Eavesdropping refers to targeted attacks to communication links, conversations, sound
sources of any kind or IT systems in order to collect information. This starts with undetected,
secret eavesdropping on a conversation and extends up to highly technical, complex attacks in
order to intercept signals that are sent via radio or lines, e.g. by means of antenna or sensors.
Due to the low risk of detection, line or radio communications tapping is a potential threat to
information security that should not be overlooked. In principle, there is no such thing as a
cable impervious to eavesdropping. Due to the low risk of detection, line tapping is a potential
threat to IT security that should not be overlooked. Whether a line is actually being tapped can
only be determined using sophisticated instruments.
The insecure transmission of authentication data using plain text protocols like HTTP, FTP or
Telnet is especially critical, since they can easily be analysed automatically due to the clear
structure of the data.
The decision to eavesdrop on information somewhere basically depends on whether the
information that could be obtained is worth the technical and financial expenditure and the
risk of detection. This question can only be answered by knowing what capabilities the
attacker has and what their particular interests are.
Examples:
• In the case of telephone calls, an attacker may be interested in more than just listening
in on conversations. The information which is transmitted during signalling can also be
misused by an attacker, e.g. if the password is transmitted as plain text when a user logs
in due to an incorrect setting on the end device.
• If wireless transmission is unprotected or inadequately protected (e.g. if a WLAN is only
secured using WEP), an attacker can easily tap the entire communication.
• E-mails can be read anywhere along their journey through the Internet if they are not
encrypted. Unencrypted emails should therefore not be compared to letters in the
classical sense, but rather to postcards.