USC's cognitive deduplication uses delta compression and content-addressed storage. This creates attack surfaces that pure compression doesn't have:

Threat: A corrupted or adversarial chunk becomes a delta base, causing all chunks that reference it to decode incorrectly.

Mitigation: IntegrityVerifier computes fast hashes (xxHash-64 or CRC32) after delta decompression and rejects corrupt outputs. Enable via:

from usc.cogdedup.integrity import IntegrityVerifier, SecurityPolicy
verifier = IntegrityVerifier(SecurityPolicy(verify_deltas=True))

Threat: A crafted delta that expands to enormous output, exhausting memory.

Mitigation: SecurityPolicy.max_delta_expansion limits the expansion ratio. Default: 100x (a 1KB delta can produce at most 100KB output).

Threat: An adversarial chunk with artificially high ref_count becomes the similarity target for everything, degrading compression quality.

Mitigation: SecurityPolicy.max_ref_count_for_similarity caps how many times a chunk can be used as a delta base. Default: 1000.

Threat: In federated mode, one agent's private data could leak to another via the shared tier.

Mitigation: Only chunks exceeding promote_threshold ref_count get promoted. Promotion copies data (not references), so the shared tier holds common patterns, not unique content. Content-specific data stays in each agent's local tier.

Threat: Compression ratio differences reveal information about input similarity to stored data.

Mitigation: This is inherent to deduplication and cannot be fully eliminated. For sensitive applications, use FULL encoding only (disable similarity search) which behaves like standard compression.

policy = SecurityPolicy(
    max_ref_count_for_similarity=1000,  # Limit delta base reuse
    verify_deltas=True,                 # Hash check after decompress
    max_delta_expansion=100.0,          # Expansion ratio limit
)
verifier = IntegrityVerifier(policy)

All USC wire formats use magic bytes for identification:

• UCOG — Cognitive dedup
• USST — Stream mode
• TPF3 — Hot-lite-full
• USZR — Raw zstd fallback
• USZD — Trained-dictionary zstd
• USBR — Raw brotli fallback
• USBZ — Raw bzip2 fallback

Unknown magic bytes are rejected at decode time.