GB2339367A

GB2339367A - Secure communication

Info

Publication number: GB2339367A
Application number: GB9805759A
Authority: GB
Inventors: Sean B Newcombe; Christopher L Royle
Original assignee: SEDEX Ltd
Current assignee: SEDEX Ltd
Priority date: 1998-03-17
Filing date: 1998-03-17
Publication date: 2000-01-19
Anticipated expiration: 2018-03-17
Also published as: GB2339367B; GB9805759D0

Description

2339367 PATENTS ACT 1977 P12142GB-ALM/LH/vt "A method and apparatus for

electronic document exchange" THIS INVENTION relates to a method and apparatus for electronic document exchange and more particularly to the secure electronic exchange of documents over an open network.

It is well known that whilst the Internet offers a flexible form of communication using electronic mail, it does have serious drawbacks such as lack of security and uncertainties over delivery. Despite these drawbacks, the use of electronic mail is widespread and is increasingly being used by law firms and the like for the transfer of sensitive documentation.

Another concern is the verification by a recipient that an electronic mail message has not been tampered with or intercepted. Should an electronic mail message be intercepted, then it is perfectly possible for the person obtaining access to the message to forward the message on to the intended recipient after possibly having corrupted or otherwise interfered with the message.

It is an object of the present invention to address the above concerns and seek to provide a method and apparatus for the secure exchange of documentation over an open network.

By way of background, the basis of encryption systems is that a form of mathematical transform is applied to a message being encrypted. Security can

2 be gained in two ways. Firstly, by keeping the transform secret. This is not very effective because once the transform is known, the encryption is useless. The second way is to use a transform that takes some sort of a key as input. This is more secure as the transform may be known but if the key is not known, then the message cannot be simply extracted. The problem here is that a very secure method has to be found of getting the key to an intended recipient so that the message can be decrypted using the key. Obviously the same transport for the key cannot be used for the message.

Some time ago 'one way' encryption algorithms were developed. These can encrypt a message, usually a password, and there is no reverse algorithm to recover the message. This is a useful verification system. When a computer is set with a new password, this can be stored by one way encryption. There is no reverse process to show the password. When the password is entered for authentication, the computer encrypts the entered password and compares the result with the stored encrypted result. If the two match, then the password has been authenticated.

Public key encryption is a key driven algorithm mechanism in which a private key is first generated. The private key is kept strictly secret. A public key is also generated which is freely distributable and which poses no security risk. Should somebody wish to send an encrypted message, then the message is encrypted using the public key. When the message is received, the private key can be used to decrypt the message. The only way of decoding a message encrypted with a public key is by using the private key. Thus, even the person originating the message is unable to decrypt the message once it has been encoded with the public key. Decryption is only possible using the private key.

3 Another useful feature of public key encryption is that messages can be electronically signed so as to prove that a message has not been altered or otherwise tampered with. Once a message has been encrypted using that person's public key, that person's private key can then be used to "sign" the message by adding a simple checksurn of the encrypted message with their private key. When the signed encrypted message is received, a public key corresponding to the sender's private key can be used to do another checksum to ensure that the message has not been changed since any change or alteration to the message after signature would invalidate the checksum. Thus, positive confirmation is able to be provided to show that the message content is exactly as originally sent.

One aspect of the present invention provides a method of electronic document exchange for sending a message from a local server over an open network to a destination server via an intermediate switch, the method comprising the steps of. encrypting the message to provide an inner encrypted message layer; further encrypting the message to provide an outer encrypted message layer; sending the message to the intermediate switch; decrypting the outer encrypted message layer; further encrypting the message to provide an outer encrypted message layer; sending the message to the destination server; decrypting the outer message layer; and providing the encrypted message to the intended recipient.

A further aspect of the present invention provides a method of secure electronic document exchange from a message originator at a local server over an open network to a destination server via an inter-mediate switch, each of the message originator, the intended recipient, the servers and the switch having a public key for encrypting messages and a private key for decrypting messages encrypted with the respective public key, the method comprising the steps of- 4 the message originator composing a message and addressing the message to the intended recipient; sending the message to the local server for transmission over the open network to the destination server; encrypting the message with the public key of the intended recipient; the local server adding a signature to the encrypted message and addressing the message to the destination server; further encrypting the message with the public key of the switch such that the message has an inner layer encrypted by the public key of the intended recipient and an outer layer encrypted by the public key of the switch; sending the message to the switch; the switch decrypting the outer encryption layer with the switch private key; the switch adding a signature to the encrypted message; the switch further encrypting the message with the public key of the destination server; sending the message to the destination server; the destination server decrypting the outer encryption layer to uncover the recipient address; and providing the encrypted message to the intended recipient.

In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawing which is a schematic representation of a system for secure electronic document exchange embodying the present invention.

Referring to the Figure, a system of a secure exchange of electronic documents over an open network such as the public Internet comprises a plurality of servers I each located at a customer's premises or in direct secure communication with a customer's premises and a plurality of switches 2 accessible by the customer servers I for the routing of messages through one or more switches 2 between the servers. The customer servers I are accessed by customers using a personal computer (PC) 3 or the like. A switch 2 is a server specifically utilised for the routing of electronic documents over the Internet.

The customer servers I and the switches 2 are in communication via the Internet 4. Preferably, each of the customer's personal computers 3 is in direct local area network communication with its server I although it is envisaged that remote access to a form of public server 5 is possible.

Each customer server I or public access server 5 and the or each switch 2 has a key pair associated with it. Thus, for example, the customer server I has a private key and a public key. The public key of the customer server I is accessible by the switches 2 and the other customer servers I or public access servers 5 so that messages can be encrypted by the switches 2 and the other servers 1,5 using the public key of the customer server I for subsequent decryption by the private key of the customer server 1. Similarly, the public key of the or each switch 2 is accessible to all the servers 1,5 so that messages can be encrypted for the switch 2 to decrypt using the switch's private key.

Each of the servers 1,5 and switches 2 incorporates signature means to append a signature to an encrypted message which is to be sent to another server 1,5 or switch 2. Preferably, the signature means is a simple algorithm to append a checksum of the encrypted message calculated by the server 1,5 or switch 2 sending the message for subsequent checking by the destination server or switch to ensure that the message has not been tampered with in any way in transit.

Referring to the Figure, a user composes a message to be sent over the document exchange system on a PC 3. The PC 3 is connected to a customer server I by a local area network. Once the message has been composed and addressed to the intended recipient, the message is sent from the PC 3 to the customer server 1. The customer server I receives the message and checks the address of the recipient. Once the customer server I has established that the 6 message is outbound to a valid destination address, the server I can start encryption. In the example shown in the Figure, the destination server is the public access server 5.

The server I requests from the nearest switch 2, via the Internet 4, the public key of the destination server 5, that is the server 5 nearest the locality of the address of the recipient. The switch 2 transmits the public key of the destination server 5 to the customer server I and the message including the address is encrypted by the customer server I with the public key of the destination server 5. The encrypted message is then addressed with the name of the destination server 5. The encrypted message is also signed, i.e. provided with a signature, by the customer server 1. As previously described, the signature can be in the form of a checksurn generated by the private key of the customer server 1.

The encrypted message is then further encrypted with the public key of the switch 2 through which the message is to be relayed to the destination server 5. The address of the switch 2 is then put on the double encrypted message. In effect, the double encrypted message comprises an inner encrypted layer of the message proper and an outer encrypted layer of the signature and address information. The double encrypted message is then sent to the switch 2.

When the switch 2 receives the double encrypted message, the outer layer is decrypted using the switch's private key to uncover the address of the destination server 5. Once this information has been decrypted, the switch 2 then signs the encrypted message, encrypts the encrypted message (so that once again the encrypted message is double encrypted) with the public key of the destination server 5 and sends the message to the destination server 5.

7 The destination server 5 receives the double encrypted message and decrypts the outer layer of encryption using its own private key to uncover the full destination address. The destination server 5 then waits for the intended recipient to collect their electronic mail.

In the present example, the intended recipient makes contact with the destination server 5, a public access server, using a lap-top computer 6. Preferably, communication with the destination server 5 is by way of a secure sockets layer (SSL) encrypted tunnel. The private key of the intended recipient is sent to the destination server 5 over the encrypted tunnel and the destination server 5 uses the private key to fully decrypt the message. The destination server 5 then forgets the intended recipient's private key. The decrypted message is then sent down the encrypted tunnel via SSL to the intended recipient's lap-top computer 6. Thus, the intended recipient receives the decrypted message.

It should be appreciated that in the above example, the intended recipient makes contact with the destination server 5 by way of a remote link. Of course, the intended recipient could be a personal computer 3 connected to the destination server 5 by way of a local area network or another form of secure and closed communication network.

In contrast to the simple example shown in the Figure, the actual system implementation will involve many switches 2 and a large number of users but the basic principles still apply to the message traffic through the system. Despite the large number of users and paths between servers 1,5, it should be fully appreciated that the use of signatures by the servers 1,5 and switches 2 serves to provide and preserve an audit trail identifying the path taken by a 8 message and providing verification that the message is exactly as originally composed before being sent over the public Internet.

With regard to the signature means, preferably each message is uniquely identified and information concerning all messages is retained. Thus, when a message is originated and sent to a server, a unique message identification code is generated and the date and time of receipt are logged. When the message arrives at the first switch 2, this information is recorded again as part of the signature. Further, the transmissions to subsequent switches 2 are also logged as is the arrival of the message at the destination server 5.

If required, the date and time of correct reception of the message by the intended recipient can be communicated back to the sender of the message so as to confirm the receipt of the message.

Thus, the present invention provides a secure method of electronic document exchange over an open network, such as the Internet, as well as offering the possibilities of message authentication and an audit trail.

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Claims

CLAIMS:

1. A method of electronic document exchange for sending a message from a local server over an open network to a destination server via an intermediate switch, the method comprising the steps ofencrypting the message to provide an inner encrypted message layer; further encrypting the message to provide an outer encrypted message layer; sending the message to the intermediate switch; decrypting the outer encrypted message layer; ftirther encrypting the message to provide an outer encrypted message layer; sending the message to the destination server; decrypting the outer message layer; and providing the encrypted message to the intended recipient.

2. A method according to Claim 1, wherein the method comprises the further steps of applying a signature to the inner encrypted message layer before further encrypting the message to provide the outer encrypted message layer; and the or each switch applying a further signature to the message before encrypting the message to provide the outer encrypted message layer.

3. A method according to Claim 2, wherein the signature provides an audit trail identifying the path taken by a message from the local server to the destination server.

4. A method according to Claim 2 or 3, wherein the signature is only applied if the message is exactly as originally composed before being sent over the open network.

5. A method according to any one of Claims 2 to 4, wherein the signature includes a unique message identification code.

6. A method according to any one of Claims 2 to 5, wherein the signature is a checksum of the encrypted message.

7. A method according to any preceding claim, wherein the message is routed via a plurality of intermediate switches between the local server and the destination server, each switch decrypting the outer encrypted message layer and further encrypting the message to provide another outer encrypted message layer.

8. A method according to any preceding claim, wherein the inner encrypted message layer is encrypted with a public key of the intended recipient.

9. A method according to any preceding claim, wherein the outer encrypted message layer is encrypted with a public key of the next switch through which the message is routed or a public key of the destination server.

10. A method according to any preceding claim, wherein confirmed receipt of the message by the destination server is communicated back to the local server.

11. A method according to any preceding claim, wherein connection to the local server or destination server is via an encrypted tunnel.

12. A method of secure electronic document exchange from a message originator at a local server over an open network to a destination server via an intermediate switch, each of the message originator, the intended recipient, the servers and the switch having a public key for encrypting messages and a private key for decrypting messages encrypted with the respective public key, the method comprising the steps of. the message originator composing a message and addressing the message to the intended recipient; sending the message to the local server for transmission over the open network to the destination server; encrypting the message with the public key of the intended recipient; the local server adding a signature to the encrypted message and addressing the message to the destination server; further encrypting the message with the public key of the switch such that the message has an inner layer encrypted by the public key of the intended recipient and an outer layer encrypted by the public key of the switch; sending the message to the switch; the switch decrypting the outer encryption layer with the switch private key; the switch adding a signature to the encrypted message; the switch further encrypting the message with the public key of the destination server; sending the message to the destination server; the destination server decrypting the outer encryption layer to uncover the recipient address; and providing the encrypted message to the intended recipient.

13. A method according to any preceding claim, wherein the open network comprises the Internet.

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14. A method according to any preceding claim, wherein the step of providing the encrypted message to the intended recipient comprises the step of the destination server forwarding the encrypted message to the intended recipient.

15. A method according to any one of Claims I to 13, wherein the step of providing the encrypted message to the intended recipient comprises the step of the destination server waiting for the intended recipient to collect the encrypted message.

16. A method according to Claim 15, wherein the private key of the intended recipient is sent to the destination server by an encrypted tunnel and the destination server decrypts the encrypted message using the private key of the intended recipient, the private key of the recipient being then forgotten by the destination server and the fully decrypted message being available to the intended recipient over the encrypted tunnel.

17. An electronic document exchange system, or component thereof, operable in accordance with the method of any preceding claim.

18. A method substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

19. An electronic document exchange system substantially as hereinbefore described and as shown in the accompanying drawing.

20. Any novel feature or combination of features disclosed herein.