Online Certificate Issuance Using Offline-Protected Device Keys
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Solution Overview
Problem
Existing systems face challenges in issuing digital certificates online with minimal delay and maintaining security, especially when device characteristics are unknown in advance and short certificate lifetimes are required, necessitating an online Certificate Authority (CA) that does not compromise the security of device private keys.
Innovation Solution
An Offline Certificate Authority (OFFCA) generates and encrypts device private keys, which are transferred to an Online Certificate Authority (ONCA) that can only sign new certificates using pre-existing information, ensuring the ONCA cannot decrypt or modify the keys, thus maintaining security while allowing flexible certificate issuance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an online Certificate Authority is used to issue certificates with device characteristics and short lifetimes, then certificate issuance flexibility and timeliness are improved, but security risk of private key exposure increases
Solution Approach 1:
The system segments the Certificate Authority into two distinct components: an offline CA that generates and securely stores private keys, and an online CA that only performs certificate signing operations. This segmentation allows the online CA to be accessible and flexible while the private keys remain securely isolated offline, resolving the contradiction between issuance flexibility and key security.
Solution Approach 2:
The private key generation and storage function is extracted from the online CA and placed in the offline CA. The online CA receives only the public key and certificate signing requests, eliminating the security risk of private key exposure while maintaining certificate issuance flexibility. This extraction resolves the contradiction by removing the vulnerable element from the online environment.
2Productivity
If certificates are issued in batches ahead of request, then productivity is improved, but certificate expiration risk increases
Solution Approach 1:
The offline CA performs preliminary actions by generating private keys and creating certificate signing requests in advance, storing them securely. However, the actual certificate issuance is triggered only when a device requests it online. This preliminary preparation maintains productivity while ensuring certificates are issued with current device information and appropriate validity periods, avoiding expiration risks.
Solution Approach 2:
The system transitions from static batch issuance to dynamic on-demand issuance. Certificates are generated with current device characteristics and tailored validity periods based on real-time requirements, ensuring they remain valid and relevant. This dynamic approach maintains efficiency while eliminating the risk of issuing nearly-expired certificates.
3Measurement precision
If device characteristics are collected at certificate request time, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The online CA acts as an intermediary that receives device characteristics from the device at request time, validates them, and incorporates them into the certificate. This intermediary process ensures accurate device information is captured while the overall timing is optimized through the pre-prepared private keys and streamlined online signing process, minimizing delay while maximizing information accuracy.
Data Source
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AI summary
A method provides an origin certificate that can be issued as a digital certificate online. The method includes receiving an origin digital certificate and an encrypted client device private key from an offline certificate authority wherein the client device private key is encrypted according to a private key encryption key PrKEK. The method further includes receiving from the client device, a request for a client device digital certificate and the encrypted client device private key, selecting a digital certificate template for the client device, the digital certificate template having attributes that vary according to the client devices, building the client device digital certificate from the origin digital certificate and the selected digital certificate template, signing the client device digital certificate with an online certificate authority signing key, and transmitting the signed client device digital certificate and the encrypted device private key.