The client and server cannot communicate, because they do not possess a common algorithm

- November 12, 2022

In this post, I describe how to fix the error:

"A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The client and server cannot communicate, because they do not possess a common algorithm.) (.Net SqlClient Data Provider)Error Number: -2146893007"

Cause

This error can occur when TLS 1.0 is disabled (perhaps for security compliance purposes) and you try to connect to a version of SQL server that has not been updated to support later versions of the protocol e.g. TLS 1.1 or TLS 1.2.

It can occur on SQL Server 2008, 2008 R2, 2012 and 2014.

This error occurs when TLS 1.0 is disabled on the computer connecting to the SQL server. If TLS 1.0 is disabled on the SQL Server, after a delay, a different error can occur:

"The system cannot find the file specified"

Resolution

Ensure the SQL server is updated to support a common algorithm that is enabled i.e. TLS 1.2. You can check which update is required on this Microsoft support article:

KB3135244 - TLS 1.2 support for Microsoft SQL Server

Alternatively, enabling TLS 1.0 on both the computer trying to connect to SQL and the SQL server will resolve this issue. However, please note that TLS 1.0 should be disabled as it is no longer considered secure.