Note: Descriptions are shown in the official language in which they were submitted.
CA 02168748 2005-O1-18
METHOD AND APPARATUS FOR UNIQUELY ENCRYPTING
A PLURALITY OF SERVICES AT A TRANSMISSION SITE
HACRGROUND OF THE INVENTION
Field of-the Invention
The present invention is related to signal
encryption and decryption, and more particularly, to a method
and apparatus for uniquely encrypting a plurality of services
at a transmission site in a multi-service communications
system and for decrypting the services at a remote reception
site. The present invention reduces the amount of encryption
related information that must be transmitted to the reception
site for decryption purposes.
Backqround of the Invention
Although the background of the invention is
described herein in the context of subscription television
systems, the present invention is by no means limited
thereto. Rather, the present invention may be employed in
any mufti-service communications system in which it is
desirable to uniquely encrypt a plurality of individual
services.
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Preventing unauthorized access to transmitted
television signals is of paramount concern to the
subscription television industry. In the subscription
television industry, "programmers" provide "services" for
distribution to various reception sites. A "service" is a
signal that contains some type of information, such as video,
audio, closed-captioning or teletext information. A single
programmer may wish to supply many services. Typically, a
programmer will supply various services via satellite to
cable television operators who, in turn, will provide the
services to cable subscribers. Alternatively, a programmer
may supply services directly to direct broadcast satellite
(DBS) subscribers. Techniques for preventing unauthorized
access to these services have become increasingly important.
Cryptographic techniques, widely used in the
computer security field, are ideal for preventing
unauthorized access to services in a subscription television
system. One form of cryptography, known as "private key"
cryptography, is particularly well suited for such purposes.
With private key cryptography, the transmitter and receiver
share a common encryption key (sometimes also referred to as
a "seed") that is used for both encrypting and decrypting.
An exemplary cryptographic system 10 employing private key
cryptography is depicted in Figure 1. As shown, a service to
be transmitted is provided to an encryptor 12. A seed
generator 14 generates a unique encryption seed which is fed
to the encryptor 12. Encryptor 12 encrypts the service in
accordance with an encryption algorithm upon the encryption
algorithm being "keyed" by the encryption seed. Encryption
seeds are typically binary values having lengths that may
range from 8 to 56 bits. Both the encryption seed and the
encrypted service data are provided to a multiplexer 11 that
multiplexes the encryption seed and encrypted service data
and provides the multiplexed data signal to a transmitter 16.
Transmitter 16 transmits the multiplexed data signal to a
remote reception site. A receiver 18 at the reception site
receives the multiplexed data signal and a demultiplexer 19
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separates the encryption seed from the encrypted service
data. The encrypted service data and encryption seed are
then provided to a decryptor 20. Decryptor 20 employs the
inverse of the encryption algorithm employed by encryptor 12,
and therefore, upon "keying" the encryption algorithm with
the received encryption seed, the decryptor 20 is able to
decrypt the received service data.
Each programmer in a subscription television system
typically provides many different services. For various
reasons, programmers prefer to uniquely encrypt each service.
Accordingly, a unique encryption seed must be generated for
each service, and each unique encryption seed must somehow be
provided to the reception site. U.S. Patent Nos. 5,029,207
(Gammie), 4,613,901 (Gilhousen et al.), 4,736,422 (Mason) and
4,802,215 (Mason) each describe systems in which the
encryption seeds used to encrypt each service are transmitted
to a reception site along with the encrypted service data.
Fvr security reasons, the encryption seeds themselves are
often encrypted prior to transmission.
U.S. patent 5,341,425
describes a method and apparatus having particular
applicability to the encryption of seeds at each of a
plurality of programmer sites.
Additional security is typically provided by
periodically changing the encryption seeds for each service
at the transmission site. Frequently changing the encryption
seeds hampers piracy efforts. However, because each new
encryption seed must be transmitted to the reception site,
bandwidth that would otherwise be available for service data
is consumed. Moreover, the encryption seeds are often
heavily error protected which results in even greater
bandwidth consumption.
When the number of services being provided to
subscribers is small, the bandwidth consumed by the
transmission of encryption seeds is not a problem. With the
advent of various compression technologies, however, the
subscription television industry is experiencing a vast
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increase in the number of individual services that can be
provided to subscribers. As the number of available services
increases, the additional bandwidth needed for the
transmission of encryption seeds becomes prohibitive.
Consequently, there is a need for encryption methods and
apparatus that reduce the amount of encryption related
information that must be transmitted to a reception site,
without sacrificing cryptographic strength. The present
invention satisfied this need.
SUMMARY OF THE INVENTION
The present invention is directed to a method and
apparatus for uniquely encrypting a plurality of services for
transmission to a reception site. The present invention
overcomes the limitations of the prior art by reducing the
amount of encryption related overhead that must be
transmitted to remote reception sites for decryption
purposes.
According to the method of the present invention, a
plurality of services, which may include, but are not limited
to, video, audio, teletext and closed-captioning services,
are each uniquely encrypted at a transmission site by (a)
generating a unique spreading function for each service to be
transmitted, (b) generating a random quantity, (c) for each
service, (i) convolving the random quantity with the
spreading function generated for that service in step (a) to
produce a unique encryption seed for that service, and (ii)
encrypting at least a portion of that service with the unique
encryption seed, and (d) transmitting the random quantity to
the reception site along with the encrypted portions of each
service, but not transmitting the unique encryption seeds
produced for each service. Because the unique encryption
seeds for each service are not transmitted to the reception
site, the amount of encryption related information
transmitted to the reception site is greatly reduced.
According to one embodiment of the method of the
present invention, a first component of the random quantity
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defines a global seed and a second component of the random
quantity defines a random seed, and for each service, step
(c)(i) comprises (a') combining the random seed with the
spreading function generated for that service in step (a) in
accordance with a data combining function, Fo, to produce a
unique data quantity, (b') combining the random seed with the
global seed and at least one other quantity in accordance
with another data combining function, Fl, to produce an
intermediate quantity, and then (c') processing the unique
data quantity in accordance with an encryption function upon
the encryption function being keyed by the intermediate
quantity. At least a portion of the processed data quantity
is then used to define the unique encryption seed for that
service. Preferably, the random quantity is encrypted with a
system key prior to transmitting the random quantity in step
(d). Also, steps (b) through (d).are preferably repeated
periodically to hamper cryptographic attacks.
At the reception site, the random quantity and the
encrypted portions of each service are received. At least
one of the services is then selected for decryption.
According to the method of the present invention, the unique
spreading function generated for the selected service at the
transmission site is regenerated at the reception site in a
manner identical to that performed at the transmission site
in step (a). Next, the received random quantity and the
regenerated spreading function for the selected service are
convolved, in a manner identical to that performed at the
transmission site in step (c)(i), to reproduce the unique
encryption seed used at the transmission site in step (c)(ii)
to encrypt the received encrypted portion of the selected
service. Using the reproduced encryption seed, the encrypted
~ portion of the selected service is then decrypted for use at
the reception site.
~ An encryption apparatus according to the present
invention comprises spreading function generator means for
generating a unique spreading function for each of the
services to be transmitted, and a random signal generator for
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generating a random quantity. Seed generator-means are
coupled to the random signal generator and to the spreading
function generator means for independently convolving the
random quantity with each of the spreading functions to
produce a unique encryption seed for each respective service.
A plurality of service encryptors are also provided. Each
service encryptor is coupled to the seed generation means and
is coupled to receive a respective one of the services for
encrypting the respective service in accordance with an
encryption algorithm upon the encryption algorithm being
keyed by the unique encryption seed produced for that
respective service. A transmitter is coupled to each of the
encryptors and to the random signal generator for
transmitting the random quantity and each of the encrypted
services to a remote reception site. The transmitter does
not transmit the unique encryption seeds produced by the
encryption seed generator means. Consequently, the amount of
encryption related information transmitted to the reception
site is greatly reduced.
A decryption apparatus according to the present
invention comprises a receiver for receiving the random
quantity and the encrypted services from the encryption
apparatus, and a selection switch for selecting one of the
received encrypted services for decryption. A spreading
function generator is provided for regenerating, in a manner
identical to that performed by the spreading function
generator means of the encryption apparatus, the unique
spreading function generated at the transmission site for the
selected service. A seed generator is coupled to the
receiver and to the spreading function generator for
convolving the regenerated spreading function with the
received random quantity, in a manner identical to that
performed by the seed generator means of the encryption
apparatus, to reproduce the unique encryption seed produced
at the transmission site and used to encrypt the selected
service. A service decryptor is coupled to the receiver and
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to the seed generator for decrypting the selected received
encrypted service using the reproduced encryption seed.
Further features and details of the present
invention will become evident hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary, as well as the following
detailed description of the preferred embodiment, is better
understood when read in conjunction with the appended
drawings. For the purpose of illustrating the invention,
there is shown in the drawings an embodiment that is
presently preferred, it being understood, however, that the
invention is not limited to the specific methods and
instrumentalities disclosed. In the drawings:
Figure 1 is a block diagram of a prior art private
key cryptographic system;
Figure 2 is a functional block diagram of an
encryption apparatus for uniquely encrypting each of a
plurality of services in accordance with a preferred
embodiment of the present invention;
Figures 3 illustrates further details of the
encryption apparatus of Figure 2;
Figure 4 is a flow chart illustrating both the
operation of the apparatus of Figure 2 and a preferred
embodiment of a method of the present invention;
Figure 5 is a functional block diagram of a
decryption apparatus for use in conjunction with the
encryption apparatus of Figure 2;
Figure 6 is a flow chart illustrating both the
operation of the apparatus of Figure 5 and further details of
the preferred embodiment of the method of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Before proceeding to the description of the
drawings, it should be understood that, although the present
invention has particular applicability to a subscription
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television system, the present invention is in no way limited
thereto. Rather, the present invention may be employed in
any mufti-service communications system that requires unique
encryption of a plurality of independent services.
Furthermore, although the present invention is described
herein as being employed to encrypt digital service signals,
the methods and apparatus disclosed herein may equally be
employed to encrypt or scramble analog service signals.
Referring now to the drawings wherein like numerals
indicate like elements throughout, there is shown in Figure 2
a functional block diagram of one embodiment of an encryption
apparatus 22 for uniquely encrypting each of a plurality of
services in accordance with the present invention. As shown,
the apparatus 22 comprises a random signal generator 24 for
generating a random quantity, which in the preferred
embodiment comprises two components: a global seed ("GS"),
and a random seed ("RS"). Preferably, the random signal
generator 24 comprises a thermal diode that generates a
digital signal comprising a random sequence of bits. In the
present embodiment, the random quantity comprises eighty-
eight (88) bits, a first fifty-six bits defining the global
seed, and the remaining thirty-two bits defining the random
seed. It is understood, however, that in other embodiments,
the number of bits in the random quantity and the number of
bits defining the global and random seeds may differ.
The apparatus 22 further comprises a seed encryptor
50 which is coupled to the random signal generator 24 for
encrypting the random quantity (GS + RS) in accordance with
an encryption algorithm upon that algorithm being "keyed" by
a system key, SK, provided to the encryptor from a register
52. According to the present embodiment, the system key
comprises a 56-bit pseudo-random data word, however, in other ,
embodiments, the system key may comprise a different number
of bits. Any encryption algorithm may be employed by the ,
seed encryptor 50. For example, the well known "Data
Encryption Standard" algorithm ("DES") may be employed.
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Services to be encrypted, e.g., services S1, SZ ...
SN, are provided to respective service encryptors 26, 28 ...
30. Each service comprises a continuous digital signal that
may contain one of several different types of information.
For example, one service may be a video service comprising a
a
digital video signal, and another service may be an audio
service comprising a digital audio signal. Other service
types include, but are not limited to, teletext, closed-
captioning, and computer data services. Each service is
assigned a unique service number. A service type identifier
and a service number identifier are provided for each
service. Assuming a system capable of transmitting a maximum
of 64 different services, each service number identifier
might comprise a unique 6-bit quantity. Similarly, assuming
a system having thirty-two different service types, each
service type identifier might comprise a unique 5-bit
quantity indicative of a particular type of service. The
combined effect of a 6 bit service number and a 5-bit service
type identifier can generate up to 2048 unique spreading
functions.
As illustrated in Figure 2, the service type and
service number identifiers for each service are provided to
respective spreading function generators 32, 34 ... 36. Each
spreading function generator 32, 34 ... 36 receives the
service type and service number identifiers for a respective
service and generates therefrom a unique spreading function
(e.g., SF1, SFa ... SFN) for that service. According to the
present embodiment, each spreading function generator 32, 34
... 36 implements a one-way function, wherein the service
type and service number identifiers define inputs to the
function. Any one-way function may be implemented so long as
it does not generate the same spreading function for two
different services. According to the present embodiment,
. each spreading function (SFl, SF2 ... SFN) comprises a unique
12-bit quantity, it being understood that in other
embodiments the spreading functions may comprise a different
number of bits.
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As an alternative, each spreading function
generator 32, 34 ... 36 may comprise an identical look-up
table memory wherein each spreading function is pre-stored as
an entry in the table, and the service type and service
number identifiers for a particular service are combined to
form an address for retrieving a unique spreading function
from the stored table.
According to the present invention, a unique
encryption seed is generated for each service by convolving
the random quantity (GS + RS) with the unique spreading
function ( i . a . , SFl, SFZ or SFN) generated for that service .
To this end, the encryption apparatus 22 of Figure 2 further
comprises a plurality of seed generators 38, 40 ... 42. As
shown, each seed generator 38, 40 ... 42 is coupled, via line
43, to the random signal generator 24 for receiving the
random quantity (GS + RS) from the random signal generator
24. Each seed generator 38, 40 ... 42 is also coupled to a
respective one of the spreading function generators 32, 34
... 36 for receiving a spreading function from the respective
spreading function generator. As described in greater detail
below, each seed generator 38, 40 ... 42 convolves the random
quantity (GS + RS) with a respective spreading function
(i.e., SF1, SF2 ... SFN) to produce a unique encryption seed
for a respective one of the services. For example, seed
generator 38 receives the random quantity via line 43 and
convolves the random quantity with the spreading function,
SFl, generated by spreading function generator 32 to produce
a unique encryption seed, ESl, for service S1. Similarly,
seed generator 40 receives. the random quantity and convolves
it with the spreading function, SF2, generated by spreading
function generator 34 to produce a unique encryption seed,
ES2, for service Sz, and so on. As explained below in
greater detail, in the preferred embodiment, each seed
generator 38, 40 ... 42 generates a unique 64-bit quantity,
any portion of which may be used to define the encryption
seed, ES, for its respective service. However, in other
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embodiments, a different number of bits may be generated by
each seed generator 38, 40 ...42.
As shown, the unique encryption seeds (i.e., ES1,
ESZ ... ESN) produced by the respective seed generators 38,
40 ... 42 are temporarily stored in respective seed registers
44, 46 ... 48. Subsequently, each encryption seed is
provided from its respective seed register 44, 46 ... 48 to a
respective service encryptor 26, 28 ... 30. Each encryptor
26, 28 ... 30 is responsible for encrypting the data of a
respective one of the services. For example, encryptor 26 is
responsible for encrypting the data of service S1, encryptor
28 is responsible for encrypting the data of service S2, and
so on. Each encryptor 26, 28 ... 30 encrypts the data of its
respective service in accordance with an encryption algorithm
upon the encryption algorithm being "keyed" with the unique
encryption seed provided from its respective seed register
44, 46 ... 48. For example, encryptor 26 encrypts the data
of service S1 in accordance with the encryption algorithm
upon that algorithm being keyed by encryption seed ES1
provided from seed register 44. According to the present
embodiment, each encryptor 26, 28 ... 30 employs the same
encryption algorithm, although, in other embodiments,
different ones of the encryptors 26, 28 ... 30 may employ
different encryption algorithms. Furthermore, any encryption
algorithm may be employed. For example, each encryptor 26,
28 ... 30 may employ the well known "Data Encryption
Standard" algorithm (DES).
According to a most preferred embodiment, each seed
generator 38, 40...42 convolves both the random quantity (GS
+ RS) and the system key (SK) with a respective one of the
spreading functions SF1, SFZ ... SFN to generate its
~ respective encryption seed ES1, ESz ... ESN. As illustrated
in Figure 2, therefore, each seed generator 38, 40 ... 42
receives the system key, SK, from register 52 via line 53.
Convolving both the random quantity and the system key with
each spreading function enhances the cryptographic strength
of the apparatus.
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As shown, the encrypted data of each service S1, SZ
... S3 is provided to a multiplexes 54. The multiplexes 54
also receives the encrypted random quantity (GS + RS)'. The
multiplexes 54 multiplexes the encrypted random quantity and
encrypted service data to produce a multiplexed data signal
that is then provided to a transmitter 56 for transmission to
a remote reception site. Thus, according to the present
invention, only the encrypted random quantity (GS + RS)' and
the encrypted data of each service S1, S2 ... SN are
transmitted to the remote reception site. None of the unique
encryption seeds ES1, ESZ ... ESN are transmitted.
Consequently, the amount of encryption related information
transmitted to the reception site is greatly reduced.
Although the encryption seeds generated from a
given random quantity (RS + GS) may be used to encrypt their
respective services for an indefinite period of time, it is
preferable to change the encryption seeds on a frequent basis
in order to hamper cryptographic attacks. According to the
present invention, the encryption seeds, i.e. ES1, ES2 ...
ESN, may be changed by simply generating a new random
quantity and providing that quantity to each seed generator
38, 40 ... 42. Upon receiving a new random quantity, each
seed generator 38, 40 ... 42 will generate a new encryption
seed in the manner described above, and once generated, the
new encryption seeds may then be employed by the respective
service encryptors 26, 28 ... 30. For a given service,
therefore, each new encryption seed is used to encrypt a
different, but consecutive, portion of that service's data
stream. As with the initial random quantity, each new random
quantity is encrypted by the seed encryptor 50 and provided
to the multiplexes 54 for transmission to the reception site.
As always, only the random quantities are transmitted to the
reception site along with the encrypted service data. None
of the encryption seeds are transmitted.
Figure 3 is a functional block diagram illustrating
further details of each seed generator 38, 40 ... 42. As
shown, each seed generator 38, 40 ... 42 comprises first and
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second data combiners 60, 62. The first data combiner 60
receives, at respective inputs, the random seed component
°(RS) of the random quantity (RS + GS) and a spreading
function SFn from a respective one of the spreading function
generators 32, 34 ... 36 (Figure 2). The first data combiner
60 combines the spreading function with the random seed in
accordance with a data combining function, Fo, to produce a
unique data quantity (i.e., data quantity = Fo(SFn, RS)),
which is then temporarily stored in a data register 62. The
data combining function Fo implemented by the first data
combiner 60 may comprise any function capable of combining
the spreading function with the random seed, and the present
invention is not limited to any one function. For example,
data combining function Fo may comprise a concatenation
function which appends selected portions of the random seed
to the spreading function to produce the data quantity.
Alternatively, the data combining function Fo may comprise a
more complex one-way function. According to the preferred
embodiment, the unique data quantity generated by the data
combiner 60 comprises 64-bits, however, in other embodiments,
the data quantity may comprise a different number of bits.
The second data combiner 64 receives both the
global seed (GS) and random seed (RS) components of the
random quantity and combines these with the system key (SK)
in accordance with another data combining function, F1, to
produce an intermediate quantity (i.e., intermediate quantity
- F1(GS, RS, SK)), which is then temporarily stored in a key
register 66. Like data combining function Fo, data combining
function F1 implemented by the second data combiner 64 may
comprise any data combining function, and the present
invention is not limited to any one function. For example,
data combining function F1 may comprise a simple
concatenation function which concatenates selected portions
of the~random seed, global seed and system key to produce the
intermediate quantity. Alternatively, the data combining
function F1 may comprise a more complex one-way function.
According to the preferred embodiment, the intermediate
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quantity produced by the second data combiner 64 comprises
56-bits, however, in other embodiments, the intermediate
quantity may comprise a different number of bits.
The data register 62 and key register 66 are both
coupled to a one-way function means 68 which processes (i.e.,
"encrypts") the data quantity in the data register 62 in
accordance with an encryption function upon the encryption
function being keyed with the intermediate quantity in the
key register 66. At least a portion of the processed data
quantity defines a unique encryption seed, ESn, which is the
provided, via an output 70, to a respective one of the seed
registers 44, 46 ... 48 (Figure 2). Although the one-way
function means 68 may implement any encryption function, in
the preferred embodiment, the one-way function means 68
implements the "Data Encryption Standard" algorithm (DES) in
electronic codebook (ECB) mode. The DES algorithm in
electronic codebook mode provides a cryptographically strong
one-way function which, upon being keyed by the 56-bit
intermediate quantity stored in the key register 66,
generates a unique 64-bit output from the 64-bit data
quantity stored in the data register 62. Accordingly, up to
64-bits are available for defining an encryption seed. Of
course, in other embodiments, the encryption function may
produce a different number of output bits, and the present
invention is by no means limited to an output of 64 bits.
Referring again to Figure 2, as mentioned above,
the encryption seeds generated by each seed generator 38, 40
... 42 are provided to respective seed registers 44, 46 ...
48. Each encryption seed is then used to encrypt a
respective one of the services S1, SZ ... SN. Although the
entire 64-bit quantity provided by a given seed generator 38,
... 42 is available for defining an encryption seed, it -
may be desirable in some applications to use less than the
entire 64-bits. For example, in some applications, the
35 service encryptors 26, 28 ... 30 may be implemented to
receive shorter encryption seeds. In such cases, each
encryption seed may be defined as a smaller portion of the
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respective 64-bit seed generator output. Also, in some
applications, certain services may not need to be encrypted
as strongly as others, and therefore, some of the encryptors
26, 28 ... 30 may implement different encryption algorithms
requiring different size encryption seeds. For example,
digital cable television operators may want to encrypt video
service signals more strongly than audio service signals.
Consequently, the service encryptors used to encrypt the
video services may implement a different encryption algorithm
than the service encryptors used to encrypt audio services,
and each of the encryption algorithms may require different
size encryption seeds. Accordingly, a different number of
bits may be used to define encryption seeds for encrypting
the different types of services.
As can be appreciated, the encryption apparatus 22
of the present invention contains a certain degree of
functional redundancy. For example, although the apparatus
22 of Figure 2 employs a separate spreading function
generator 32, 34 ... 36, seed generator 38, 40 ... 42, seed
register 44, 46 ... 48 and service encryptor 26, 28 ... 30
for each service, much of the functionality of these elements
is identical from service to service and can be combined into
a single functional element. For example, a single spreading
function generator, seed generator, seed register and service
encryptor could be employed in place of the multiple elements
illustrated in Figure 2. Of course, in such an embodiment,
the single set of elements would have to be shared among the
services, only one service being encrypted at any given time.
According to one embodiment of the encryption
apparatus 22 of the present invention, the functionality of
the spreading function generators 32, 34 ... 36, seed
generators 38, 40 ... 42, seed registers 44, 46 ... 48, and
service encryptors 26, 28 ... 30 is implemented in a secure
microprocessor (not shown). Any suitable secure
microprocessor may be employed. For example, a Motorola
MC68HC05SC21 secure microprocessor may be employed.
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Figure 4 is a flow chart illustrating both the
operation of the apparatus of Figure 2 and a preferred
embodiment of a method of uniquely encrypting a plurality of
services at a transmission site in accordance with the
present invention. As shown, the method of the present
invention begins at step 80 wherein a unique spreading
function is generated for each service based on a service
number identifier and a service type identifier for that
service. Next, at step 82, a random quantity comprising two
components, a global seed and a random seed, is generated.
At step 84, each of the unique spreading functions is
independently convolved with the random quantity generated in
step 82 to produce a unique encryption seed for each of the
services to be transmitted.
At step 86, the unique encryption seeds generated
for each service are fed to their respective service
encryptors (e. g., service encryptors 26, 28 ... 30 of Fig.
2), which begin encrypting their respective services in
accordance with an encryption algorithm upon the encryption
algorithm being "keyed" with the respective unique
encryption seeds generated in step 84. At step 88, the
random quantity generated in step 82 is encrypted with a
system key. As illustrated at step 90, as the data for each
service is encrypted, the encrypted data is transmitted to a
remote reception site along with the encrypted random
quantity. As shown at step 92, encryption of each service
continues using the current encryption seeds until a
predetermined period of time expires.
When the predetermined period of time expires,
control passes back to step 82 where a new random quantity is
generated. At step 84, each unique spreading function is
convolved with the new random quantity to generate a new
unique encryption seed for each service. At step 86, the
previous set of unique encryption seeds are replaced with the
newly generated encryption seeds, and independent encryption
of each service continues using the new encryption seeds,
i.e., the new encryption seeds replace the previous
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encryption seeds as the initiating values for the encryption
algorithm implemented by each of the respective service
encryptors 26, 28 ... 30.
For reasons which will become evident hereinafter,
each new random quantity must be transmitted to the reception
site. Accordingly, like the previous random quantity, the
new random quantity is encrypted at step 88, and as shown at
step 90, the encrypted new random quantity is transmitted to
the reception site along with the encrypted data for each
service. As explained above, each service comprises a
continuous data stream, and therefore, the encrypted data of
each service is continuously being transmitted in step 90.
Each new random quantity, however, need only be transmitted
once (i.e., when it is generated). Of course, each new
random quantity could be transmitted multiple times if
desired.
As with the previous set of encryption seeds
(produced with the previous random quantity), encryption of
each service continues with the current set of respective
encryption seeds until the predetermined period of time again
expires. After the predetermined period of time has expired,
control again passes back to step 80 where yet another random
quantity is generated. The process may continue in this
manner indefinitely. As can be appreciated, each new random
quantity is used to generate a new set of respective
encryption seeds, one for each service to be transmitted.
For each service, each new encryption seed is used to encrypt
a different, but consecutive portion of that service. Most
importantly, in accordance with the present invention, only
each new random quantity is transmitted to the reception site
along with the encrypted service data; none of the unique
encryption seeds are transmitted. As explained hereinafter,
at the reception site, the unique encryption seeds used to
encrypt each service can be reproduced using the transmitted
random quantity. Because only the random quantity need be
transmitted to the reception site, the amount of encryption
CA 02168748 2005-O1-18
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related information transmitted to the reception site is
greatly reduced without sacrificing cryptographic strength.
Figure 5 is a functional block diagram of a
decryption apparatus 100 for use at a remote reception site
in conjunction with the encryption apparatus 22 of Figure 2.
In particular, the decryption apparatus 100 provides a means
for decrypting a selected one of the encrypted services
transmitted to the reception site by the encryption apparatus
22 of Figure 2. As shown, the decryption apparatus 100
10 comprises a receiver 102 for receiving a multiplexed data
signal containing the encrypted data for each of a plurality
of services and at least one encrypted random quantity (GS +
RS) comprising two components, a global seed (GS) and a
random seed (RS). Once received, the multiplexed data signal
15 is provided to a data extractor 106 and a service
demultiplexer 110.
The data extractor 106 monitors the incoming data
signal and extracts the encrypted random quantity from the
signal. Once extracted, the encrypted random quantity is
20 provided to a seed decryptor 108 which implements the inverse
of the encryption algorithm implemented by the seed eneryptor
50 of the encryption apparatus 22 of Figure 2. A register
52' in the decryption apparatus 100 stores a copy of the
system key, SK, used to encrypt the random quantity in the
25 encryption apparatus 22. Any means may be employed for
providing the decryption apparatus 100 with a copy of the
system key, SK. For example, the system key may be delivered
to the reception site via human courier and then manually
stored in the decryption apparatus 100. Alternatively, the
30 system key may be transmitted to the reception site, however,
if the system key is to be transmitted, it too must be
encrypted prior to transmission. Encryption of the system
key may be achieved using a unique secret serial number
assigned to the decryption apparatus 100 and permanently
35 stored in a secure memory (not shown) of the apparatus 100 at
the time of manufacture. Such a technique is described in
U.S. Patent No. 5,029,207, issued to the same assignee,
CA 02168748 2005-O1-18
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(as described therein, the
system key is referred to as a "key-of-the-month"?.
Using the system key as the initiating value for
the encryption algorithm, the seed decryptor 108 decrypts the
encrypted random quantity and provides the decrypted random
quantity to a seed generator 112 via line 115. Seed
generator 112 is identical to the seed generators 38, 40 ...
42 of the encryption apparatus 22 (Fig. 2>, details of which
are described above and illustrated in Figure 3. As shown,
l0 the seed generator 112 also receives the system key via line
53' .
The service demultiplexer 110 receives the
multiplexed data signal via line 104 and a service selection
signal via line 111. A user at the reception site provides
the service selection signal using a selection switch (not
shown?, which may take the form of a hand-held remote control
device, or some other input device. Based an the user's
selection, the service demultiplexer 110 extracts the
encrypted data of the selected service from the incoming
multiplexed data signal and provides the encrypted data of
the selected service to a service decryptor 124. Service
decryptor 124 must implement the inverse of the encryption
algorithm implemented by the particular service encryptor 26,
28 ... or 30 used in the encryption apparatus 22 to encrypt
the data of the selected service.
Based on the user's service selection, the service
demultiplexer 110 also provides the service number identifier
and service type identifier for the selected service to a
spreading function generator 120 which is identical to each
of the spreading function generators 32, 34 ... 36 of the
encryption apparatus 22 of Figure 2. The service number and
service type identifiers for each service may either be
stored in the service demultiplexer~or transmitted to the
decryption apparatus as part of the multiplexed data signal.
The spreading function generator 12o receives the service
number and service type identifiers from the service de-
multiplexer 110 and regenerates therefrom the unique
WO 95/05043 PCT/US94/08864
- 20 -
spreading function generated for the selected service by the
respective spreading function generator 32, 34 ... or 36 in
the encryption apparatus 22 of Figure 2. The regenerated
spreading function for the selected service is then provided
to the seed generator 112.
According to the present invention, the seed
generator 112 convolves the regenerated spreading function
with the received random quantity and the system key, in a
manner identical to that performed by each seed generator 38,
40 ... 42 in the encryption apparatus 22, to reproduce the
unique encryption seed used in the encryption apparatus 22 to
encrypt the data of the selected service. Once reproduced,
the unique encryption seed for the selected service is
provided as a "key" to the service decryptor 124. Using the
reproduced encryption seed as an initiating value, the
service decryptor 124 decrypts the encrypted data for the
selected service and provides the decrypted service data at
an output 126 of the apparatus 100.
As explained above, in the preferred embodiment, a
new random quantity is periodically generated by the
encryption apparatus 22 of Figure 2 to hamper cryptographic
attacks, and for a particular service, each new random
quantity produces a new unique encryption seed and each new
encryption seed is used to encrypt a different, but
consecutive, portion of the service's data stream. As with
the initial random quantity, each new random quantity is
transmitted to the reception site in encrypted form.
Accordingly, at the reception site, each new random quantity
must be received by the receiver 102 of the decryption
apparatus 100, extracted from the incoming data stream by the
data extractor 106, decrypted by the seed decryptor 108 and
provided to the seed generator 112 so that, for the selected ,
service, the seed generator 112 can reproduce the unique
encryption seed generated for that service from that random
quantity. Furthermore, as can be appreciated, a means (not
shown) must be provided for synchronizing the reproduction of
each successive encryption seed with the incoming encrypted
95/05043 PCT/US94108864
- 21 -
data of the selected service so that each reproduced
encryption seed is provided to the service decryptor 124 in
time for decrypting its respective portion of the selected
service's data stream.
Although the decryption apparatus 100 of Figure 5
is illustrated as being capable of only selecting one service
from the incoming multiplexed data signal, the decryption
apparatus 100 of the present invention is by no means limited
to operation in this manner. For example, more than one
service could be selected at a given time, and the decryption
apparatus could include additional spreading function
generators, seed generators, seed registers and service
decryptors (not shown) for each of the selected services.
Such an embodiment might find particular applicability in a
subscription television system wherein subscribers typically
select "programs" which comprise a combination of related
services, such as a video service, and its associated audio
and closed-captioning services. Moreover, in such an
embodiment, the service decryptors used to decrypt each of
the different types of services may employ different
encryption algorithms, and as mentioned above, a different
number of bits may be used to define the unique encryption
seeds for each of the different service types.
Figure 6 is a flow chart illustrating both the
operation of the apparatus of Figure 5 and further details of
the preferred embodiment of the method of the present
invention. At step 130, an encrypted random quantity (GS +
RS)' and the encrypted data for each service transmitted from
an encryption apparatus (e.g. apparatus 22 of Fig. 2) are
received at a reception site. At step 132, one of the
services is selected for decryption, and at step 134, the
- unique spreading function generated for that service in the
encryption apparatus is regenerated at the reception site.
At step 136, the received encrypted random quantity is
decrypted, and at step 138, the decrypted random quantity is
convolved with the regenerated spreading function, in a
manner identical to that performed in the encryption
CA 02168748 2005-O1-18
- 22 -
apparatus, to reproduce the unique encryption seed used in
the encryption apparatus to encrypt the data of the selected
service. Next, at step 140, the data for the selected
service is decrypted using the reproduced encryption seed.
5 So long as the user does not select a different service (step
142), decryption of the incoming data of the currently
selected service continues until a next random quantity is
received. As illustrated at step 144, when a new random
quantity is received, control passes to step 136 wherein the
10 newly received random quantity is decrypted. Next, at step
138, the new random quantity is convolved with the
regenerated spreading function to reproduce the encryption
seed used in the encryption apparatus to encrypt the next
subsequent portion of the selected service's data stream. At
15 step 140, decryption of that next portion of the selected
service's data stream is begun using the new reproduced
encryption seed. As can be appreciated, the process
continues in this manner as each successive portion of the
- selected service's data stream is decrypted with its
20 respective reproduced encryption seed. If, at steg 142, it
is determined that a new service has been selected, then
control passes to step 134 where the unique spreading
function for the newly selected service is regenerated.
Steps 136 through 144 are then performed as described above
25 for the new service.
According to one embodiment of the decryption
apparatus 100 of the present invention, the functionality of
the spreading function generator 120, seed generator 112,
seed register 122, and service decryptor 124 is implemented
30 in a secure microprocessor (not shown). Any suitable secure
microprocessor may be employed. Fox example, a Motorola
MC68HCOSSC21 secure microprocessor may be employed.
As described herein, the encrypted service data and
the encrypted random quantities are transmitted in a
35 multiplexed form. An exemplary multiplexed communication
system in which the present invention may be employed is
described in U.S. patent 5,400,401,
CA 02168748 2005-O1-18
- 23 -
filed October 30, 1992, and entitled "System and
Method for Transmitting a Plurality of Digital Services".
The
aforementioned application describes an exemplary multiplex
data stream format and the structure and operation of a
multiplexer and demultiplexer for implementing that multiplex
format. As is understood, however, the present invention is
by no means limited to application in a multiplexed
communications system. For example, the data for each
service and the encrypted random quantities may be
transmitted to the remote reception site on separate
frequencies, and a separate receiver used at the reception
site for each signal.
As the foregoing illustrates, the present invention
is directed to a method and apparatus for uniquely encrypting
a plurality of services for transmission to a reception site.
The present invention overcomes the limitations of the prior
art by reducing the amount of encryption related overhead
that must be transmitted to remote reception sites. It is
understood that changes may be made to the embodiments
described above without departing from the broad inventive
concepts thereof. Accordingly, this invention is not limited
to the particular embodiments disclosed, but it is intended
to cover all modifications that are within the scope and
spirit of the invention as defined by the appended claims.
