Note: Descriptions are shown in the official language in which they were submitted.
CA 02309463 2000-08-09
DIGITAL SIGNATURE SYSTEM
FIELD OF THE INVENTION
The present invention relates to a system for maintaining security of
electronic
documents. In particular, the present invention relates to a method and system
for
securely incorporating digital signatures into electronic documents.
BACKGROUND OF THE INVENTION
The Internet has provided network users with a mechanism for reducing
communication
costs by distributing maintenance costs of the network amongst a number of
different
network servers. This requirement has provided the Internet with a distinctly
"open"
character, with the result that electronic documents transmitted over the
Internet can be
intercepted by parties other than the intended recipients, altered by the
intercepting
parties, and then transmitted to the original intended recipients without the
recipients
having knowledge of the alteration. This weakness can be particularly
problematic,
particularly for parties engaged in e-commerce transactions over the Internet,
since the
terms of an order can be altered by a third party without authorization from
the ordering
party. Alternately, credit card numbers, bank account numbers or other
financial
information necessary for completion of e-commerce transactions can be
intercepted and
used by unscrupulous parties to generate unauthorized orders for goods or
services.
To address this problem, the concept of a digital signature was developed as a
means for
allowing recipients of electronic documents to verify the authenticity of the
electronic
document. To use a digital signature, an originator of an electronic document
first
obtains from a trusted source a private encryption key uniquely associated
with the
document originator. The private encryption key is also uniquely associated
with a
publicly available encryption key which allows recipients of electronic
documents
encrypted with the associated private encryption key to decrypt the encrypted
document
using the associated public encryption key. Since the private encryption key
is provided
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only to the document originator, recipients of the encrypted document can use
the public
encryption key to verify that the encrypted document originated from the
document
originator. The trusted source maintains a database of publicly available
digital
certificates, each of which identify the name of the holder of a private
encryption key, and
the public encryption key associated with the private encryption key.
After the document originator is assigned a private encryption key, the
document
originator applies a hash algorithm to the electronic document. Preferably,
the hash
algorithm returns a data word which is uniquely associated with the electronic
document,
but does not allow the electronic document to be recreated from the data word.
The
document originator then encrypts the hashed data word with the assigned
private
encryption key, thereby producing a digital signature which is uniquely
associated with
the electronic document and the document originator. The digital signature is
appended
to the electronic document, and is transmitted to the intended recipient
together with a
copy of the originator's digital certificate. Typically, each digital
certificate also includes
the digital signature of the trusted source.
Upon receipt of the electronic document, the recipient verifies the
authenticity of the
document by first decrypting the digital signature attached to the digital
certificate using
the public encryption key supplied by the trusted source. The recipient then
applies the
hash algorithm to the digital certificate, and then compares the data word
returned from
the hash algorithm with the data word extracted from the digital signature of
the digital
certificate. If the hash values match, the recipient has verification that the
digital
certificate is authentic, and that the public encryption key included with the
digital
certificate was assigned by the trusted source. After the digital certificate
is
authenticated, the document recipient decrypts the digital signature attached
to the
electronic document using the public encryption key included with the digital
certificate,
applies the hash algorithm to the electronic document, and then compares the
data word
returned from the hash algorithm with the hashed data word extracted from the
digital
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signature of the electronic document. If the hash values match, then the
document
recipient has verification that the electronic document originated from the
named
originator, and was not altered during transmission by third parties.
Although digital signatures have significantly enhanced the ability of
document recipients
to verify the authenticity of an electronic document, the mechanism by which
digital
signatures are employed has remained cumbersome. For instance, if the document
originator wishes to transmit a digitally signed e-mail message, the
originator must obtain
and install e-mail software capable of generating a hash value and using a
private
encryption key for encrypting the hash value. Further, typically the
originator must have
access to an Internet browser capable of establishing a secure communications
path with
the encryption key provider for providing the e-mail software with the private
encryption
key. Although digital encryption compliant e-mail software packages and secure
Internet
browsers are now available for use on Windows-based operating systems, digital
encryption compliant e-mail software packages are not available for all
operating
systems. Also, the transmission of digitally signed electronic documents from
portable
wireless devices is often hindered by the computing power and memory resource
limitations of such devices.
Digital signatures have also gained popularity for use with electronic cheques
as a
mechanism to avoid repudiation. For instance, the Financial Services
Technology
Consortium (US 5,677,955) has developed an electronic funds transfer
instrument
(electronic cheque) as a venue for electronic bill payment. The electronic
cheque is
generated on a computer-based system which includes a hardware peripheral
device for
receiving a PCMCIA card. The PCMCIA card is used by cheque issuer's bank, and
securely stores the user's private encryption key, and a personal
identification number to
prevent unauthorized access to the encryption key. The PCMCIA card also
includes a
register for identifying cheques signed and issued, a mechanism to calculate
the hash
value of the electronic cheques, and a mechanism to calculate digital
signatures from the
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hash values using the private encryption key. The computer-based system
interfaces with
the PCMCIA card, and is configured to endorse the electronic cheque with the
digital
signature received from the PCMCIA card, and to electronically transmit the
endorsed
electronic cheque to the recipient. Although the computer-based system
provides a
mechanism for securely generating and transmitting electronic cheques, rapid
deployment
of the system is limited by the need for a PCMCIA interface device and by the
requirement that the issuing bank encode the user's PCMCIA card with the
user's private
encryption key.
Therefore, there remains a need for a mechanism which facilitates the use of
digital
signatures across a variety of computing platforms, and without the necessity
of hardware
peripheral devices.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a digital signature
system and a
method of providing digital signatures for electronic documents which
addresses
deficiencies of the prior art.
The digital signature system, according to a first aspect of the present
invention, includes
a data receiver for receiving an electronic document over a network; an
encryption key
database, and a signature processor in communication with the encryption key
database
and the data receiver. The encryption key database includes encryption key
records, each
being associated with a subscriber of the database and identifying an
encryption key
uniquely associated with the subscriber. The signature processor is configured
for
receiving an indicator of one of the subscribers and for deriving a digital
signature from
the received electronic data and the encryption key associated with the one
subscriber.
The method of providing digital signatures, according to the first aspect of
the present
invention, includes the steps of (1) providing an encryption key database
including
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encryption key records, each record being associated with a subscriber of the
database
and identifying an encryption key uniquely associated with the subscriber; (2)
receiving
electronic data over a network; (3) receiving an indicator of one of the
database
subscribers; and (4) deriving a digital signature from the received electronic
data and the
encryption key associated with the one database subscriber.
The digital signature system, according to a second aspect of the present
invention,
includes a data receiver, an encryption key database, a data processor in
communication
with the encryption key database and the data receiver, and a data transmitter
in
communication with the data processor. The data receiver is configured for
receiving
over a network electronic data from one of a number of network users. The
encryption
key database includes encryption key records, each being associated with a
respective one
of the network users and identifying an encryption key uniquely associated
with the one
network user. The data processor is configured for deriving a digital
signature from the
received electronic data and the encryption key associated with the one
network user.
The signature transmitter is configured for providing the one network user
with the
derived digital signature.
The method of providing digital signatures, according to the second aspect of
the present
invention, includes the steps of (1) providing an encryption key database
including
encryption key records, each record being associated with a subscriber of the
database
and identifying an encryption key uniquely associated with the subscriber; (2)
receiving
over a network electronic data from one of the database subscribers; (3)
deriving a digital
signature from the received electronic data and the encryption key associated
with the one
database subscriber; and (4) transmitting the derived digital signature to the
one database
subscriber.
In accordance with a preferred implementation of the invention, the one
database
subscriber is also the originator of the electronic data, and the data
originator identifies
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itself by providing the signature processor with an personal identification
number
assigned to the data originator. Upon receipt of the personal identification
number, the
signature processor derives the digital signature with the encryption key
assigned to the
data originator. After the digital signature is derived, the digital signature
system
transmits the derived digital signature to the data originator. In one
variation, the
signature processor includes a document database including template records,
each
template record including at least one document data item. The data receiver
is
configured to receive from the one database subscriber an indicator of a
selected one of
the template records, and the signature processor is configured for assembling
an
electronic document from the received electronic data and the at least one
document data
items of the selected one template record, and for deriving the digital
signature from the
assembled electronic document. The data transmitter is configured to transmit
the
assembled electronic document together with the derived digital signature to
the one
database subscriber.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiment of the invention will now be described, by way of
example
only, with reference to the drawings, in which:
Fig. 1 is a schematic diagram of a digital signature system, according to the
present
invention, showing the data receiver, the encryption key database, the
signature data
processor, and the data transmitter;
Fig. 2 is a schematic view of a sample electronic document template suitable
for use with
the digital signature system shown in Fig. 1; and
Fig. 3 is a schematic view of a sample electronic document produced by the
digital
signature system.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning to Fig. 1, a digital signature system, denoted generally as 100, is
shown
comprising a data receiver 102, a data transmitter 104, an encryption key
database 106,
and a data processor 108. Typically, the digital signature system 100
comprises a server
computer, and is accessible over a land-based wide area network, such as the
Internet, to
provide digital signatures to land-based client computers. However, the
digital signature
system 100 may also be accessible over a local area network, or a wireless
network to
provide digital signatures to wireless-based client computers, such as
portable data
assistants, wireless pagers and wireless telephones.
The data receiver 102 interfaces the digital signature system 100 with the
network, and is
configured to receive electronic data over the network from users of the
network. The
data transmitter 104 also interfaces the digital signature system 100 with the
network, but
is configured to transmit electronic data to the network users over the
network. However,
it should be understood that it is not imperative that the digital signature
system 100
transmits electronic data over the same network which it receives electronic
data. For
instance, the digital signature system 100 may be configured to receive
electronic data
over a wireless network and to transmit electronic data over a land-based
network.
Further, the digital signature system 100 may be configured to transmit
electronic data to
a network user different from the network user from which it receives
electronic data.
Other network configurations will be apparent to those of ordinary skill.
Preferably, the encryption key database 106 is stored in a non-volatile
storage medium,
such as a magnetic hard drive or optical drive, and includes a plurality of
encryption key
records. Each encryption key record includes a user identification code
associated with a
respective one of the network users, a private encryption key uniquely
associated with the
user identification code, and a public encryption key uniquely associated with
the private
encryption key. The private encryption keys are not provided to members of the
public,
and are used by the digital signature system 100 to derive the digital
signature for each
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electronic document. The public encryption keys are provided to members of the
public,
and are used by members of the public to decrypt each digital signature so as
to provide
verification of the integrity of each electronic document received from a
network user.
The data processor 108 is in communication with the data receiver 102, the
data
transmitter 104, and the encryption key database 106, and is configured for
deriving a
digital signature from the electronic data received by the data receiver 102.
The data
processor 108 comprises a user interface 110, a central processing unit (CPU)
112 in
communication with the user interface 110, a document database 114 in
communication
with the CPU 112, and a non-volatile memory (DISC) 116 and a read/write memory
(RAM) 118 both in communication with the CPU 110. The user interface 110
comprises
a data entry device 120, such as a keyboard, for entering data into the
encryption key
database 106 and the document database 114, and a display device 122, such as
a CRT or
LCD, for viewing the contents of the encryption key database 106 and the
document
database 114.
The DISC 116 includes processor instructions for the CPU 112. The processor
instructions establish in the RAM 118 a memory object defining a user
identification
processor 124, a memory object defining a document assembly processor 126, and
a
memory object defining a digital signature processor 128. However, the user
identification processor 124, the document assembly processor 126, and the
digital
signature processor 128 need not be implemented as memory objects, but instead
may be
implemented in electronic hardware, if desired.
Preferably, the document database 114 is stored in a non-volatile storage
medium, such as
a magnetic hard drive, optical drive, EEPROM or flash memory, and includes a
plurality
of template records. Further, preferably each template record includes a
document
identification code, and at least one document data item, with the document
data items of
each template record together defining an electronic document template.
Alternately,
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each template record may include, either in addition to or in replacement of
the document
identification code, a user identification code identifying a network user
authorized to
access the electronic document template. A sample electronic document template
200,
configured as an electronic cheque, is shown in Fig. 2 including a plurality
of document
data items 202. As shown in Fig. 2, the document data items 202 may comprise
text data
and/or graphical data. Preferably, each document data item 202 includes
positional code,
implemented in Standard Graphic Markup Language (SGML), Extensible Markup
Language (XML), Financial Services Markup Language (FSML), or other suitable
markup language, to define the relative orientation of the document data items
202 within
the electronic document template 200.
The user identification processor 124 is configured to receive personal
identification
numbers (PINs) from the network users, via the data receiver 102, and to query
the user
identification codes stored in the encryption key database 106 with each
received PIN and
thereby extract from the encryption key database 106 the private encryption
key
associated with each received PIN. The document assembly processor 126 is
configured
to receive document identification numbers from the network users, via the
data receiver
102, and to query the document identification codes stored in the document
database 114
with each received document identification number and thereby extract from the
document database 114 the electronic document template 200 associated with
each
received document identification number. If the template records of the
document
database 114 include a user identification code, preferably the document
assembly
processor 126 is also configured to receive personal identification numbers
(PINs) from
the network users and to query the user identification codes of the template
records so as
to extract the required electronic document template 200. The document
assembly
processor 126 is also configured to assemble an electronic document from the
retrieved
electronic document template 200 by receiving electronic data records from the
network
users, via the data receiver 102, for insertion into the retrieved electronic
document
template 200. A sample assembled electronic document 300, configured as an
electronic
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cheque, is shown in Fig. 3 including a plurality of electronic data records
302 and a
plurality of the document data items 202.
The digital signature processor 128 is configured to derive a digital
signature from the
assembled electronic document 300 and the encryption key associated with the
provided
user identification code. The document assembly processor 126 is configured to
append
the derived digital signature to the assembled electronic document 300, and to
transmit
the electronic document 300 (appended with the digital signature) to the data
transmitter
104 for transmission over the network to the intended network user. Typically,
the data
transmitter 104 is configured to transmit the electronic document 300 and
digital
signature to the network user which initiated communication with the digital
signature
system 100. However, in one variation, the data processor 108 is configured to
receive
(via the data receiver 102) the target network address, such as an e-mail
address, of the
desired recipient of the electronic document 300 and digital signature, and
the data
transmitter 104 is configured to transmit the electronic document 300 and
digital
signature to the specified target network address. Further, in another
variation, the data
transmitter 104 is configured to only transmit the derived digital signature
to the specified
target network address.
In operation, a network user desiring to transmit an electronic document 300
with a
digital signature first registers itself with the digital signature system
100. Preferably, the
network user registers itself with the digital signature system 100 by
attending personally
at an establishment operating the digital signature system 100, and provides
the system
operator of the digital signature system 100 with one or more items of
identification, such
as a photographic drivers license or passport. Alternately, the network user
may access a
network server (associated with the digital signature system 100) over the
network using
a secure communications link, established for example by a Secure Sockets
Layer (SSL)
or Secure Hypertext Transfer Protocol (SHTTP), so as to provide the digital
signature
system 100 with electronic documentation, such as credit card information
and/or bank
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account information, to establish the identity of the network user. Once the
system
operator is satisfied as to the validity of the identification information
provided, the
system operator enters the identification information into the digital
signature system 100
via the user interface 110. The system operator then provides the network user
with a
personal identification number (PIN) to subsequently identify itself to the
digital
signature system 100, creates a unique private encryption key for the network
user and a
public encryption key uniquely associated with the private encryption key, and
then
inserts an encryption key record in the encryption key database 106 which
specifies the
PIN and the encryption keys assigned to the network user. Preferably, the
system
operator then provides the network user with a digital certificate which
includes the
network user's public encryption key.
Preferably, the network user also provides the system operator of the digital
signature
system 100 with an electronic document template 200 which the network user
requests
the digital signature system 100 use to assemble an electronic document 300.
As
discussed above, preferably the document data items 202 of the electronic
document
template 200 include positional code to define the relative orientation of
each document
data item 202 within the electronic document template 200. The network user
then
assigns a document identification code to the electronic document template
200, and
inserts a template record into the document database 114 which includes the
user
identification code assigned to the network user, the document identification
code
assigned to the electronic document template 200, and the document data items
202 of the
electronic document template 200.
After the registration process is complete, the system operator provides the
network user
with a network address from which the network user downloads a client software
module
to allow the network user to access the digital signature system 100 over the
network.
Preferably, the client software module is configured to establish a secure
communications
path (for example via SSL or SHTTP) with the digital signature system 100 so
as to allow
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the network user to provide the digital signature system 100 with network
user's PIN, the
document identification number of the desired electronic document template
200, and the
electronic data records for inclusion with the desired electronic document
template 200.
After the client software module is installed on the network user's computing
platform,
the network user invokes the client software module and establishes a secure
communications link with the digital signature system 100. After the secure
communications link is established, the network user uses a suitable interface
provided in
the client software module to transmit to the digital signature system 100
electronic data
records which the network users requires to be incorporated with the network
user's
electronic template 200 into the electronic document 300. The electronic data
records are
received by the document assembly processor 126 over the secure communications
link,
via the data receiver 102. In response, the user identification processor 124
transmits an
electronic message, via the data transmitter 104, to the network user's client
software
module requesting the network user enter the assigned PIN. The network user
then enters
the assigned PIN via a suitable interface provided in the client software
module, and then
transmits the assigned PIN to the digital signature system 100 over the secure
communications link. The PIN data is received by the data receiver 102 of the
digital
signature system 100.
Upon receipt of the PIN data from the network user, the user identification
processor 124
queries the user identification codes stored in the encryption key database
106 with the
PIN data. If an encryption key record is found in the encryption key database
106 having
a user identification code corresponding to the PIN data received from the
network user,
the user identification processor 124 extracts from the encryption key
database 106 the
private encryption key associated with the PIN data. After the encryption key
is
extracted, if the document database 114 includes document identification
codes, the
document assembly processor 126 transmits an electronic message, via the data
transmitter 104, to the network user's client software module requesting the
network user
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enter a document identification number identifying the requested electronic
document
template 200. The network user then enters the document identification number
via a
suitable interface provided in the client software module, and then transmits
the
document identification number to the digital signature system 100 over the
secure
communications link. The document identification number is received by the
data
receiver 102 of the digital signature system 100.
Upon receipt of the document identification number, the document assembly
processor
126 queries the document identification codes stored in the document database
114 with
the received document identification number. If a template record is found in
the
document database 114 having a document identification code corresponding to
the
received document identification number, the document assembly processor 126
extracts
from the document database 114 the electronic document template 200 associated
with
the document identification number. Alternately, if the document database 114
includes
both document identification codes and user identification codes, the document
assembly
processor 126 only extracts the electronic document template 200 from the
document
database 114 if the user identification code of template record having the
electronic
document template 200 corresponds to the network user's PIN. On the other
hand, if the
document database 114 includes only user identification codes, the document
assembly
processor 126 does not transmit a message to the network user requesting
submission of a
document identification number, but instead queries the user identification
codes stored
in the document database 114 with the network user's PIN, and then extracts
from the
document database 114 the electronic template 200 associated with the user's
PIN.
After the specified electronic document template 200 is extracted from the
document
database 114, the document assembly processor 126 assembles the desired
electronic
document 300 from the electronic document template 200 and from the electronic
data
records received from the network user. It should be understood, however, that
the step
of predefining an electronic document template 200 with the electronic
signature system
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100 is not essential to the invention. For instance, in one variation, the
network user
transmits to the digital signature system 100 a completed electronic document
300 instead
of electronic data records 302 or document identification numbers. It will be
appreciated
that in this variation, the electronic data transmitted to the digital
signature system 100
immediately after the secure communications link is established include both
document
data items 202 and electronic data records 302 for inclusion with the document
data items
202 into the electronic document 300.
After the electronic document 300 is established, the digital signature
processor 122
derives a hash code for the electronic document 300, and then derives the
digital
signature for the electronic document 300 by encrypting the hash code with the
private
encryption key extracted from the encryption key database 106. Preferably the
digital
signature also includes a time stamp identifying the time and date that the
digital
signature was created. Preferably, the digital signature processor 122 then
transmits the
derived digital signature to the data transmitter 104 for transmission back to
the network
user over the secure communications link. The network user then appends the
received
digital signature to the electronic document 300, and transmits the digitally
signed
electronic document to the intended recipient, together with a copy of the
network user's
digital certificate.
Alternately, in one variation, the document assembly processor 126 appends the
digital
signature to the data transmitter 104, and includes therewith the network
user's digital
certificate identifying the public encryption key associated with the
extracted private
encryption key. The document assembly processor 126 then transmits the
electronic
document 300, digital signature and digital certificate to the data
transmitter 104 for
transmission back to the network user over the secure communications link.
However, it
should be understood that the data transmitter 104 need not transmit the
digital signature
(and electronic document 300) to the same network user which originated
communication
with the digital signature system 100. Accordingly, in one variation, upon
receipt of the
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data necessary to derive the digital signature, the data receiver 102
relinquishes the secure
connection with the network user, and the data transmitter 104 transmits the
digital
signature (and electronic document 300 and digital certificate) to a network
address
specified by the originating network user. In this variation, the specified
network address
can include an e-mail address.
The present invention is defined by the claims appended hereto, with the
foregoing
description being merely illustrative of the preferred embodiment of the
invention. Those
of ordinary skill may envisage certain additions, deletions and/or
modifications to the
described embodiment, which although not explicitly described herein, do not
depart
from the spirit or scope of the invention, as defined by the appended claims.
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