stunnel: Authentication

Either the TLS client, the TLS server, or both need to be authenticated:

  • Server authentication prevents Man-In-The-Middle (MITM) attacks on the encryption protocol.
  • Client authentication allows for restricting access for individual clients (access control).

PSK

The easiest way to configure authentication is with PSK (Pre-Shared Key). It provides both client and server authentication. PSK is also the fastest TLS authentication.

 

PSK authentication requires stunnel version 5.09 or higher.

Server Configuration

A trivial configuration example:

[PSK server]
accept = <server_port>
connect = <dst_port>
ciphers = PSK
PSKsecrets = psk.txt

The psk.txt file contains one line for each client:

test1:oaP4EishaeSaishei6rio6xeeph3az
test2:yah5uS4aijooxilier8iaphuwah1Lo

Client Configuration

A trivial configuration example:

[PSK client 1]
client = yes
accept = 127.0.0.1:<src_port>
connect = <server_host>:<server_port>
PSKsecrets = psk1.txt

The psk1.txt file only needs a single line:

test1:oaP4EishaeSaishei6rio6xeeph3az

Each client needs a separate secret. Otherwise, all the clients sharing the same key will have to be reconfigured if the key is compromised.

Certificates

For simplicity, this tutorial only covers server authentication. The advantage of this configuration is that it does not require individual secrets for each of the clients.

Server Configuration

Unless PSK authentication is configured, each stunnel server needs a certificate with the corresponding private key. The Windows installer of stunnel automatically builds a certificate. On Unix platforms, a certificate can be built with "make cert". A certificate can also be purchased from one of the available commercial certificate authorities.

A trivial configuration example:

[certificate-based server]
accept = <server_port>
connect = <dst_port>
cert = cert.pem
key = key.pem

The "key" option may be omitted if cert.pem also contains the private key.

Client Configuration

stunnel can use an existing PKI (Public Key Infrastructure). The following configuration requires stunnel 5.15 or later:

[PKI client]
client = yes
accept = 127.0.0.1:<src_port>
connect = <server_host>:<server_port>
verifyChain = yes
CAfile = ca-certs.pem
checkHost = <server_host>

The ca-certs.pem file contains the certificates of trusted certificate authorities.

Alternatively, a technique known as certificate pinning can be used. The following configuration requires stunnel version 4.46 or higher:

[pinning client]
client = yes
accept = 127.0.0.1:<src_port>
connect = <server_host>:<server_port>
verifyPeer = yes
CAfile = peer-certificate.pem

The peer-certificate.pem file needs to contain the server certificate.

0 (0)
Article Rating (No Votes)
Rate this article
Attachments
There are no attachments for this article.
Comments
There are no comments for this article. Be the first to post a comment.
Full Name
Email Address
Security Code Security Code
Related Articles RSS Feed
Modifying the inode count for an ext2/ext3/ext4 file system
Viewed 15220 times since Fri, Sep 18, 2020
How To Add Swap Space on Ubuntu 16.04
Viewed 2372 times since Fri, Jun 8, 2018
CONFIGURE OCFS2
Viewed 8085 times since Sat, Jun 2, 2018
Transform XML to CSV Format | Unix String Pattern Manipulation The Ugly Way
Viewed 5512 times since Sun, Jan 9, 2022
Understanding logrotate utility part 1
Viewed 1767 times since Fri, Nov 30, 2018
A Quick and Practical Reference for tcpdump
Viewed 12534 times since Fri, Jul 27, 2018
HowTo: Send Email from an SMTP Server using the Command Line
Viewed 1979 times since Mon, Feb 18, 2019
RHEL: Services basic management - systemd
Viewed 18718 times since Sat, Jun 2, 2018
Linux An introduction to swap space on Linux systems
Viewed 2441 times since Thu, Jan 23, 2020
linux manual tools
Viewed 2822 times since Fri, Sep 28, 2018