Auditable Middleboxes
An auditable middlebox is a middlebox that has its own certificate logged in the middlebox transparency system
Middlebox Certificates
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▸ A client is not aware of involved middleboxes
To minigate the problems in SplitTLS, it is desirable to make middleboxes visible and publicly auditable.
▸ X.509 certificates are relevant to make middleboxes public
X.509 certificates are public and static; thus, it is appropriate to describe the properties of the middleboxes.
Fields of Middlebox Certificates
▸ Type of Service
This field describes the type of the service provided by the middlebox. Examples are web application firewalls, anti-virus software, and parental filterings.
▸ URL
This field indicates the URL pointing to the web page of information about the middlebox or the middlebox service provider.
▸ Permission
This field represents the permission of the middlebox, e.g., read or write.
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Middlebox Transparency
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▸ The middlebox transparency system records all the middlebox certificates
The middlebox transparency log server manages the middlebox certificates in the form of a merkle tree
▸ The middlebox transparency system issues a signed certificate timestamp
The signed certificate timestamp (SCT) represents a promise that the corresponding certificate will be logged in the log server within the next period as the certificate transparency (CT) system does.
Advantages
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▸ No impersonation
Middleboxes now have their own key pairs and do not need to impersonate others (in TLS).
▸ Awareness
Anyone can know the name and the properties of the middlebox by the middlebox certificate.
▸ Auditability
Any interested parties can check fraudulent certificates with the middlebox transparency system.
▸ Information Enforcement
A CA can enforce middlebox service providers to provide sufficient information about the middleboxes by marking important fields as "critical"; the client should abort the session if the critical field is not filled.
▸ Revocability
Any incorrect middleboxes can be blocked following the certificate revocation mechanisms such as CRL or OCSP.