Glossary
The encryption & privacy glossary
Plain-language definitions of the cryptography, metadata-privacy and on-device-security ideas behind private messaging — written not by a content farm, but by the people who actually implement them. Every entry cites primary sources and links to how RVNT does it in practice.
Protocols & Handshakes
How two devices agree on keys and keep a conversation encrypted, message after message.
Double Ratchet The Double Ratchet is the algorithm that gives end-to-end encrypted chats a fresh key for every single message. It combines a Diffie-Hellman “ratchet” that turns over with each reply and a symmetric key-derivation “ratchet” that advances per message, so a stolen key exposes neither past nor future messages. X3DH X3DH (Extended Triple Diffie-Hellman) is an asynchronous key-agreement handshake that lets two people establish a shared secret even when one of them is offline. The initiator fetches a published bundle of the recipient's public keys and performs three or four Diffie-Hellman operations to derive one session key, which then seeds the Double Ratchet for ongoing messaging. Prekey Bundle A prekey bundle is a small package of a user's public keys, published to a server in advance, that lets anyone start an encrypted conversation with them while they are offline. It typically holds a long-term identity key, a signed medium-term prekey, and a batch of single-use one-time prekeys that the sender combines to derive a shared secret. Sealed Sender Sealed sender is a technique that encrypts the sender's identity inside the message envelope, so the relay or server delivering the message learns the recipient but never sees who sent it. A short-lived signed sender certificate is sealed alongside the ciphertext; only the recipient can unwrap it. It removes the cleartext "from" field that would otherwise let an intermediary build a social graph of who talks to whom. Cryptographic Deniability Cryptographic deniability is a property of a messaging protocol where conversation partners can verify each other's messages in real time, yet neither can later produce mathematical proof to a third party of what was said or even that the two communicated. Authentication relies on shared symmetric keys both sides hold, so any transcript could have been forged by either participant.
Cryptographic Primitives
The building blocks — ciphers, key-derivation, authenticated encryption — everything else is built from.
Forward Secrecy Forward secrecy is the property that compromising your long-term keys today cannot decrypt messages you sent or received in the past. In messaging it is achieved by deriving a fresh, single-use key for every message and deleting it immediately after, so an attacker who seizes a device captures only the keys still live at that moment, not the conversation's history. AEAD AEAD stands for Authenticated Encryption with Associated Data, a class of cipher that delivers confidentiality and integrity in one operation. It encrypts the plaintext and produces an authentication tag covering both the ciphertext and optional associated data. The associated data is authenticated but left in plaintext, so any tampering with either part makes decryption fail outright. AES-256-GCM AES-256-GCM is an authenticated cipher pairing the AES block cipher with a 256-bit key and Galois/Counter Mode. It encrypts data using counter mode and computes a 128-bit authentication tag over the ciphertext plus any associated data in the same pass. The result gives confidentiality and tamper detection together, provided each nonce is used only once per key. Argon2id Argon2id is the recommended variant of Argon2, the winner of the 2015 Password Hashing Competition, standardized in RFC 9106. It is a memory-hard key derivation function that turns a password or PIN into a key by forcing the computation to fill a large block of RAM. That memory cost makes large-scale GPU and ASIC brute-forcing slow and expensive. SQLCipher SQLCipher is an open-source fork of SQLite that transparently encrypts the entire database file with 256-bit AES. Applications read and write SQL normally while every page is encrypted on disk and decrypted only in memory. It derives the key from a passphrase using PBKDF2 and authenticates each page with HMAC, making it a standard tool for at-rest encryption on mobile and desktop apps. End-to-End Encryption End-to-end encryption (E2EE) is a way of protecting data so that only the communicating endpoints hold the keys to decrypt it. The message is encrypted on the sender's device and decrypted only on the recipient's; every party in between — the network, the relay, the service operator — sees ciphertext they cannot read. It guarantees content confidentiality even against the provider running the service.
Post-Quantum
The encryption designed to survive a quantum computer that can break today’s elliptic curves.
ML-KEM-768 ML-KEM-768 is the NIST-standardized lattice key-encapsulation mechanism defined in FIPS 203, formerly the CRYSTALS-Kyber proposal. It lets two parties agree on a shared secret that resists both classical computers and quantum computers running Shor's algorithm. The 768 parameter set targets NIST security level 3, roughly AES-192, and its security rests on the hardness of the Module Learning With Errors problem. Harvest Now, Decrypt Later Harvest Now, Decrypt Later is an attack strategy where an adversary records encrypted traffic today and stores it, intending to decrypt it years from now once a cryptographically relevant quantum computer exists. Because encrypted data does not expire, any message protected only by classical public-key cryptography becomes retroactively readable the day quantum computers arrive. It is the core reason to deploy post-quantum encryption before such machines exist. Post-Quantum Cryptography Post-quantum cryptography is the field of public-key algorithms designed to stay secure against attackers using quantum computers, specifically Shor's algorithm, which breaks RSA and elliptic-curve cryptography. PQC schemes rest on math problems such as lattices, codes, and hashes that have no known efficient quantum solution. In 2024 NIST published the first standards, FIPS 203, 204, and 205, formalizing lattice and hash-based replacements for today's vulnerable public-key crypto.
Metadata & Anonymity
Hiding not just what you say, but who you talk to, when, and from where.
Metadata Communication metadata is the data about a message rather than its content: who contacted whom, when, how often, for how long, from what location, and over what size of message. Even when the content is end-to-end encrypted, this surrounding data is usually visible to servers and networks. Aggregated across many messages it can reveal relationships, routines, and intent as clearly as reading the words themselves. Traffic Analysis Traffic analysis is the practice of inferring relationships and activity from the observable shape of network traffic — the timing, size, direction, and volume of packets — even when the contents are fully encrypted. By correlating when one party sends and another receives, or by fingerprinting characteristic flow patterns, an observer can deduce who is talking to whom and what they are doing without ever decrypting a single byte. Mixnet A mixnet, or mix network, is an anonymity system that collects messages from many senders into a batch, then reorders, delays, and re-encrypts them before forwarding, so an observer cannot link an incoming message to an outgoing one. Adding indistinguishable cover traffic further hides who is actually communicating. The technique, invented by David Chaum in 1981, specifically targets timing and traffic-correlation attacks that ordinary encryption leaves wide open. Onion Routing Onion routing is a technique for anonymous communication in which a message is wrapped in successive layers of encryption, like an onion, and relayed through a chain of volunteer-run nodes. Each node peels off one layer to learn only the next hop, so no single relay ever knows both who sent the message and where it is heading. Invented at the U.S. Naval Research Laboratory in 1996, it is the basis of Tor.
On-Device Defenses
What protects your messages when someone is holding your unlocked phone.
Duress PIN A duress PIN is a second unlock code that opens a believable decoy version of an app instead of your real data. If you are forced to unlock your phone — at a border, by police, or by an attacker — you enter the duress PIN, they see an innocuous account, and your genuine messages and identity stay sealed and hidden. Panic Wipe A panic wipe is an emergency function that cryptographically destroys a device's secrets so a seized or stolen device yields nothing. Rather than slowly overwriting gigabytes, it deletes the small encryption keys that unlock everything; the remaining encrypted data becomes permanent noise. RVNT's version also wipes the database, media cache, and hardware-backed keys, and is irreversible by design. Proof-of-Work Identity Proof-of-work identity claims a username by spending measurable computation instead of a phone number, email, or ID. To register, your device must find a hash that meets a difficulty target — cheap to verify, expensive to mass-produce. This makes creating thousands of fake accounts costly, providing Sybil resistance without any central registrar or KYC, and without tying you to a real-world identifier.
Threats & Attacks
The surveillance techniques and attacks the rest of the glossary exists to defeat.
SS7 Attack An SS7 attack abuses Signaling System 7, the trusted global telecom signaling network that routes calls and texts between carriers, to intercept SMS, eavesdrop on calls, and locate a phone using only its number. Because SS7 was built in the 1970s with no authentication between operators, anyone with network access can impersonate a carrier node, reroute one-time passcodes, and silently track a target worldwide. IMSI Catcher An IMSI catcher is a portable fake cell tower that broadcasts a stronger signal than nearby real towers so phones nearby automatically connect to it. Once a phone connects, the device can harvest its IMSI, the unique SIM identifier that carriers map to a subscriber's name, pinpoint the phone's location, and on some models force a downgrade to weak 2G to intercept calls and texts.
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