  In this paper, bounds to the rate-equivocation region for the general
3-receiver broadcast channel (BC) with degraded message sets, are presented for
confidential messages to be kept secret from one of the receivers. This model
is more general than the 2-receiver BCs with confidential messages with an
external wiretapper, and the recently studied 3-receiver degraded BCs with
confidential messages, since in the model studied in this paper, the conditions
on the receivers are general and the wiretapper receives the common message.
Wyner's code partitioning combined with double-binning is used to show the
achievable rate tuples. Error probability analysis and equivocation calculation
are also provided. The secure coding scheme is sufficient to provide security
for the 3-receiver BC with 2 or 3 degraded message sets, for the scenarios: (i)
3 degraded message sets, where the first confidential message is sent to
receivers 1 and 2 and the second confidential message is sent to receiver 1,
(ii) 2 degraded message sets, where one confidential message is sent to
receiver 1, and (iii) 2 degraded message sets, where one confidential message
is sent to receivers 1 and 2. The proof for the outer bound is shown for the
cases where receiver 1 is more capable than the wiretap receiver 3, for the
first two scenarios. Under the condition that both receivers 1 and 2 are less
noisy than the wiretap receiver 3, the inner and outer bounds coincide, giving
the rate-equivocation region for (iii). In addition, a new outer bound for the
general 3-receiver BC with 3 degraded messages is obtained.
