U.S. patent application number 11/376501 was filed with the patent office on 2006-07-20 for protection of digital content using block cipher crytography.
Invention is credited to Pierre Chavanne, Motomasa Futagami, Ralph Hill, John Hwa, Atsushi Mituszawa, Lakshmana Pamarthy, Carl Quinn, Eric Swenson.
Application Number | 20060159266 11/376501 |
Document ID | / |
Family ID | 33135320 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060159266 |
Kind Code |
A1 |
Chavanne; Pierre ; et
al. |
July 20, 2006 |
Protection of digital content using block cipher crytography
Abstract
Protection of digital content using a specific application of
block cipher cryptography is described. The digital content is
encrypted using an encryption key and a calculated initialization
vector. The digital content includes a plurality of strides of data
and each stride includes a string of data to be encrypted and a
block of data to be encrypted. The calculated initialization vector
to be used to encrypt the block of data is derived from the string
of data in the stride to be encrypted. Furthermore, the
initialization vector is calculated by performing an exclusive
disjunction function on a seed value and the string of data for
each stride.
Inventors: |
Chavanne; Pierre; (Davis,
CA) ; Hwa; John; (Fremont, CA) ; Pamarthy;
Lakshmana; (Santa Clara, CA) ; Quinn; Carl;
(San Jose, CA) ; Hill; Ralph; (Los Gatos, CA)
; Swenson; Eric; (Soquel, CA) ; Futagami;
Motomasa; (Sunnyvale, CA) ; Mituszawa; Atsushi;
(Kanagawa, JP) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD
SEVENTH FLOOR
LOS ANGELES
CA
90025-1030
US
|
Family ID: |
33135320 |
Appl. No.: |
11/376501 |
Filed: |
March 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10675430 |
Sep 29, 2003 |
7055039 |
|
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11376501 |
Mar 14, 2006 |
|
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60462987 |
Apr 14, 2003 |
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Current U.S.
Class: |
380/262 |
Current CPC
Class: |
H04L 2209/60 20130101;
H04L 9/0637 20130101 |
Class at
Publication: |
380/262 |
International
Class: |
H04L 9/00 20060101
H04L009/00 |
Claims
1. A computerized method comprising: encrypting digital content
using an encryption key and a calculated initialization vector
(IV), wherein the digital content comprises a plurality of strides,
each stride comprising a string of data to be encrypted and a block
of data, and the calculated IV derived from each string of data
from each stride.
2-44. (canceled)
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/462,987, filed Apr. 14, 2003.
TECHNICAL FIELD
[0002] This invention relates generally to the protection of
digital content using cryptology, and more particularly to the
protection of digital content using cipher block chaining.
COPYWRIGHT NOTICE/PERMISSION
[0003] A portion of the disclosure of this patent document contains
material which is subject to copyright protection. The copyright
owner has no objection to the facsimile reproduction by anyone of
the patent document or the patent disclosure as it appears in the
Patent and Trademark Office patent file or records, but otherwise
reserves all copyright rights whatsoever. The following notice
applies to the software and data as described below and in the
drawings hereto: Copyright .COPYRGT. 2003, Sony Electronics, Inc.,
All Rights Reserved.
BACKGROUND
[0004] Digital Rights Management is a term used to describe the
concept of protecting copyrighted material via encryption and
governing its access via rules, typically distributed independently
of the content. The protected content is usually inaccessible
without a legitimately acquired license (embodying the rules
governing the access) and software that securely interprets and
releases the content if the appropriate license is available. This
technology is promoted widely to music labels and other
music/content distribution companies to use as a core technology
for protecting their content.
[0005] Certain content encryption problems arise especially in the
context of streamable media (e.g. media such as music or video that
may be streamed across a network and rendered (e.g., played) while
being streamed rather than after the entire content is received or
when read from a local file). In these cases, encryption may need
to be done in real time, and lossy transport protocols may cause
situations where not all the content sent is ever received at the
client. For example, lost blocks of encrypted data may cause the
entire file to be unreadable. Furthermore, certain encryption
techniques may increase the size of the digital content file.
SUMMARY OF THE INVENTION
[0006] Protection of digital content using a specific application
of block cipher cryptography is described. The digital content is
encrypted using an encryption key and a calculated initialization
vector. The digital content includes a plurality of strides of data
and each stride includes a string of data to be encrypted and a
block of data to be encrypted. The calculated initialization vector
to be used to encrypt the block of data is derived from the string
of data in the stride to be encrypted. Furthermore, the
initialization vector is calculated by performing an exclusive
disjunction function on a seed value and the string of data for
each stride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a diagram illustrating a system-level overview of
an embodiment of the invention.
[0008] FIG. 2 illustrates one embodiment of a process flow for
exchanging digital content within the network environment of FIG.
1.
[0009] FIG. 3A illustrates one embodiment of a digital content
having multiple access units.
[0010] FIG. 3B illustrates one embodiment of the access unit of
digital content having multiple strides.
[0011] FIG. 3C illustrates one embodiment of a calculated IV value
being derived from the access unit.
[0012] FIG. 3D illustrates one embodiment of a process flow for
deriving the calculated IV value in conjunction with FIG. 3C.
[0013] FIG. 3E illustrates one embodiment of a conceptual view for
encrypting the access unit.
[0014] FIG. 3F illustrates one embodiment of a process flow for
encrypting the access unit in FIG. 3E.
[0015] FIG. 4 illustrates one embodiment of a process flow of the
digital rights management software to encrypt the copyrighted raw
digital content.
[0016] FIG. 5 illustrates one embodiment of a process flow for
encrypting a partial stride.
[0017] FIG. 6 illustrates one embodiment of a process flow of the
client decryption software to decrypt the encrypted digital content
on a client device.
[0018] FIG. 7 illustrates one embodiment of a process flow for
decrypting a partial stride.
[0019] FIG. 8 illustrates one embodiment of a computer system
suitable for implementation.
DETAILED DESCRIPTION
[0020] In the following detailed description of embodiments of the
invention, reference is made to the accompanying drawings in which
like references indicate similar elements, and in which is shown by
way of illustration specific embodiments in which the invention may
be practiced. These embodiments are described in sufficient detail
to enable those skilled in the art to practice the invention, and
it is to be understood that other embodiments may be utilized and
that logical, mechanical, electrical, functional and other changes
may be made without departing from the scope of the present
invention. The following detailed description is, therefore, not to
be taken in a limiting sense, and the scope of the present
invention is defined only by the appended claims.
[0021] FIG. 1 illustrates one embodiment of a network environment
100. The network environment 100 includes a digital content
provider server 10, client device 20, client device 25, and client
device 30. The digital content provider server 10 is part of, or
coupled to a network 40, such as the Internet, to exchange data
with each of the client devices (20, 25, 30), as either a client or
a server computer. It is readily apparent that the present
invention is not limited to use with the Internet; alternatively
directly coupled and private networks are also contemplated.
[0022] The digital content provider server 10 may store public
domain or copyrighted digital content, such as digital music,
electronic books, software source code, movies, etc. The digital
content provider server 10 also includes a digital rights
management component 5. The digital rights management component 5
includes encryption algorithms to encrypt the raw digital content
for use by one or more authorized users of the digital content
using the client devices (20, 25, 30).
[0023] Each client device (20, 25, 30) includes a decryption
component 7 and a digital content player component 8. The
decryption component 7 provides for the decryption of encrypted
digital content (e.g., digital content encrypted by the digital
rights management component 5). The digital content player
component 8 provides for the rendering of the digital content. Each
client device (20, 25, 30) may be, for example, a personal
computer, a portable digital music player, a portable digital video
player, among other well-known examples of devices used to render
digital content.
[0024] FIG. 2 illustrates one embodiment of a process flow (200)
for exchanging digital content within the network environment of
FIG. 1.
[0025] At block 210, the digital rights management component 5
receives raw digital content. For example, the raw digital content
may be a copyrighted digital music file or movie file.
[0026] At block 220, the digital rights management component 5
encrypts the raw digital content using block cipher cryptology and
a calculated initialization vector value derived from the digital
content, as described below and in conjunction with FIGS. 3A, 3B,
3C, 3D, 3E, and 4. In this way, the size of the digital content
need not be increased, for example, by adding multiple
initialization vectors when encrypted.
[0027] At block 230, the digital rights management component 5
transmits the encrypted digital content to a client device (e.g.,
the client device 20) over the network 40. The digital rights
management component 5 also transmits the decryption key to decrypt
the encrypted digital content. The decryption key may be the same
as the encryption key value. The digital rights management
component 5 may transmit the decryption key as part of the
encrypted digital content or separately from the encrypted digital
content. The digital rights management component 5 may also
transmit a seed value as part of the encrypted digital content
(e.g., a parameter value) or separately from the encrypted digital
content.
[0028] At block 235, the client device 20 receives the encrypted
digital content.
[0029] At block 240, the decryption component 7 of client device 20
decrypts the digital content using at least the decryption key and
a calculated initialization vector derived from the digital
content, as will be further described below and in conjunction with
FIG. 6.
[0030] At block 250, the digital content player component 8 on the
client device 20 facilitates the rendering of the decrypted digital
content. For example, the digital content player component 8 may be
a music player software application to render the decrypted music
file.
[0031] The following will define various parameters of an
encryption and decryption algorithm process, and illustrate various
examples of applying the algorithm process to streaming media using
parameter values. Specifically, the following describes encryption
and decryption of logical units (e.g., access units) of the digital
content based on block cipher cryptology using a calculated IV
value, as will be described. A block cipher is a method of
encrypting plaintext (to produce ciphertext) in which a
cryptographic key (e.g., an encryption key) and an algorithm are
simultaneously applied to all bits in a block of data (for example,
64 contiguous bits) at once as a group rather than to one bit at a
time. It should be understood that plaintext and ciphertext are
terms of art that represent unencrypted and encrypted data
respectively.
[0032] As will be shown, the digital content is subdivided into
logical units (e.g., access units) and each of these logical units
is encrypted independently using block cipher cryptography. In this
way, if a specific portion of the encrypted digital content file is
lost (e.g., while transmitting the digital content file), the
decryption of the remaining portion of the digital content file can
be restarted at the next logical section.
[0033] FIG. 3A illustrates one embodiment of a digital content 300
having multiple access units. Specifically, the digital content 300
includes access unit 310, access unit 315, access unit 320, and
access unit 325. The access units are chosen so that their content
is a logical subdivision of the digital content, definable and
addressable without knowledge of the data content itself. The
access units are also small enough so that losing part of the
digital content during transmission, for example, will not
drastically affect rendering. The access unit may be an intrinsic
property of the digital content (e.g., mpeg4 defined access unit)
or defined as a parameter to the decryption component 7. Each
access unit includes multiple strides.
[0034] FIG. 3B illustrates one embodiment of the access unit 310 of
digital content 300 having multiple strides. A stride is a
predefined length of data within an access unit. Specifically,
access unit 310 includes stride 340, stride 345, stride 350, and
stride 355. Within each stride (340, 345, 350, 355) there exists a
block of data to be encrypted. The following describes a portion of
the strides being encrypted with one or more block cipher modes of
operation. For example, one mode is the electronic codebook (ECB)
mode, in which a string of data to be encrypted is split into
blocks (e.g., 16 byte blocks) and each block is encrypted
separately.
[0035] Another example of a mode of block cipher is cipher-block
chaining (CBC), in which each block of plaintext is split into
blocks (e.g., 16 byte blocks) and is XORed with a previous
ciphertext block before being encrypted. In order to prevent
repeated encryption of same plaintext to result in identical
ciphertext, CBC typically uses a different initialization vector
(IV) to start each encryption sequence (e.g., access unit).
[0036] Typically, the inclusion of the initialization vector
alongside each encrypted block sequence (or logical unit) would
cause the file size to increase because one or more initialization
vectors are embedded into the encrypted digital content to be
delivered to the decryption component 7. This may be problematic if
the digital content includes an index to specific locations in the
digital file (e.g., a location of a scene in a digital movie file,
a location of a specific song track on a music CD (compact disk),
etc.) because the inclusion of the initialization vector will cause
a shift of the physical header locations, thereby possibly making
the files unreadable (unless they are recalculated prior to
transmitting the file.
[0037] In one embodiment, the digital rights management component 5
encrypts the raw digital content using an initialization vector
algorithmically calculated from a chosen string of data chosen from
each stride of data to be encrypted for each access unit, under the
assumption that the chosen string of data will be different enough
from access unit to access unit that the result is a different
initialization vector for each access unit to be encrypted.
[0038] FIG. 3C illustrates one embodiment of a calculated IV value
being derived from the access unit 310. The first 16 bytes of each
stride are illustrated as string of data 342, string of data 347,
string of data 352, and string of data 357. FIG. 3D illustrates one
embodiment of a process flow 360 for deriving the calculated IV
value in conjunction with FIG. 3C.
[0039] At block 365,the digital rights management component 5
obtains a seed value 328. The seed value defines the initial value
of the initialization vector.
[0040] At block 370, the digital rights management component 5
performs an exclusive disjunction function (e.g., XOR function) on
the seed value 328 and the string of data 342 of the first stride
340 of the access unit 310 resulting in an initial IV value.
[0041] At block 375, the digital rights management component 5
determines whether there is another stride in the access unit 310.
If there is another stride in the access unit 310, control passes
to block 380. If there is not another stride in the access unit
310, control passes to block 385. Continuing the example, the
digital rights management component 5 would determine the next
stride to be stride 345.
[0042] At block 380, the digital rights management component 5
performs an XOR on the current initial IV value with the string of
data 347 of the stride 345, resulting in an updated initial IV
value. Control passes back to block 375 where the process repeats
for string of data 352 and 357.
[0043] At block 385, the digital rights management component 5 sets
a calculated IV value 305 to the current initial IV value. In one
embodiment, the calculated IV value 305 is supplied to the
underlying AES CBC cipher of the digital rights management
component 5 to encrypt specific blocks of data within the access
unit 310.
[0044] It should be understood that the invention is not limited to
deriving the calculated IV value based on the first 16 bytes of
each stride. Rather, in alternative embodiments, the calculated IV
value may be derived from a set of implementation specific sections
(e.g., 16 byte string of data) of an access unit, so that the
decryption software knows where to find the specific sections.
Preferably, the specific sections should have a high probability of
resulting in sufficient randomness to generate a reasonably unique
calculated IV value for each access unit.
[0045] It should also be noted that although the embodiments
described herein use the seed value 328 when deriving the
calculated IV value, the seed value 328 is not necessary, and the
calculated IV value may be derived without using the seed value
328. For example, the calculated IV value may be calculated from
XORing the first 16 bytes of each stride of an access unit without
including the seed value 328.
[0046] FIG. 3E illustrates one embodiment of a conceptual view for
encrypting the access unit 310 using the calculated IV value 305
described above and in conjunction with FIGS. 3C and 3D. FIG. 3F
illustrates one embodiment of a process flow 390 for encrypting the
access unit 310 in FIG. 3C. The following shows the encryption
process using an encryption key value (Kc) and a calculated IV
value, as input parameters.
[0047] At block 392, the digital rights management component 5
obtains the calculated IV value 305, as described above.
[0048] At block 394, the digital rights management component 5
encrypts 85 the blocks of data 344, 349, 354, and 359 using the
calculated IV value 305 and an encryption key 82 (K.sub.C). In one
embodiment, the encryption key value is a 16-byte (128-bit) value,
randomly regenerated, that serves as the encryption key in the AES
algorithm. The blocks of data 344, 349, 354, and 359 are encrypted
using a cipher block chaining block cipher mode. Block of data
344c, 349c, 354c, and 359c represent the resulting encrypted blocks
of data.
[0049] At block 396, the strings of data 342, 347, 352, and 357 are
encrypted. The strings of data 342, 347, 352, and 357 are encrypted
using an electronic code book block cipher mode. Strings of data
342c, 347c, 352c, and 357c represent the resulting encrypted
strings of data.
[0050] Processes 360 and 390 may be repeated for each access unit
of the digital content to be encrypted. It should be appreciated
that in this way the digital content 300 will not increase in size
nor cause header location shifts. That is, the encrypted digital
content will remain the same size as the unencrypted digital
content. This is because the encrypted digital content does not
include an initialization vector from another source, such as from
the data of a previously encrypted stride or a timestamp.
Furthermore, the data required to reconstruct the IV is accessible
from the cipher text block at decryption time, as will be
described.
[0051] In one embodiment, the digital rights management component 5
includes an encryption algorithm based on the Advanced Encryption
Standard, more commonly referred to as AES, which is a block cipher
with a block size of 128 bits (e.g., 16 bytes) and key sizes of
128, 192, and 256 bits. However, the invention is not limited to
using AES. Alternative algorithms well known to those of ordinary
skill in the art may be used and are not described herein so as not
to obscure the description.
[0052] In one embodiment, the digital rights management component 5
and the decryption component 7 use a number of parameter values in
addition to the encryption key value, and the calculated IV value,
to facilitate the encryption and decryption of the digital content.
The parameter values may include, but are not limited to, an access
unit size value, an encryption stride size value, a complete
encryption value, an encryption chunk offset value, an encryption
chunk size value, and an IV stride count value.
[0053] The access unit size value defines the size of the access
unit being processed by the digital rights management component 5.
In one embodiment, each access unit may be of different sizes and
its boundaries are identifiable, which is well known to those of
ordinary skill in the art.
[0054] The encryption stride size value defines the length of a
stride. In one embodiment, a typical value for the encryption
stride size value is 512 bytes. An access unit need not be an even
multiple of the encryption stride size value. The last stride in an
access unit may, therefore, be shorter than the encryption stride
size value.
[0055] The complete encryption value is a flag used to identify a
percentage of encryption to be applied or the percentage of
encryption that has been applied to a digital content file. The
following description describes processing performed at 100%
encryption and 25% encryption, for example. However, the invention
is not limited to these encryption percentages. Alternatively, the
digital rights management software may encrypt the digital content
at other percentages.
[0056] The encryption chunk offset value defines an offset from the
beginning of a stride to a block of data to be encrypted, as will
be further described.
[0057] The IV stride count value defines the number of strides that
contribute to a calculated IV value. In one embodiment, the IV
value used in the AES CBC processing (e.g., the calculated IV
value) is calculated from the contents of the access unit to be
encrypted. If the size of the access unit is less than the (IV
stride count value * the encryption stride size value), the IV
stride count value is adjusted by the digital rights management
component 5 such that only as many strides as there are full
strides in the access unit contribute to the calculated IV value.
If the last stride is partial (e.g., if the last stride is less
than the encryption stride size value), the IV stride count value
is such that this partial stride should contribute to the
calculated IV value. Furthermore, the partial stride does
contribute if it is at least 16 bytes in length. Otherwise, that
stride is ignored as far as the calculated IV value contribution is
concerned. In our example we also limit the number of blocks
contributing to the calculated IV value to four.
[0058] The encryption chunk size value defines a size of the block
of data to be encrypted. In one embodiment, the encryption chunk
size should be less than or equal to (the encryption stride size
value minus the encryption chunk offset value). Since the AES
implementation requires block sizes greater than or equal to 16
bytes (equal to key size . . . ), the encryption chunk size value
is greater than or equal to 16 bytes. Also, the encryption chunk
size value should be a multiple of the AES block size (16 bytes).
For example, in one embodiment, there are two values of the
encryption chunk size: 496 bytes and 128 bytes. For 100%
encryption, the value of the complete encryption parameter is set
to "true", and the entire stride (512 bytes) is encrypted where 496
bytes are encrypted using AES CBC and the 16 bytes of content
contributing to the calculated IV value are encrypted with AES
ECB.
[0059] FIG. 4 illustrates one embodiment of a process flow 400 of
the digital rights management component 5 to encrypt the
copyrighted raw digital content based on the parameter values.
[0060] At block 405, the digital rights management component 5
determines the access unit size value of an access unit to be
encrypted. If the access unit size value is less than 32 bytes,
control passes to block 410. If the access unit size value is
greater than or equal to 32 bytes, control passes to block 440.
[0061] At block 410, the digital rights management component 5
determines the complete encryption value. If the complete
encryption value is set to "false," control passes to block 411. If
the complete encryption value is set to "true," control passes to
block 413.
[0062] At block 411, the access unit is not encrypted but remains
plaintext and control passes to block 465. The access unit may not
be encrypted here because the access unit size is less than 32
bytes and other portions of the digital content may have been
encrypted enough to make encrypting this access unit
unnecessary.
[0063] At block 413, the digital rights management component 5
determines if the access unit size value is greater than zero bytes
and less than 16 bytes, control passes to block 415. At block 414,
if the access unit size value is 16 bytes, control passes to block
420. If the access unit size value is greater than 16 bytes and
less than 32 bytes, control passes to block 425.
[0064] At block 415, the digital rights management component 5
performs an XOR function on the data comprising the access unit
(e.g., the n access unit bytes) with the n leftmost bytes of
E(K.sub.c, seed value), and control passes to block 465.
[0065] At block 420, the digital rights management component 5
encrypts the 16 access unit bytes with AES using ECB mode and
control passes to block 465.
[0066] At block 425, the digital rights management component 5
calculates the calculated IV value by performing an XOR function on
the seed value and the first 16 bytes of the access unit.
[0067] At block 430, the digital rights management component 5
encrypts the first 16 bytes of the access unit with AES using ECB
mode.
[0068] At block 435, the digital rights management component 5
performs an XOR function on the remaining n-16 bytes, with the n
leftmost bytes of E(K.sub.C, calculated IV value) and control
passes to block 465.
[0069] At block 440, the digital rights management component 5
checks and initializes the parameters values previously described
above. The digital rights management component 5 sets the IV stride
count value to the number of strides in the access unit. The IV
stride count value is calculated as being the access unit size
value divided by the encryption stride size value.
[0070] Any fractional stride left over counts as a partial stride.
However, it should be understood that if the last (possibly
partial) stride is less than 16 bytes in length, and this stride
would contribute to the calculated IV value due to the IV stride
count's value being equal to the number of strides in the access
unit, then the IV stride count value is decremented by one, so that
less-than-16-byte fragments are not used.
[0071] The digital rights management component 5 sets the
encryption chunk offset value. In one embodiment, the encryption
chunk offset value is set to 16 bytes.
[0072] At block 445, the digital rights management component 5
determines a calculated IV value. In one embodiment, the calculated
IV value is derived from the first 16 bytes of each of the first IV
stride count values of the access unit as described above and in
conjunction with FIGS. 3C and 3D.
[0073] At block 450, the digital rights management component 5
determines whether to encrypt the entire raw digital content. If
the value of the complete encryption value is set to "true,"
control passes to block 455. If the complete encryption value is
set to "false," control passes to block 460.
[0074] At block 455, the digital rights management component 5
encrypts the random 16 byte string of data of each stride used to
calculate the calculated IV value. For example, the digital rights
management component 5 encrypts the first 16 byte string of data of
each stride using AES with the Electronic Code Book (ECB) mode. In
one embodiment, no calculated IV value is involved in this
calculation.
[0075] At block 460, the digital rights management component 5
encrypts the remaining block of data with AES using CBC mode. For
example, the digital rights management component 5 encrypts the
block of data starting at the encryption chunk offset from the
start of the stride and encryption chunk size in length. Hence, the
calculated IV value is used as the initial IV value for the AES
cipher (as described in 3E and 3F for each access unit). In one
embodiment, each applicable block of data in each stride are part
of the same AES cipher block chain started for each access unit. In
an alternative embodiment, AES is restarted with each stride.
[0076] At block 465, the digital rights management component 5
transmits the encrypted digital content to the client device.
[0077] It should be understood that the calculated IV value is not
limited to being derived from the first 16 bytes of each stride of
the access unit to be encrypted. Rather, in alternative
embodiments, the calculated IV value may be derived from any random
16 byte (but well specified in location) string of data from each
stride of the access unit to be encrypted.
[0078] It should be appreciated that special processing occurs for
the remaining blocks that are not an exact multiple of the AES
block size (16 bytes). For all strides except the last one, the
blocks will be an integral multiple of the AES block size (e.g., 16
bytes). However, a short access unit may result in a partial stride
(e.g., having a block size less than 16 bytes).
[0079] FIG. 5 illustrates one embodiment of a process flow 500 for
encrypting a partial stride.
[0080] At block 510, the digital rights management component 5
encrypts the cipher text of the last full block with AES ECB (e.g.
not, for example, the block used to derive the calculated IV if
that happens to be the previous full block) using AES ECB (all
encryption is done using the same, original, input encryption
key).
[0081] At block 520, the digital rights management component 5
calculates a partial bit value as the number of bits in the partial
block.
[0082] At block 530, the digital rights management component 5
performs an XOR function on the left-most bits of the last full
block equaling the partial bits value with the partial block of the
stride to generate the corresponding cipher text.
[0083] It should be understood that process 400 and process 500
will be repeated for each access unit in the digital content.
Alternatively, the digital rights management component 5 may
encrypt specific or partial strides of the digital content for
quick encryption of digital content, for example.
[0084] FIG. 6 illustrates one embodiment of a process flow 600 of
the decryption component 7 to decrypt the encrypted digital content
on a client device.
[0085] At block 605, the client device receives encrypted digital
content (and determines the decryption parameters--possibly from
data in the content file, e.g. partial or full encryption, seed IV
value, stride size, etc . . . ).
[0086] At block 610, the decryption component 7 determines the
access unit size value of an access unit to be decrypted. If the
access unit size value is less than 32 bytes, control passes to
block 615. If the access unit size value is greater than 32 bytes,
control passes to block 655.
[0087] At block 615, the decryption component 7 determines the
complete encryption value. If the complete encryption value is set
to "false," control passes to block 620. If the complete encryption
value is set to "true," control passes to block 625.
[0088] At block 620, the decryption component 7 determines the
access unit is not encrypted and process 600 ends.
[0089] At block 625, the decryption component 7 determines if the
access unit size value is greater than zero bytes and less than 16
bytes, control passes to block 630. At block 626, if the access
unit size value is 16 bytes, control passes to block 635. If the
access unit size value is greater than 16 bytes and less than 32
bytes, control passes to block 640.
[0090] At block 630, the decryption component 7 performs an XOR
function on the data comprising the access unit (e.g., the n access
unit bytes) with the n leftmost bytes of D(K.sub.C, seed value),
and the process 600 ends.
[0091] At block 635, the decryption component 7 decrypts the 16
access unit bytes with AES using ECB mode and the process 600
ends.
[0092] At block 640, the decryption component 7 decrypts the first
16 access unit bytes with AES using ECB mode.
[0093] At block 645, the decryption component 7 calculates the
calculated IV value by performing an XOR function on the seed value
and the remaining 16 bytes of the access unit.
[0094] At block 650, the digital rights management component 5
performs an XOR function on the remaining n-16 bytes with the n
leftmost bytes of D(K.sub.C, IV calculated value).
[0095] At block 655, the digital rights management component 5
checks and initializes the parameter values. The digital rights
management component 5 sets the IV stride count value to the number
of strides in the access unit. The IV stride count value is
calculated as being the value of access unit size value divided by
the encryption stride size value.
[0096] At block 660, the decryption component 7 determines the
complete encryption value of the received digital content. If the
complete encryption value is "True," control passes to block 665.
If the complete encryption value is "False," control passes to
block 675.
[0097] At block 665, the decryption component 7 decrypts the block
of data contributing to the calculated IV value. For example, the
first 16 byte string of data of the stride (cipher text) for each
of IV stride count values are decrypted. The decryption may
intrinsically know the location of the blocks of data contributing
to the calculated IV value or locations may be passed as parameters
in an alternative embodiment. In one embodiment, no IV is involved
in the decryption.
[0098] At block 675, the decryption component 7 determines the
calculated IV value. In one embodiment, the calculated IV value is
derived by performing an XOR function on a 16 byte string of data
from each stride with a seed value, as described above. The seed
value may have been transmitted separately from the digital content
or appended to the digital content.
[0099] At block 685, the decryption component 7 decrypts the
remaining encrypted block of data using AES CBC and the calculated
IV value.
[0100] At block 690, the decryption component 7 decrypts the
partial stride, if necessary. In one embodiment the partial stride
is decrypted as described in FIG. 7.
[0101] It should be understood the process 600 may be repeated for
each access unit in the digital content as needed.
[0102] FIG. 7 illustrates one embodiment of a process flow 700 for
decrypting a partial block (as in less than key length).
[0103] At block 720, the digital rights management component 5
calculates a partial bits value as the number of bits in the
partial block.
[0104] At block 730, the digital rights management component 5
performs an XOR function of the bits of the partial block with the
n left-most bits of the last full block (n equaling the number of
bits in the partial block), to generate the corresponding cipher
text.
[0105] FIG. 8 illustrates one embodiment of a computer system
suitable for performing the features of an embodiment of the
invention. The computer system 840 includes a processor 850, a
memory 855, and an input/output capability 860, all coupled to a
system bus 865. Such a configuration encompasses personal computer
systems, network computers, television based systems, such as Web
TVs or set-top boxes, handheld devices, such as portable music
players, digital video players, mobile phones and personal digital
assistants, and similar devices.
[0106] The processor 850 represents a central processing unit of
any type of architecture, such as a CISC, RISC, VLIW, DSP, or
hybrid architecture. In addition, the processor 850 could be
implemented on one or more chips. The memory 855 is configured to
store instructions which, when executed by the processor 850,
performs the methods described herein. The memory 855 may also
store the user information and the contact information.
[0107] Input/output 860 may include components to facilitate user
interaction with the computer system 840 such as a keyboard, a
mouse, a display monitor, a microphone, a speaker, a display, a
network card (e.g., Ethernet, Inferred, cable modem, Fax/Modem,
etc.), etc. Input/output 860 also encompasses various types of
machine-readable media, including any type of storage device that
is accessible by the processor 850. For example, a machine-readable
medium may include read only memory ("ROM"); random access memory
("RAM"); magnetic disk storage media; optical storage media; flash
memory devices; electrical, optical, acoustical, or other forms of
propagated signals (e.g., carrier waves, infrared signals, digital
signals, etc.). Thus, a machine-readable medium includes any
mechanism that provides (i.e., stores and/or transmits) information
in a form readable by a machine (e.g., a computer). One of skill in
the art will immediately recognize that the term "machine-readable
medium/media" further encompasses a carrier wave that encodes a
data signal.
[0108] It will also be appreciated that the operating system
software executing the digital rights management component 5, the
decryption component 7, and the digital content player 8 stored in
memory 855 may control the computer system 840. The operating
system may be, for example, PC-based, Mac-based, Unix-based, Palm
OS, etc. Input/output and related media 860 store the
machine-executable instructions for the operating system and
methods of the present invention.
[0109] In addition, the bus 865 may represent one or more busses
(e.g., PCI, ISA, X-Bus, EISA, VESA, etc.) and bridges (also termed
as bus controllers). While this embodiment is described in relation
to a single processor computer system, the invention could be
implemented in a multi-processor computer system.
[0110] The description of FIG. 8 is intended to provide an overview
of computer hardware and other operating components suitable for
implementing the invention, but is not intended to limit the
applicable environments. It will be appreciated that the computer
system 840 is one example of many possible computer systems that
have different architectures. A typical computer system will
usually include at least a processor, a memory, and a bus coupling
the memory to the processor. One of skill in the art will
immediately appreciate that the invention can be practiced with
other computer system configurations, including multiprocessor
systems, minicomputers, mainframe computers, and the like. The
invention can also be practiced in distributed computing
environments where tasks are performed by remote processing devices
that are linked through a communications network.
[0111] It will be appreciated that more or fewer processes may be
incorporated into the methods illustrated in FIGS. 2, 3D, 3F, 4, 5,
6, and 7, without departing from the scope of the invention and
that no particular order is implied by the arrangement of blocks
shown and described herein. It will be further appreciated that the
method described in conjunction with FIGS. 2, 3D, 3F, 4, 5, 6, and
7, may be embodied in machine-executable instructions, (e.g.,
software). The instructions can be used to cause a general-purpose
or special-purpose processor that is programmed with the
instructions to perform the operations described. Alternatively,
the operations might be performed by specific hardware components
that contain hardwired logic for performing the operations, or by
any combination of programmed computer components and custom
hardware components. The methods may be provided as a computer
program product that may include a machine-readable medium having
stored thereon instructions, which may be used to program a
computer (or other electronic devices) to perform the methods. For
the purposes of this specification, the term "machine-readable
medium" shall be taken to include any medium that is capable of
storing or encoding a sequence of instructions for execution by the
machine and that causes the machine to perform any one of the
methodologies of the present invention. The term "machine-readable
medium" shall accordingly be taken to include, but not be limited
to, solid-state memories, optical and magnetic disks, and carrier
wave signals. Furthermore, it is common in the art to speak of
software, in one form or another (e.g., program, procedure,
process, application, module, logic, etc.), as taking an action or
causing a result. Such expressions are merely a shorthand way of
saying that execution of the software by a computer causes the
processor of the computer to perform an action or to produce a
result.
[0112] Protection of digital content using block cipher
cryptography has been described. It should be appreciated that the
encryption does not change the size of the encrypted data and
therefore any additional headers necessary to decrypt do not need
to be adjusted. Furthermore, it is possible to resume decrypting
the streamed content even if some packets are lost during
transmission. Encryption chains are and can be restarted at close
enough intervals so as to not destroy the viewing experience when
packet loss occurs. This is due to the capability to derive the
calculated IV value at whichever point the decryption is restarted,
and to the fact that the CBC is restarted at well defined intervals
(e.g., access units) that are known without decrypting the content.
Also, it should be appreciated that to improve the security of CBC,
the calculated IV value is different each time it is used with the
same key. Since one of the goals of the method is to not add data
to the file, the calculated IV value is generated from reasonably
random data collected from the sample to be encrypted itself.
[0113] Furthermore, a mechanism for partial media encryption has
been disclosed that parameterizes the amount of encryption so that
for less capable devices, less than 100% encryption can be
used.
[0114] It should be understood that the digital rights management
component 5 may perform additional checks and initializations than
those disclosed above. For example, the digital rights management
component 5 checks if the encryption chunk size value is less than
or equal to (the encryption stride size value minus the encryption
chunk offset value). Furthermore, the encryption chunk size value
may be checked to ensure it is a multiple of the AES block size (16
bytes).
[0115] While the invention has been described in terms of several
embodiments, those skilled in the art will recognize that the
invention is not limited to the embodiments described. The method
and apparatus of the invention can be practiced with modification
and alteration within the scope of the appended claims. The
description is thus to be regarded as illustrative instead of
limiting on the invention.
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