How to Upgrade an Existing Plain-text Connection to TLS in Go?

Upgrading a Connection to TLS in Go

Background

In secure communication, it's common practice to upgrade an existing plain-text connection to a Transport Layer Security (TLS) connection. This allows for encryption and authentication, improving the security of the communication channel.

Problem

While attempting to upgrade an open TCP connection to TLS using the tls.Server function, a segmentation fault occurs on the client during the handshake.

Solution

The following steps outline how to successfully upgrade a connection from plain-text to TLS in Go:

1. Create a TLS configuration structure (TLSconfig) containing the desired security parameters.
2. Accept a normal net.Conn connection (conn).
3. Initialize the TLS connection by calling tlsConn = tls.Server(conn, TLSconfig) and perform a handshake (tlsConn.Handshake()).
4. Convert the TLS connection (tlsConn) back to a net.Conn type using type conversion (conn = net.Conn(tlsConn)).

Handling STARTTLS Command

In the case of a SMTP server, when the client issues the STARTTLS command, follow these steps:

1. Create a TLS connection using tlsConn = tls.Server(client.socket, TLSconfig).
2. Perform a handshake (tlsConn.Handshake()).
3. Convert tlsConn to a net.Conn (conn = net.Conn(tlsConn)).

TLS Connection Behavior

When a TLS connection is established from an existing plain-text connection, the client doesn't create a new connection on a different port. Instead, the same connection is reused, allowing the handshake and secure communication to take place on the established channel.

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