I wrote about this in 2023. Here’s the story:

Three Dutch security analysts discovered the vulnerabilities­—five in total—­in a European radio standard called TETRA (Terrestrial Trunked Radio), which is used in radios made by Motorola, Damm, Hytera, and others. The standard has been used in radios since the ’90s, but the flaws remained unknown because encryption algorithms used in TETRA were kept secret until now.

There’s new news:

In 2023, Carlo Meijer, Wouter Bokslag, and Jos Wetzels of security firm Midnight Blue, based in the Netherlands, discovered vulnerabilities in encryption algorithms that are part of a European radio standard created by ETSI called TETRA (Terrestrial Trunked Radio), which has been baked into radio systems made by Motorola, Damm, Sepura, and others since the ’90s. The flaws remained unknown publicly until their disclosure, because ETSI refused for decades to let anyone examine the proprietary algorithms.

[…]

But now the same researchers have found that at least one implementation of the end-to-end encryption solution endorsed by ETSI has a similar issue that makes it equally vulnerable to eavesdropping. The encryption algorithm used for the device they examined starts with a 128-bit key, but this gets compressed to 56 bits before it encrypts traffic, making it easier to crack. It’s not clear who is using this implementation of the end-to-end encryption algorithm, nor if anyone using devices with the end-to-end encryption is aware of the security vulnerability in them.

[…]

The end-to-end encryption the researchers examined recently is designed to run on top of TETRA encryption algorithms.

The researchers found the issue with the end-to-end encryption (E2EE) only after extracting and reverse-engineering the E2EE algorithm used in a radio made by Sepura.

These seem to be deliberately implemented backdoors.