Subordinate Digital Certificates Pits Trustwave vs Mozilla

Tuesday, February 14, 2012

Plagiarist Paganini

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After the attacks against Certification Authorities (CA) such as VeriSign, Comodo and DigiNotar, the level of confidence in the model based on certificates has been in sharp decline.

There have been widespread accusations aimed at the PKI paradigm (public key infrastructure ) which is based on the concept of requesting trusted and credited third-parties to guarantee the authenticity of an entity in the digital world.

On more than one occasion, researchers have been identified vulnerabilities in the model and demonstrated the dangers arising from impairment of such architectures, and these risks pose a serious threat to both the private sector and the government. 

Unfortunately, criticism of the model have had little impact for technical reasons, and we are faced with challenging a powerful industry built around the monetization of our digital identity.

The news that we are going to discuss here is undoubtedly disconcerting, and raises serious doubts about the trustworthiness of trusted "third parties", the main component of the PKI model.

Digital Certificate Authority Trustwave revealed that it has issued a digital certificate that enabled an unnamed private company to spy on SSL protected connections within its corporate network. The news has literally shocked the Mozilla community, and they immediately requested to remove Trustwave's root certificate from Firefox.

The certificate in question issued by Trustwave was recognized as a subordinate root which enabled the signing of digital certificates for virtually any domain on the Internet.

Trustwave decided to make a public declaration on the event to reassure their customers. According the declaration by the company, the certificate has been updated in their legal repository (https://ssl.trustwave.com/CA) has been revoked as a subordinate root:

"This single certificate was issued for an internal corporate network customer and not to a 'government', 'ISP' or to 'law enforcement'. It was to be used within a private network within a data loss prevention (DLP) system. The subordinate certificate was subject to a Certification Practice Statement (CPS), Subscriber Agreement and Relying Party Agreement crafted by Trustwave after an audit of the customer physical security, network security, and security policies."

"The system was created using dedicated hardware device designed for SSL proxy and acceleration, with a FIPS-140-2 Level 3 compliant Hardware Security Module (HSM) (http://en.wikipedia.org/wiki/Hardware_security_module) for subordinate root storage and for the purpose of private key generation of the re-signed SSL certificates. This means that once the trusted subordinate root was placed into the device it could not be extracted."

The statement has two main aspects:

1. The company said the subordinate root certificate could not be stolen or abused because it was stored in a HMS (Hardware Security Module) device used for the management of digital keys. It's usage guarantees that it's impossible to extract the keys from the device. 

These modules are physical devices that traditionally come in the form of a plug-in card or an external TCP/IP security device designed for:

  • onboard secure generation
  • onboard secure storage
  • use with cryptographic and sensitive data material
  • offloading application servers for complete asymmetric and symmetric cryptography

HSMs provides both logical and physical protection of these materials from unauthorized use by potential adversaries.

Trustwave declared that the issuing of subordinate roots to private companies has been done with the purpose of allowing inspection of the SSL-encrypted traffic that passes through their networks. Trustwave decided to stop issuing this type of certificate in the future, and revoked the existing ones.

2. The company has performed physical security audits to make sure that the system could not be used to intercept SSL-encrypted (Secure Sockets Layer-encrypted) traffic on different networks.

The unsubstantiated allegations and charges coming from many quarters allege that the presence of the subordinate root certificate could be used to generate ad hoc SSL certificates that would allow extraction of the keys for use them elsewhere .

These allegations were promptly rejected by the company, Brian Trzupek, Trustwave's vice president for managed identity and authentication said: "...nor could the subordinate root keys ever get exported from the device."

Mozilla's community does not accept this assurance and is currently debating whether the issuing of such certificates represents a serious breach of the Certification Practice Statement policy implemented by Trustwave. To preserve users' security, the community is inclined to exclude Trustwave certificates.

Several users are asking Mozilla to remove Trustwave's root certificate from Firefox and Thunderbird because the domain name owners were not aware that Trustwave was re-signing certificates in their name through a subordinate root.

In my opinion, Trustwave has managed the situation in a reasonable way and the observations of the Mozilla community has produced excessive worry. The company has operated in absolute transparency when applying the corrections required, and preceded with the certificate revocation.

What I do not agree is the different approach followed by the company in the government and private sectors. Cyber threats transverse to areas which are inextricably linked, and the exploit of a vulnerability in the private sector could have serious repercussions in other areas.

Another aspect of which I have strong doubts is that a certification authority can distribute to everyone  'weak CA' certificates, even in a safe manner. Doing so is in my opinion contrary to any reasonable security policy, and may expose organizations to significant risks.

Cross-posted from Security Affairs

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