DESCRIPTION
COMMUNICATION SYSTEM, COMMUNICATION APPARATUS,
COMMUNICATION METHOD, AND COMPUTER PROGRAM
5 TECHNICAL FIELD
[0001]
The present invention relates to a communication
system, a communication apparatus, a communication method,
and a computer program for preventing an illegal use in a
10 content transmission and, in particular, to a
communication system, a communication apparatus, a
communication method, and a computer program for
transmitting encrypted content after exchanging the
decryption key of the encrypted content according to a
15 predetermined mutual authentication and key exchange
(AKE) algorithm.
BACKGROUND ART
[0002]
20 Broadcast content or the content in packaged media
has basically been used at the place at which the content
using apparatus or a replay equipment is positioned, or
at an equipment connected to the apparatus and the
equipment through a home network (hereinafter, also
25 referred to as a "local access (LA)") in the past. For
example, from technical terms related to a communication
channel or a codec, it is difficult to use content with a
transmission through an external network such as a Wide
Area Network (WAN) by connecting to the above-mentioned
30 content using apparatus or replay equipment from outside
with a mobile equipment (hereinafter, also referred to as
1
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a "remote access (RA)"). However, a data communication
technology such as a Long Term Evolution (LTE) or a World
Interoperability for Microwave Access (WiMAX) and a highcompression
codec such as the H.264 are expected to
5 become popular so that using the technology or the codec
is likely to make a remote access implementable in the
future. For example, the user can remotely access the
server of user's home on the go in order to replay
content.
10 [0003]
It is relatively easy to perform an illegal
operation on digital content, for example, copy or
falsification. Among others, in a remote access, it is
necessary to prevent an illegal use in content
15 transmission in order to protect the copyright of the
content while permitting the use of the content for a
personal or home purpose.
[0004]
The Digital Transmission Content Protection (DTCP)
20 developed by the Digital Transmission Licensing
Administrator (DTLA) is cited as an industry-standard
technology relating to protection for a digital content
transmission. An authentication protocol between the
equipment in a content transmission and a transmission
25 protocol for encrypted content are prescribed in the DTCP.
In summary, the prescription includes that a DTCPcompatible
equipment does not transmit an easy-to-use
compressed content in an unencrypted state out of the
equipment, that the key exchange required to decrypt an
30 encrypted content is conducted according to a
predetermined mutual authentication and key exchange
2
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(AKE) algorithm, and that the range of equipment among
which the key is exchanged according to an AKE command is
limited.
[ 0005]
Further, the DTCP technology that has been ported
to an IP network or, namely, a DTCP-IP (DTCP mapping to
IP) can circulate digital content also at home through
the IP network. The current DTCP-IP (DTCP Volume 1
Specification Supple~ent E Revision 1.2) mainly intends
10 to secure the use of contents only at home and set
limitations on the round trip time (RTT) and the hop
number of IP routers or, namely, the Time To Live (TTL)
for an AKE command.
[ 0006]
15 • For example, there is proposed a information
communication system for continuing monitoring each
received AKE command and continuing updating the maximum
value of the TTL value during the period from the time
when a Source starts a DTCP-IP authentication until the
20 time just before the Source completes the authentication,
and checking the maximum TTL value just before the
completion of the authentication process in order to
complete the authentication process with exchanging the
key when the maximum value is three or less, or in order
25 to complete the authentication process without performing
the process in the final phase when the maxim~ value
exceeds three (for example, see Patent Document 1) .
[0007]
Further, the owner of the content can prohibit a
30 content providing apparatus (Source) from transmitting
content to many content using apparatuses (Sinks) at.the
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same time in order to restrict an illegal use of the
content.
[ 0008]
On the other hand, the user who uses the content
5 can separately use a plurality of content using
apparatuses depending on the situation, or a family can
share a content providing apparatus positioned at home.
In such utility forms, a content transmission from a
content providing apparatus to a plurality of content
10 using apparatuses at home is in a range of the legitimate
use of content. Thus, if the owner of the content limits
the number of apparatuses in order to prohibit a content
transmission as described above, it follows that the
owner unduly restricts the user's use of the content.
15
CITATION LIST
PATENT DOCUMENT
[0009]
Patent Document 1: Japanese Patent Application Laid-Open
20 No. 2007-36351
25
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0010]
An objective of the present invention is to provide
a communication system, a communication apparatus, a
communication method, and a computer program that are
excellent and capable of preferably transmitting
encrypted content after exchanging the decryption key of
30 the encrypted content according to a predetermined mutual
authentication and key exchange algorithm.
4
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[0011]
Another objective of the present invention is to
provide a communication system, a communication apparatus,
a communication method, and a computer program that are
5 excellent and capable of transmitting content within a
range of the user's legitimate use while limiting the
number of apparatuses to which content that requires a
protection for a copyright or another purpose is
transmitted at the same time.
10
SOLUTIONS TO PROBLEMS
[0012]
The present application has been made in view of
the above problems, and an invention according to claim 1
15 is a communication system that performs a communication
for transmitting content between a content providing
apparatus for providing the content and one or more
content using apparatuses for using the content,
including:
20 mutual authentication and key exchange means for a
mutual authentication and for exchanging a key for
encrypting the content between the content providing
apparatus and the content using apparatus;
key recording means for recording a key transmitted
25 by the content providing apparatus to each of the content
using apparatuses after combining the key with a key ID
for specifying the key and an equipment ID for specifying
the content using apparatus; and
key management means for maintaining information on
30 the key ID in the key recording means only while the
content using apparatus periodically transmits a key life
5
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management command including the key ID to the content
providing apparatus.
[0013]
Note that the "system" in this case denotes a
5 logical co~lection of a plurality of apparatuses (or
functional modules for implementing a specific function)
so that it does not especially make any difference
whether each equipment and function module is provided at
a chassis.
10 [0014]
An invention according to claim 2 of the present
application is a communication apparatus including:
mutual authentication and key exchange means for a
mutual authentication and for exchanging a key for
15 encrypting content with one or more content using
apparatuses that are to be destinations of the content;
key recording means for recording a key transmitted
to each of the content using apparatuses after combining
the key with a key ID for specifying the key and an
20 equipment ID for specifying the content using apparatus;
and
key management means for maintaining information
corresponding to the key ID in the key recording means
only while a key life management command including the
25 key ID is received from the content using apparatus at
predetermined reception cycles.
[0015]
In an invention according to claim 3 of the present
application, the key management means of the
30 communication apparatus according to claim 2 is
configured to destroy, from the key recording means,
6
•
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SP308039WOOO
information corresponding to a key ID of which key life
management command has not been received at the
predetermined reception cycles.
[ 0016]
In an invention according to claim 4 of the present
application, the key management means of the
communication apparatus according to claim 2 is
configured to, in response to receiving the key life
management command from the content using apparatus,
10 return a response indicating that the key is valid when
the information corresponding to the key ID included in
the received key life management command is maintained in
the key recording means, and return a response indicating
that the key is invalid after the corresponding
15 information has been destroyed from the key recording
means.
[0017]
In an invention according to claim 5 of the present
application, the key management means of the
20 communication apparatus according to claim 2 is
configured to, in response to receiving a key life
management command on which information indicating
destruction of the key is set, destroy information
corresponding to the key from the key management means.
25 [ 0018]
In an invention according to claim 6 of the present
application, the communication apparatus according to
claim 2 further includes registration means for preregistering
a content using apparatus with which a key is
30 to be exchanged. The key management means is configured
to, in response to receiving a key life management
7
•
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command from a content using apparatus that has not been
pre-registered in the registration means, return a
response indicating absence of the registration.
[ 0019]
An invention according to claim 7 of the present
application is a communication apparatus including:
mutual authentication and key exchange means for a
mutual authentication and for exchanging a key for
encrypting content with a content providing apparatus
10 that is to be a source of the content; and
key life management means for transmitting a key
life management command including a key ID for specifying
the key transmitted from the content providing apparatus
by the mutual authentication and key exchange means.
15 [ 0020]
In an invention according to claim 8 of the present
application, the key life management means of the
communication apparatus according to claim 7 is
configured to transmit a key life management command on
20 which information indicating destruction of the key is
set when the key becomes unnecessary.
[0021]
An invention according to claim 9 of the present
application is a communication method including:
25 a mutual authentication and key exchange step for a
mutual authentication and for exchanging a key for
encrypting content with one or more content using
apparatuses that are to be destinations of the content;
a key recording step for recording a key
30 transmitted to each of the content using apparatuses
after combining the key with a key ID for specifying the
8
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key and an equipment ID for specifying the content using
apparatus; and
a key management step for maintaining information
corresponding to the key ID in the key recording means
5 only while a key life management command including the
key ID is received from the content using apparatus at
predetermined reception cycles.
[0022]
An invention according to claim 10 of the present
10 application is a communication method including:
a mutual authentication and key exchange step for a
mutual authentication and for exchanging a key for
encrypting content with a content providing apparatus
that is to be a source of the content; and
15 a key life management step for transmitting a key
20
life management command including a key ID for specifying
the key transmitted from the content providing apparatus
in the mutual authentication and key exchange step.
[0023]
An invention according to claim 11 of the present
application is a computer program described in a
computer-readable format for implementing a process for
operating as a content providing apparatus on a computer
in a communication system that performs a communication
25 for transmitting content petween the content providing
apparatus for providing the content and one or more
content using apparatuses for using the content, the
program causing the computer to function as:
mutual authentication and key exchange means for a
30 mutual authentication and for exchanging a key for
encrypting content with one or more content using
9
SP308039WOOO
apparatuses that are to be destinations of the content;
key recording means for recording a key transmitted
to each of the content using apparatuses after combining
the key with a key ID for specifying the key and an
5 equipment ID for specifying the content using apparatus;
and
key management means for maintaining information
corresponding to the key ID in the key recording means
only while a key life management command including the
10 key ID is received from the content using apparatus at
predetermined reception cycles.
[0024]
An invention according to claim 12 of the present
application is a computer program described in a
15 computer-readable format for implementing a process for
operating as a content using apparatus on a computer in a
communication system that performs a communication for
transmitting content between a content providing
apparatus for providing the content and one or more
20 content using apparatuses for using the content, the
program causing the computer to function as:
mutual authentication and key exchange means for a
mutual authentication and for exchanging a key for
encrypting content with a content providing apparatus
25 that is to be a source of the content; and
key life management means for transmitting a key
life management command including a key ID for specifying
the key transmitted from the content providing apparatus
by the mutual authentication and key exchange means.
30 [0025]
Each of the computer programs according to claims
10
' SP308039WOOO
11 and 12 of the present application is for defining a
computer program that is described in a computer readable
format in order to implement a predetermined process on
the computer. In other words, installing the computer
5 programs according to claims 11 and 12 of the invention
on the computer provides a cooperative action on the
computer so that an action effect similar to that of the
communication apparatus according to each of claims 2 and
7 of the present invention.
10
EFFECTS OF THE INVENTION
[0026]
According to the invention, there can be provided a
communication system, a communication apparatus, a
15 communication method, and a computer program that are
excellent and capable of transmitting content within a
range of the user's legitimate use while limiting the
number of apparatuses to which content that requires a
protection for a copyright or another purpose is
20 transmitted at the same time.
[0027]
According to the invention described in claims 1, 2,
3, 7, and 9 to 12 of the present application, the content
using apparatus periodically transmits a key life
25 management command including a key ID to the content
providing apparatus at predetermined transmission cycles,
and the content providing apparatus maintains the
corresponding key only while receiving the key life
management command at predetermined reception cycles so
30 that it is possible to limit, to a predetermined number
or less, the number of the content using apparatus to
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which the content providing apparatus can transmit
content at the same time.
[0028]
According to the invention described in claim 4 of
5 the present application, in response to receiving the key
life management command, the content providing apparatus
returns a response indicating that the key is valid when
maintaining the corresponding key. Alternately, the
content providing apparatus returns a response indicating
10 that the key is invalid when receiving the command after
the content providing apparatus has destroyed the
corresponding key because not receiving the key life
management command at predetermined reception cycles.
Thus, the content using apparatus can confirm the current
15 status of its own key.
[0029]
According to the invention described in claims 5
and 8 of the present application, the content using
apparatus sets the information indicating the key is
20 unnecessary on the key life management command
corresponding to the unnecessary key, and the content
providing apparatus, in response to receiving the key
life management command on which the information
indicating the key is unnecessary is set, destroys the
25 cor~esponding key so that the content providing apparatus
can newly exchange a key with other content using
apparatuses within the upper limit of the number of the
content using apparatuses.
30
[0030]
According to the invention described in claim 6 of
the present application, the content providing apparatus
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SP308039WOOO
can pre-register a content using apparatus with which a
key is to be exchanged, for example, in response to the
request of the owner of the content. The content
providing apparatus, in response to receiving the key
5 life management command from a content using apparatus
that has not been pre~registered, returns a response
indicating that the key has not been registered so that
the content using apparatus can confirm the absence of
registration of itself.
10 [ 0031]
15
Other objectives, features, and advantages of the
present invention will be apparent from the detailed
description based on the embodiments of the present
invention described below and the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0032]
Fig. 1 is a schematic view of an exemplary
structure of a communication system according to the
20 present invention.
Fig. 2 is a schematic view of anther exemplary
structure of the communication system according to the
present invention.
Fig. 3 is a schematic view of a functional
25 structure of a content providing apparatus 10.
FigL 4 is a schematic view of a functional
structure of a content using apparatus 20.
Fig. 5 is a view for describing a mechanism for
transmitting encrypted content between a Source and a
30 Sink according to the DTCP-IP.
Fig. 6 is a view for illustrating an operation
13
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SP308039WOOO
sequence that is for a mutual authentication and key
exchange using an AKE command and that is performed
between a Source and a Sink according to the current
DTCP-IP.
Fig. 7 is a view for illustrating an operation
sequence that is for a mutual authentication and key
exchange, that includes limiting the number of content
using apparatuses to which content can be transmitted at
the same time, and that is performed between a Source
10 corresponding to a content providing apparatus and a Sink
corresponding to the content using apparatus.
Fig. 8 is a view for illustrating an exemplary
process for updating a connection table.
Fig. 9 is a view for illustrating an exemplary
15 format of a KEEP ALIVE command.
20
Fig. 10 is a view for illustrating an exemplary
operation sequence that is for updating the life of an
exchange key Kr and that is performed between the Source
and the Sink.
Fig. 11 is a view for illustrating another
exemplary operation sequence that is for updating the
life of the exchange key Kr and that is performed between
the Source and the Sink.
25 MODE FOR CARRYING OUT THE INVENTION
[0033]
Hereinafter, embodiments of the present invention
will be described with reference to the drawings.
[0034]
30 The present invention relates to a communication
system for safely transmitting content via a remote
14
SP308039WOOO
access (RA) through an external network such as a WAN.
The communication system basically includes a server
configured to provide content via the remote access (RASource)
and a client configured to request content via
5 the remote access (RA-Sink) . Herein, an AKE procedure
performed at a remote access will be referred to as an
"RA-AKE". Hereinafter, embodiments of the present
invention will be described in detail with reference to
the drawings.
10 [ 0035]
Fig. 1 schematically illustrates an exemplary
structure of a communication system according to the
present invention. In the communication system
illustrated in the drawing, a content providing apparatus
15 10 corresponding to the RA-Source is positioned at home,
and a content using apparatus 20 corresponding to the RASink
is positioned at the outside. Then, the content
using apparatus 20 remotely accesses the content
providing apparatus 10 with a communication function such
20 as a mobile phone.
[ 003 6]
The content providing apparatus 10 is generally
connected to an external network such as a WAN 50 through
a router 30 and a modem 40. The WAN 50, for example, is
25 the Internet. An IP address of the WAN 50 side is
· allocated to the router 30 from an Intenet Accsess
Service (IAS) provider 60 for which the user signs up.
Basically, the content using apparatus 20 also accesses
the IP address. The router 30 allocates a private IP
30 address to the content providing apparatus 10, and relays
the communication of the access from the WAN 50 by port
15
SP308039WOOO
forwarding. Note that, in the case where the IP address
to be allocated to the router 30 is updated by the IAS
provider 60, a DONS service 70 is used in that case for
using the Dynamic Domain Name System (DNS) (DONS)
5 functions of the router 30 to the content providing
apparatus 10 in order to accept the update.
[0037]
Further, Fig. 2 schematically illustrates anther
exemplary structure of the communication system according
10 to the present invention. In the communication system
illustrated in the drawing, a content using apparatus 20
corresponding to the RA-Sink is also positioned at home,
and is connected to a WAN 50 through a router 31 and a
modem 41. The address of a Transmission Control
15 Protocol/Internet Protocol (TCP/IP) communication that is
transmitted from the content using apparatus 20 is
c~anged by the Network Address Translation (NAT) function
of the router 31. However, other than that, the case
illustrated in Fig. 2 is the same as the case illustrated
20 in Fig. 1.
[0038]
Fig. 3 schematically illustrates a functional
structure of the content providin~ apparatus 10. The
content providing apparatus 10 includes a Central
25 Processing Unit (CPU) 11, a content receiving/replaying
unit 12, a communication unit 13, a storage unit 14, and
a timer 15 in order to function as the RA-Source and
transmit content via a remote access.
30
[ 0039]
The content receiving/replaying unit 12 includes a
broadcast receiving function, and a packaged media
16
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replaying function. The CPU 11 provides a proper
protection to a remotely-accessible content among the
content obtained in the content receiving/replaying unit
12, and then transmits the content, through the
5 communication unit 13, to the RA-Sink (the content using
apparatus 20) on which the mutual authentication and key
exchange has been performed according to the RA-AKE.
[0040]
The storage unit 14 stores, for example, the
10 identification data of the RA-Sink that is determined to
be stored by the registration process described below,
the exchange key for a remote assess that has been shared
by the RA-Sink through the RA-AKE, and the identification
data ot the key (hereinafter, also referred to as a "key
15 ID"). In the present embodiment, the number of sets of
the exchange key and the key ID that can simultaneously
be registered is limited to n (note that the n is a
positive integer). A connection table and a receiving
equipment table described below are also stored in the
20 storage unit 14. The storage unit 14 can further be used
for the purpose for storing content obtained by the
content receiving/replaying unit 12.
[0041]
The timer 15 is used when a time management is
25 necessary (for example, when the reception cycle of the
key ID from the RA-Sink is managed as described below)
while a remotely-accessible content is handled.
[0042]
Fig. 4 schematically illustrates a functional
30 structure of the content using apparatus 20. The content
using apparatus 20 includes a CPU 21, a communication
17
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unit 22, a content output unit 23, and a storage unit 24
in order to function as the RA-Sink and receive content
via a remote access.
[0043]
The content using apparatus 20 as the RA-Sink
performs the RA-AKE in order to obtain an exchange key
from the RA-Source, stores the key in the storage unit 24,
decrypt the encrypted content that has been obtained from
the RA-Source using an encryption key calculated based on
10 the exchange key, and output the content from the content
output unit 23, in addition to performing the
registration process of the exchange key and the key ID
described below on the RA-Source (the content providing
apparatus 10) through the communication unit 22. The
15 storage unit 24 is used for the purpose for storing the
exchange key and the content that has been received from
the RA--Source.
[0044]
A timer 25 is used when a time management is
20 necessary (for example, when the transmission cycle of
the key ID from the RA-Source is managed as described
below) while a remotely-accessible content is handled.
[0045]
It is assumed in the description below that the
25 method for calculating the encryption key from the
exchange key is according to the DTCP-IP (note that the
gist of the present invention is not necessarily limited
to the method) .
[0046]
30 Here, the mechanism for transmitting encrypted
content according to the DTCP-IP between the Source
18
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corresponding to a content providing apparatus and the
Sink corresponding to a content using apparatus will be
described with reference to Fig. 5 (note that the
mechanism between the RA-Source and the RA-Sink is the
5 same as the mechanism) . While the forms of content
transmission include a method to copy the content on the
Source onto the Sink, and a method to move the content
from the Source to the Sink in order not to leave the
content in the Source (widely-known), the mechanism will
10 be described in the drawing on the premise of the former
method for transmitting content by copying.
[0047]
First, the Source and the Sink establish a TCP/IP
connection in order to authenticate each other's
15 equipment (AKE procedure) . An equipment certificate
issued by the DTLA (mentioned above) is embedded in the
DTCP-compatible equipment. In the AKE procedure, after
the equipment confirms each other to be a legitimate
DTCP-compatible equipment, the Source and the Sink can
20 share an authentication key Kauth·
[0048]
When the AKE procedure has succeeded, the Source
generates an exchange key Kx that becomes a seed of
content key Kc in order to encrypt the key with the
25 authentication key Kauth and transmit the exchange key to
the Sink. Applying a predetermined calculation process
to the exchange key Kx in each of the Source and the Sink
can generate the content key Kc used for encrypting
content when the content is transmitted.
30 [0049]
After the authentication and key exchange procedure
19
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between DTCP-compatible equipment according to the AKE
has been completed, the transmission of the content is
started using a protocol such as a Hyper Text Transfer
Protocol (HTTP) or a Real Time Protocol (RTP) . In the
5 example illustrated in the drawing, the content is
transmitted according to the HTTP procedure. At that
time, a TCP/IP connection for the HTTP is created
separately from the TCP/IP connection for the AKE
procedure (in other words, each of the Source and the
10 Sink has different socket information (sets of an IP
address and a port number) for the AKE procedure and for
a content transmission) .
[0050]
There are two ways to transmit content according to
15 the HTTP protocol. One is a download style in which the
Sink requests content from the Source and the other is an
upload style in which content is pushed from the Source
side to the Sink. In the former style, the Sink as an
HTTP client requests content from the Source as an HTTP
20 server, for example, by an HTTP request using an HTTP GET
method and, in response, the requested content is
transmitted from the Sauce as the HTTP response. On the
other hand, in the latter style, the Source as an HTTP
client starts a transmission with the Sink as an HTTP
25 server, for example, by an HTTP request using an HTTP
POST method.
[0051]
The data transmitted from the Source is derived
from content that has been encrypted using the key shared
30 after the AKE authentication by the Source. Concretely,
the Source generates a nonce Nc using a random number in
20
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order to generate a content key Kc according to the
exchange key Kx, the nonce Nc and an encryption mode.
Then, the Source encrypts the content requested by the
Sink using the content key Kc in order to transmit a
5 packet that includes a payload including the encrypted
content and a header including information about the
nonce Nc and the encryption mode on a TCP stream. The IP
protocol divides the TCP stream into the size to become a
predetermined unit, and further adds a header part to the
10 divided stream in order to get an IP packet and transmit
the packet to a designated IP address.
[0052]
At the Sink side, when each IP packet from the
Source is received, the packets are assembled into a TCP
15 stream. Then, the nonce Nc and an E-EMI are extracted
from the stream, and then a content key Kc is calculated
using the nonce Nc and the E-EMI, and the exchange key Kx,
so that the encrypted content can be decrypted using the
content key Kc. Then, the decrypted plain text content
20 can be replayed. On the other hand, the Sink does not
decrypt the encrypted content and stores the content in
the storage unit 24 or passes the content to the other
equipment. When the content transmission using the HTTP
protocol as described above is completed, the TCP
25 connection used for the content transmission is properly
cut, for example, from the Sink side. (In the DTCP-IP,
the transmission of the copy control information
associated with the content is implemented by two
mechanisms. One is an Extended Encryption Mode Indicator
30 (E-EMI) for indication at the header part of a packet and
the other is an Embedded Copy Control Information (CCI).)
21
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[0053]
Note that the destruction of the exchange key Kx
before the continuous disuse time exceeds a predetermined
period (for example, two hours) is prescribed in the
5 DTCP-IP. If the Sink cannot obtain the latest exchange
key Kx from the Source, the Sink cannot use the encrypted
content. Further, the methods to use the exchange key Kx
include a method in which a key is prepared at each Sink,
and a method in which a key is used regardless of the
10 Sinks. In the present embodiment, an exchange key Kx is
prepared at each of the Sinks and identification data
(key ID) is allocated to each exchange key Kx.
[ 0054]
Fig. 6 illustrates an operation sequence that is
15 for a mutual authentication and key exchange using an AKE
command and that is performed between the Source
corresponding to a content providing apparatus and the
Sink corresponding to a content using apparatus according
to the current DTCP-IP (RTT-AKE) .
20 [ 0055]
At the Challenge-Response portion of AKE, first, an
Rx challenge including an Rx random number and an Rx
certificate is transmitted from the Sink requesting
content. On the other hand; the Source returns a Tx
25 challenge including a Tx random number and a Tx
certificate. After that, an Rx response including the Rx
random number, a Tx message, and a Tx signature is
transmitted from the Source, and a Tx response including
the Tx random number, an Rx message, and an Rx signature
30 is transmitted from the Sink in order to continue a
normal challenge-response authentication procedure. Each
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SP308039WOOO
challenge command of the commands transmitted at the
challenge-response portion includes the Device ID that is
equipment-specific identification data.
[ 0056]
5 At the above-mentioned response procedure in the
Challenge-Response, the TTL (the hop number of the IP
routers) is limited. In other words, according to the
current DTCP-IP, the TTL in the TCP/IP communication for
transmitting a command used in the AKE is set as three or
10 less in the transmitting equipment, and the receiving
equipment needs to disable the received data when the TTL
is larger than three.
[0057]
After that, an EXCHANGE_KEY command is .transmitted
15 from the Source to the Sink through a Protected RTT
Protocol and, in response, a response (not shown in the
drawing) is returned from the Sink.
[0058]
In the RTT-AKE according- to the current DTCP-IP
20 illustrated in Fig. 6, an upper limit of the round-trip
time (RTT) and the hop number of IP routers (TTL) is set
on the AKE command in order to restrict the range where
content can be transmitted through the IP network.
Depending on the owner of content, an upper limit is set
25 on the number of a content using apparatuses (RA-Sinks)
to which a content providing apparatus (RA-Source)
transmits content at the same time in order to further
restrict an illegal use of the content.
[ 0059]
30 However, the user who uses the content can
separately use a plurality of content using apparatuses
23
..
SP308039WOOO
(RA-Sinks) depending on the situation, or a family can
share content providing apparatus (RA-Source) positioned
at home. A content transmission from a content providing
apparatus to a plurality of content using apparatuses at
5 home is in a range of the legitimate use of content.
Thus, if the owner of the content limits the number of
content using apparatuses in order to prohibit a content
transmission as described above, it follows that the
owner unduly restricts the user's use of the content.
10 [0060]
In light of the foregoing, the communication system
according to the present embodiment introduces a
mechanism to secure the legitimate use of content by the
user while responding to the request of content
15 protection by the owner of the content by means of
setting the upper limit of the number of content using
apparatuses to which a content providing apparatus
transmits content at the same time as n (note that the n
is a positive integer), and properly switching the
20 content using apparatuses included in the upper limit n
without a special switching operation by the user.
[0061]
To limit, to a predetermined number or less, the
number of content using apparatuses to which a content
25 providing apparatus can transmit content at the same time,
the content using apparatus transmits an exchange key and
a corresponding key ID to the content providing apparatus
using a command at each of predetermined transmission
cycles. Then, the content providing apparatus stores the
30 corresponding exchange key only while receiving the key
ID at each of predetermined reception cycles. On the
24
• SP308039WOOO
other hand, when not receiving a command including the
key ID at the predetermined reception cycles, the content
providing apparatus destroys the corresponding exchange
key. While the destruction of the exchange key Kx before
5 the continuous disuse time exceeds a predetermined period
is prescribed in the DTCP-IP (as described above), the
content providing apparatus destroys the corresponding
exchange key once the content providing apparatus cannot
periodically receive the command including the key ID
10 even within two hours in the present embodiment.
[0062]
When receiving the command including the key ID,
the content providing apparatus confirms whether to store
the corresponding exchange key. When the content
15 providing apparatus has received the corresponding
command while storing the exchange key, the content
providing apparatus returns a response including
information indicating that the exchange key is valid to
the source content using apparatus. On the other hand,
20 when the content providing apparatus has received the
command after destroying the corresponding exchange key
because the content providing apparatus has not received
the command including the key ID at the predetermined
reception cycles, the content providing apparatus returns
25 a response including information indicating that the
exchange key is invalid to the source content using
apparatus.
[0063]
Further, when the content providing apparatus has
30 received the command including the corresponding key ID
after destroying the exchange key because the content
25
SP308039WOOO
providing apparatus has not periodically received the
command including the key ID at the predetermined
reception cycles, the content providing apparatus returns
a response including information indicating that the
5 exchange key (or the content key generated from the
exchange key) is invalid to the source content using
apparatus.
[0064]
Further, when the content using apparatus no longer
10 need the exchange key due to the completion of the
communication process with the content providing
apparatus, the content using apparatus sets the
information indicating that fact on a command to be
periodically transmitted. When receiving the command on
15 which the information indicating that the exchange key
has been unnecessary has been set, the content providing
apparatus destroys the corresponding exchange key.
[0065]
Further, the content providing apparatus can manage
20 the life of a key only with a content using apparatus
that has been registered in advance. The content using
apparatus includes an equipment ID for specifying itself
in a command to be periodically transmitted and, in
response, the content providing apparatus that has
25 received the command confirms whether the content using
apparatus corresponding to the equipment ID included in
the received command has been registered. When the
command source content using apparatus has not been
registered, the content providing apparatus returns a
30 response including the information indicating that the
content using apparatus has not been registered to the
26
•
5
SP308039WOOO
source content using apparatus before confirming whether
the exchange key corresponding to the key ID included in
the command is valid.
[0066]
Fig. 7 illustrates an operation sequence that is
for a mutual authentication and key exchange, that
includes limiting the number of content using apparatuses
to which content can be transmitted at the same time, and
that is performed between a Source corresponding to a
10 content providing apparatus and a Sink corresponding to a
content using apparatus according to the current DTCP-IP.
Note that the sequence illustrated in the drawing is
mainly used for the Full Authentication process in the
DTCP. Further, although it is considered that the
15 operation that is not set in a remote access is general,
the upper limits of the round-trip time (RTT) and the hop
number of IP routers (TTL) can be set on the AKE command
in the same manner as the operation sequence illustrated
in Fig. 6. However, it is omitted in the drawings.
20 [0067]
When requiring content, the Sink transmits a
CHALLENGE command to the Source. At that time, to
indicate that the mutual authentication and key exchange
procedure is intended to share a key (Kr) for the remote
25 access to the Source, the Sink sets a Kr-bit in the
CHALLENGE command. A Device ID that is the specific
information on the Sink is also transmitted in the
CHALLENGE command.
30
[0068]
After that, based on the Full Authentication
protocol in the DTCP, a CHALLENGE command is transmitted
27
5
SP308039WOOO
from the Source, a RESPONSE command is transmitted from
the Sink, and a RESPONSE command or a RESPONSE 2 command
is transmitted from the Source in sequence.
[0069]
Note that, at the Challenge-Response portion, a
"RESPONSE 2" is sometimes transmitted as a response from
the Sink to the Source. This is conducted when the
Device ID does not work as the specific information on
the Sink because the equipment implements a Common Device
10 Key and a Common Device Certificate. An ID u transmitted
in the RESPONSE 2 command is used as the specific
information on the Sink.
[0070]
The Source determines the equipment ID for
15 specifying the Sink (step S71). The Source uses the ID u
as the equipment ID when receiving the RESPONSE 2, and
uses the Device ID as the equipment ID when not receiving
the RESPONSE 2 command.
20
[0071]
When transmitting, to the Sink, the exchange key Kr
for the remote access as a result of the mutual
authentication and key exchange procedure with the Sink,
the Source stores an entry including the set of the
exchange key Kr, the key ID for specifying the Kr, and
25 the equipment ID of the Sink in a connection table as
described in the following table. It is assumed that as
many entries as the limited number of the Sinks to which
content can be transmitted at the same time can be stored
in the connection table. Although the number of entries
30 is two in the following table, the limited number is not
limited to two in the gist of the present invention.
28
[0072]
[Table 1]
Key ID
1
2
[0073]
Key (Kr)
Ox9a813f770d469b0e26dc0528
Ox5762e08f14a9013d8946fe02
SP308039W000
Equipment ID (Device ID/ID
Ox0000e0cd38
Ox000102187f
Further, the Source manages a receiving equipment
5 table for a remote access as described in the following
table in order to store the equipment IDs of the Sinks to
which content is to be transmitted at the same time in
the table. When the content of the content requests the
pre-registration of the Sink to be remotely accessed, the
10 equipment ID of the Sink is registered in the receiving
equipment table in advance. Although the upper limit can
be set on the number of the Sinks that can be preregistered
in the receiving equipment table, the gist of
the present invention is not limited to a specific upper
15 limit on the number. Note that, as an exemplary method
for registering the equipment ID of the Sink in the
receiving equipment table, a method in which the Source
registers the Sink at the RTT-AKE in the DTCP can be
cited.
20 [0074]
[Table 2]
Equipment ID
(Device ID/ID u)
Ox0000e0cd38
Ox0000f8024a
Ox000102187f
[0075]
After determining the equipment ID of the Sink
(step S71) in the mutual authentication and key exchange
29
u)
• SP308039WOOO
procedure with the Sink as described above, the Source
determines whether the equipment ID of the Sink has been
registered in the receiving equipment table {step S72).
This process is for confirming the registration in the
5 case where the owner of the content requests to preregister
the Sink to be remotely accessed in the Source.
[0076]
When the equipment ID of the Sink has not been
registered in the receiving equipment table {No in step
10 S72), the Source transmits an AKE_CANCEL command
indicating the interruption of the mutual authentication
and key exchange procedure to the Sink in order to
terminate the process. The Source can also include, in
the AKE_CANCEL command, the information indicating that
15 the Sink has not been registered in the receiving
equipment table. The Sink can also be registered in the
receiving equipment table before the key exchange.
[0077]
On the other hand, when the equipment ID of the
20 Sink has been registered in the receiving equipment table
{Yes in step S72), the Sauce, next, confirms whether the
equipment ID of the Sink has been registered in the
connection table {step S73).
25
[0078]
When the equipment ID of the Sink has not been
registered in the connection table {No in step S73), the
Source further confirms whether the connection table has
space to record a new equipment ID {step S75). In the
present embodiment, it is assumed that the Source uses a
30 key counter to manage the number of the key IDs that can
be recorded on the connection table, and that the
30
• SP308039WOOO
connection table can record the IDs when the value of the
key counter is lower than an upper limit value n. The
Source regulates the value of the key counter to keep the
same as the number of the key IDs recorded in the
5 connection table.
[0079]
When the value of the key counter has already
reached then (No in step S75), the Source transmits an
AKE_CANCEL command indicating the interruption of the
10 mutual authentication and key exchange procedure to the
Sink in order to terminate the process. The Source can
also include, in the AKE_CANCEL command, the information
indicating that the number of the entries registered in
the connection table has reached the upper limit n.
15 [0080]
When the value of the key counter is lower than the
n (Yes in step S75), the Source adds one to the value of
the key counter (step S76), generates an exchange key Kr
for a remote access and a key ID for specifying the Kr
20 (step S77), and adds the entry including the set of the
exchange key Kr, the key ID, and the equipment ID of the
Sink to the connection table (step S78).
[0081]
When the equipment ID of the Sink has already been
25 recorded in the connection table (Yes in step S73), the
Source deletes the entry corresponding to the equipment
ID from the connection table (step S74), newly generates
an exchange key Kr for a remote access and a key ID for
specifying the Kr (step S77), and adds the entry
30 including the set of the exchange key Kr, the key ID, and
the equipment ID of the Sink to the connection table
31
• SP308039WOOO
(step S78). Note that, as another pattern, instead of
deleting the entry corresponding to the equipment ID from
the connection table, it is considered that the Source
extracts the exchange key Kr and the key ID corresponding
5 to the equipment ID from the connection table and does
not add the information to the connection table again.
However, the pattern is not illustrated in the drawings.
[0082]
Then, after encrypting, according to the method
10 prescribed by the DTCP specification, the exchange key Kr
for a remote access that has been generated in step S77,
the Source transmits the exchange key Kr together with
the key ID to the Sink using an EXCHANGE KEY command.
[0083]
15 At the same time as transmitting the exchange key
Kr to the Sink, the Source starts the management of the
life of the exchange key Kr using a timer (step S79).
Concretely, the Source makes available a timer
corresponding to the key ID (in other words, makes
20 available a timer for each of the key IDs stored in the
25
30
connection table), sets a predetermined value (for
example, a value corresponding to a minute), and starts
counting down.
[0084]
After that, the Source automatically reduces the
value of the timer to zero at predetermined clocks. When
the value of the timer reaches zero, the Source activates
the process for updating the connection table.
[0085]
Fig. 8 illustrates an exemplary process for
updating the connection table. Updating the connection
32
SP308039WOOO
table deletes, from the connection table, the entry
including the key ID that has not periodically been
received according to a key life management command
(AKE_ALIVE. CMD).
5 [0086]
The Source, first, checks whether an entry
including the key ID corresponding to the timer of which
value has been zero is in the connection table (step S81) .
When such an entry is not in the connection table (No in
10 step S81), the process is terminated.
[0087]
When such an entry is in the connection table (Yes
in step S81), the Source deletes, from the connection
table, the entry including the key ID corresponding to
15 the timer of which value has been zero(step S82), and
subtracts only one from the value of the key counter
(step S83). As a result of that, the Source can newly
exchange a key with another Sink (or the same Sink).
[0088]
20 Note that, in consideration of the delay due to a
command communication, there may be operations, for
example, ~n operation in which a margin is provided
between the time when the value of the time becomes zero
and the time when the exchange key is destroyed, or an
25 operation in which the process illustrated in Fig. 8 is
not performed until another Sink newly requests an
exchange key.
[0089]
While the Souorce manages the life of the exchange
30 key Kr as described above, the Sink can request to update
the life of the exchange key Kr in use.
33
• SP308039WOOO
[0090]
In the present embodiment, the Sink requests to
update the life of the exchange key Kr by transmitting a
KEEP ALIVE command at predetermined transmission cycles.
5 Further, the Source maintains the corresponding key by
receiving the KEEP_ALIVE command at predetermined
reception cycles. Fig. 9 illustrates an exemplary format
of the KEEP ALIVE command. In the example illustrated in
the drawing, the KEEP ALIVE command includes, in the
10 payload, a field including an equipment ID that is the
information for specifying the source Sink, and a field
including a key ID that is the information for specifying
the exchange key Kr of which life is to be requested to
be updated. The last bit is used as a destruction flag
15 indicating the destruction of the exchange key Kr.
[ 0091]
When receiving the KEEP ALIVE command, the Source
returns a KEEP ALIVE response after performing the
process for updating the life. Note that, although it is
20 omitted in the drawings, it is considered that the status
field that is defined in the AKE Control Command Format
in the DTCP is used for the response information of the
KEEP ALIVE response.
[0092]
25 The Source sets a value indicating a predetermined
time on the timer corresponding to the key ID included in
the KEEP ALIVE command received from the Sink in order to
control the timer to newly count down from the value in
order to update the life. Note that, even after the
30 value of the timer has been zero, the process for
updating the life is performed as long as the
34
•
corresponding key has not been destroyed yet.
[0093]
SP308039WOOO
Fig. 10 illustrates an exemplary operation sequence
that is for updating the life of an exchange key Kr and
5 that is performed between the Source and the Sink. When
receiving an exchange key Kr and its key ID from the
Source, the Sink transmits a KEEP ALIVE command at
predetermined transmission cycles.
10
15
[0094]
When receiving the KEEP_ALIVE command from the Sink,
the Source confirms whether the equipment ID included in
the command has been registered in the receiving
equipment table (step S101).
[0095]
When the equipment ID in the KEEP_ALIVE command has
not been registered in the receiving equipment table (No
in step S101), the Source describes the response
information as "the equipment has not been registered"
(step S105), and transmits a KEEP_ALIVE response
20 including the response information to the Sink that is
the requestor in order to terminate the process.
[ 0096]
On the other hand, when the equipment ID in the
KEEP ALIVE command has been registered in the receiving
25 equ~pment table (Yes in step S101), the Source
subsequently confirms whether the key ID in the
KEEP ALIVE command is in the connection table (step S102) .
[0097]
When the key ID in the KEEP ALIVE command is not in
30 the connection table (No in step S102), the Source
describes the response information as "the key is
35
•
5
SP308039WOOO
invalid" (step S106), and transmits a KEEP_ALIVE response
including the response information to the Sink that is
the requestor in order to terminate the process.
[0098]
When the key ID in the KEEP ALIVE command is in the
connection table (Yes in step S102), the Source
initializes the value of the timer corresponding to the
key ID using a value indicating a predetermined time in
order to start counting down again (step S103) . Then,
10 the Source describes the response information as "the key
is valid" (step S104), and transmits a KEEP ALIVE
15
response including the response information to the Sink
that is the requestor in order to terminate the process.
[ 0099]
After the completion of the mutual authentication
and key exchange procedure with the Source, the Sink
repeatedly transmits the KEEP ALIVE command at the
transmission cycles in a predetermined period as long as
it is necessary to maintain the obtained exchange key Kr.
20 [ 0100]
Further, when the exchange key Kr has been
unnecessary because of the completion of the
communication with the Source (content reception), the
Sink can request the destruction of the exchange key Kr
25 from the Source. Deleting the appropriate entry from the
connection table newly connects other Sinks to the Source
within the upper limit number n so that the Source can
perform a communication (content transmission) .
30
[0101]
The Sink can request the destruction of the
exchange key Kr from the Source, for example, by
36
t
SP308039WOOO
including the information requesting the destruction of
the exchange key Kr in the KEEP_ALIVE command to be
transmitted at predetermined transmission cycles. In the
exemplary format of the KEEP ALIVE command illustrated in
5 Fig. 9, the payload includes a destruction flag. Setting
the destruction flag can indicate the destruction of the
exchange key Kr.
[0102]
Fig. 11 illustrates another exemplary operation
10 sequence that is for updating the life of the exchange
key Kr and that is performed between the Source and the
Sink. The operation sequence illustrated in the drawing
differs from the operation sequence illustrated in Fig.
10 in that the operation sequence illustrated in the
15 drawing includes the process for destroying the
unnecessary exchange key Kr.
[0103]
When receiving a·KEEP ALIVE command from the Sink,
the Source confirms whether the equipment ID included in
20 the command has been registered in the receiving
equipment table (step S111).
[ 0104]
When the equipment ID in the KEEP_ALIVE command has
not been registered in the receiving equipment table (No
25 in step S111), the Source describes response information
as "the equipment has not been registered" (step S116),
and transmits a KEEP_ALIVE response including the
response information to the Sink that is the requestor in
order to terminate the process.
30 [0105]
On the other hand, when the equipment ID in the
37
SP308039WOOO
KEEP_ALIVE command has been registered in the receiving
equipment table (Yes in step S111), the Source
subsequently confirms whether the key ID in the
KEEP ALIVE command is in the connection table (step S112) .
5 [ 0106]
When the key ID in the KEEP ALIVE command is not in
the connection table (No in step S112), the Source
describes the response information as "the key is
invalid" (step S120), and transmits a KEEP_ALIVE response
10 including the response information to the Sink that is
the requestor in order to terminate the process.
[0107]
On the other hand, when the key ID in the
KEEP ALIVE command is in the connection table (Yes in
15 step S112), the Source further confirms whether the
destruction- flag in the KEEP ALIVE command is set (step
S113).
[0108]
When the destruction flag in the KEEP_ALIVE command
20 is set (Yes in step S113), the Source· destroys the key ID
in the command and the exchange key corresponding to the
key ID (step S117), deletes the entry including the key
ID in the command, the corresponding exchange key, and
the equipment ID from the connection table (step S118),
25 and subtracts only one from the value of the key counter
(step S119). Then, the Source describes the response
information as "the key is invalid" (step S120), and
transmits a KEEP_ALIVE response including the response
information to the Sink that is the requestor in order to
30 terminate the process.
[0109]
38
t
SP308039WOOO
On the other hand, when the destruction flag in the
KEEP ALIVE command is not set (No in step S113), the
Source initializes the value of the timer corresponding
to the key ID using a value indicating a predetermined
5 time in order to start counting down again (step S114).
Then, the Source describes the response information as
"the key is valid" (step S115), and transmits a
KEEP_ALIVE response including the response information to
the Sink that is the requestor in order to terminate the
10 process.
[0110]
According to the operation sequences illustrated in
Figs. 10 and 11, even though it is necessary to strictly
limit the number of content using apparatuses (Sinks)
15 that use content at the same time in a case where the
content in a content providing apparatus (Source)
positioned at home is used from the outside, each of the
content using apparatuses that has performed the mutual
authentication and key exchange procedure with the
20 content providing apparatus transmits a KEEP ALIVE
command at predetermined transmission cycles of each
content using apparatuses. Thus, the content providing
apparatus can accurately obtain the exchange key to be
maintained, and can newly communicate with another
25 content using apparatus by destroying an unnecessary
exchange key.
[0111]
Because the content providing apparatus manages the
exchange key to be maintained using a key ID, the content
30 providing apparatus can unaffectedly perform a process
even though the content using apparatus has changed its
39
5
address during a mobile communication.
INDUSTRIAL APPLICABILITY
[0112]
SP308039WOOO
Hereinabove, with reference to the specific
embodiments, the present invention has been described in
detail. However, it is obvious that a person with an
ordinary skill in the art can modify or alter the
embodiments without departing from the gist of the
10 invention.
[0113]
As an exemplary application of the present
invention, a communication system for using content by
remotely accessing a server on a home network applying
15 the DTCP-IP from a client outside the house can be cited.
However, the gist of the present invention is not limited
to a communication system applying the DTCP-IP or a
communication system for remotely accessing content.
Similarly, the present invention can be applied to a
20 communication system for transmitting content within a
range of the user's legitimate use while limiting the
number of equipment to which content that requires a
protection for a copyright or another purpose is
transmitted at the same time.
25 [0114]
In summary, the contents described herein shall not
be interrupted to a limited extent because the present
invention has been disclosed as examples. To judge the
gist of the present invention, the scope of claims should
30 be taken in consideration.
40
SP308039W000
REFERENCE SIGNS LIST
[0115]
10 Content providing apparatus (RA-source)
11 CPU
5 12 Content receiving/replaying unit
13 Communication unit
14 Storage unit
15 Timer
20 Content using apparatus (RA-sink)
10 21 CPU
22 Communication unit
23 Content output unit
24 Storage unit
25 Timer
15 30, 31 Router
40, 41 Modem
50 WAN
60 lAS service
70 DONS service

CLAIMS
1. A coiranunication system that performs a
communication for transmitting content between a content
5 providing apparatus for providing the content and one or
more content using apparatuses for using the content,
comprising:
mutual authentication and key exchange means for a
mutual authentication and for exchanging a key for
10 encrypting the content between the content providing
apparatus and the content using apparatus;
key recording means for recording a key transmitted
by the content providing apparatus to each of the content
using apparatuses after combining the key with a key ID
15 for specifying the key and an equipment ID for specifying
the content using apparatus; and
key management means for maintaining information on
the key ID in the key recording means only while the
content using apparatus periodically transmits a key life
20 management command including the key ID to the content
providing apparatus.
2. A communication apparatus comprising:
mutual authentication and key exchange means for a
25 mutual authentication and for exchanging a key for
encrypting content with one or more content using
apparatuses that are to be destinations of the content;
key recording means for recording a key transmitted
to each of the content using apparatuses after combining
30 the key with a key ID for specifying the key and an
equipment ID for specifying the content using apparatus;
42
SP308039WO00
and
key management means for maintaining information
corresponding to the key ID in the key recording means
only while a key life management command including the
5 key ID is received from the content using apparatus at
predeteirmined reception cycles.
3. The communication apparatus according to claim 2,
wherein the key management means destroys, from the key
10 recording means, information corresponding to a key ID of
which key life management command has not been received
at the predetermined reception cycles.
4. The communication apparatus according to claim 2,
15 wherein the key management means, in response to
receiving the key life management command from the
content using apparatus, returns a response indicating
that the key is valid when the information corresponding
to the key ID included in the received key life
20 management command is maintained in the key recording
means, and returns a response indicating that the key is
invalid after the corresponding information has been
destroyed from the key recording means.
25 5. The communication apparatus according to claim 2,
wherein the key management means, in response to
receiving a key life management command on which
information indicating destruction of the key is set,
destroys information corresponding to the key from the
30 key management means.
43
SP308039WO00
6. The communication apparatus according to claim 2,
further comprising registration means for pre-registering
a content using apparatus with which a key is to be
exchanged,
5 wherein the key management means, in response to
receiving a key life management command from a content
using apparatus that has not been pre-registered in the
registration means, returns a response indicating absence
of the registration.
10
7. A communication apparatus comprising:
mutual authentication and key exchange means for a
mutual authentication and for exchanging a key for
encrypting content with a content providing apparatus
15 that is to be a source of the content; and
key life management means for transmitting a key
life management command including a key ID for specifying
the key transmitted from the content providing apparatus
by the mutual authentication and key exchange means.
20
8. The communication apparatus according to claim 7,
wherein the key life management means transmits a key
life management command on which information indicating
destruction of the key is set when the key becomes
25 unnecessary.
9. A communication method comprising:
a mutual authentication and key exchange step for a
mutual authentication and for exchanging a key for
30 encrypting content with one or more content using
apparatuses that are to be destinations of the content;
44
SP308039WO00
a key recording step for recording a key
transmitted to each of the content using apparatuses
after combining the key with a key ID for specifying the
key and an equipment ID for specifying the content using
5 apparatus; and
a key management step for maintaining infoirmation
corresponding to the key ID in the key recording means
only while a key life management command including the
key ID is received from the content using apparatus at
10 predetermined reception cycles.
10. A communication method comprising:
a mutual authentication and key exchange step for a
mutual authentication and for exchanging a key for
15 encrypting content with a content providing apparatus
that is to be a source of the content; and
a key life management step for transmitting a key
life management command including a key ID for specifying
the key transmitted from the content providing apparatus
20 in the mutual authentication and key exchange step.
11. A computer program described in a computer-readable
format for implementing a process for operating as a
content providing apparatus on a computer in a
25 communication system that performs a communication for
transmitting content between the content providing
apparatus for providing the content and one or more
content using apparatuses for using the content, the
program causing the computer to function as:
30 mutual authentication and key exchange means for a
mutual authentication and for exchanging a key for
45
SP308039WO00
encrypting content with one or more content using
apparatuses that are to be destinations of the content;
key recording means for recording a key transmitted
to each of the content using apparatuses after combining
5 the key with a key ID for specifying the key and an
equipment ID for specifying the content using apparatus;
and
key management means for maintaining information
corresponding to the key ID in the key recording means
10 only while a key life management command including the
key ID is received from the content using apparatus at
predetermined reception cycles.
12. A computer program described in a computer-readable
15 format for implementing a process for operating as a
content using apparatus on a computer in a communication
system that performs a communication for transmitting
content between a content providing apparatus for
providing the content and one or more content using
20 apparatuses for using the content, the program causing
the computer to function as:
mutual authentication and key exchange means for a
mutual authentication and for exchanging a key for
encrypting content with a content providing apparatus
25 that is to be a source of the content; and
key life management means for transmitting a key
life management command including a key ID for specifying
the key transmitted from the content providing apparatus
by the mutual authentication and key exchange means.