High-level summary (one-liner)
I would build an automated collector → signer → immutable store pipeline with HSM-backed keys, append-only chain-of-custody metadata, RBAC enforced at gateway and object level, and GDPR-capable deletion via redaction/consent workflows plus verifiable cryptographic attestations.
Architecture components
- Collectors/agents: lightweight agents in cloud, VMs, endpoints that capture artifacts and generate envelope metadata.
- Ingestion gateway/queue: TLS-authenticated API + Kafka/SQS to normalize and buffer.
- Processing & Integrity service: canonicalizes artifacts, builds a manifest, computes hashes (SHA-256), signs manifests.
- Key Management: HSM/KMS (cloud + on-prem HSM cluster), CMKs for envelope encryption, separate signing keys (private in HSM, non-exportable).
- Chain-of-custody store: append-only metadata DB (immutable ledger or ledger-backed DB like Amazon QLDB / PostgreSQL with WAL hashing).
- Immutable storage: WORM-capable object store (S3 Object Lock / on-prem WORM) + optional blockchain hash-chain for tamper-evidence.
- Access control/Audit: RBAC via IAM + attribute-based access (ABAC) for case IDs; SIEM/UEBA for monitoring.
- Orchestration & Workflows: SOAR engine for automated triage and GDPR deletion/legal-hold management.
- Forensic UI / API: read-only views, export, and key-holder workflows for approved release.
Data flow
- Collector captures artifact, timestamps, collects provenance (host, process, user, sensor id).
- Collector encrypts artifact with ephemeral data key; sends artifact + metadata to gateway.
- Gateway stores artifact to staging object store, publishes message to queue.
- Processing service canonicalizes, computes hash, assembles signed manifest (manifest includes artifact hash, collector signature, timestamp, case id).
- Signing service requests HSM to sign manifest; signed manifest stored in chain-of-custody ledger and appended to artifact metadata.
- Artifact moved to final WORM storage with metadata pointer to manifest; a compact hash is pushed into optional blockchain or Merkle tree root stored in ledger for global tamper-evidence.
- RBAC enforced on retrieval; all access events logged to immutable audit trail.
Key management
- Separation of duties: different keys for encryption vs signing vs ledger protection.
- HSM-backed keys (FIPS 140-2/3). KMS for envelope encryption (data key generated, encrypted by CMK).
- Signing keys non-exportable; key rotation via staged re-signing of manifests only for future artifacts; old manifests remain verifiable by stored public keys.
- Recovery & escrow: split-key (Shamir) escrow stored in secure vaults across legal/infosec stakeholders; emergency access via quorum and logged process.
- Key lifecycle: rotate CMKs regularly, preserve previous public keys to verify historic signatures; record key IDs in manifests.
GDPR-compliant deletion
- Immutability vs right-to-erasure trade-off handled by:
- Logical deletion: redact PII fields in metadata, replace encrypted blob with a sealed tombstone while retaining tamper-evident manifest that proves deletion time and approver signature.
- If physical deletion required: delete object encryption key (crypto-shredding) — destroys the ability to decrypt while leaving signed manifest stating deletion (signed by HSM).
- Legal hold: workflow toggles hold flag preventing deletion.
- All deletion actions produce signed audit records stored in ledger.
Trade-offs
- Immutability vs regulatory deletion: pure physical immutability conflict with GDPR; crypto-shredding + signed tombstones balances compliance and forensic integrity.
- Performance vs cryptographic assurance: per-artifact HSM signing adds latency; mitigate via batching and Merkle trees (sign tree root).
- Cost vs availability: multi-region HSM and WORM increase cost; choose regions based on threat model and jurisdiction.
- Complexity vs auditability: ledger/blockchain increases system complexity but provides stronger tamper evidence.
Security controls & operational notes
- Mutual TLS and mTLS for agents, attestations for collector integrity (node identity).
- Least-privilege IAM + ABAC for case-based access.
- Continuous verification: periodic integrity scans that recompute hashes and compare to signed manifests.
- Incident playbooks: revoke keys, snapshot ledger, invoke legal/forensic teams.
I would present a diagram mapping collectors → gateway → processing/signing → ledger + WORM store, plus a short PoC: agent producing signed manifest and storing artifact in S3 Object Lock with KMS CMK and HSM signing. This design balances forensic rigor, tamper-evidence, and GDPR obligations appropriate for an Information Security Analyst leading investigations.
