diff --git a/doc/sphinx/arm/tls.rst b/doc/sphinx/arm/tls.rst
index 5f3729bf70..9d69e87a12 100644
--- a/doc/sphinx/arm/tls.rst
+++ b/doc/sphinx/arm/tls.rst
@@ -10,7 +10,8 @@ protection:
 
 - no TLS i.e. the only option available in prior versions.
 
-- encryption i.e. protection against passive attacks and eavesdropping.
+- encryption i.e. protection against passive attacks and eavesdropping,
+  the server is still authenticated but the client is not.
 
 - mutual authentication between the client and the server.
 
@@ -70,11 +71,6 @@ with some constraints including on the boost library:
 TLS/HTTPS configuration
 =======================
 
-TLS is asymmetric: the authentication of the server by the client is
-mandatory but the authentication of the client by the server is optional.
-In TLS terms this means the server can require the client certificate or
-not.
-
 The new TLS configuration parameters are:
 
 - the ``trust-anchor`` string parameter specifies the name of a file
@@ -89,14 +85,20 @@ The new TLS configuration parameters are:
 - the ``key-file`` string parameter specifies the private key of the
   end-entity certificate.
 
-- the ``cert-required`` boolean parameter allows a server to not
-  require the client certificate. Its default value is true which
-  means to require the client certificate and to authenticate it. This
-  flag has no meaning on the client side.
-
 The three string parameters must be either all not specified (TLS disabled)
 or all specified (TLS enabled).
 
+TLS is asymmetric: the authentication of the server by the client is
+mandatory but the authentication of the client by the server is optional.
+In TLS terms this means the server can require the client certificate or
+not so there is a server specific TLS parameter.
+
+- the ``cert-required`` boolean parameter allows a server to not
+  require the client certificate. Its default value is true which
+  means to require the client certificate and to authenticate the
+  client. This flag has no meaning on the client side: the server
+  always provides a certificate which is validated by the client.
+
 Objects in files must be in the PEM format. Files can contain more
 than one certificate but this was not tested and is not supported.
 
@@ -114,3 +116,8 @@ A sample set of certificates and associated objects is available at
 ``src/lib/asiolink/testutils/ca`` in sources with a ``doc.txt`` file
 explaining how they were generated using the openssl command.
 
+TLS handshake, the phase where the cryptographic parameters are exchanged
+and authentication is verified, can fail in a lot of ways. Error messages
+often do not really help to find the source of the problem.
+Both OpenSSL and Botan provide a command line tool with a verify command
+which can be used to understand and fix it.