Method and apparatus for enhancing software security and distributing software

37 Pages·2013·4.47 MB·English

1 US 00572445A ‘
United States Patent [19] [11] Patent Number: 5,724,425
Chang et a]. [45] Date of Patent: Mar. 3, 1998
[54] METHOD AND APPARATUS FOR [57] ABSTRACT
ENHANCING SOFTWARE SECURITY AND
Source code to be protected. a software application writer’s
DISTRIBUTING SOFTWARE
private key. along with an application writer’s license pro
[75] Inventors : Sheue-Ling Chang. Cupertino; James vided to the ?rst computer. The application writer’s license
Gosling. Woodside. both of Calif. includes identifying information such as the application
writer’s name as well as the application writer’s public key.
[73] Assignee: Sun Microsystems, Inc. A compiler program executed by the ?rst computer compiles
the source code into binary code. and computes a message
digest for the binary code. The ?rst computer then encrypts
[21] Appl. No.: 258,244
the message digest using the application writer’s private key.
[22] Filed: Jun. 10, 1994 such that the encrypted message digest is de?ned as a digital
“signature" of the application writer. A software passport is
[51] Int. Cl.6 .............................. .. n04]. 9/00; H04L 9/30; then generated which includes the application writer’s digi
tal signature. the application writer’s license and the binary
[52] US. Cl. ................................. .. 380/25; 380/4; 380/23; code. The software passport is then distributed to a user
380/30; 380/49; 380/50 using any number of software distribution models known in
[53] Field of Search .................................. .. 380/4. 23. 25. the industry. A user. upon receipt of the software passport.
380/30. 49. 50 loads the passport into a computer which determines
whether the software passport includes the application writ
[56] References Cited er’s license and digital signature. In the event that the
software passport does not include the application writer’s
U.S. PATENT DOCUMENTS license. or the application writer’s digital signature. then the
user’s computer system discards the software passport and
4,558,176 12/1985 Arnold et alv ............................ .. 380/4 does not execute the binary code. As an additional security
4,634,807 V1987 Chorley et al. .. step. the user’s computer computes a second message digest
4,670,857 6/1987 Rackman .... .. for the software passport and compares it to the ?rst message
5,343,527
digest. such that if the ?rst and second message digests are
not equal. the software passport is also rejected by the user’s
UT HER PUBLICATIONS
computer and the code is not executed. If the ?rst and second
Davida et al.. “Defending Systems Against Viruses through message digests are equal. the user’s computer extracts the
Cryptographic Authentication", IEEE Symposium. 1989. application writm"s public key ?'om the application writer’s
pp. 312-313. license for veri?cation. The application writer’s digital sig
nature is decrypted using the applican'on writer’s public key.
RSA Data Security. Inc.. “RSA Certi?cate Services”. Jul. 15.
The user’s computer then compares a message digest of the
1993. pp. 1-41.
binary code to be executed. with the decrypted application
writer’s digital signature. such that if they are equal. the
Primary Examiner-Bernarr E. Gregory
user’s computer executes the binary code.
Attorney Agent, or Firm--McCutchen. Doyle. Brown &
Enersen LLP; Ronald S. Lain‘ie. Esq.; Joseph Yang 72 Claims, 5 Drawing Sheets
15
\
UUUUUEIUUUEIUU DUE]
UEIEIUUUEIDEIDEIU BED
UUUUUUUEIUUUU [:lElEl
UUEHZUDD Ell-JD
12 10
F
5 //0 i
i CPU Elf“
l MEMORY f H
I i
US. Patent Mar. 3, 1998 Sheet 1 of 5 5,724,425
FIG. 7
15
\
UEIDDEIEJEIUDUEIU DUE!
UEIEIUEIEIUEJUEIUEI DUE]
DUEIUEIEIUDUEIUU EIDEI
UEJUIIIIEJEIE! EIEH'J
APPUCA 7'I ON
WRITE/P
APP WRITER'S LICENSE 24
APP. WR/TER'S
‘ SOURCéEO CODE ’ APP WRITERS NAME .30
PRfl/ATE KEY 22
APP WR/TER'S PUBLIC KEY .32
VALID/TY DATE 34
COMP/LEI?
26
FIG. 4
PASSPORT P 38
[El
(-5i A?NY DISTRIBUTION CMNNEL
p
PM TFORM
US. Patent 5,724,425
Mar. 3, 1998 Sheet 2 0f 5
FIG. 2
PRODUCT INFO...
COMPANY INF0 ....
MUD/TY D/UE...
RESTRICTED RIGHTS LEGEND...
APP WRITERS‘ NAME
APP WR/TER'S PUBLIC KEY-#1”
IDENUHCA 270w AUTHOR/7)’: THE PIATFORM BUILDER
PUHFORM BUILDER'S S/GNA J’l/R??’ff
APP WR/TER’S SIGNA ruRE-f?'f
CODE BODY
PRODUCT INFO...
COMPANY INFO...
VALID/7}’ DADS...
RESTRICTED R/CHTS LEGEND...
APP n/PnEP's NAME
APP WP/IEP'S PUBLIC Kmfff‘f
IDENT/F/CA new AUTHOR/TY: THE PLA zroPM BUILDER
PEAIEOPM BUILDER'S s/aNAn/PEfm/
APP WR/TER’S s/cNAn/mf/W
CODE BODY
FIG. 3
US. Patent Mar. 3, 1998 Sheet 3 of 5 5,724,425
FIG. 5
PLA TFDRM
BUILDER
APPL/CA TIDN
WRITER 60
APP WR/TER'S LICENSE 52
APP. '
PRlmu?ilaitg)’ SOURCE CODE APP WR/TER'S NAME
58 APP WRUER'S PUBLIC KEY 62
VALID/7')’ DATE
PLA TEDRM BUILDER '5 S/CNA LURE
COMP/LER
68
PASSPORT M50
1
PIA TFORM BUILDER ‘S
PM TEDRM
US. Patent Mar. 3, 1998 Sheet 4 of 5 5,724,425
I-MRDWARE PLATFORM
WITH PUBLIC KEY IN
REGISTER F/G. 6(a)
ATTEMPT TO LOAD
SOHWARE
H?’l?gom REJECT SOFTWARE
?
PASSPORT REJECT SOHWARE
HAS LICENSE PASSPORT
?
YES
EXI RAC T LICENSE FROM
SOH'WARE PASSPORT
OECRYPT ISSUER'S SIGNATURE
USING PUBLIC KEY IN REGISTER
RECOMPUTE MESSAGE
DIGEST OF LICENSE
ARE MESS‘IOE
OICESIS E0 SW LICENSE NOT GENUINE
'2
YES
US. Patent Mar. 3, 1998 Sheet 5 of 5 5,724,425
F/G. 6(b)
EXTRACT sw's PUBLIC
KEY FROM APPLICATION WR/TER'S
LICENSE
EXTRACT CODE BODY
FROM THE PASSPORT
EXTRACT SW'S
S/CNA TURE
I
RECOMPUTE MESSAGE M0 = MESSAGE DIGEST
0/ 5r 0; 0 5 SW = SOHWARE
GE 8007315 c D (APPL/O! no/v)
WRITER
DECRYPT SW'S
SIGNATURE USING
SW'S PUBLIC KEY
1
COMPARE RECOMPUTED
MESSACE DIGEST WITH
SW’S OECRYPTED SIC
NO REJECT SOFTWARE
PASSPORT
YES
EXECUTE CODE
5.724.425
1 2
METHOD AND APPARATUS FOR Moreover. security breaches are more easily accomplished
ENHANCING SOFTWARE SECURITY AND when a corporate network is connected to a public network.
DISTRIBUTING SOFTWARE such as the Internet. Companies take a variety of measures
to guard against breaches of network security. either through
frontal assaults or infections. without cutting themselves off
BACKGROUND OF THE INVENTION
from the bene?ts of being connected to a world-wide
1. Field of the Invention network.
The present invention relates to the use of public key The solution adopted by most companies that wish to reap
encryption. and more particularly. the present invention the bene?ts of connecting to the Internet. while maintaining
security. is the installation of a ?rewall. Firewalls generally
relates to the use of public key encryption to achieve 10
enhanced security and product authentication in the distri restrict Internet ?le transfers and telnet connections. Such
transfers and connections can only be initiated from within
bution of software.
the corporate network. such that externally initiated file
2. Art Background
transfers and telnet connections are refused by the ?rewall.
Public key encryption is based on encryption algorithms Firewalls allow electronic mail and network news to freely
that have two keys. One key used for encryption. and the 15 ?ow inside the ?rewall’s private network. The use of cor
other key is used for decryption. There is a known algorithm porate ?rewalls allows employees to readily exchange infor
that computes the second key given the ?rst. However. mation within the corporate environment. without having to
without full knowledge of all the parameters. one cannot adopt extreme security measures. A good ?rewall imple
compute the ?rst key given the second key. The ?rst key is mentation can defend against most of the typical frontal
referred to as the “private key”. and the second key is 20 assaults on system security.
referred to as the “public key”. In practice. either the private One method of preventing viruses and worms from infect
key or the public key may be used to encrypt a mes sage. with ing a corporate network is to never execute a program that
the opposite key used to decrypt it. In general. the private may contain viruses. In general. programs legitimately
key must be kept private. but the public key may be provided deployed throughout the corporate network should be con
to anyone. A variety of public key cryptographic schemes 25 sidered virus free. All binary executables. all unreviewed
shell scripts. and all source code fetched from outside the
have been developed for the protection of messages and data
?rewall are software that may contain a worm or virus.
(See. Whit?eld Di?ie. "The First Ten Years of Public Key
However. outside binary executables. shell scripts. and
Cryptography” (IEEE Proceedings. Vol. 76. No. 5. 1988)
source code may enter a corporate ?rewall through an
and Fahn. “Answers to Frequently Asked Questions about
E-mail attachment. For example. the shell scripts that are
Today’s Cryptography (RSA Laboratories 1992). 30
used to make and send multiple ?les using Email and the
Public key cryptography is used to send secure messages surveytools that start up by activating the E-mail attachment
across public communication links on which an intruder may allow virus entry. Executables can also be directly
may eavesdrop. and solves the problem of sending the fetched through the iftp program. through a world-wide web
encryption password to the other side securely.
browser such as Mosaic. or from an outside contractor
35
Public key systems may also be used to encrypt messages. whose network has already been compromised.
and also to effectively sign messages. allowing the received In addition. the commercial software release and distri
party to authenticate the sender of the message. One can also bution process presents security and authentication prob
use public key cryptography to seal or render tamper-proof lems. For example. some of the information associated with
a piece of data. In such event. the sender computes a software. such as the originating company or author.
message digest from the data using specially designed restricted rights legends. and the like are not attached to the
cryptographically strong digests designed for this purpose. code itself. Instead. such information is provided as printed
The sender then uses the private key to encrypt the message matter. and is separated from the code once the package is
digest. wherein this encrypted message digest is called a opened and the code installed. Even applications that
digital “signature”. The sender then packages the data. the attempt to identify themselves on start-up are susceptible to
45
message digest and the public key together. The receiver having the identi?cation forged or otherwise counterfeited
may check for tampering by computing the message digest A user has no mechanism to authenticate that the software
again. then decrypting the received message digest with the sold is actually from the manufacturer shown on the label.
public key. If the recomputed and decrypted message digests Unauthorized copying and the sale of software is a signi?
are identical. there was no tampering of the data. cant problem. and users who believe that they are buying
50
“Viruses” and “worms” are computer code cleverly software with a manufacturer‘s warranty instead purchase
inserted into legitimate programs which are subsequently pirated software. with neither a warranty nor software sup~
executed on computers. Each time the program is executed port. The problem of authenticating the original source of
the virus or worm can cause damage to the system by the software is accentuated when software is intended to be
destroying valuable information. and/or further infect and SS distributed through networks. and a user‘s source for the
spread to other machines on the network. While there are software may be far removed from the original writer of the
subtle dilferences between a virus and a worm. a critical software. In addition. a user does not have that ability to
component for both is that they typically require help from verify that the software purchased contains only the original
an unsuspecting computer user to successfully infect a manufacturer’s code. A user also does not have a method for
computer or a corporate network. detecting any tampering. such as the existence of a virus.
Infection of computers by viruses and worms is a general that may cause undesirable effects.
problem in the computer industry today. In addition. corpo All of the above problems are related to the transport of
rate networks are vulnerable to frontal assaults. where an software both from manufacturers to users and from user to
intruder breaks into the network and steals or destroys user. Furthermore. the transport problem is independent of
information. Security breaches of any kind on large corpo 65 the transport medium The problem applies to all transport
rate networks are a particularly worrisome problem. because media. including ?oppy disk. magnetic tape. CD-ROM and
of the potential for large-scale damage and economic loss. networks.
5.724.425
3 4
As will be described. the present invention provides a execute only authorized software. A platform builder pro
method and apparatus for authenticating that software dis vides an application writer with a platform builder’s digital
tributed by a manufacturer is a legitimate copy of an signature which is included in the application writer’s
authorized software release. and that the software contains license. The ?rst computer compiles the software into binary
only the original manufacturers code without tampering. code and computes a ?rst message digest for the binary
The present invention solves the above identi?ed problems code. The ?rst computer further encrypts the ?rst message
through the use of a “software passport” which includes the digest using the application writer's private key. such that
digital signature of the application writer and manufacturer. the encrypted ?rst message digest is de?ned as the applica
As will be described. the present invention may also be used tion writer’s digital signature. A software passport is gen
to protect intellectual property. in the form of copyrighted erated which includes the application writer’s digital
computer code. by utilizing cryptographic techniques signature. the application writer’s license and the binary
referred to herein as public key encryption. code. The software passport is then distributed to a user
through existing software distribution channels. The user’s
SUMMARY OF THE INVENTION
computing platform. which may be a computer. a video
This invention provides a method and apparatus utilizing game box or a set top box. is provided with the platform
public key encryption techniques for enhancing software builder’s public key. Upon receipt of the software passport.
security and for distributing software. The present invention the computing platform determines if the software passport
includes a ?rst computer which is provided with source code includes an application writer’s license. If it does not. the
to be protected using the teachings of the present invention. hardware platform rejects the execution of the code. If a
In addition. a software application writer’s private key. 20 software passport is present. the hardware platform extracts
along with an application writer’s license provided to the the application writer’s license from the passport and deter
?rst computer. An application writer generally means a mines whether or not the passport includes the platform
software company such as Microsoft Corporation. Adobe or builder’s signature. The platform builder’s signature is then
Apple Computer. Inc. The application writer’s license decrypted using the public key provided in the platform The
includes identifying information such as the application 25 computing platform recomputes the message digest of the
writer’s name as well as the application writer’s public key. application writer’s license. and compares the received
A compiler program executed by the ?rst computer compiles message digest with the recomputed message digest. such
the source code into binary code. and computes a message that if the digests are not equal. the software passport is not
digest for the binary code. The ?rst computer then encrypts considered genuine and is rejected. If the message digests
the message digest using the application writer’ s private key. are equal. the hardware platform extracts the application
such that the encrypted message digest is de?ned as a digital writer’s public key from the application writer’s license. and
“signature” of the application writer. A software passport is extracts the application writer's digital signature. The hard
then generated which includes the application writer’s digi ware platform then recomputes the message digest of the
tal signature. the application writer’s license and the binary binary code comprising the application software to be
code. The software passport is then distributed to a user 35 executed. and decrypts the application writer’s digital sig
using any number of software distribution models known in nature using the application writer’s public key. The hard
the industry. ware platform then compares the recomputed message
A user. upon receipt of the software passport. loads the digest for the binary code with the application writer’s
passport into a computer which determines whether the decrypted signature. such that if they are equal. the binary
software passport includes the application writer’s license code is executed by the hardware platform. If the recom
and digital signature. In the event that the software passport puted message digest and the application writer’s decrypted
does not include the application writer’s license. or the signature are not equal. the software passport is rejected and
application writer’s digital signature. then the user‘s com the code is not executed
puter system discards the software passport and does not
BRIEF DESCRIPTION OF THE DRAWINGS
execute the binary code. As an additional security step. the 45
user’s computer computes a second message digest for the FIG. 1 illustrates a data processing system incorporating
software pas sport and compares it to the ?rst message digest. the teachings of the present invention.
such that if the ?rst and second message digests are not FIG. 2 conceptually illustrates use of the present inven
equal. the software passport is also rejected by the user’s tion’s software passport where the application code and the
computer and the code is not executed. If the ?rst and second software passport are provided in separate ?les.
message digests are equal. the user’s computer extracts the FIG. 3 conceptually illustrates use of the present inven
application writer’s public key from the application writer’s tion’s use of the software passport where the application
license for veri?cation. The application writer’s digital sig code and the software passport are distributed in the same
nature is decrypted using the application writer’s public key. ?le.
The user‘s computer then compares a message digest of the FIG. 4 diagrammatically illustrates the present inven
binary code to be executed. with the decrypted application tion’s process for generating a software passport.
writer’s digital signature. such that if they are equal. the FIG. 5 diagrammatically illustrates the use of the present
user’s computer executes the binary code. Accordingly. invention for platform producer licensing.
software products distributed with the present invention's FIGS. 6a and 6b are ?owcharts illustrating the steps
software passport permits the user’s computer to authenti executed by the present invention for verifying that a valid
cate the software as created by an authorized application software license exists. and that the software writer’s
writer who has been issued a valid application writer’s (“SW’s”) signature is valid. prior to permitting the execution
license. Any unauthorized changes to the binary code com
of a computer program.
prising the distributed software is evident through the com
parison of the calculated and encrypted message digests. 65 NUI‘ATION AND NOMENCLATURE
The present invention is also described with reference to The detailed descriptions which follow are presented
an embodiment used by computing platforms designed to largely in terms of symbolic representations of operations of
5 .724.425
5 6
data processing devices. These process descriptions and Exemplary Hardware
representations are the means used by those skilled in the FIG. 1 illustrates a data processing system in accordance
data processing arts to most effectively convey the substance with the teachings of the present invention. Shown is a
of their work to others skilled in the art. computer 10. which comprises three major components. The
An algorithm is here. and generally. conceived to be a ?rst of these is an input/output (IIO) circuit 12 which is used
self-consistent sequence of steps leading to a desired result. to communicate information in appropriately structured
These steps are those requiring physical manipulations of form to and from other portions of the computer 10. In
physical quantities. Usually. though not necessarily. these addition. computer 10 includes a central processing (CPU)
quantities may take the form of electrical or magnetic 13 coupled to the I/O circuit 12 and a memory 14. These
signals capable of being stored. transferred. combined. elements are those typically found in most general purpose
compared. displayed and otherwise manipulated. It proves computers and. in fact. computer 10 is intended to be
convenient at times. principally for reasons of common representative of a broad category of data processing
usage. to refer to these signals as bits. values. messages. devices. Also. the computer 10 may be coupled to a network.
names. elements. symbols. operations. messages. terms. in accordance with the teachings herein. The computer 10
numbers. or the like. It should be borne in mind. however. 15 may further include encrypting and decrypting circuitry
that all of these similar terms are to be associated with the incorporating the present invention. or as will be
appropriate physical quantities and are merely convenient appreciated. the present invention may be implemented in
labels applied to these quantities. software executed by computer 10. Araster display monitor
In the present invention. the operations referred to are 16 is shown coupled to the I/O circuit 12 and issued to
machine operations. Useful machines for performing the 20 display images generated by CPU 13 in accordance with the
operations of the present invention include general purpose present invention. Any well known variety of cathode ray
digital computers or other similar devices. In all cases. the tube (CRT) or other type of display may be utilized as
reader is advised to keep in mind the distinction between the display 16.
method operations of operating a computer and the method The present invention’s software passport identi?es a
of computation itself. The present invention relates to 25 portion of software. or some machine code (hereinafter
method steps for operating a computer. coupled to a series “code”). in a manner similar to how a physical passport
of networks. and processing electrical or other physical identi?es a person. The concept is similar to the real-life
signals to generate other desired physical signals. passport system which forms the basis of a trust model
The present invention also relates to apparatus for per among different nations. Physical passports enable border
forming these operations. This apparatus may be specially entry o?icers to identify each individual and make certain
constructed for the required purposes or it may comprise a decisions based on his/her passport. As will be described
general purpose computer selectively activated or recon?g below. a software passport is a modern release process for
ured by a computer program stored in the computer. The distributing software products. A software passport gives a
method/process steps presented herein are not inherently software product an identity and a brand name. The software
related to any particular computer or other apparatus. Vari 35 passport provides the basis of a trust model and allows
ous general purpose machines may be used with programs in computer users to identify and determine the genuineness of
accordance with the teachings herein. or it may prove more a software product based on the information contained in its
convenient to construct specialized apparatus to perform the passport.
required method steps. The required structure for a variety of Referring now to FIG. 2. the present invention is illus
these machines will be apparent from the description given trated in conceptual form for the case where the computer
below. code (comprising a piece of software) and the software
passport are in separate ?les. FIG. 3 illustrates the use of the
DETAILED DESCRIPTION OF THE
present invention where the computer code comprising a
INVENTION
piece of software and the software passport are in the same
In the following description. numerous speci?c details are 45 ?le.
set forth such as system con?gurations. representative data. As illustrated in FIGS. 2 and 3. the information included
computer code organization. encryption methods. and
in the present invention’s software passport may include:
devices. etc.. to provide a thorough understanding of the
product information. such as the software product’s name
present invention. However. it will be apparent to one skilled
and any other relevant information to the speci?c
in the art that the present invention may be practiced without 50 product;
these speci?c details. In other instances. well known circuits
company information including the name of the company
and structures are not described in detail in order to not
or the software application writer who has produced the
obscure the present invention. Moreover. certain terms such product;
as “knows”. “veri?es”. “compares”. “examines”. “utilizes".
a validity date which includes the issue date of the
“?nds”. “determines”. “challenges”. “authenticates”. etc.. 55
software passport and the expiration date of the pass
are used in this Speci?cation and are considered to be terms
port;
of art. The use of these terms. which to a casual reader may
a restricted rights legend including copyright notices and
be considered personi?cations of computer or electronic
other similar legends;
systems. refers to the functions of the system as having
the software code body including executable application
human-like attributes. for simplicity. For example. a refer
ence herein to an electronic system as “determining” some code distributed to the user;
thing is simply a shorthand method of describing that the an application writer’s license; and.
electronic system has been programmed or otherwise modi a software application writer‘s digital signature.
?ed in accordance with the teachings herein. The reader is It will be appreciated that the components of a software
cautioned not to confuse the functions described with every passport are genm'ally self-explanatory. with the application
day human attributes. These functions are machine functions writer’s license and digital signature explained in more
in every sense. detail below.
5 v724,425
7 8
SOFTWARE PRODUCER’S DIGITAL SIGNATURE In accordance with the teachings of the present invention.
A digital “signature” is produced by using certain cryp a software application writer (“SW") supplies three major
tographic techniques of computing a message digest of a pieces of information to a compiler prior to compilation of
piece of software code (hereinafter “code”). and encrypting the code:
the message digest using the signer‘s private key. There are the source code written by the application writer;
many known message digest algorithms. such as the MD2. the application writer’s private key; and
MD4. and MDS algorithms published by RSA. Inc. The use the application writer’s license.
of private cryptographic techniques makes this signature The code included in a passport may comprise source
very difficult to forge since the signer keeps the private key code in various computer languages. assembly code.
secret. The reader is referred to the papers by Whit?eld machine binary code. or data. The code may be stored in
1O
Dif?e. “The First Ten Years of Public Key Cryptography”. various formats. For example. a piece of source code may be
Vol. 76. No. 5 (IEEE Proceedings. May 1988). which is stored in a clear text form in the passport. Aportion of binary
attached hereto as Appendix A; and Whit?eld Di?ie. et al.. executable machine code may also be stored in a compacted
“Authentication and Authenticated Key Exchanges” (1992 format in the passport. using certain well known compaction
Kluwer Academic Publishers) attached hereto as Appendix algorithms such as Huffman encoding. The format used in a
B. for a detailed description of the operation of Di?ie particular implementation is indicated by a ?ag in the
Helman certi?cates and public key cryptography. passport.
One may conceptualize the computing of the message Binary executable code may further be stored in a
digest for a piece of code as a mechanism of taking a photo printable-character set format to allow the passport to be
snapshot of the software. When the code changes. its mes printed A user would then reverse the printable-format to
sage digest re?ects any differences. In the system of the 20 recover the software. Moreover. code protected by intellec
present invention. this “digital signature” is stamped on the tual property. such as copyright or patent. may be stored in
product prior to its release. The digital signature associates an encrypted format in the passport. In such case. it is
contemplated that a user may be required to pay a license fee
a product with the entity that has produced it. and enables
prior to gaining access to the software.
consumers to evaluate the quality of a product based on the
reputation of the producer. The signature also permits a 25 Referring now to FIG. 4. to generate the software pas sport
of the present invention. the original source code 20. the
consumer to distinguish the genuineness of a product.
application writer’s private key 22. and the application
SOFTWARE PRODUCER’S LICENSE
writer’s license 24 is provided to a compiler 26. As
The present invention’s software producer's license (at
illustrated. the application writer's license 24 includes the
time referred to herein as the “application writer’s license”)
30 writer‘s name 30. the writer's public key 32 and a validity
is an identi?cation similar to the home repair contractor’s
date 34.
license issued by a state. A software producer’s license
The compiler 26 then compiles the source code 20 into
identi?es and certi?es that the producer is authorized to
binary code. The compiler 26 further computes the message
perform certain software production activities. It is contem
digest of the binary code. and encrypts the message digest
plated that the software producer’s license will be issued by
using the private key 22 supplied by the application writer.
some commonly-trusted authority established by the com
This encrypted message digest constitutes the application
puter software industry. Before issuing an license to a
writer’s signature.
software producer. this authority performs a de?ned process
A digital signature of the application writer is produced
to authenticate the person or company. and to verify their job
and embedded in the passport. The compiler 26 also embeds
skill; as a state does before issuing a contractor's license. For
the application writer‘s license 24 in the passport. The
convenience. in this Speci?cation. this commonly-trusted
application writer’s license 24 allows any user who has
entity is referred to as the Software Publishing Authority
purchased the product to recognize the maker of the product.
(“SP ").
The application writer‘s digital signature in the passport
A software producer’s license contains the following
allows any user to verify the genuineness of the product. The
information:
SPA‘s digital signature in the application writer’s license 24
the producer’s name;
provides the user with the ability to verify that an application
the license‘s issue date; writer is a licensed application writer by using SPA’s public
the license’s expiration date; key to encrypt the signature.
the producer‘s public key; As shown in FIG. 4. the generated software passport 38.
the name of the issuing authority. SPA; and 50 including the application code is then distributed using any
the SPA‘s digital signature. desired software distribution model. The passport 38 is
A software producer’s license associates an application received by a user and is executed using an operating system
writer with a name and a public key. It enables a software (OS) running on a computer system (“platform”) such as the
producer to produce multiple products. and to sign every system of FIG. 1.
product produced. The public key embedded in a license 55 Referring now to FIG. 5. the use of the present invention
belongs to the person who owns the license. This public key by platform builders will be described. In the electronic
can later be used by any third party to verify the producer's game industry and the interactive television cable set-top
digital signature. A user who has purchased a product can box industry. platform producers often desire to allow only
determine the genuineness of a product by using the public authorized code to be executed on their particular platform.
key embedded in the producer's identi?cation to authenti To be able to control the accessibility of a platform. the
cate the digital signature. received code must be identi?able and the platform must be
The SPA’ s digital signature is generated by computing the able to identify the software when it arrives. As illustrated in
message digest of the producer’s identi?cation and encrypt FIG. 5. the present invention may be applied in a platform
ing the message digest using the SPA’s private key. Since the producer licensing scheme with particular application for
SPA’s private key is kept private to the SPA. third parties are 65 use in settop box and video game environments.
not able to easily forge the SPA’s signature to produce afake Referring now to FIGS. 6a and 6b. a platform producer
identi?cation. may issue a "programmer’s license" to a set of application