TETRA (Terrestrial Trunked Radio) is a digital radio communication standard used worldwide by government, emergency, and critical infrastructure organizations such as police, fire brigades, ambulance services, military units, railways, and utility providers. A key feature of such networks is robust, encrypted communication that protects against eavesdropping and misuse.
In recent years, however, several researchers and security experts have warned that some of TETRA’s encryption algorithms are outdated or potentially contain hidden vulnerabilities due to their closed specifications. The 2023 publication of the TETRA:BURST security analysis reignited the debate: how secure are TETRA-based systems really, and is it ethical to research or exploit their weaknesses?
In this article, we explore:
- How TETRA encryption works
- Which algorithms are used
- What TETRA:BURST revealed and its practical implications
- What tools can receive and decode TETRA signals — and where the legal and ethical boundaries lie
- Future directions and alternatives for secure digital radio communication
Basics of TETRA technology
TETRA originated in the 1990s as an open standard developed by the ETSI (European Telecommunications Standards Institute). Its goal was to establish a unified digital trunked radio system across Europe and internationally.
Features:
- Uses TDMA technology (4 time slots / 25 kHz)
- Supports group calls, prioritization, tracking
- Operates in several modes: DMO (Direct Mode), TMO (Trunked Mode)
- Expanded with IP-based transmission options
Advantages over traditional analog radios:
- Digital audio quality
- Better spectrum efficiency
- Strong user and access control
- Built-in encryption capabilities
TETRA encryption algorithms
TETRA systems use multiple layers of encryption to:
- Protect the content of conversations (end-to-end)
- Prevent eavesdropping on the radio channel
- Ensure network authentication
Most common algorithms:
- TEA1: Used in Western Europe, for lower security requirements
- TEA2: High-security algorithm for EU/NATO countries only
- TEA3: Globally deployable, but less secure
- TEA4: Intended for civil and commercial use
These were closed, non-public algorithms — until researchers managed to reverse-engineer them.
The TETRA:BURST discovery
In July 2023, a Dutch security research team published their findings known as TETRA:BURST. The study successfully reverse-engineered several TETRA encryption algorithms.
Key findings:
- TEA1 is weaker than previously believed — potentially vulnerable to real-time decryption
- Key exchange protocols don’t always provide strong protection
- Many networks use default or simple keys
- Weak key management enables passive eavesdropping on some networks
Practical implications:
- Theoretically, an SDR (software-defined radio) device and the right software can intercept poorly configured TETRA systems
- Network metadata (e.g., call routing, identifiers) may be readable even if content is encrypted
SDR and TETRA: what can hobbyists do?
With software-defined radios (e.g., RTL-SDR, Airspy, HackRF) and open-source decoder software, anyone can receive TETRA signals. This does not necessarily mean access to encrypted content, but the following is possible:
- Identifying frequencies
- Mapping the network topology
- Reading unencrypted data packets (e.g., location info, status messages)
Unauthorized decryption, however — meaning decrypting protected content — has legal consequences. In Hungary and the EU, unauthorized decryption of encrypted communication is a criminal offense.
Ethical issues and the boundaries of research
Studying the security of TETRA systems is important, but also sensitive. The right to information, national security, and technical progress may conflict.
Ethical dilemmas:
- Should the reverse-engineering of closed algorithms be published?
- Where is the line between responsible research and illegal hacking?
- When does disclosure improve security, and when does it harm it?
According to the responsible disclosure principle, vendors must be notified in advance and publication should follow coordinated disclosure practices.
How can network operators protect themselves?
TETRA network administrators are advised to:
- Implement strong key management
- Use the highest available security level algorithm (e.g., TEA2)
- Rotate and update encryption keys regularly
- Disable unused functions (e.g., DMO)
- Monitor for suspicious traffic or eavesdropping attempts
Alternatives and the future
As TETRA is a decades-old standard, the industry is already developing next-gen solutions:
- Broadband Push-to-Talk systems (MCPTT) – LTE/5G-based critical communication
- Open-source radio ecosystems (e.g., GNU Radio, SDR Angel)
- Post-quantum encryption for long-term resilience
Summary
Encryption in TETRA radio systems is vital for protecting public safety and critical infrastructure. Recent research has shown that even these closed, professional-grade systems can harbor serious vulnerabilities.
As technical capabilities advance and SDR becomes more accessible, understanding these systems is increasing — but research must always remain within ethical and legal boundaries.
The future lies in more open, auditable, and secure communication infrastructure — because trust is built not on secrecy, but on transparency.
