Simplified addressing for private communications

Description of equivalent WO 0044128 A1

SIMPLIFIED ADDRESSING FOR PRIVATE COMMUNICATIONS

BACKGROUND OF THE INVENTION

TECHNICAL FIELD

The present invention relates generally to cryptographic communications,

and more particularly, to a system and method for simplifying the addressing of

public key-encrypted communications.

DESCRIPTION OF BACKGROUND ART

In symmetric key cryptography, both the sender and receiver of a message use the same secret key. The sender uses the secret key to encrypt the message

and the receiver uses the same secret key to decrypt the message. However, a

difficulty arises when the sender and receiver attempt to agree on the secret key

without anyone else finding out. For example, if the sender and receiver are in

separate physical locations, they must trust a courier, a telephone system, or

some other transmission medium to prevent the disclosure of the secret key.

Anyone who overhears or intercepts the key in transit can later read, modify,

and forge all messages encrypted or authenticated with that key. Thus,

symmetric key encryption systems present a difficult problem of key

management. Public key cryptography was developed as a solution to the key

management problem. In public key cryptography, two keys are used — a public

key and a private key. The public key is published, while the private key is kept

secret. Although the public and private keys are mathematically related, neither

can be feasibly derived from the other.

To send a private message using public key cryptography, a message is

encrypted using the recipient's public key, which is freely available, and

decrypted using recipient's private key, which only the recipient knows. Thus,

the need for the sender and recipient to share secret information is eliminated. A

sender only needs to know the recipient's public key, and no private keys are

ever transmitted or shared.

Public key cryptography has another advantage over symmetric key

cryptography in the ability to create digital signatures. One of the significant problems in cryptography is determining whether an encrypted message was

forged or modified during transmission. As noted above, if a symmetric key is

lost or stolen, any person in possession of the key can create forged messages or

modify legitimate messages.

Using public key cryptography, however, a sender can digitally "sign" a

message using the sender's private key. Thereafter, the recipient uses the

sender's public key to verify that the message was actually sent by the sender

and was not modified during transmission. Thus, a recipient can be confident that a message was actually sent by a particular sender and was not modified during transmission.

Despite its many advantages, public key cryptography presents three

basic difficulties. First, in order to send private messages, the sender must know

beforehand the public key of the recipient. Conventional public key systems

typically rely on a sender's locally-maintained address book of public keys.

Thus, if the recipient's public key is not in the sender's address book, the sender

must somehow contact the recipient by telephone or e-mail, for example, to

request the recipient's public key. Such systems are cumbersome and

inconvenient, and prevent widespread adoption and use of public key cryptography.

More fundamentally, another problem with public key cryptography is

that a recipient must first have a public key in order to receive an encrypted message. Because the technology is relatively new, only a few users have

currently obtained public keys. This fact, alone, represents a significant barrier

to adoption because a sender cannot encrypt a message to the recipient until the

recipient has completed the process of obtaining a public key.

Yet another problem with public key cryptography is the relatively ease

for "spoofing" a public key. In other words, a first user may publish his public

key in the name of a second user and thereby receive private communications

intended for the second user. Various solutions, such as digital certificates and certificate authorities (CA's), have been proposed to address this problem, but are not relevant to present application.

Accordingly, what is needed is a system and method for securely

transmitting an information package using public key cryptography in which the

sender is not required to know the recipient's public key before the package is

sent. Indeed, what is needed is a system and method for securely transmitting

an information package using public key cryptography in which the recipient is not required to have a public key before the package is sent.

DISCLOSURE OF INVENTION

The present invention solves the foregoing problems by providing a system and method for securely transmitting an information package (10) to an addressee via a network (108). In accordance with the present invention, a

dⁱrectory (112) of public keys is checked to determine whether the addressee of the package (10) has a public key. If the addressee does not have a public key ir

the directory (112), the package (10) is encrypted with an escrow encryption key

Thereafter, the package (10) is stored in escrow for the addressee pending

notification of, and acknowledgment by, the addressee. A notification, such as

an e-mail message, is sent to the addressee of the package (10) in escrow. When

the addressee acknowledges the notification, the addressee is issued new public

and private keys. Thereafter, the addressee's new public key is added to the directory (112) such that future packages (10) to the addressee may be encrypted using the addressee's public key. Finally, the package (10) is transmitted to the addressee.

Additionally, in accordance with the present invention, a system (100) for

securely transmitting an information package (10) to an addressee via a network

(108) includes a directory interface (110) adapted to check a directory (112) to

determine whether the addressee has a public key; an escrow key manager (116),

coupled to the directory interface (110), adapted to provide an escrow encryption

key for encrypting the package (10); an encryption module (114), coupled to the escrow key manager (116), adapted to encrypt the package (10) with the escrow encryption key; a computer-readable medium (118), coupled to the encryption module (114), adapted to store the package (10) in escrow for the addressee; a notification module (120), coupled to the computer-readable medium (118), adapted to send a notification to the addressee via the network (108); a key registration module (124), coupled to the notification module (120), adapted to issue, in response to the addressee acknowledging the notification, new public

and private keys to the addressee; and a transmission module (122), coupled to

the key registration module (124) and the computer-readable medium (118),

adapted to transmit the package (10) to the addressee via the network (108).

Using the present invention, a sender is not required to know the

addressee's public key before a package (10) is sent. Indeed, the addressee is not required to have a public key before the package (10) is sent. If the addressee does not currently have a public key, the addressee will be issued new public

and private keys, and the public key will be stored for future reference such that

subsequent private communications may be encrypted using the addressee's

public key. Thus, the present invention removes significant barriers to adoption

of public key cryptography, while increasing the security of private

communications.

BRIEF DESCRIPTION OF THE DRAWINGS These and other more detailed and specific objects and features of the present invention are more fully disclosed in the following specification, reference being had to the accompanying drawings, in which

Figure 1 is a functional block diagram of a secure communications system for transmitting information packages according to an embodiment of the present invention;

Figure 2 is a physical block diagram showing additional implementation

details of a sending system according to an embodiment of the present invention;

Figure 3 is a flow diagram of a secure communication system according to

an embodiment of the present invention;

Figure 4 is a flow diagram of a first embodiment of a transmission module and a decryption module according to an embodiment of the present invention; and

Figure 5 is a flow diagram of a second embodiment of a transmission

module and a decryption module according to an embodiment of the present

invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the invention is now described with reference to the Figures, where like reference numbers indicate identical or functionally

similar elements. Also in the Figures, the left most digit of each reference number corresponds to the Figure in which the reference number is first used.

Referring now to Figure 1, there is shown a functional block diagram of a secure

communications system 100 for transmitting information packages 10 according

to an embodiment of the present invention.

The principal components of the system 100 include a sending system 102,

a server system 104, and a receiving system 106. The sending system 102 is

coupled to the server system 104, and the server system 104 is coupled to the

receiving system 106, via an "open" computer network 108, such as the Internet.

Preferably, all transmissions over the network 108 are by a secure protocol, such as the Secure Multipurpose Internet Mail Extension (S/MIME) and/or the Secure Sockets Layer (SSL).

The sending system 102 is used by a sender to securely transmit a _, n information package 10 to at least one intended "recipient", who is

interchangeably referred to herein as an "addressee". In one embodiment, the

sending system 102 includes a directory interface 110 for communicating via the

network 108 with an external public key directory 112. The directory 112 is a

database of the public keys of registered addressees and may be selectively

queried to determine the public key of each addressee of the information

package 10. Preferably, the directory 112 may be queried using the addressee's e-mail address.

In one embodiment, the public key directory 112 is implemented using an existing online directory infrastructure provided, for example, by VeriSign, Inc. of Mountain View, California. In alternative embodiments, however, the directory is implemented using a conventional database system, such as one

available from SyBase, Inc., of Emeryville, California, although other databases

could be used without departing from the spirit of the invention. Preferably, the

directory 112 is accessed by the directory interface 110 using the Lightweight Directory Access Protocol (LDAP).

The sending system 102 also includes an encryption module 114 for

encrypting information packages 10. The encryption module 114 is coupled to receive an escrow encryption key from an escrow key manager 116, as described

in greater detail below. Preferably, the encryption module 114 uses a public key

cryptosystem, available, for example, from RSA Data Security, Inc., of San Mateo,

California. In alternative embodiments, however, a symmetric key algorithm,

such as the Data Encryption Standard (DES), is used. Preferably, each encrypted

package 10 conforms to the S/MIME standard, which is well known to those

skilled in the art. In addition, key lengths of at least 128 bits (in the case of

symmetric key cryptography) are preferably used to provide a high level of data security.

The escrow key manager 116 generates keys and/or provides stored keys

for use in encrypting and decrypting information packages 10 to be stored in

escrow. In one embodiment, the escrow key manager 116 is a process running

on an separate escrow key management server (not shown), and the encryption module 114 communicates with the escrow key manager 116 via the network

108. Alternatively, the escrow key manager 112 is a functional unit contained

within one or more of the sending system 102, the server system 104, or the

receiving system 106.

The encryption module 114 is coupled via the network 108 to an escrow

storage area 118 within the server system 104. In one embodiment, the escrow

storage area 118 is a database for storing encrypted information packages and is

managed, for example, by a SyBase database system. Once encrypted, an information package 10 is sent using a conventional protocol, such as the

Hypertext Transfer Protocol (HTTP), to be stored within the escrow storage area

118 pending notification and authentication of the addressee. In alternative

embodiments, however, the escrow storage area 118 is contained within the

sending system 102, and packages 10 are stored locally until an addressee is

notified and properly authenticated.

The server system 104 additionally includes a notification module 120 for

sending a notification of the package 10 to an addressee at the receiving system

106. In one embodiment, the notification is an e-mail message, and the

notification module 120 is an e-mail server, such as the Microsoft Exchange®

Server 5.5, available from Microsoft Corporation of Redmond, Washington, although those skilled in the art will recognize that other notification systems

and methods could be used within the scope of the present invention.

The server system 104 also includes a transmission module 122, the

purpose of which is to transmit the package 10 from the escrow storage area 118

to a decryption module 126 in the receiving system 106. In one embodiment, the

transmission module 122 is a standard Web server, such as the Windows NT^®

Server 4.0, available from Microsoft Corporation. Additionally, the decryption

module 126 may be implemented using a standard Web browser, such as the

Microsoft Internet Explorer^®, with decryption logic being contained within a

plug-in or Java applet. Those skilled in the art, however, will recognize that varⁱous other transmission systems and methods could be used without

departing from the spirit of the invention. Preferably, communication between

the transmission and decryption modules 122, 126 is by HTTP using SSL.

Additionally, in one embodiment, the transmission module 122 is coupled to

receive an addressee's public key from the directory 112 in order to authenticate the addressee, as described in greater detail below.

The notification module 120 is coupled via the network 108 to a key

registration module 124 in the receiving system 106. The key registration

module 124 is configured to issue new public and private keys to an addressee who does not currently have such keys, and is additionally configured to

automatically add the addressee's new public key to the public key directory 112.

In one embodiment, the key registration module 124 is resident in the

receiving system 106 before an information package 10 is sent by the sender. In

an alternative embodiment, however, the notification module 120 is configured to send the key registration module 124 to the receiving system 106 as an

attachment to an e-mail notification. In yet another embodiment, the e-mail

notification includes a hyperlink, such as a Uniform Resource Locator (URL),

which allows an addressee at a receiving system 106 to download the key

regⁱstration module 124 using a conventional Web browser, such as the Netscape

Communicator^®, available from Netscape Communications Corporation of Mountain View, California. As noted above, the receiving system 106 also includes a decryption module 126 for decrypting information packages 10. Like the encryption module 114, the decryption module 126 preferably uses a public key

cryptosystem, available, for example, from RSA Data Security, Inc. However, in

alternative embodiments, a symmetric key algorithm, such as the Data Encryption Standard (DES), may be used.

In one embodiment, the decryption module 126 is coupled to receive an

escrow decryption key from the escrow key manager 116. Alternatively, the . decryption module 126 is coupled to receive the addressee's private key from the key registration module 124. Using either the escrow decryption key or the

private key, the decryption module 126 decrypts the information package 10 and provides the decrypted package 10 to the addressee.

Preferably, the systems 102, 104, and 106 described above, as well as the public key directory 112 and escrow key manager 116, are each implemented usⁱng convenrional personal computers or workstations, such as IBM® PC-

compatible personal computers or workstations available from Sun

Microsystems of Mountain View, California. For example, Figure 2 is a physical

block diagram showing additional implementation details of the sending system

102, and is similar in all relevant respects to other systems described above.

As illustrated in Figure 2, a central processing unit (CPU) 202 executes

software instructions and interacts with other system components to perform the methods of the present invention. A storage device 204, coupled to the CPU 202, provides long-term storage of data and software programs, and may be

implemented as a hard disk drive or other suitable mass storage device. A

network interface 206, coupled to the CPU 202, connects the sending system 102

to the network 108. A display device 208, coupled to the CPU 202, displays text

and graphics under the control of the CPU 202. An input device 210, coupled to

the CPU 202, such as a mouse or keyboard, facilities user control of the sending system 102.

An addressable memory 212, coupled to the CPU 202, stores software

instructions to be executed by the CPU 202, and is implemented using a combination

of standard memory devices, such as random access memory (RAM) and read-only memory (ROM) devices. In one embodiment, the memory 212 stores a number of

software objects or modules, including the directory interface 110 and encryption

module 114 described above. Throughout this discussion, the foregoing modules are

described as separate functional units, but those skilled in the art will recognize that

the various modules may be combined and integrated into a single software

application or device.

Referring now to Figure 3, there is shown a flow diagram of the system

100 according to an embodiment of the present invention. Referring also to

Figure 1, the sending system 102 initially receives 302 from the sender the

addressee's e-mail address. Although the addressee's e-mail address is used in one embodiment, those skilled in the art will recognize that the sender may

specify an addressee by name, which is associated, in the sending system 102,

with an e-mail address or other unique identifier of the addressee. Although the

addressee is referred to hereafter in the singular, those skilled in the art will

recognize that a package 10 may have a plurality of addressees.

After the e-mail address is received, the sending system 102 searches 304

the public key directory 112 using the addressee's e-mail address to locate the

public key of the addressee. As noted earlier, this is accomplished by means of a

directory interface 110 in the sending system 102, which accesses the directory

112 using a standard protocol such as LDAP.

A determination 306 is then made whether the addressee's key was found in the directory 112. If the key was found, the package 10 is encrypted 308 by the

encryption module 114 using the addressee's public key and is sent to the server system 104, where it is stored 310 as a "regular" package. The term "regular" is

used to distinguish the package 10 from one being stored in "escrow" for an

addressee who does not yet have a public key. In one embodiment, a separate

storage area (not shown) in the server system 104 is provided for regular

packages.

Next, the server system 104 notifies 312 the addressee about the package

10 being stored for the addressee. As noted earlier, this is done, in one

embodiment, by the notification module 120, which uses an e-mail notification system. However, those skilled in the art will recognize that other notification systems and methods could be used without departing from the spirit of the

ⁱnvention. For example, the receiving system 106 may include a notification

clⁱent (not shown) which receives user datagram protocol (UDP) notifications

from the notification module 120. Upon receipt of a UDP notification, the

notification client generates a visual or audible desktop notification to the

addressee, such as a blinking icon, a chime, a pop-up dialog box, or the like.

Other forms of notification could include a voice notification via a voice

synthesis module, a pager notification via a conventional pager, or a facsimile notification via a standard facsimile.

After the addressee receives 314 and acknowledges the notification, such as by a return e-mail message, the person claiming to be the addressee is

authenticated 316 to determine whether that person is, in fact, the addressee. Those skilled in the art will recognize that there are many ways to authenticate an addressee. For example, passwords or the like could be used.

Public key cryptography, however, provides a convenient and highly

secure way for authenticating an addressee. In one embodiment, the addressee

encrypts a standard message using the addressee's private key and sends the

encrypted message to the transmission module 122 in the server system 104.

The transmission module 122 obtains the addressee's public key from the public

key dⁱrectory 112, and attempts to decrypt the message using the addressee's public key. If the message is successfully decrypted, the addressee is known to hold the private key corresponding to the public key in the directory 112 and is

therefore authentic. Those skilled in the art will recognize that the above

authentication steps may be performed automatically by a Web server and Web

browser (or by custom software programs), with little active intervention required by the addressee.

After the addressee is properly authenticated, the transmission module

122 sends 318 the package 10 via the network 108 to the receiving system 106,

and the receiving system 106 receives 320 the package from the server 104.

Those skilled in the art will recognize that either "push" or "pull" mechanisms

could be used within the scope of the present invention. Preferably, HTTP and SSL are used, although other standard protocols could also be used without

departing from the spirit of the invention. When the package 10 is received, the

decryption module 126 decrypts 322 the package 10 using the addressee's private key, and provides the decrypted package 10 to the addressee.

The foregoing discussion was in the context of the addressee's public key

being found in the directory 112. However, a more difficult situation arises

when the addressee's public key is not in the directory 112. Indeed, when the

addressee does not yet have a public key, conventional public key systems are

wholly unable to send encrypted messages to the addressee. This represents a

serious shortcoming of prior systems. The present invention solves this problem by holding the addressee's package 10 in escrow, as described in greater detail below.

Returning to step 306, if the addressee's public key was not found in the

directory 112, the escrow key manager 116 issues 324, for the package 10, an

escrow encryption key and an escrow decryption key. The escrow encryption

key is used for encrypting the package 10 prior to being stored in escrow, and the

escrow decryption key is used for decrypting the package 10.

The escrow encryption/ decryption keys should not be confused with the

new public and private keys issued to the addressee, as described in step 336. If

the escrow encryption/ decryption keys were to be issued to the addressee, they

would need to be transmitted to the addressee via the network 108, resulting in

the same drawbacks as symmetric key cryptography. In public key

cryptosystems, the addressee's private key should never be sent to the addressee. Thus, in accordance with the present invention, the addressee's private key is generated locally at the receiving computer 106, and only the addressee's public

key is sent via the network 108 to the directory 112.

In one embodiment, the escrow encryption/ decryption keys are

asymmetric keys generated according to the RSA algorithm for key generation.

Alternatively, the keys are symmetric keys. In yet another embodiment, the

keys are stored, not generated, by the escrow key manager 116, and are either

hard-coded into the escrow key manager 116 or are added and periodically updated by an external agent or process. In still another embodiment, the public

escrow key is published in the directory 112, and the server system 104 keeps the

private escrow key in a hardware device that protects it from tampering,

providing the highest level of security against tampering with the escrow keys.

After the keys are issued, the encryption module 114 within the sending

system 102 retrieves 326 the escrow encryption key, encrypts the package 10

using the escrow encryption key, and sends the encrypted package 10 to the

server system 104. The package 10 is then stored 328 in the escrow storage area

118. As described hereafter, the server system 104 holds the package in escrow

for the addressee until the addressee has properly registered and received new

public and private keys.

As in the case of a regular package, the addressee is then notified 330 of the package 10 being stored in escrow and the need to register for public and

private keys. In one embodiment, the notification is an e-mail message.

Preferably, the notification message includes a copy of the key registration

^■ module 124 as an e-mail attachment. Preferably, the notification message

including the key registration module 124 is digitally signed in order to verify

the source of the message. In alternative embodiments, however, the notification

includes a hyperlink, such as a URL, to permit the addressee to download the

key registration module 124 from the server system 104 or another location. After the addressee has received 332 and acknowledged the notification and has either extracted or downloaded the key registration module 124, the

addressee uses the key registration module 124 to register 334 for new public and

private keys. As noted above, these keys are not the same as those issued by the

escrow key manager 116. Preferably, the new public and private keys are

generated according to the RSA algoritlim for key generation, and are issued

locally at the receiving system 106.

In one embodiment, the registration process is similar to the procedure

used by VeriSign, Inc. and other certificate authorities to issue certificates, and

involves prompting the addressee for various personal data, including, for

example, the addressee's name, address, telephone number, e-mail address, and the like. Those skilled in the art will recognize that various procedural

safeguards may be used to increase the reliability of the data obtained from the addressee.

After the addressee has registered, the addressee's new public key is

.automatically transmitted via the network 108 and stored 335 in the public key

directory 112. This is advantageous because a subsequent package 10 being sent

to the same addressee will be encrypted using the addressee's public key,

providing a higher degree of security since no escrow keys are involved.

Next, the addressee is authenticated 336 to determine whether the person

claiming to be the addressee is, in fact, the addressee. As described previously with respect to step 316, authentication may involve encrypting a standard

message at the receiving computer 106 using the addressee's private key, and

decrypting the message at the server computer 102 using the addressee's public

key as obtained from the directory 112.

After the addressee is authenticated, the transmission module 122 in the

server system 104 sends 338 the package 10 of the authenticated addressee to the

decryption module 126 in the receiving system 106. The decryption module 126

then decrypts 340 the package 10 and provides the decrypted package 10 to the

addressee. As described below, this process may be done in a number of ways.

Referring now to Figure 4, there is shown a first embodiment of the

interaction between the transmission and decryption modules 122, 126.

Initially, the transmission module 122 retrieves 342 the package 10 being stored

in escrow for the authenticated addressee and sends the package 10 via the

network 108 to the decryption module 122, which receives 344 the package 10. Thereafter, the decryption module 126 retrieves 346 the escrow decryption key

for the package 10 from the escrow key manager 116. Using the escrow

decryption key, the decryption module 126 then decrypts 348 the package 10.

Referring now to Figure 5, there is shown a second and more secure

embodiment of the interaction between the transmission and decryption

modules 122, 126. Initially, the transmission module 122 retrieves 350 the

package 10 being stored in escrow for the authenticated user. Thereafter, the transmission module 120 retrieves 352 the escrow decryption key from the

escrow key manager 116, and decrypts the package 10 using the escroλv

decryption key. Next, the transmission module 120 re-encrypts 354 the package

10 using the addressee's new public key, which may be obtained from the

directory 112 or the key registration module 124. After the package 10 is re-

encrypted, it is sent via the network 108 to the decryption module 126, which

receives 356 the package 10 and decrypts 358 the package 10 using the

addressee's private key.

The above description is included to illustrate the operation of the preferred

embodinients and is not meant to limit the scope of the invention. The scope of the

invention is to be limited only by the following claims. From the above discussion, many variations will be apparent to one skilled in the art that would yet be

encompassed by the spirit and scope of the present invention.

What is claimed is: