Cryptography Concepts

Core cryptographic concepts that underpin the platform's encryption and key management — explained without exposing implementation details.

Authenticated Encryption

An encryption mode that provides both confidentiality (data is unreadable without the key) and integrity (any tampering with the ciphertext is detected). The platform uses authenticated encryption to ensure that encrypted data has not been modified, truncated, or replayed.

Analogy: A tamper-evident envelope with a unique seal — if someone opens it to change the contents, the seal breaks and the recipient immediately knows the letter was compromised.

Blind Index

A one-way derived value computed on your device from plaintext data and sent to the server for matching. The server can compare blind index values to find records — but cannot reverse the index to recover the original data. This enables equality lookups on encrypted fields.

Analogy: A library catalog entry where you can find "book about X" by its index code, but the card itself doesn't tell you the book's title, author, or contents — only that it matches your search.

Client-Side Encryption

A model where encryption and decryption of sensitive content happens on your device, not on the server's general compute layer. The server only ever receives, stores, and returns ciphertext for stored content. For operations that require plaintext access — such as OCR, document verification, and blind index generation — decryption occurs exclusively inside the secure enclave, a hardware-isolated environment that enforces the same zero-knowledge boundary.

Analogy: Writing a message in your own cipher before handing it to the postal service — the postal worker transports and stores the sealed letter but never sees the plaintext inside.

Data Encryption Key (DEK)

A key used to encrypt a specific piece of data (such as a document or its content). DEKs are per-document — each protects only the data it was created for. DEKs themselves are encrypted by higher-level keys (wrapped) and never stored in plaintext.

Analogy: A unique padlock for one specific storage unit — the key to open that padlock is itself locked inside a safe (the wrapping key) so it cannot be used unless you first unlock the safe.

End-to-End Encryption (E2EE)

A security model where data is encrypted on the sender's device and can only be decrypted by the intended recipient. No intermediary — including the platform's servers — can read the plaintext at any point during transmission or storage.

Analogy: A sealed envelope that only the recipient can open — the postal carrier transports it but cannot see inside, and the envelope remains sealed until the intended recipient's hands open it.

Envelope Encryption

A pattern where data is encrypted with a DEK, and the DEK itself is encrypted (wrapped) with a higher-level key. The encrypted data and the wrapped DEK are stored together as an "envelope." To read the data, a client first unwraps the DEK, then uses it to decrypt the content.

Analogy: A locked box (encrypted data) inside a courier's locked bag (wrapped DEK) — the courier only holds the bag key, not the box key, so they can transport the envelope without ever accessing the contents inside.

Forward Security

A property where compromising a current key does not compromise past encrypted data. Each session or time period uses independently derived keys, so even if an attacker obtains a key today, previously encrypted data remains protected.

Analogy: A hotel that generates a new door code for every room every night — yesterday's code is useless today, so a stolen code only opens that single room for that single night.

Hybrid Encryption

A technique that combines two types of encryption: a fast symmetric method for encrypting the actual data, and a slower asymmetric (public-key) method for securely exchanging the symmetric key. This gives the efficiency of symmetric encryption with the key-distribution benefits of asymmetric encryption.

For entity keys, delivery keys, grant keys, and user keypairs, the platform uses ML-KEM-1024 + X25519 for key encapsulation and ML-DSA-65 + Ed25519 for digital signatures — pairing a classical algorithm with a post-quantum algorithm in each case, so both must be broken simultaneously to compromise the operation.

Analogy: Using a fast combination lock for your luggage, but sending the combination via a secure method to the recipient — you get the speed of a simple lock with the security of a proven key-exchange protocol.

Key Hierarchy

A structured system of cryptographic keys organized in layers, where higher-level keys protect lower-level ones. The platform uses a hierarchy of key types — platform keys, organization keys, and data encryption keys — each with a specific scope and purpose. This layered approach limits the blast radius if any single key is compromised.

Analogy: A master key that unlocks a key cabinet, which holds keys for individual doors — even if someone steals a door key, they still cannot break into the cabinet without the master key.

Key Rotation

The process of periodically replacing cryptographic keys with new ones. Rotation limits the window of exposure if a key is compromised — old data is re-encrypted under the new key, and the old key is retired. The platform supports rotation at every level of the key hierarchy.

For organization-level keys, rotation is tracked by epoch — each rotation increments the epoch counter and triggers re-wrapping of all member and document keys under the new epoch.

Analogy: Changing the locks on a building periodically so that a stolen copy of an old key eventually becomes useless — the older the stolen key, the less damage it can do.

Key Wrapping

The practice of encrypting one key with another key. In the platform's hierarchy, higher-level keys "wrap" lower-level keys so they can be safely stored or transmitted. Unwrapping (decrypting) a key requires access to the wrapping key, which enforces the chain of trust.

Analogy: Putting a key inside a lockbox — to access the inner key, you must first unlock the lockbox using the outer key, establishing a clear chain of access.

Platform Key

A top-level key managed within a hardware-isolated environment that protects other keys in the hierarchy. Platform keys are never exposed to application code or transmitted over the network.

Analogy: A master key held in a bank vault that never leaves the premises — even the bank employees do not carry it; it only leaves the vault to unlock the key cabinet itself.

Post-Quantum Cryptography

Cryptographic approaches designed to remain secure against attacks from quantum computers. The platform has deployed post-quantum cryptography in production for entity keys, delivery keys, grant keys, and user keypairs: hybrid ML-KEM-1024 + X25519 for key encapsulation and hybrid ML-DSA-65 + Ed25519 for digital signatures. Each operation pairs a classical algorithm with a post-quantum one — both must be broken simultaneously to compromise the scheme.

Example: Upgrading a standard padlock to a model that resists both bolt cutters (current attacks) and power tools yet to be invented (quantum attacks) — the new lock works with your existing key-management system.

Public Key Cryptography

An encryption system using key pairs: a public key (shared openly) for encrypting data, and a private key (kept secret) for decrypting it. This allows secure communication without the parties needing to share a secret key in advance.

Analogy: A mailbox slot — anyone can drop a letter in (encrypt with the public key), but only the mailbox owner has the key to open it (decrypt with the private key).

Searchable Encryption

A family of techniques that allow queries to be executed over encrypted data without decrypting it. The platform's encrypted search infrastructure uses these techniques to return relevant results while the server never learns the query terms or document contents.

Analogy: A filing clerk who can find folders by their label (encrypted index) without reading the contents — they match your request to a label and hand over the folder, never seeing what's inside.