Blossom

Blobs Stored Simply on Mediaservers. Decentralized, censorship-resistant media hosting for Nostr.

Overview

Blossom is a protocol for storing and retrieving binary data (images, videos, audio) across multiple servers. Using hash-based addressing and Nostr for authorization, Blossom ensures your media remains available even if individual servers go down.

How It Works

┌─────────────────────────────────────────────────────────┐
│                   Blossom Protocol                       │
├─────────────────────────────────────────────────────────┤
│                                                          │
│  1. Upload image to Blossom server                      │
│     ┌───────────────────────────────────────────────┐  │
│     │  image.jpg ──► SHA256 hash ──► Store blob     │  │
│     │  Result: abc123...                             │  │
│     └───────────────────────────────────────────────┘  │
│                                                          │
│  2. Publish Nostr event with hash                       │
│     ┌───────────────────────────────────────────────┐  │
│     │  Event references: https://server.com/abc123  │  │
│     └───────────────────────────────────────────────┘  │
│                                                          │
│  3. Any client can fetch from any Blossom server        │
│     ┌───────────────────────────────────────────────┐  │
│     │  Server A down? → Try Server B with same hash │  │
│     │  Same file, verified by hash                   │  │
│     └───────────────────────────────────────────────┘  │
│                                                          │
└─────────────────────────────────────────────────────────┘

Key Features

Hash-Based Addressing

Files are addressed by their SHA-256 hash:

┌─────────────────────────────────────────┐
│  File: photo.jpg                         │
│  Hash: a1b2c3d4e5f6...                  │
│                                          │
│  URL: https://blossom.server/a1b2c3d4   │
│                                          │
│  Any server with this hash = same file  │
│  Hash verifies file integrity            │
└─────────────────────────────────────────┘

Benefits:

• Verification — Prove you got the right file
• Deduplication — Same file, one hash
• Server-agnostic — Get from any mirror

Mirroring

┌─────────────────────────────────────────────────────────┐
│                   Mirror Setup                           │
├─────────────────────────────────────────────────────────┤
│                                                          │
│  Primary Server: blossom.example.com                    │
│  Mirrors:                                                │
│  ├── blossom.nostr.build                               │
│  └── cdn.backup.com                                     │
│                                                          │
│  Upload Flow:                                           │
│  File → Primary → Auto-mirror to backups               │
│                                                          │
│  Retrieval Flow:                                        │
│  Primary down? → Try Mirror 1 → Try Mirror 2           │
│                                                          │
│  Always available, always the same file                 │
│                                                          │
└─────────────────────────────────────────────────────────┘

Nostr Integration

Your Blossom settings are published to Nostr:

{
  "kind": 10063,
  "tags": [
    ["server", "https://blossom.primary.com", "primary"],
    ["server", "https://blossom.mirror.com", "mirror"]
  ],
  "content": ""
}

Clients read your settings to know where to fetch your media.

Censorship Resistance

Scenario	Traditional Hosting	Blossom
Server bans you	Content gone	Use another server
Server goes down	Content unavailable	Mirrors still work
Regional block	Can't access	Try different server

BUD Specifications

Blossom is defined by BUDs (Blossom Upgrade Documents):

BUD	Name	Description
BUD-01	Basic Operations	Upload, download, delete
BUD-02	Blob Descriptors	Metadata for blobs
BUD-04	Mirroring	Auto-copy to backups
BUD-05	Media Endpoints	Standard URLs
BUD-06	HEAD Requests	Check existence
BUD-08	File Metadata	Extended info

NIP-B7

The Nostr Integration Proposal for Blossom:

{
  "kind": 1,
  "content": "Check out this image!",
  "tags": [
    ["imeta",
      "url https://blossom.server/abc123",
      "x abc123...",
      "m image/jpeg",
      "dim 1920x1080",
      "blurhash LKJHGF..."
    ]
  ]
}

Clients supporting NIP-B7:

• Know the file hash
• Can verify downloads
• Can find mirrors if needed

Public Servers

Server	Provider	Features
blossom.nostr.build	nostr.build	Global CDN
blossom.primal.net	Primal	Default in Primal
Various self-hosted	Community	Your own control

Using nostr.build

Upload: POST https://blossom.nostr.build/upload
Fetch:  GET https://npub...blossom.nostr.build/hash

Each user gets their own subdomain for organization.

Client Support

Client	Blossom Support
Primal	Native, default
noStrudel	Optional, settings
Amethyst	Supported
Coracle	Supported

Running Your Own

Docker

# docker-compose.yml
version: '3'
services:
  blossom:
    image: hzrd149/blossom:latest
    ports:
      - "3000:3000"
    volumes:
      - ./data:/app/data
    environment:
      PUBLIC_URL: https://blossom.yourdomain.com

Configuration

{
  "port": 3000,
  "dataDir": "./data",
  "maxUploadSize": 100000000,
  "allowedMimeTypes": [
    "image/*",
    "video/*",
    "audio/*"
  ]
}

Authorization

Uploads require Nostr-signed auth events:

{
  "kind": 24242,
  "tags": [
    ["t", "upload"],
    ["size", "1234567"],
    ["x", "sha256hash"]
  ],
  "content": ""
}

The signature proves you own the keypair, authorizing the upload.

Comparison

Feature	Blossom	IPFS	Traditional CDN
Addressing	Hash	Hash	URL
Authorization	Nostr	None	API keys
Mirroring	Native	P2P	Manual
Nostr integration	Native	None	None
Self-hosting	Easy	Complex	Complex

Use Cases

Social Media

• Profile pictures
• Post images/videos
• Media in DMs

Content Publishing

• Blog images
• Podcast hosting
• Video content

Backups

• Redundant storage
• Personal archives
• Distributed hosting

Links

• Specification: github.com/hzrd149/blossom
• NIP-B7: nips.nostr.com/B7
• nostr.build: blossom.nostr.build

See Also

• Nostr Protocol — The protocol
• noStrudel — Client with Blossom support
• Primal — Native Blossom integration
• Zapstr — Audio hosting