PKI security service examples
Public Key Infrastructures (PKI) can effectively be used to support a variety of security services for environments looking to link communities of interest and to expand the use of the Internet as a business communications tool.
Here's how authentication and non-repudiation operate using this platform. (For more information about PKIs, see story, p. 150.)
Authentication
Conducting sensitive business transactions such as e-commerce (electronic commerce) or patient record transfer over the Internet should use strong mutual authentication. In a PKI environment, both the end user and the resource (application) possess a digital certificate.
When an end user queries a secured application, an authentication challenge is launched by the application. The challenge contains a random value generated by the application. The end user client takes the random value and encrypts it using the end user's private key, which is located on a smart card token.
Opening the private key requires the end user to input a PIN. This follows a widely accepted security practice of something you have (smart card) plus something you know (PIN). The encryption process is performed on the smart card ensuring confidentiality of the private key.
The resulting encrypted value is returned to the application. The application queries the public key repository for the end user digital certificate. The application then uses the public key of the end user to decrypt the encrypted message. If the resultant value matches the original random value generated by challenge, the application has a high degree of certainty that the end user is who he or she claims to be.
A similar process is invoked by the end user launching a challenge to the application. Here, the application encrypts the message using it's own private key, and the end user client decrypts it using the public key of the application obtained from the digital certificate in the public key repository. If the values match, the end user is ensured of the legitimacy of the application.
>Non-repudiation
Non-repudiation is the process of minimizing the probability for an end user to forge or deny a transaction. Using the functionality offered by the PKI, a transaction that is digitally signed affords near indisputable evidence that a transaction did occur and that it was originated by the party whose digital signature is associated with the transaction.
For example, a hospital administrator submits an electronic claim to an insurance carrier. The form is completed and is digitally signed by the administrator before being electronically forwarded to the carrier. The digital signature process calculates a cryptographic hash (a fixed-length mathematical representation of the completed claim), which is called the "message digest." The message digest is then encrypted using the administrator's private key that only he or she possesses. The encrypted message digest is the digital signature and is attached to the electronic claim.
The insurance processor receiving the claim now has the ability to verify two critical items:
4 The person who signed and generated the claim is in fact an authenticated "participant" in the network.
4 The contents of the claim have not been altered.
First, the claim processor retrieves the digital certificate of the sender from the public key repository. The public key is used to decrypt the digital signature attached to the claim. This produces the original message digest or cryptographic hash. The claim processor then applies the same cryptographic hash function to the original claim and compares the two message digests.
If they match, the insurance claim processor is assured of the identity of the person submitting the claim and that the information on the claim has not been altered. While these two levels of protection do not unequivocally guarantee the sender, they do provide extremely strong proof that the claim is accurate and was submitted by the party identified by the public key.
Non-repudiation, therefore, provides an environment that deters hackers and users from tampering with or misrepresenting sensitive information. It can also assist in providing strong evidence that a specific party identified by the public key originated a transaction.
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