EP1370919A2

EP1370919A2 - Encryption module with physical security or protection

Info

Publication number: EP1370919A2
Application number: EP02708363A
Authority: EP
Inventors: Michael John Jackson
Original assignee: Eracom Technologies Australia Pty Ltd; Eracom Technologies AG
Current assignee: SafeNet Australia Pty Ltd; Eracom Technologies AG
Priority date: 2001-03-22
Filing date: 2002-03-22
Publication date: 2003-12-17
Also published as: AU2002242733A1; AUPR389801A0; WO2002077778A3; WO2002077778A2

Abstract

This invention concerns an encryption module having a cryptographic adapter configured for connection to a host system bus to manage host computer access via a secure access policy implemented in firmware on the adapter. The invention in particular concerns the physical security measures applied to such a module to maintain its operational integrity. To do this the adapter is encased in a sealed cover which is designed with thermal characteristics so that a steady state temperature is achieved during use that is safe for continuous operation. The module further comprises tamper detection devices including a software configurable tamper detection component to induce a tamper response upon removal of adapter from the host system bus.

Description

An Encryption Module

Technical Field

This invention concerns an encryption module, and in particular the physical security measures applied to such a module to maintain its operational integrity.

Background Art

Encryption of data is commonly used to provide secure communication between parties over insecure networks, such as the Internet. Encryption may be performed by the software or hardware, or by a combination of both. Cryptographic adapters are used to enhance the security and speed of encryption and decryption. The cryptographic adapter manages host computer access via a secure access policy implemented in firmware on the adapter. Delegating central processing unit (CPU) intensive cryptographic processing from the host to such a dedicated device, enables faster transaction throughput without degradation to the host's CPU. Steel enclosures are sometimes secured around cryptographic adapters to provide a physical security barrier. Attempts to remove the steel will often destroy the adapter within. The steel enclosures are generally provided with perforated areas to ventilate the adapter and limit heat build up during use. Additional physical security measures include fine line circuit patterns around the electronics to complicate probing, and micro-pressure actuators to trigger tamper mechanisms.

In US 5,998,858, which constitutes the most closely related prior art, a microcircuit with memory which is protected by both hardware and software is shown and described. To ensure a high enough security, additional measures on top of encryption are used such as sealing. In US 5,563,450, a computer peripheral card, which is not capable of encrypting is shown with a planar printed wiring board for surface mounted circuit components. The peripheral card further features a cover serving to discharge static charges and to electro-magnetically shield the enclosed compo- nents. The upper and lower parts of the cover are ultrasonically welded together.

In US 6,121 ,544, an electromagnetic shield for contactless smartcards is shown. The electromagnetic shield has the purpose to prevent unauthorized access to the information on the smartcards. The electromagnetic shield may consist of two halves of plastic reinforcing shells in which an encasement made of magnetic metal alloy is contained. In order to operate the smartcard needs to be removed from the shield. Thus, the smartcard of US 6,121 ,544 cannot be used within the electromagnetic shield. Rather, the electromagnetic shield prevents usage of the smartcard and the cover does not have thermal characteris- tics such that a steady state temperature is achieved during use.

In US 6,068,192, a tamper resistance smartcard and a method of protecting the data in a smartcard are disclosed. The smartcard may use a personal identification number to encrypt the private information. The smartcard further uses a battery and volatile memory which is erased if the battery is dis- connected. The covers of the casing of the smartcard are sealed together with adhesive material.

In US 6,1 1 1 ,760, an enclosure for electronic components is shown, that is adapted for cellular phones. The enclosure comprises two housing portions which may be ultrasonically welded. The problem with the devices known from the prior art is that they do not sufficiently protect critical data on encryption modules. This problem is solved by the encryption module according to the invention. Summary of the Invention

The invention is an encryption module having a cryptographic adapter configured for connection to a host system bus to manage host computer access via a secure access policy implemented in firmware on the adapter, the adapter being encased in a sealed cover which is designed with thermal characteristics so that a steady state temperature is achieved during use that is safe for continuous operation of the cryptographic adapter. Also included in the module are tamper detection devices to provide an alert should attempts be made to remove the cover, and software configurable tamper detection to in- duce a tamper response upon removal of adapter from the host system bus.

The electronics of the adapter may be mounted on a PCB (Printed Circuit Board) which include slots and rebates to cooperate with flanges and recesses on the half covers to allow them to fit together capturing the PCB between them. The cover may comprise two half covers made of opaque poly- carbonate material and ultrasonically welded together.

A daughterboard may be included, sitting above the PCB, to house memory devices.

The tamper detecting mechanisms may include:

Light sensing devices, Micro-pressure switches. The physical barrier provided by the cover prevents physical access to the printed circuit board and electronic components.

Polycarbonate is the preferred material because of its physical properties, such as impact resistance, fire retardation, good dimensional stability and low creep. Polycarbonate is a physically strong material but is able to display evidence of an attack and signs of forced entry to the module, such as scrapes and scratches and the traces of knife cuts and stabs on its surfaces. Polycarbonate has a Rockwell hardness of M70 and Izod Impact strength (J m^"1) of 600-850. Polycarbonate has a thermal conductivity at 230C (W m^"1K^"1) with results 0.19-0.22 and thermal expansivity (x10^"6K^"1) with results 66-70. Packing the circuitry densely also helps to prevent logic probes being used effectively. Constant or random exponentiation times may be used to countermeasure timing attacks.

Brief Description of the Drawings

An Example of the invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is an exploded view of a encryption module comprising of the front cover, cryptographic adapter and rear cover. Fig. 2 is a diagram of the rear side of the cryptographic adapter indicating the location of micro-pressure switches.

Fig. 3 is a diagram of the front side of the cryptographic adapter indicating the location of other tamper detection switches.

Best Modes of the Invention

Referring to figure 1 , the encryption module comprises a front cover 1 and a rear cover 2 enclosing the electronics components of a cryptographic adapter indicated generally at 3. The electronics components are housed on a one half length PCB 4, with dimensions 98mm by 205mm, and memory devices are housed on an upside down daughterboard 5. The daughterboard is connected to the PCB and separated from it using a spacer 6. The daughterboard is arranged upside down against the PCB to minimise space within the enclosure and to provide added security for the memory devices by facing them inwardly and also by having the rear side of the daughterboard fac- ing the front cover.

Front cover 1 has recesses 10, 11 , 12 and 13, and rear cover 2 has flanges 20, 21 , 22 and 23. The PCB 4 has four slots at 40, 41 , 42, and 43 and two rebates 44 and 45.

Front cover 1 and rear cover 2 are made of- polycarbonate material and are fitted together so that slot 40 in PCB 4 allows flange 20 in rear cover 2 to pass through it and join with recess 10 in front cover 1. Similarly, slot 41 allows flange 21 to join with recess 1 1. Slot 42 allows flange 22 to join with recess 12. Slot 43 allows flange 23 to join with recess 13.

After the front and rear covers are fitted together, they are ultrasonically welded to form a sealed enclosure. Rebates 44 and 45 allow for the covers 1 and 3 to fully enclose the PCB 4 and the daughterboard 5. Also rebate 30 allows flange 31 to fully seal rear cover 2 beneath front cover 1 . This seal is continuous along the top section of the PCB 4 which is a vulnerable section once installed into a computer. The rebate 30 provides additional strength to the enclosure when flange 31 is ultrasonically welded to the top section of front cover 1 . The rebates on PCB 4 allow an interlocking configuration of front cover 1 , rear cover 2 and PCB 4, resulting in permanent destruction to the PCB 4 when attempts are made at opening the enclosure.

When ultrasonically welding thermoplastics, a thermal rise occurs in the bonding areas, that is the contact points between the flanges of the rear cover 2 and the recesses of front cover 1. The thermal rise is produced by the absorption of mechanical vibrations, the reflection of the vibrations in the connecting area, and the friction of the surfaces. Vibrations are introduced vertically, and frictional heat is produced so that the polycarbonate plasticises locally, forging an insoluble connection between the front and rear covers within a very short period of time. The joint quality is very uniform because the energy transfer, and the released internal heat remains constant and is limited to the joining area. The bonds between the front and rear covers are solid and homogenous since there is diffusion of polycarbonate material between the covers. A mm seam will have a strength approaching that of the original material. The enclosure formed by the front and rear covers prevents direct external access to the cryptographic processing elements and memory containing sensitive data. The seal between the front and rear covers has almost equal strength to the covers themselves, which makes it difficult to distinguish the seam after the-front and rear covers have been ultrasonically welded-together. Low heat producing components have been specifically selected, such as a microprocessor designed for embedded applications to reduce the overall heat production of the adapter. Heat balancing ensures that the PCB and daughterboard reach a steady state temperature during use that is safe for con- tinuous operation of the electronics. This removes the need for ventilation holes or perforations in the covers allowing for additional tamper detection such as the light sensitive switches, to be installed. The thermal conductivity of the polycarbonate covers is low in comparison with materials such as metal, heat transfer convection is kept low as the heat transferred by the electronic compo- nents is proportional to the exposed surface area of the covers, and this ensures that radiation heat transfer is kept to a minimum, providing for very favourable thermal characteristics. When in operation, the thermal characteristics of the covers allow the adapter to reach a steady state temperature for safe operation of the electronic components on the PCB and daughterboard. With- out having perforations in the enclosure would provide more effective and reliable operation of tamper detection components used within the enclosure and would also prevent other undetectable physical probing.

Within the enclosure formed by the covers there are tamper-detecting devices. These devices may include light sensitive devices, activated by open- ing the covers and allowing light to penetrate the enclosure. Also there are pressure switches, activated by lifting the covers away from the PCB.

As shown in figure 2, on the rear side of PCB 4, micro-pressure switches and actuators 50, 51 , 52, 53 and 54 are strategically located. Turning to figure 3, on the front side of the PCB 4, micro-pressure switches with inbuilt actuators forming a single component 55, 56, 57 and 58 are strategically located. These components are part of the integrated physical protection of the module in addition to the enclosure.

A tamper response mechanism is activated when an attempt to open the covers is detected or when-the-adapter is removed from the PCI slot. The tarn- per response mechanism removes power from the memory devices, resulting in an unknown and corrupt state within the memory devices, effectively erasing data stored within the memory devices. The module's tamper response will effectively destroy all sensitive information and cryptographic keys rather than exposing them.

Optical remote visible and audible alarms, or monitoring, can be at- tached to the PCB via an output link.

An authenticated user can place the adapter into Transport Mode by disabling the "tamper upon removal of the adapter from the PCI slot" condition.

Tamper detection is active in poweron and poweroff states.

Although we have used the example of polycarbonate as the material for the covers, any other polymers or plastic resins would be a suitable substitute such as polyester or fibreglass. While plastics are all related, each resin has attributes that make it best suited to a particular environment or situation.

It is to be understood that numerous modifications may be made in the illustrative embodiment of the invention and other arrangements may be devised without departing from the spirit and scope of the invention.

Claims

1. An encryption module comprising a cryptographic adapter, said cryptographic adapter being configured to be connected to a host system bus and being encased in a sealed enclosure having thermal characteristics such that a steady state temperature is achieved during use that is safe for continuous operation of the cryptographic adapter, further comprising tamper detection devices within the enclosure, characterized in that the tamper detection devices include a software configurable tamper detection component configured to activate a tamper response mechanism upon removal of the encryption module from the host system bus.

2. The encryption module according to claim 1 , characterized in that the electronics of the adapter are mounted on a printed circuit board having slots and rebates, and in that the enclosure comprises flanges and recesses, said slots and rebates of said printed circuit board cooperating with said flanges and recesses of said enclosure.

3. The encryption module according to claim 1 or 2, characterized in that the enclosure comprises a front cover and a rear cover, said rear cover being sealed to the front cover, said rear cover and said front cover being interlocked with the printed circuit board in such a way that opening of the enclosure results in destruction of the printed circuit board.

4. The encryption board according to claim 3, characterized in that the printed circuit board is captured between the half covers.

5. The encryption module according to any one of the above claims, characterized in that the enclosure is ultrasonically welded together from two half covers.

6. The encryption module according to any"one of the above claims, characterized in that the enclosure is made from polycarbonate material.

7. The encryption module according to any one of the above claims,- characterized in that a daughter board connected to^x'the printed circuit board is provided within the enclosure, said daughter board housing electronics and being separated from the printed circuit board using a spacer.

8. The encryption module according to any one of the above claims, characterized by memory modules, which are mounted on a daughter board that is placed within the enclosure in an upside-down position sitting above the printed circuit board.

9. The encryption module according to any one of the above claims, characterized in that the tamper detection devices are configured to issue an alert signal if it is attempted to remove the sealed cover.

10. The encryption module according to any one of the above claims, characterized in that the tamper detection devices include light sensing devices.

11. The encryption module according to any one of the above claims, characterized in that the tamper detection devices include micro pressure switches.

12. The encryption module according to any one of the above claims, characterized in that the circuitry is packed densely to prevent logic probes from being used effectively.

13. The encryption module according to any one of the above claims, characterized in that the tamper response mechanism upon activation removes power from the memory devices and to destroy the cryptographic keys stored in the encryption module upon activation.

14. The encryption module according to any one of the above claims, characterized in that the tamper response mechanism upon activation provides an alert.