From 1 November 2026, every Calisero address will accept connections over TLS 1.2 and TLS 1.3 only: the site, your account, the documentation, the short links and the API (https://rest.calisero.ro). A client that offers only TLS 1.0 or TLS 1.1 will be refused. Until then, everything works as it does today.
Why
TLS 1.0 and TLS 1.1 have known weaknesses and were formally retired in 2021, by RFC 8996. Browsers dropped them back in 2020. As long as we accept them, an old client can negotiate a weaker connection than the API keys and the data going through it deserve.
What you need to do
Most likely, nothing. Every current browser and every operating system that still gets updates uses TLS 1.2 or TLS 1.3. The official Calisero libraries (PHP, Laravel, Symfony, Node.js, Go, Python) use their runtime's TLS settings, and the supported versions of those runtimes negotiate TLS 1.2 or TLS 1.3 without any configuration.
Check your integration by 31 October only if you send SMS from a very old system:
- PHP or Python built against OpenSSL older than 1.0.1;
- .NET Framework 4.5 or older: add
SecurityProtocolType.Tls12toServicePointManager.SecurityProtocol, or move to .NET Framework 4.7 or newer; - Java 7: start the application with
-Dhttps.protocols=TLSv1.2; - Windows 7 or Windows Server 2008 R2 without the updates that enable TLS 1.2;
- Android 4.4 or older.
What a refused connection looks like
The request never reaches Calisero: the connection stops before any HTTP response. You get no error code, but a connection error such as protocol version, handshake failure or unsupported protocol. No message is created and nothing is billed.
You can check from a terminal on the server that sends your messages:
curl -sS -o /dev/null -H 'Accept: application/json' -w 'HTTP %{http_code}\n' 'https://rest.calisero.ro/api/v1/messages'
If you get an HTTP code, for example HTTP 401, the TLS connection works. The test shows what the server's curl supports; for a Java or .NET application, its own settings above are what counts.
The delivery callbacks Calisero sends to your server do not change. If you cannot update an old system by 1 November, write to us and we will find a way together.
