Aiming at transmitting secret classical messages through noisy quantum channels, the present work proposes quantum codes in which no decoding erros occur nor information leakage out to a wiretapper. These codes are based on error- free codes and on decoherence-free subspaces and subsystems. A consequence of such proposition is the rise of the quantum zero-error secrecy capacity (ZESC), the maximum rate in which information can be transmitted through a noisy quantum channel using such codes with unconditional security. We also propose a graph-theoretic approach to obtain ZESC, and show that, in certain situations, this capacity is single-letter characterized.