The spies never stay silent – now they speak on the blockchain

The history of covert communications is filled with clever, sometimes deceptively simple, sometimes mind-bendingly sophisticated inventions. In our earlier article on SRAC – Short Range Agent Communications – we explored how, during the Cold War, spies used pocket-sized transmitters to send bursts of encrypted data in under two seconds, avoiding the deadly game of radio direction finding.

Today, decades later, the same question still drives intelligence officers, field agents, dissidents, and yes – cybercriminals: how can you exchange information in plain sight, yet ensure only the intended recipient understands it?

In the 20th century, the answer was found in bursts of radio static. In the 21st century, it might be hidden inside a blockchain transaction. This article explores the evolution from SRAC to what could be called “Numbers Stations 2.0” – the public, yet hidden, messaging channels of the digital era.

Looking back: when spies worked at close range

During the Cold War, not all agents relied on long-distance shortwave. SRAC devices thrived in urban environments where the sender and receiver could be within a few hundred meters of each other.

The key was the flash: a prearranged micro-transmission carrying just enough encrypted data for the handler to decode. Outsiders might see nothing more than meaningless blips. SRAC was the art of stealth – not by making the transmission impenetrable (though it was), but by making it practically invisible.

What has changed? The channel, not the principle

While SRAC was an analog-era tool, its underlying principle remains relevant:

1. The channel is open to everyone.

2. The content is only readable to insiders.

3. The signal is brief, but leaves a trace.

In the digital age, short range has given way to open internet. Blockchain has become the new medium. At first glance, that’s a radical shift: blockchain data is permanent, public, and retrievable. But therein lies the advantage – with the right mix of encryption and steganography, a message can hide in plain sight forever, without anyone even proving it exists.

Numbers stations: a distant cousin of SRAC

Another Cold War legend: the numbers station. Over shortwave, monotonous male or female voices read strings of numbers, often preceded by odd little melodies. To anyone with a one-time pad, these numbers were orders, instructions, or warnings. To everyone else, they were gibberish.

Numbers stations and SRAC shared the same foundation: public channel, private meaning. The differences lay in range and delivery format – not in the logic.

And in its own way, blockchain follows that same model, only now the “frequency” is a distributed ledger.

Blockchain as the modern spy channel

Three blockchain traits are particularly intriguing to anyone thinking about covert messaging:

• Public visibility – every transaction can be seen by anyone.

• Immutability – once it’s there, it cannot be erased.

• Timestamping – every entry comes with a verifiable time of origin.

When used for covert communications, blockchain doesn’t move files around like email; instead, it hides the message in transaction fields, NFT metadata, or smart contract behavior. The ledger is the channel, the decryption key is the meaning.

Steganography in the crypto age

Steganography isn’t just about hiding the contents of a message – it’s about hiding the fact that a message exists. On a blockchain, this is tricky, because everything is public and permanent – but it can be done.

Conceptual examples (not operational instructions):

• Transaction data fields – short codes, hashes, or timestamp patterns.

• NFT metadata – embedding hidden text or data within image descriptions.

• Smart contract triggers – certain functions executing (or failing to execute) act as a signal.

To the casual observer, it’s just blockchain data. To the intended recipient, it’s a message.

A digital SRAC: short time instead of short range

In the SRAC world, “short range” meant physical proximity. A digital SRAC would rely on short time windows and noise blending:

• The message is only relevant for a brief period, then becomes meaningless.

• Activity is masked by blending into normal transaction traffic.

• Communication is asynchronous – sender and receiver don’t need to be online together.

Spycraft scenarios for the blockchain era

Some purely hypothetical situations to illustrate the logic:

• A prearranged low-value transaction at a specific time acts as a signal.

• Publishing a cryptographic hash on-chain proves that an (off-chain) document existed at a certain time.

• Multiple unrelated accounts perform timed actions that, when read together, form a code.

The key is that the blockchain isn’t just storing data – it’s storing behavior, and behavior can be encoded.

Risks and countermeasures

The public nature of blockchain cuts both ways. Pattern recognition systems can flag suspicious behavior: unusual timing, repeated structures, rare data patterns. For forensic analysts, the blockchain is an open book – albeit one written in code.

Defenses and counter-intel measures might include:

• Policy – clear rules for how blockchain is used in an organization.

• Monitoring – anomaly detection to catch odd transaction patterns.

• Awareness – making developers and users aware of the permanence and visibility of their data.

Lessons from history

The SRAC and numbers station eras leave us with three enduring lessons:

1. The channel can be public if the content is private.

2. Short, unpredictable messages draw less attention.

3. Key security is everything – lose it, and the whole system collapses.

The road ahead

Beyond blockchain, new technologies could shape the next generation of covert communication:

• AI-based pattern hiding – automatically blending covert signals into normal data streams.

• Homomorphic encryption – enabling computation on encrypted data without revealing it.

• Quantum-resistant cryptography – securing messages for decades to come.

The essence of the secret message hasn’t changed – only the medium. What once hid in the hiss of the shortwave ether now sleeps between the blocks of a global ledger.