Note: Descriptions are shown in the official language in which they were submitted.
CA 02641728 2008-10-15
TRUSTED THIRD PARTY AUTHENTICATION AND NOTARIZATION FOR
EMAIL
FIELD OF THE INVENTION
This invention relates generally to fhe use of a trusted tliird party to
provide authentication of
message integrity and non-repudiation.
BACKGROUND OF THE INVENTION
Electronic mail (email) has become a ubiquitous form of communication between
a vat-iety of
parties. Email is favored for its low cost and rapid delivery, which nlany
people see as a
benefit and advantage over traditional mail secvices.
Multipurpose Internet Mail Extension (MIME) is a standard that defines how
content such as
text and non-text attachments are formatted. It should be noted that altllough
MIME defines
how the data is str.uctu.red and formatted, it is the Simple Mail Transfer
Protocol (SMTP) that
defines how email is sent to a server, and how it is sent between servers.
SMTP, for its
ubiquity, popularity and general robustness has been considered to be the
"killer-app" of the
Internet, that is, the application whose utility brought the Intenaet to the
atte.ntion of the
general public and provided the incentive for beginning a mass adoption of the
Internet as a
setvice.
As email gained in popularity, its uses expanded and features that were not
anticipated by the
researchers who developed SMTP have now become desirable if not essential.
One failing in SMTP is the inability to verify the identity of the sender of
an ernail message.
So-called spoofrng techniques and the use of open mail relays have allowed
entities to
transmit email while iinpersonating a sender. This impairs the trust that a
recipient of an email
message has in the provenance of the message, and diminishes the value of a
trust-based
system. Despite the ubiquity of email, these issues hamper the utility of
email and could be
used to reduce the evidentiary weight accorded to email messages in a judicial
hearing.
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CA 02641728 2008-10-15
A further problem with SMTP and MIME based email is that there is no robust
mechanism to
authenticate the content and header information of a message. A nuznber of
work around
solutions have been developed, but while remedying some of these issues these
work around
solutions typically introduce additional complexity as well as other related
issues.
To understand existing solutions, it is first important to examine how a
standard
MIME/SMTI' mail session functions. Figure 1 illustrates aii SMTP based email
excliange.
User A 100 composes an email niessage using a standard email client A 102.
Client A 102
can be any of a number of standard applications such as Apple Mail, Microsoft
Outlook,
Mozilla Thunderbird, or another such application. The composed message is
addressed to an
email address associated with user B 112, and is sent from client 102 to mail
server A 104
using SMTP. Client 102 and seiver 104 can be integrated as is the case with
web-based email
platforms such as hotmail.com, Yahoo Mail, or gmail.com where the client is a
web-based
interface that has direct connections to the server ar-d may not einploy SMTP.
The email
message is then transmitted through Internet 106 to mail seiver B 108 which is
associated
with the destination email address. Email client B 110 connects to server B
108 using a
standard protocol such as the Internet Message Access Protocol (IMAP) or the
Post Office
Protocol (POP) so that the message can be downloaded. The message is then
presented to
User B 112.
This implementation does not necessarily provide autllentication of the
sender, nor of the
content of the email message. Because the content of the message cannot be
veriFed as being
the same as they were when sent, and the message cannot be authenticated as
being sent by a
particular user, the message can be repudiated by the sender at a later date.
A public-private encryption key based infrastructure can be employed to
mitigate some of the
problems associated with the system of Figure 1. Figure 2 illustrates one such
example. User
A 100 employs a secure email. client A 114 and a private encryption key 116 to
sign the body
122 of a message 118. The header 120 of message 118 is not signed as the
message 118 is
transmitted using SMTP which does not provide a field for a signature that
could be used to
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CA 02641728 2008-10-15
verify the header infortnation. The message 11.8 with signed message body 122
is transmitted
to email server A 104 ttsing SMTP. The message is routed tlirough Intemet 106
to email
server B 108 as any message would be in the system of Figure 1. The signed
body 122 of
message 118 is never inspected along the route as the infrastructure makes use
of the standard
MIME and SMTP protocols. Secure email client B 124 connects to email server B
108 using a
standard protocol such as IMAP or POP and retrieves message 118 Secure email
client B 124
niakes use of the public key 126 uniquely associated with private key 116 to
veri fy the
signature of the body 122 of the received message 118. The verified message
128 is then
displayed to user B 112.
One skilled in the art will appreciate that using the public key 126, user B
112 is able to
determine that the message body 122 was not tampered with. The signature can
include a
tiniestainp based on the clock/calendar ftinction of the system ru.nning
secure email client A
114. The inessage can be repudiated by the sender, if the public-private key
pair (keys 116
and 126) is not associated with User A 100 in a public manner.
To associate the key pair to User A 100, a certificate authority can bind the
public key 126 to
identifying information associated with User A 100. The certificate binding
public key 126 to
user A 100 can be sent to user B 112 in advance so that it can be added to a
key ring in secure
ernail ciient B 124. User B 112 could use public key 1.26 to encrypt a message
to User A 100,
who would then use private key 116 to decrypt the message. For User B 11.2 to
sign any
message (encrypted or otherwise) User B would need a different key pair.
Aithough this provides a degree of authentication of the message contents and
a limited
degree of non-repudiation, it requi.res that User A 100 obtain a certificate
binding lcey 126 to
him, and requires that User B 112 have a copy of the publ.ic key 126 (and
preferably the
certifcate) and a secure email client to verify the signature. Although this
does not seem like
a large burden, it only appears this way because of the limited number of
parties in the
illustrated transaction. If there are multiple parties, each party will be
required to obtain a
certificate from a certificate authority, and will be required to transmit the
certificate to every
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CA 02641728 2008-10-15
other party. Specialized software to manage the ring of public keys, along
with the relevant
private keys must then be used to allow automated verification. This is a
cunZbersome
process. As the number of parties grows the number of keys required to allow
verification of a
message also grows. Furthermore, if the security of private key 116 is
compromised, it must
be revoked, wluch can otily effectively be done if a certificate autliority
issued a certif cate for
the key. When a certificate is revoked a cumbersome process must be undertaken
by any party
holding the compromised key to obtain a new certified key.
A public key infrastructure (PKI) employing a Certificate Authority (CA) does
address a
nLuiiber of the issues around authenticating the integrity of a message body,
but it requires a
large number of changes to the email infrastructure as well as an
understanding of the
complex nature of a PKI . As a result of the added complexity caused, PKI has
been slow to
gain traction with the broader public though it has proponents in the security
field.
One system that has attempted to address these issues is provided through the
use of Digital
Postmarks. Digital Postmarks are intended for use in an enterprise
environment, and are
designed to specifically provide authentication of inessage contents.
Fundamentally it is
designed as a non-repudiation service. Figure 3 illustrates an exemplary
installation of a
system to use Digital Postmarking. User A 100 uses a client to generate an
email message.
This message is sent from a client to an outgoing mail server 130, typically
provided by an
enterprise associated with User A 100. Outgoing naail server 130 receives the
niessage and
forwards it to the digital postmarking server 132. Server 130 preferably signs
the message
prior to transmission to digital postmarking server 132 so that postmarking
server 132 can
verify that the message was not altered in transit. Digital postmarking server
132 then
validates the authenticity of the signature against a Icnown key associated
with either user A
100 or with inail server 130. Upon successful verification., the digital
postmarking seiver 132
generates a timestamp that, along with the message, the signature and
validation results are
stored in a digital postmark non-repudiation database 134. This inforination
can then be
accessed at a later date to establish a non-repudiation ftinction. The
postmarlcs sezver 132 and
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CA 02641728 2008-10-15
database 134 generate a digital postmarking receipt that is transmitted back
to the outgoing
mail server 130. The outgoing mail server 130 wraps the original message in
the digital
postmarking receipt and traiismits the message to the incoming mail sewer 136.
User B 112
retrieves the message in the proprietary digital postmarking wrapper 138 using
a proprietary
client 140. The client 140 can then retiieve the authentication information
from the digital
postmarlc non-repudiation database 134. Client 140 does not need to perform
any verification
processes on the message itself, as the verification, receipt and even the
original document
can. be retrieved from database 134, alternately a local cryptographic
verification can be
performed by client 140.
Although the digital postmarking system discussed with relation to Figure 3
can provide both
authentication of a sender and the message, it requires proprietary software,
and is
cumbersome. The system is designed for implementation in an enteiprise
environnlent, and
does not take into account the needs of individuals. The digital postmarking
server 132 is
often dedicated to a particular outgoing mail server 130. As such digital
postmarking server
132 requires that the enterprise obtain a dedicated hardware device and
inZplement a complex
process of having either client software sign a message or having the mail
server 130 sign a
message prior to beginning the verification process. The storage requirements
for database
134 can be immense if all messages and attachments are stored for a number of
different
organizations. As such, the verification information is typically only stored
for a predefined
period. If this period expires, the ability to authenticate the message can be
adversely affected.
To provide a mechanism for secure email, without needing a proprietary
infrastructure, an
ei-diancement to the MIME standard entitled Secure/MIME (S/MIME) has been
introduced.
S/MIME defines a fonnat for a signed or encrypted message that requires that
the verification
information be included in the message in a particular fashion.. S/MIME
fitnctionality has
been incorporated into most common modem email clients as its implementation
is not
conlplex and can be used to provide authentication of the message contents
using digital
signatures (non-repudiation is provided if a certificate is employed) as well
an encryptian
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CA 02641728 2008-10-15
functionality. In operation, an S/MIME client will encrypt the message body
and transmit the
resulting object as a MIME attachment (specifically an application/pkcs7-mime
MIME
entity). One advantage of S/MIME is that standard mail servers are used, tlius
requiring no
additional infrastructure.
For a user to make use of an S/MIME compliant client, an individual key or
certificate must
be obtained (preferably from a certificate authority). To encrypt a message,
the recipient's
public key must be known, whereas for signing, the recipient must have access
to the sender's
public key to allow for verification. By using a basic certificate, the only
identifying
information bound to the key (and thus the signed message) is an email
address. To associate
additional information, such as actual individual identity information, a
certificate must be
provided by a CA that has verified the identity infoiTnation. The certificate
is then typically
publicly available from the CA, and at a mininlum a certificate serial
nurriber is made
available to allow for revocation of a certificate (as described above witli
respect to an
encryption based mail client).
Figure 4 illustrates an S/MIME compliant exchange. One skilled in the art will
appreciate that
this makes use of a PKI infrastructure, and thus bears similarity to the
encryption based
signature system described earlier. A user 100 employs an S/MIME compliant
email client A
142, to create a digitally signed email message 144 using private key 116. The
message is sent
to email server A 104 using SMTP and is then routed tluough Internet 106 to
email server B
108. The digitally signed email message 144 is retrieved by S/MIME client B
124. S/MIME
client B 124 can parse message 144, wluch has a structure defined by the
S/1VIIME standards.
As such, if the message has been encrypted, the encrypted package is provided
in the
application/pkcs7-mime MIME entity. Similarly, a defined entity is used for
storing the
cryptographic signature used to ensure data integrity (application/(x-pkcs7-
signature).
Upon generation of the signature at client 142, the public key used to sigit
the message is
identified by the serial nutnber and certificate issuer. This allows the
recipient to retrieve the
cei-tificate to obtain the key to verify the signature. The certificate
binding the user
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CA 02641728 2008-10-15
information to the key provides non-repudiation. However, it should be noted
that at a later
date if the certificate expires and is deleted, verification of the message
can no longer be
performed, reducing the archival qtialities of the verification process. When
a certificate
expires, a new certificate is often generated, even if the sanie key pair is
used. This often leads
users to assume that the old certificate can be deleted. Recipients often
delete downloaded
cei-tificates when they notice that a sender has multiple certificates, which
can cause
unexpected inability to verify signatures.
Because the signature is carried separate from the body of the message (in
contrast to many
other signattire implementations) mailing list software that changes the
message body often
resttlts in the invalidation of the signature. Addi.tionally, because message
attachments may be
encrypted using S/MIME, the ability of a server to perfomi scans to detect
malware such as
worms or virii is adversely affected. Stich scanning can only be perfomied at
the client side,
which is often too late in the process.
One skilled in the art wil.l appreciate that though there are many systems for
providing digital
signatures on email messages to allow for verification of the integrity of the
message body,
they all introduce a number of different layers of complexity. Addition of
authenticated time
stamping functionality is difficult to provide without the addition of
additional server side
hardware, much as the ability to authenticate the sender of a message requires
the
cumbersome management of encryption keys.
It is, therefore, desirable to provide a mechanism providing trusted
authentication of a
message and its contents.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at least one
disadvantage of the
prior art.
In a first aspect of the present invention, there is provided a method
providing tn.isted third
party verification of an electronic message. The method comprises the steps of
receiving the
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CA 02641728 2008-10-15
electronic message from a sender addressed to at least one recipient;
processing the electronic
message to determine a digital signature associated with both the electronic
message and a
ptiblicly accessible key not associated with the sender of the electronic
message; attaching the
detei-mined digital signatLtre to the electronic message; and transmitting the
electronic
message with the attached digital signature to the at least one recipient.
In an embodiment of the first aspect of the present invention, the step of
processing the
message includes determining the digital signature by encrypting a
cryptographic hash of the
electronic message, possibly just the body of the electronic message, using
the private portion
of a private-public key pair. In another embodiment, the step of processing
the electronic
message can incltide overwriting header values such as time and date values in
using verified
header values (e.g. verified time and date values).
In a further embodiment of the present invention, the step of processing the
electronic
message includes performing a virus scan of the electronic message, and
optionally removing
a virus identified by the vinis scan. In another embodiment, the step of
processing the
electronic message can include copying header information from the electronic
message into
the electronic message body prior to determining the digital signature. In yet
another
embodiment of the first aspect of the present invention, the step of attaching
the deterniined
digital signature includes attaching the digital signature as a Secure
Multipurpose Liternet
Mail Extensions compliant digital signature.
In another embodiment of the first aspect of the present invention, the method
can further
include the step of authenticating an account associated with the sender of
the electronic
message after i-eceiving the electronic message. Authentication of the account
can include
receiving authentication credentials from the sender of the electronic message
and verifying
the credentials against known data. The receipt of authentication credentials
can include
receiving login credentials from the sender in accordance to the Simple Mail
Transfer
Protocol Authentication standard. In another embodiment, the step of
authenticating includes
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CA 02641728 2008-10-15
verifying an address in a From: field in a header to the electronic message
against a lcnown
value.
In fiirther embodiments, the method can include billing an entity associated
with the sender of
the email message, and the message can be a Multipurpose Internet Mail
Extensions based
eniail message.
In a second aspect of the present invention, there is provided a trustworthy
processor for
providing verification of an electronic message, sent by a sender, to at least
one recipient of
the electronic message. The processor comprises a message interface and a
signature engine.
The message interface receives electronic messages from the sender and
transmits messages
to the at least one recipient after processing by the signature engine. The
signature engine
signs the received message using a signature not associated with the sender to
allow the at
least one recipient to verify that the message .has not been altered and
forwards the signed
message to the at least one recipient through the message interface.
In an embodiment of the second aspect of the present invention, the message
interface is a
Simple Mail Transfer Protocol interface. In another embodiment of the second
aspect of the
present invention, the processor further includes a message processor for
overwriting values
in a header of the message with verified values, for copying the contents of
the header into a
message body prior, and for forwarding the modified message to the signature
engine for
signing. The message processor can also include a timestamping unit for
overwriting the time
and date of values in the header with verified time and date values. The
message processor
can also optionally include a sender verification unit for overwriting FROM
values in the
header with verified name and email address values.
In a fuc-ther embodiment, the signature engine can include a dedicated
cryptographic engine
for digitally signing the message using a cryptographic key.
In another embodiment of the second aspect of the present invention, the
processor fiirther
includes an account authenticator for authenticating the identity of the
message sender pr.ior to
transmission of the signed message to the at least one recipient, and
optionally includes a
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CA 02641728 2008-10-15
billing processor for assessing a charge to an account associated with the
authenticated
identity of the message sender.
Other aspects and features of the present invention will become apparent to
those ordinarily
skilled in the art upon review of the following description of specific
embodiments of the
invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example
only, with
reference to the attached Figures, wherein:
Figure 1 is a block diagram illustrating the data flow in a prior art
messaging process;
Figtire 2 illustrates the data flow in a prior art cryptographic signature
based
messaging process;
Figure 3 illustrates the data flow in a prior art digital postmarking based
messaging
process;
Figure 4 illustrates the data flow in a prior art S/MIME based messaging
process;
Figure 5 is a block diagram illustrating a data flow involving trustworthy
processing of
electronic messaging;
Figure 6 is a flow chart illustrating a method of trustworthy processing;
Figure 7 is a flow chart illustrating a method of authenticating an account in
a
trustworthy processing method;
Figure 8 is a flow chart illustrating a method of message processing in a
trustwortlty
processing method;
Figure 9 is a flowchart illustrating a metliod of billing in a trustworthy
processing
method; and
Figure 10 is a block diagram illustrating logical elements of a trustworthy
processor of
the present invention.
CA 02641728 2008-10-15
DETAILED DESCRIPTION
The present invention is directed to a system and method for electronic
messaging with a
simplified authentication and message integrity verification mechanism.
Reference nlay be made below to specific elements, numbered in accordance with
the
attached figures. The discussion below should be taken to be exemplary in
nature, and not as
limiting of the scope of the present invention. The scope of the present
invention is defined in
the claims, and should not be considered as limited by the implementation
details described
below, which. as one skilled in the art will appreciate, can be modified by
replacing elements
with equivalent ftinctional elements.
In the present invention, the troubles associated with user management of a
PKI key ring are
mitigated by the use of a single digital signature for verifying the contents
of messages from
any of a number of different individuals. This signattire is associated with a
trusted tliird
party. Instead of relyuig on a user to obtain a certificate from a CA, the
user obtains an
account with a trusted third party that processes messages and performs the
signature process
on behalf of the user. The recipient of the message can tnist that the message
was verified. by
the trusted third party, and that the third party performed a publicly defined
autlientication of
the user. Thus, users do not need to obtain certificates, and recipients do
not need to manage
large and tulwieldy key rings. Additional services such as time stamping,
sender
authentication and virus scaiming can also be offered.
Because users are authenticated prior to the signed message being transmitted
to recipients, a
billing process can be implemented. The authentication and optional billing
also reduce the
likelihood that a message is unsolicited commercial email. As a result, the
messages
processed by the seiver can be trusted to a higher degree, allowing them to
bypass so-called
SPAM filters. Other benefits of the present invention will be discussed below
with relation to
the illustration of an exemplary system and method. One skilled in the art
will appreciate that
the description below is intended to be exeinplary in nature and should not be
regarded as
liniiting the scope of the present invention.
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CA 02641728 2008-10-15
Figure 5 illustrates an architecture in which the present invention can be
implemented. Two
different types of senders are considei-ed, those in an enterpi-ise
environment, and those who
do not have access to such a system. Corporate Sender 200 creates an email
message 204
using client A 202. The message 204 can. include attachments, but there is no
requirement that
attaclunents be appended to the message. The message is transmitted to the
corporate mail
seiver 206. Sender 200 is authenticated by corporate mail server 206. The
message can either
be flagged for sending as conventional email, or it can be flagged to be sent
as a trusted third
party signed message. The flagging of the message can be done at the client
202, or using
corporate rules enforced by server 206. When a message is to be signed by the
trusted third
party, it is routed from seiver 206 to a trustworthy processor 208.
To provide service to individual users, the present invention can be accessed
by individual
users much as any other mail server would be used. An individual sender 200a
composes a
message 204a on client A' 202a. When the message is to be sent, it is relayed
to trustworthy
processor 208 through Internet 106. Connections to tnastworthy processor 208
from either
client A' or from server 206 can be made using a conventional protocol such as
SMTP with
Transport Layer Security (TLS) for enhanced confidentiality and integrity of
communication
with the trustworthy processor 208 if so desired. This allows for existing
infrastructure to be
used without requiring either individuals or enterprises to update their
software or hardware.
One skilled in the art will appreciate that Client A' 202a can be a web-based
mail client
without departing from the scope of the present invention.
Trustworthy processor 208 can perform a number of different processes on
received
messages. It preferably begins by authenticating the party initiating the
session. In the case of
an individual user, such as sender 200a, the authentication can be done using
standard
techniques such as SMTP-Aut11 or POP before SMTP. In the case of enterprise
access, the
enterpt-ise server 206 can be authenticated using any of a number of luiown
techniques. The
uset=s of enterprise mail server 206 are authenticated by seiver 206, and the
server
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CA 02641728 2008-10-15
authentication of the user can then be passed along to trustworthy processor
208 en lieu of
individual authentications.
Authentication of a user is done so that the trustwortliy processor can
provide user
authentication and non-repudiation. After authenticating the user, the
ttlistworthy processor
can ensure that the message header includes the correct infar.mation
associated witlz the user
account. The header information can optionally be copied into the body of the
email so that it
is signed. In conventional systems, the body of the email message is the only
portion of the
message that is signed. This is done to allow the message to be easily routed
using the
existing SMTP infrastructure; however, it causes the drawback that the sender
and recipient
information is n.ot signed. By copying header information into the body of the
message, it can
be signed along with the message body. The trustworthy processo:r 208 then
signs the
message, preferably using a standard based format, such as S/MIME, using the
private portion
of the postmarking key pair 210. The signed message is then transmitted to the
addresses
recipients, and is received by recipient mail seiver 212. The signed message
214 is retrieved
by S/MIME email client B 216. The signed message 214 can be verified by client
B 216 using
the public portion of the postmark key pair 210. The verified message 218 can
then be
displayed to the recipient 220.
Before digitally siDung message 204 or 204a, trustworthy processor 208 can
modify the
message body to add in additional content including branding information
designed to provide
an immediate syi-nbol that recipients can associate with an assurance that the
message was
signed by a trusted third party.
Figure 6 is a flowchart illustrating a method of the present invention carried
out by a
trustworthy processor. The process starts when the processor receives a mail
message for
processing. The user account is authenticated in step 250. Upon successful
authentication of
the user, the message is processed in step 252. This processing step can
include value added
functionality, but also ineludes the d.etermination of a digital signature
based on the content of
the received message. The trusted third party signature deteri.nined in step
252 is attached to
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CA 02641728 2008-10-15
the message in step 254. This is preferably done in compliance with the foimat
defined in the
S/MIME standard. In the final step of the process, the message is transmitted
to the addressed
recipients.
In contrast to prior art methods, the signature applied is the signature of a
trusted third party,
not the signature of the sender. By making use of existing infiastructure,
such as the S/MIME
infrastructure, the present invention can provide a foi-in of user
authentication, message
integrity verification and time stamping without requiring additional hardware
installed in an
enterprise, and without requiring users to make use of proprietary email
clients to read or
conzpose email.
In Figure 6, the first step is authenticating the account associated with an
incoming message
250. The authentieation, of an account can be carried out using a nuniber of
optional steps as
illustrated in the flow chart of Figure 7. In step 258, the authentication
credentials are
received, and they are verified in step 260. This can be done by having the
tnistworthy
processor malce use of standard authentication mechanisms such as SMTP-Auth or
POP
before SMTP. Other authentieation techniques can be employed, especially where
the
connection is received from an enterprise mail seiver. When an enterprise
server connects, it
can do so on behalf of an individual user, or can do so on behalf of the
enterprise, with the
trustworthy processor identifying individual information on the basis of the
email address of
the From: field in the message.
The tnistworthy processor may also elect to verify the From: field against
addresses
associated witll the verified authentication credentials. If the From.: field
is not verified, the
processor can. generate an error inessage, or optionally it can oveitivrite
the From: field in the
message. By performing a verification of the From: field, a further security
barrier is
provided, which can be important if the processor is intended to be able to
airthenticate the
sender information.
Upon finishing any or all of these steps, the process continues to step 252.
14
CA 02641728 2008-10-15
A brealcdown of optional steps in the processing of the message in step 252 is
provided in the
flowchart of Figure 8. One skilled in the art will appreciate that a number of
these steps are
optional as they provide added value to the system and method of the present
invention, but
are not essential for the operation of the system. After cornpleting step 250,
the time and date
associated with tlie message can be overwritten in step 264. This effectively
embeds a
timestamp in the message header that can be trusted by the recipient. The From
Name field in
the message can be overwritten with a name associated with the account if it
does not match
in step 266. In one simplified implementation, regardless of the From name
field value, the
name is overwritten to ensure that all messages are handled in the same
fashion. In step 268 a
virus scan of the message contents and any attachments can be performed. By
perfomiing this
scan, malware and inappropriate content can be identified and removed, or the
message can
be rejected and the user informed of a problem. By performing the scan before
signing the
message, the signature will still be valid. Server side scanning at either the
sender or recipient
.mail server in prior art implementations results in invalidating the
signature if virii are to be
removed when identified, which defeats the purpose of providing authenticated
email.
In step 270, the header information of the message is copied into the body of
the message.
This allows the To: From: Date: and Subject: information, along with other
header
information, to be incorporated into the body of the message before it is
signed. Because
earlier processes allow for the overwriting of name fields, time and date
values and other
infonnation to ensure that they are accurate, this information can. be sigiied
along with the
message body. This allows the recipient to archive the message and have non-
repudiable
evidence as to when a message was sent, who sent it and what it contained,
without needing to
consult an exteinal archive. The verification can be guaranteed so long as
access to the
cet-tificate of the trustworthy processor is available.
In step 272, a digital signature is generated using a private key associated
with a public key
stored in a publicly available certificate. The signature can be generated
using conventional
CA 02641728 2008-10-15
processes used over the entire message body. This digital signature is the
trusted third party
signature attached in step 254.
Because the sender inforination is verified before the message is transmitted
to the addressed
recipients, a billing process can be added to the method illustrated in Figure
6. One sueh
process is illustrated in the flowchart of Figure 9. After the account
verification process, the
billing information associated with accaunt is processed as illustrated in
step 274. A number
of different implementations of a billing process can be employed. For
exemplary purposes, a
method is illustrated in Figure 9. In this exemplary method, the account is
verified as being in
good staiiding in step 276. The cost of the rnessage verification and
signature is deternrined in
step 278 and is transmitted to the accounting system in step 280. The process
may require a
response from the accounting system before proceeding if it is based on
prepaid credits, or
can be allowed to immediately proceed in other cases. The determination of the
cost can be
done using any of a number of different models, including either flat rate
billing systems that
bill a fixed amount per message, or a per-byte charge that is determined based
on the size of
the message. The specific implementation can be varied without departing from
the scope of
the present invention.
Figure 10 is a block diagram illustrating an implementation of the system of
the present
invention as fiinctional elements. One skilled in the art will appreciate that
the fimction of a
particular element can be spread across a number of other logical elements, or
two or more
logical elements illustrated in this diagram could be combined in one logical
unit. The
trustworthy processor 208 receives communications 282 from clients (either
directly or
thz=ougll a registered enterprise server) that contain botli mail messages and
account
credentials. The comniunications are received by an inbound mail interface,
such as the
illustrated inbound SMTP interface 284. The account credentials are forwarded
to the account
authenticator 286 and to the optional billing processor 288 if present. The
account
authenticator 286 authenticates the communication as being frotn a valid user
account using
any of a number of known techniques including those discussed above. The mail
message is
16
CA 02641728 2008-10-15
provided to both the billing processor 288 if present and the message
processor 290. The
billing processor 288 can be used to determine if a valid account is in
arrears before a
message is processed. It also can be used to detennine the cost associated
with handling each
i-eceived message. The billing processor 288 can be in communication with an
accounting
system (not shown) so that accurate billing inforniation can be recorded and
invoiced. The
message processor 290 processes the message after receiving the go ahead from
both the
account autlaenticator 286 and the billing processor 288. The message
processor is not
essential and can be omitted if the sole function of trustworthy processor is
to obtain a trusted
third party verification of the message contents. If added value setvices
including time
stamping, non-repudiable authentication of the message sender, virLts scanning
and
embedding of the header in the message body are to be provided they can be
provided by the
message processor 290. After the message processor 290 (or directly from the
inbound SMTP
Interface) the message is provided to the signature engine 292 which uses the
private portion
of the postniarking key pair 210 to generate a signature that can be used to
verify the contents
of the message body. This signature is preferably 1landled in accordance with
the S/MIME
standards when attached to the message. Signature engine can be a general
purpose processor,
or can optionally include a specific cryptographic engine designed for
compu.ting
cryptographic signatures of messages using key 210. The signed message is then
provided to
outbound SMTP interface 294 which transmits the message to the addressed
parties.
Embodiments of the invention may be represented as a software product stored
in a machine-
readable medium (also refetred to as a computer-readable medium, a processor-
readable
medium, or a computer usable medium having a computer readable program code
embodied
tllet-ein). The machine-readable medium may be any suitable tangible medium
including a
magnetic, optical, chemical, or electrical storage medium including a
diskette, compact disk
read only memory (CD-ROM), digital versatile disc read only memory (DVD-ROM)
memory
device (volatile or non-volatile), or similar storage mechanism. The machine-
readable
nzedium nlay contain various sets of instructions, code sequences,
configuration information,
17
CA 02641728 2008-10-15
or other data, which, when executed, cause a processor to perfonn steps in a
niethod
according to an embodiment of the invention. Those of ordinary skill in the
art will appreciate
that other instructions and operations necessary to implement the described
invention may
also be stored on the machine-readable medium. Software running fi=om the
machine-readable
medium may interface with circuitry to perfoim the described tasks.
The above-described embodiments of the present invention are intended to be
examples only.
Alterations, modifications and variations may be effected to the particular
embodiments by
those of skill in the art without departing frorn the scope of the invention,
which is defined
solely by the claims appended hereto.
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