Domainless Encrypt · offline edition

What this file is

The complete Domainless Encrypt application in one self-contained HTML file, using only your browser's built-in Web Crypto engine. It exists so that anything you encrypted with domainless.fun/files/encrypt stays yours to decrypt forever — independent of the website, its server, or its operator. It never makes a network request.

What it can open

• .dlenc files — both generations: DLE1 (original) and DLE2 (chunked, any size)
• dlenc1: text blocks — passphrase-encrypted text
• dlkey1: messages — public-key (ECDH P-256) messages

The one thing that cannot work offline is one-time secret links (domainless.fun/files/encrypt/secret?id=…): their ciphertext lives on the server and burns after one read. Treat those as ephemeral by design.

Cryptography

• Key derivation: PBKDF2-HMAC-SHA-256 — DLE1/dlenc1: fixed 250,000 rounds; DLE2: rounds stored in the header (600,000 at build time)
• Encryption: AES-256-GCM, 128-bit auth tag (tamper-evident)
• Public-key mode: ephemeral ECDH on P-256, shared x-coordinate used as the AES-256-GCM key
• base64url = base64 with +→-, /→_, no padding

Byte-level formats (so this survives even as a printout)

DLE1 file / dlenc1: text (base64url of the same bytes behind "dlenc1:")
  "DLE1"(4) | salt(16) | iv(12) | AES-256-GCM ciphertext+tag
  key = PBKDF2-SHA256(passphrase, salt, 250000) -> 32 bytes

DLE2 file (chunked)
  fixed header, 45 bytes:
    "DLE2"(4) | version(1)=0x01 | iterations(4,BE) | salt(16) |
    ivPrefix(8) | chunkSize(4,BE) | totalChunks(4,BE) | nameCtLen(4,BE)
  then: nameCt (encrypted filename, absent if nameCtLen=0)
  then: totalChunks chunks; each = AES-256-GCM(chunkSize plaintext bytes,
        last chunk short; empty file = 1 empty chunk) + 16-byte tag
  chunk i:  IV  = ivPrefix || uint32BE(i)
            AAD = header(45 bytes) || uint32BE(i)
  filename: IV/AAD as above with i = 0xFFFFFFFF; plaintext = UTF-8 name
  key = PBKDF2-SHA256(passphrase, salt, iterations) -> 32 bytes

dlkey1: message (base64url behind "dlkey1:")
  "DLK1"(4) | ephemeral public key, uncompressed P-256 point(65) |
  iv(12) | AES-256-GCM ciphertext+tag
  key = x-coordinate of ECDH(ephemeral priv, recipient pub) (32 bytes)
  private keys travel as base64url PKCS#8; public keys as the raw 65-byte point
    

Verify or rebuild this file

The full source (server, CLI tool, tests, this file's template) is published at domainless.fun/files/encrypt/source with SHA-256 checksums, and mirrors may exist. Any implementation that follows the layouts above will interoperate — nothing here is secret except your passphrases and private keys.