2 - Raspberry PI Community Projects

BACK TO BASICS
Client, server
A system where several processes communicate with each other is oen described
with the “client/server” metaphor. The server is the program that
takes requests coming from a client and executes them. It is the client that
controls operations, the server doesn't take any initiative of its own.
9.2.1. Remote Login: telnet
The telnet protocol, the oldest remote login service, is the worst in terms of security. Data and
passwords are sent in clear text — that is, not encrypted — leaving them vulnerable to anyone
snooping on the network. If necessary, take care to remove this obsolete service, that is no
longer installed by default:
# apt-get remove telnetd
There is, however, an adaptation that corrects its most crippling defects; it uses SSL (Secure
Socket Layer) to authenticate the partner and encrypt communications. The telnetd-ssl and
telnet-ssl packages provide, respectively, the server and client software.
VOCABULARY
Authentication, encryption
When you need to give a client the ability to conduct or trigger actions on a
server, security is important. You must ensure the identity of the client; this
is authentication. This identity usually consists of a password that must be
kept secret, or any other client could get the password. This is the purpose of
encryption, which is a form of encoding that allows two systems to communicate
confidential information on a public channel while protecting it from
being readable to others.
Authentication and encryption are oen mentioned together, both because
they are frequently used together, and because they are usually implemented
with similar mathematical concepts.
9.2.2. Secure Remote Login: SSH
The SSH (Secure Shell) protocol, contrary to telnet, was designed with security and reliability in
mind. Connections using SSH are secure: the partner is authenticated and all data exchanges
are encrypted.
CULTURE
SSH compared to RSH
SSH tools provide secure variants of the programs from the classic RSH (Remote
Shell) family — rsh, rlogin, and rcp. These are still available in the
rsh-server and rsh-client packages, but their usage is strongly discouraged.
SSH also offers two file transfer services. scp is a command line tool that can be used like cp,
except that any path to another machine is prefixed with the machine's name, followed by a
colon.
Chapter 9 — Unix Services
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