  The general individual (non-coherent) attack on the ping-pong protocol with
completely entangled pairs of three-dimensional quantum systems (qutrits) is
analyzed. The expression for amount of the eavesdropper's information as
functions from probability of attack detection is derived. It is shown, that
the security of the ping-pong protocol with pairs of qutrits is higher the
security of the protocol with pairs of qubits. It is also shown, that with the
use by legitimate users in a control mode two mutually unbiased measuring bases
the ping-pong protocol with pairs of qutrits, similar to the protocol with
groups of qubits, possesses only asymptotic security and requires additional
methods for its security amplification.

Quantum Physics