Portable Data Carrier Authentication Using Segmented Key Hierarchy
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Solution Overview
Problem
Existing authentication methods for portable data carriers compromise user anonymity and incur significant costs and efforts when one data carrier is compromised, as the entire group must be replaced if a group secret key is leaked.
Innovation Solution
A method where a public session key and secret session key are derived from data carrier-specific keys, which are in turn derived from a group key, allowing authentication without storing the group secret key, thus preventing compromise of other data carriers and maintaining user anonymity by using changing session keys and a group-specific certificate for verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If each data carrier is personalized with an individual pair of keys, then authentication security is improved, but user anonymity is lost and complete movement profiles can be created
Solution Approach 1:
The key system is segmented into three levels: group key pair (common to all carriers), data carrier-specific key pair (unique to each carrier), and session key pair (generated per authentication). This segmentation allows individual carrier authentication while maintaining group-level anonymity through the shared group keys.
Solution Approach 2:
The system transitions from static key pairs to dynamic session keys that are generated anew for each authentication event. The session keys are derived from the data carrier-specific keys and are used only for the current authentication, then discarded. This dynamic key generation prevents tracking across multiple authentication events while maintaining security.
2Loss of information
If a group key pair is used for all data carriers, then user anonymity is restored, but security deteriorates as compromise of one carrier affects the entire group
Solution Approach 1:
The key system is segmented into three levels: group key pair (common to all carriers), data carrier-specific key pair (unique to each carrier), and session key pair (generated per authentication). This segmentation allows individual carrier authentication while maintaining group-level anonymity through the shared group keys.
Solution Approach 2:
The data carrier-specific key pair is extracted and stored in the data carrier itself, separating the sensitive individual authentication material from the shared group infrastructure. This extraction means that even if the group key infrastructure is compromised, the individual carrier keys remain secure and can be used for authentication.
3Ease of operation
If data carrier-specific keys are stored in the data carrier, then authentication capability is improved, but vulnerability to compromise increases
Solution Approach 1:
The system transitions from static key pairs to dynamic session keys that are generated anew for each authentication event. The session keys are derived from the data carrier-specific keys and are used only for the current authentication, then discarded. This dynamic key generation prevents tracking across multiple authentication events while maintaining security.
Solution Approach 2:
The data carrier-specific key pair is pre-generated and stored in the data carrier during manufacturing, enabling immediate authentication capability. However, the system is designed so that these keys are never used directly for authentication - instead, session keys are derived from them during each authentication event, limiting the exposure window of the stored keys.
Data Source
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AI summary
The invention relates to a method for authenticating a portable data carrier (10) with respect to a terminal, comprising the following steps: in the data carrier (10) a public session key (PKSession) is derived (S5) from a public key (PK1) that is individual to the data carrier. The public key (PK1) that is individual to the data carrier has in turn been derived (TS32; S1) from a public group key (PK). Furthermore, a secret session key (SKSession) is derived (S4) from a secret key (SKi) that is individual to the data carrier, said secret key (SKi) that is individual to the data carrier having in turn been derived (TS31) from a secret group key (SK). A secret communication key (KK) is subsequently agreed (S7) between the data carrier (10) and the terminal. Finally, the terminal verifies (S8) the public session key (PKSession) of the data carrier (10).