TL;DR
For digital communications: use Signal. It is free, open-source, and provides genuine end-to-end encryption for text, voice, and video. For radio: practice communications discipline (brevity, pre-arranged code language, frequency rotation) rather than encryption, which is prohibited on amateur frequencies. For physical messages: pre-agreed code systems or one-time pads provide strong security without any technology.
The Threat Model Question
Before choosing a communications security method, define your threat model. Who are you protecting against, and what are they capable of?
Individual opportunists: Someone who overhears your conversation, reads an unencrypted text, or scans your unprotected radio transmissions. Relatively easy to defend against.
Organized criminal groups or personal adversaries: Motivated actors who may specifically target your communications. Require stronger measures.
State-level surveillance: The most capable threat. Nation-state intelligence agencies have capabilities that defeat most commercial encryption given enough motivation. For preppers, this is rarely the relevant threat model.
Most prepper communications security is correctly aimed at the first two categories. Signal and basic radio discipline address both.
Digital Encryption: Signal
Why Signal over SMS/iMessage/WhatsApp:
SMS is not encrypted — your carrier can read every message. Law enforcement subpoenas can access SMS records easily.
iMessage is end-to-end encrypted between Apple devices but backed up to iCloud by default (and iCloud backups are accessible to law enforcement with a warrant). Turn off iCloud Messages backup or accept that your messages are recoverable.
WhatsApp uses the Signal Protocol for encryption (strong) but is owned by Meta and collects substantial metadata. WhatsApp knows who you talk to and when.
Signal: end-to-end encrypted by default, minimal metadata, open-source code independently audited, non-profit foundation with no commercial incentive to compromise your privacy. The current standard for private communication.
Setup: Download Signal from the official app store (Signal.org). Your phone number is the identifier. Enable "Disappearing messages" on sensitive conversations (messages auto-delete after a set period, even from recipient's phone). Enable Screen Lock. Use a strong PIN or biometric lock on the phone itself.
Limitations: Signal requires both parties to have Signal installed. It requires an internet or cellular data connection. It does not work when infrastructure is down.
Radio Communications Discipline
Encryption on amateur radio is prohibited by the FCC. What is allowed — and what is effective — is communications discipline.
Brevity: Longer transmissions are easier to analyze. Short, complete messages are harder to gain intelligence from even when the words are known. The military Q-code system and phonetic alphabet exist partly for this reason — they reduce the information content per transmission.
Pre-arranged code language: Two parties who have previously agreed on what specific phrases mean can communicate in plain language that sounds innocuous. "The weather looks good for camping" means something specific to the intended recipients and nothing to a scanner monitor. This is not encryption (it is prohibited as "coded transmissions to obscure meaning" in the strict reading of FCC rules) but it is in common practice in prepper communities. Use it with awareness of the regulatory environment.
Frequency rotation: Pre-agree on multiple frequencies and a rotation schedule or sequence. "Channel 3 at odd hours" or a specific list of frequencies to try in order gives you frequency agility without encryption.
Brevity codes: Develop a short list of pre-agreed brevity codes for common situations: a number that means "situation normal," a different number that means "come now," another that means "stay away." Three-number codes are harder to correlate without context than full-sentence transmissions.
Timing discipline: Transmit at pre-arranged times, briefly. A 30-second transmission at a specific scheduled time exposes less than an ongoing conversation. Listening costs nothing and exposes nothing.
Physical Message Security
When digital and radio communications are compromised, unavailable, or insufficiently secure, physical messages are the oldest and most resilient option.
Dead drops: A pre-arranged physical location where messages are left and retrieved without the parties meeting in person. Classic intelligence tradecraft.
Setup: identify a specific location known to both parties but not to others. A specific stone in a garden wall, a specific hollow tree, a magnetic key box under a specific park bench. The sender leaves a message; the receiver retrieves it. No direct contact, no electronic record.
Signal indicators: a chalk mark on a specific wall, a specific rock placed in a visible location, a thumbtack in a specific post. The indicator tells the receiver there is a message without requiring any communication.
One-time pad messages: Print or write two copies of the same random number table (the pad). Each party keeps a copy. Messages are encrypted by XOR-ing plaintext characters against pad characters, advancing through the pad one character per letter. The pad page used is destroyed after each message.
For a prepper group that meets regularly, printing fresh OTP sheets on meeting occasions is practical. The sheets are only useful if you have the matching copy — an intercepted message without the pad is mathematically indistinguishable from random noise.
Simple substitution ciphers: Not cryptographically strong (can be broken by frequency analysis), but adequate against casual interception. A pre-agreed alphabet substitution, known only to the group, prevents casual reading of a intercepted physical message.
Invisible ink: Lemon juice, milk, or diluted urine as invisible ink (revealed by heat), written between the lines of an innocuous letter. Useful for hiding the existence of the message, not for cryptographic security.
Operational Security for Communications
The strongest encryption in the world fails if you tell someone what you are communicating about, leave your device unlocked and unattended, or communicate with someone who is compromised.
Need-to-know: Only people who need a piece of information to carry out their role should have it. A general group communication including your bug-out route, your safe house location, and your defensive capabilities creates a liability from any member who is compromised.
Device hygiene: Enable full-device encryption (iOS is encrypted by default; Android requires manual enabling on some models). Use a strong PIN (not biometric alone — biometric can be compelled, PINs generally cannot). Set up auto-lock after 30 seconds.
Who is in your communication group: The weakest link in any encrypted communication system is the humans at the endpoints. Signal cannot protect you from a contact who screenshots your conversation. Vet who you communicate with about sensitive topics and what you include them in.
Pro Tip
The most practical immediate improvement to your communications security is this: move your primary family group chat from SMS to Signal. Install Signal on every family member's phone. Set up a group. This takes 10 minutes and upgrades every routine communication from zero encryption to genuine end-to-end encryption. It is the single highest-return security action most preppers can take today.
Sources
Frequently Asked Questions
Is Signal actually secure?
Signal's encryption protocol (the Signal Protocol) is open-source and has been audited by independent security researchers. It is used as the basis for WhatsApp's encryption and several other secure messaging platforms. The metadata (who you talked to, when, how long) is also protected — Signal collects minimal metadata. The main vulnerabilities are not cryptographic: physical access to an unlocked phone, a compromised contact who shares your messages, or a compromised device with screen-reading malware. For most threat models, Signal is the current best-practice standard.
Can ham radio communications be encrypted?
Under FCC Part 97 rules, amateur radio operators are prohibited from using encryption or secret codes to obscure the meaning of transmissions. This is a legal restriction, not a technical one — encryption is technically possible on ham radio. GMRS and FRS radio users also cannot legally encrypt. Winlink and other digital modes are permitted because they use standardized (not secret) encoding. For encrypted radio communications, commercial digital radio systems or licensed two-way radio systems (under Part 90) can use encryption legally.
What is a one-time pad and does it still work?
A one-time pad (OTP) is a theoretically unbreakable encryption method when used correctly. Each message is encrypted with a truly random key the same length as the message, and the key is used only once. The encrypted message is mathematically indistinguishable from random noise. It still works. The problem is key distribution (both parties must securely possess matching pads in advance) and the requirement for truly random keys. For face-to-face groups that meet periodically, physical OTP pads are a viable low-tech option.
How do I communicate securely when internet is down?
Options in order of ease: Winlink (email via amateur radio — requires ham license, uses standardized encoding not encryption), Meshtastic (LoRa mesh network, local range, encrypted by default), physical dead drops (pre-arranged exchange of written messages), one-time pad encrypted written messages. Each has tradeoffs in range, speed, and technical requirements.