Encrypted Attachment Storage Blueprint

Issue signed upload descriptors so authenticated clients can upload client-side encrypted attachments directly to cloud object storage, with server-enforced size limits and dual rate limiting

   
Feature encrypted-attachment-storage
Category Data
Version 1.0.0
Tags attachments, encryption, upload, resumable, cloud-storage, signed-url, e2ee
YAML Source View on GitHub
JSON API encrypted-attachment-storage.json

Fields

Name Type Required Label Description
upload_length number No Upload Length (bytes) Validations: min
cdn_number number No CDN Number  
attachment_key token No Attachment Key  
signed_upload_location url No Signed Upload Location  
upload_headers json No Upload Headers  
max_upload_bytes number No Maximum Upload Size (bytes)  

Rules

  • authentication:
    • require_active_session: true
  • privacy:
    • server_never_receives_plaintext: true
    • client_must_encrypt_before_upload: true
  • size_limits:
    • reject_before_rate_limiting: true
  • rate_limiting:
    • upload_count_limiter: per_account
    • byte_quota_limiter: per_account
    • restore_count_permit_on_byte_failure: true
  • upload_protocol:
    • selection: server_side_experiment_enrollment
    • key_generation: cryptographically_secure_random

Outcomes

Unauthenticated (Priority: 1) — Error: ATTACHMENT_UNAUTHENTICATED

Given:

  • account_identifier (session) not_exists

Result: Request rejected with 401 Unauthorized

Upload_too_large (Priority: 2) — Error: ATTACHMENT_TOO_LARGE

Given:

  • upload_length (input) gt max_upload_bytes

Result: Request rejected with 413 Request Entity Too Large

Rate_limited (Priority: 3) — Error: ATTACHMENT_RATE_LIMITED

Given:

  • per-account upload count or byte quota rate limiter is exhausted

Then:

  • emit_event event: attachment.rate_limited

Result: Request rejected with 429 Too Many Requests and Retry-After header

Descriptor_issued (Priority: 10)

Given:

  • account_identifier (session) exists
  • upload_length (input) lte max_upload_bytes
  • per-account upload count rate limiter has available permits
  • per-account byte quota rate limiter has available permits when upload_length is provided

Then:

  • create_record target: descriptor — Generate a random attachment key, select the storage backend, produce signed upload headers and location URL
  • emit_event event: attachment.descriptor_issued

Result: Returns a JSON object with cdn number, attachment key, upload headers, and a pre-signed upload URL; client uploads encrypted bytes directly to the returned location

Errors

Code Status Message Retry
ATTACHMENT_UNAUTHENTICATED 401 Authentication required to upload attachments. No
ATTACHMENT_TOO_LARGE 413 Attachment exceeds the maximum allowed size. No
ATTACHMENT_RATE_LIMITED 429 Too many attachment uploads. Please wait before trying again. Yes

Events

Event Description Payload
attachment.descriptor_issued A signed upload descriptor was successfully issued to an authenticated client account_identifier, cdn_number, attachment_key, upload_length
attachment.rate_limited An attachment upload descriptor request was rejected due to rate limiting account_identifier
Feature Relationship Reason
login required User must hold a valid authenticated session before requesting an upload descriptor
rate-limiting-abuse-prevention required Both upload count and byte quota are enforced through leaky-bucket rate limiters
cloud-storage required Attachment bytes are stored in and retrieved from cloud object storage via the issued signed URL
e2e-key-exchange recommended Attachment encryption keys are typically exchanged via the end-to-end key infrastructure before upload

AGI Readiness

Goals

Reliable Encrypted Attachment Storage

Issue signed upload descriptors so authenticated clients can upload client-side encrypted attachments directly to cloud object storage, with server-enforced size limits and dual rate limiting

Success Metrics:

Metric Target Measurement
data_accuracy 100% Records matching source of truth
duplicate_rate 0% Duplicate records detected post-creation

Constraints:

  • performance (non-negotiable): Data consistency must be maintained across concurrent operations
  • security (non-negotiable): Sensitive fields must be encrypted at rest and never logged in plaintext

Autonomy

Level: supervised

Escalation Triggers:

  • error_rate > 5

Verification

Invariants:

  • sensitive fields are never logged in plaintext
  • all data access is authenticated and authorized
  • error messages never expose internal system details

Tradeoffs

Prefer Over Reason
data_integrity performance data consistency must be maintained across all operations

Coordination

Protocol: request_response

Consumes:

Capability From Fallback
login login degrade
rate_limiting_abuse_prevention rate-limiting-abuse-prevention degrade
cloud_storage cloud-storage degrade

Safety

Action Permission Cooldown Max Auto
descriptor_issued autonomous - -
unauthenticated autonomous - -
upload_too_large autonomous - -
rate_limited autonomous - -