.py        # needs tshark + python-cryptography

Flag

output 
hiCTF{c8c46fdbd6e5e4eacabfba53a156ff9ab10567f2}

Verification

The final step is an AES-256-GCM decrypt_seal - authenticated decryption of the committee seal, so the plaintext is cryptographically proven, not guessed.