Most network communications occur in a plaintext, or non-encrypted, format, which allows an attacker, with access to data paths in a network, to monitor and interpret the traffic. Different from password-based attacks, the denial-of-service attack prevents normal use of a computer or network by valid users. The attacker can also introduce a sniffing program to analyze the network and obtain information that can eventually be used to cause the network to stop responding or become corrupted, to close data applications or operating systems abnormally, and to disable other security controls to allow future attacks. Security mechanisms in the transport layer include the protection of confidentiality of transmitted data based on symmetric encryption algorithms. These systems are, for the most part, based on the establishment of the cryptographic tunnel between two nodes of the network, at the transport level, which is preceded by a strong authentication procedure.