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IBM Security


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IBM Security

Ultimately it is necessary to depend on the integrity of IBM in order to trust the information provided by the 4758. There are several ways that IBM or its agents could misbehave.

IBM Insider Attacks

IBM is supposed to use its root key (and the class keys to which it delegates authority, which are also under IBM's control) only to certify genuine 4758 device keys as being such. Since genuine 4758 device private keys never leave the card, this is the basis for concluding that a given certification comes from a 4758 card. However, IBM could create certifications on non-4758 keys and claim that they are actually keys from a valid 4758. IBM, or whomever held those other keys, could then issue bogus certificates that would claim to be from a 4758 and claim to accurately describe the software configuration, but they could lie. This would bypass all of the architectural protections of the 4758 because the falsely certified key would not even be in a 4758.

Similarly, IBM could create a weak or bogus 4758 card which did not defend its security in the manner specified and documented by IBM. Such a card could be attacked or manipulated by its owner to defeat the security provisions, and remote observers would not be aware of the falsification.

It's also possible that even if IBM as an institution would not violate its trust in this way, IBM employees or others who got access to the root keys could steal them or misuse them. IBM is supposed to exercise diligence and careful control over these valuable keys, but their procedures could be inadequate or could fail under some insider attack. This would allow the attacks above to go forward.

It is important for users of the RPOW system to be aware that ultimately they are trusting the integrity of IBM, and of the procedures and policies it has established to guard the security of the 4758 coprocessor cards and the root keys that authenticate them. However, in the context of the RPOW system, we gain the advantage that IBM is held to an extremely high level of diligence and care due to the fact that the cards are widely used for financial services. In those areas, the kinds of attacks described above could be devastatingly effective and damaging to the financial interests of the banks and other powerful institutions involved. Compared to the need for security in the financial sector, RPOW is small fry indeed. On this basis I think it is very safe to assume that IBM's level of diligence and care in maintaining the security of the 4758 and its attestations is more than sufficient for the needs of the RPOW system.

Development Tools

One of the principle goals of the RPOW system is to allow third parties to verify that the published source code of the RPOW server is what is running on the IBM 4758 card. This raises certain issues, some practical, and some related to security.

The main practical issue is the need to be using identical development tools as were used to build the memory image that was loaded into the IBM 4758 card and is presently running there. The RPOW server is built using the GNU C Compiler and the free Alphaworks development system from IBM. It will be necessary to make sure that the same version of GCC is used, and the same Alphaworks tool version. The Alphaworks tools do not work with present-day versions of GCC due to incompatibilities in the object file formats, but old versions are widely available. I built the actual memory image using GCC version 2.95.3. For more information on building a matching memory image, see the download page.

The security issue relates to possible weaknesses in the Alphaworks tool suite. IBM allows the Alphaworks tools to be used for personal and non-commercial use. IBM Research ported them to run under Linux. This was done to facilitate experimentation with custom programming for the 4758, and to find novel applications for it. I think the RPOW project is a perfect example of a novel application for the 4758 and an ideal usage for the Alphaworks tools.

However, IBM views the Alphaworks version as for experimental use, and has not maintained or updated it recently (at the time of writing). The 4758 Operating System file shipped with the Alphaworks tools is version 2.31 and dates back to 2001. Meanwhile, IBM sells a commercial version of the toolkit which has gone through several subsequent revisions, and is now up to version 2.41. The commercial version is very expensive and is not practical for an experimental, volunteer, private project like RPOW. So we are forced to use the free version, which is somewhat out of date. Therefore there is the danger that known bugs exist in version 2.31 of the OS, which someone could use to defeat the security of the RPOW system. I have not yet found any information at IBM about errata or known bugs in the 2.31 release.

Another potential problem with the use of the free development tools relates to the security model enforced by the IBM 4758. This is relatively technical and is described further on the page on the 4758 security model. The conclusion is that the RPOW server has several features designed to protect itself against the possibility that the owner of the card could reload a new software version while preserving secret information from the old version. If this were possible, it would allow the owner to extract the secret RPOW signing keys and other sensitive data, and then to masquerade as an RPOW server. In order to prevent this, the RPOW server encrypts all of its sensitive persistent data using a special "configuration" key provided by the operating system. The configuration key is guaranteed to have its private part deleted on any reload of any software component. This ensures that even the owner of the card will not be able to reload the application or the operating system and get access to the card's secrets.

Guarding against such attacks has been the primary consideration driving the architectural design of the RPOW server. Everything about the system is designed from the perspective that the card has to view the outside world, even its owner and operator, as well as the host computer where it resides, as an enemy. This is a controversial perspective in the context of end-users systems, where Digital Rights Management (DRM) and similar technologies also take the perspective that the owner is the enemy (although few companies are so honest as to say this publicly!). However, in the context of server systems like RPOW, this assumption of an untrusted owner/operator is crucial for adding to the security and privacy of end users.