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diff --git a/news/phase4-encryption-sealed/index.html b/news/phase4-encryption-sealed/index.html new file mode 100644 index 0000000..dd7b5eb --- /dev/null +++ b/news/phase4-encryption-sealed/index.html @@ -0,0 +1,178 @@ +<!DOCTYPE html> +<html lang="en"> +<head> + <meta charset="utf-8"> + <meta name="viewport" content="width=device-width, initial-scale=1"> + <title>Phase 4: Encryption and Sealed Tesseras — Tesseras</title> + <meta name="description" content="Tesseras now supports private and sealed memories with hybrid post-quantum encryption — AES-256-GCM, X25519 + ML-KEM-768, and time-lock key publication."> + <!-- Open Graph --> + <meta property="og:type" content="article"> + <meta property="og:title" content="Phase 4: Encryption and Sealed Tesseras"> + <meta property="og:description" content="Tesseras now supports private and sealed memories with hybrid post-quantum encryption — AES-256-GCM, X25519 + ML-KEM-768, and time-lock key publication."> + <meta property="og:image" content="https://tesseras.net/images/social.jpg"> + <meta property="og:image:width" content="1200"> + <meta property="og:image:height" content="630"> + <meta property="og:site_name" content="Tesseras"> + <!-- Twitter Card --> + <meta name="twitter:card" content="summary_large_image"> + <meta name="twitter:title" content="Phase 4: Encryption and Sealed Tesseras"> + <meta name="twitter:description" content="Tesseras now supports private and sealed memories with hybrid post-quantum encryption — AES-256-GCM, X25519 + ML-KEM-768, and time-lock key publication."> + <meta name="twitter:image" content="https://tesseras.net/images/social.jpg"> + <link rel="stylesheet" href="https://tesseras.net/style.css?h=21f0f32121928ee5c690"> + + + <link rel="alternate" type="application/atom+xml" title="Tesseras" href="https://tesseras.net/atom.xml"> + + + <link rel="icon" type="image/png" sizes="32x32" href="https://tesseras.net/images/favicon.png?h=be4e123a23393b1a027d"> + +</head> +<body> + <header> + <h1> + <a href="https://tesseras.net/"> + <img src="https://tesseras.net/images/logo-64.png?h=c1b8d0c4c5f93b49d40b" alt="Tesseras" width="40" height="40" class="logo"> + Tesseras + </a> + </h1> + <nav> + + <a href="https://tesseras.net/about/">About</a> + <a href="https://tesseras.net/news/">News</a> + <a href="https://tesseras.net/releases/">Releases</a> + <a href="https://tesseras.net/faq/">FAQ</a> + <a href="https://tesseras.net/subscriptions/">Subscriptions</a> + <a href="https://tesseras.net/contact/">Contact</a> + + </nav> + <nav class="lang-switch"> + + <strong>English</strong> | <a href="/pt-br/news/phase4-encryption-sealed/">Português</a> + + </nav> + </header> + + <main> + +<article> + <h2>Phase 4: Encryption and Sealed Tesseras</h2> + <p class="news-date">2026-02-14</p> + <p>Some memories are not meant for everyone. A private journal, a letter to be +opened in 2050, a family secret sealed until the grandchildren are old enough. +Until now, every tessera on the network was open. Phase 4 changes that: Tesseras +now encrypts private and sealed content with a hybrid cryptographic scheme +designed to resist both classical and quantum attacks.</p> +<p>The principle remains the same — encrypt as little as possible. Public memories +need availability, not secrecy. But when someone creates a private or sealed +tessera, the content is now locked behind AES-256-GCM encryption with keys +protected by a hybrid key encapsulation mechanism combining X25519 and +ML-KEM-768. Both algorithms must be broken to access the content.</p> +<h2 id="what-was-built">What was built</h2> +<p><strong>AES-256-GCM encryptor</strong> (<code>tesseras-crypto/src/encryption.rs</code>) — Symmetric +content encryption with random 12-byte nonces and authenticated associated data +(AAD). The AAD binds ciphertext to its context: for private tesseras, the +content hash is included; for sealed tesseras, both the content hash and the +<code>open_after</code> timestamp are bound into the AAD. This means moving ciphertext +between tesseras with different open dates causes decryption failure — you +cannot trick the system into opening a sealed memory early by swapping its +ciphertext into a tessera with an earlier seal date.</p> +<p><strong>Hybrid Key Encapsulation Mechanism</strong> (<code>tesseras-crypto/src/kem.rs</code>) — Key +exchange using X25519 (classical elliptic curve Diffie-Hellman) combined with +ML-KEM-768 (the NIST-standardized post-quantum lattice-based KEM, formerly +Kyber). Both shared secrets are combined via <code>blake3::derive_key</code> with a fixed +context string ("tesseras hybrid kem v1") to produce a single 256-bit content +encryption key. This follows the same "dual from day one" philosophy as the +project's dual signing (Ed25519 + ML-DSA): if either algorithm is broken in the +future, the other still protects the content.</p> +<p><strong>Sealed Key Envelope</strong> (<code>tesseras-crypto/src/sealed.rs</code>) — Wraps a content +encryption key using the hybrid KEM, so only the tessera owner can recover it. +The KEM produces a transport key, which is XORed with the content key to produce +a wrapped key stored alongside the KEM ciphertext. On unsealing, the owner +decapsulates the KEM ciphertext to recover the transport key, then XORs again to +recover the content key.</p> +<p><strong>Key Publication</strong> (<code>tesseras-crypto/src/sealed.rs</code>) — A standalone signed +artifact for publishing a sealed tessera's content key after its <code>open_after</code> +date has passed. The owner signs the content key, tessera hash, and publication +timestamp with their dual keys (Ed25519, with ML-DSA placeholder). The manifest +stays immutable — the key publication is a separate document. Other nodes verify +the signature against the owner's public key before using the published key to +decrypt the content.</p> +<p><strong>EncryptionContext</strong> (<code>tesseras-core/src/enums.rs</code>) — A domain type that +represents the AAD context for encryption. It lives in tesseras-core rather than +tesseras-crypto because it's a domain concept (not a crypto implementation +detail). The <code>to_aad_bytes()</code> method produces deterministic serialization: a tag +byte (0x00 for Private, 0x01 for Sealed), followed by the content hash, and for +Sealed, the <code>open_after</code> timestamp as little-endian i64.</p> +<p><strong>Domain validation</strong> (<code>tesseras-core/src/service.rs</code>) — +<code>TesseraService::create()</code> now rejects Sealed and Private tesseras that don't +provide encryption keys. This is a domain-level validation: the service layer +enforces that you cannot create a sealed memory without the cryptographic +machinery to protect it. The error message is clear: "missing encryption keys +for visibility sealed until 2050-01-01."</p> +<p><strong>Core type updates</strong> — <code>TesseraIdentity</code> now includes an optional +<code>encryption_public: Option<HybridEncryptionPublic></code> field containing both the +X25519 and ML-KEM-768 public keys. <code>KeyAlgorithm</code> gained <code>X25519</code> and <code>MlKem768</code> +variants. The identity filesystem layout now supports <code>node.x25519.key</code>/<code>.pub</code> +and <code>node.mlkem768.key</code>/<code>.pub</code>.</p> +<p><strong>Testing</strong> — 8 unit tests for AES-256-GCM (roundtrip, wrong key, tampered +ciphertext, wrong AAD, cross-context decryption failure, unique nonces, plus 2 +property-based tests for arbitrary payloads and nonce uniqueness). 5 unit tests +for HybridKem (roundtrip, wrong keypair, tampered X25519, KDF determinism, plus +1 property-based test). 4 unit tests for SealedKeyEnvelope and KeyPublication. 2 +integration tests covering the complete sealed and private tessera lifecycle: +generate keys, create content key, encrypt, seal, unseal, decrypt, publish key, +and verify — the full cycle.</p> +<h2 id="architecture-decisions">Architecture decisions</h2> +<ul> +<li><strong>Hybrid KEM from day one</strong>: X25519 + ML-KEM-768 follows the same philosophy +as dual signing. We don't know which cryptographic assumptions will hold over +millennia, so we combine classical and post-quantum algorithms. The cost is +~1.2 KB of additional key material per identity — trivial compared to the +photos and videos in a tessera.</li> +<li><strong>BLAKE3 for KDF</strong>: rather than adding <code>hkdf</code> + <code>sha2</code> as new dependencies, we +use <code>blake3::derive_key</code> with a fixed context string. BLAKE3's key derivation +mode is specifically designed for this use case, and the project already +depends on BLAKE3 for content hashing.</li> +<li><strong>Immutable manifests</strong>: when a sealed tessera's <code>open_after</code> date passes, the +content key is published as a separate signed artifact (<code>KeyPublication</code>), not +by modifying the manifest. This preserves the append-only, content-addressed +nature of tesseras. The manifest was signed at creation time and never +changes.</li> +<li><strong>AAD binding prevents ciphertext swapping</strong>: the <code>EncryptionContext</code> binds +both the content hash and (for sealed tesseras) the <code>open_after</code> timestamp +into the AES-GCM authenticated data. An attacker who copies encrypted content +from a "sealed until 2050" tessera into a "sealed until 2025" tessera will +find that decryption fails — the AAD no longer matches.</li> +<li><strong>XOR key wrapping</strong>: the sealed key envelope uses a simple XOR of the content +key with the KEM-derived transport key, rather than an additional layer of +AES-GCM. Since the transport key is a fresh random value from the KEM and is +used exactly once, XOR is information-theoretically secure for this specific +use case and avoids unnecessary complexity.</li> +<li><strong>Domain validation, not storage validation</strong>: the "missing encryption keys" +check lives in <code>TesseraService::create()</code>, not in the storage layer. This +follows the hexagonal architecture pattern: domain rules are enforced at the +service boundary, not scattered across adapters.</li> +</ul> +<h2 id="what-comes-next">What comes next</h2> +<ul> +<li><strong>Phase 4 continued: Resilience and Scale</strong> — Shamir's Secret Sharing for heir +key distribution, advanced NAT traversal (STUN/TURN), performance tuning, +security audits, OS packaging</li> +<li><strong>Phase 5: Exploration and Culture</strong> — Public tessera browser by +era/location/theme/language, institutional curation, genealogy integration, +physical media export (M-DISC, microfilm, acid-free paper with QR)</li> +</ul> +<p>Sealed tesseras make Tesseras a true time capsule. A father can now record a +message for his unborn grandchild, seal it until 2060, and know that the +cryptographic envelope will hold — even if the quantum computers of the future +try to break it open early.</p> + +</article> + + </main> + + <footer> + <p>© 2026 Tesseras Project. <a href="/atom.xml">News Feed</a> · <a href="https://git.sr.ht/~ijanc/tesseras">Source</a></p> + </footer> +</body> +</html> |