HP UX IPSec Software Digital Signatures, IKE Public Key Distribution, Certificate Revocation List (CRL)

Using Certificates with HP-UX IPSec

Overview

Certificates are issued with a specific lifetime, defined by a start date/time and an expiration date/time. However, situations can arise, such as a compromised key value, that necessitate the revocation of the certificate. In this case, the certificate authority can revoke the certificate. This is accomplished by including the certificate’s serial number on a Certificate Revocation List (CRL) updated and published on a regular basis by the CA and made available to certificate users.

Digital Signatures

With digital signatures, the sender uses its private key to create a digital signature value, and sends the digital signature with the data. The recipient uses the sender’s public key and the data to verify the digital signature.

There are different methods to generate and verify the digital signature. In one method, the sender generates a one-way hash value and encrypts it with its private key to form the digital signature. The recipient uses the sender’s public key to decrypt the digital signature and extract the hash value; it then generates its own hash value and compares the hash values. In another method, the sender uses its private key and the data as input to a keyed secure hash algorithm that outputs the digital signature. The receiver uses the data, the sender's public key and the digital signature as input to a verification algorithm that verifies the digital signature.

One difference between a digital signature and a symmetric-key hash value is that only the holder of the private key can generate the digital signature, while either holder of a symmetric key can generate a symmetric-key hash value. Since only the private key holder can generate the digital signature, a digital signature also provides non-repudiation which makes it difficult for the sender to deny sending the message.

IKE Public Key Distribution

IKE primary authentication with digital signatures requires that the IKE initiator and responder obtain the other entity’s public key, using security certificates. This may be done as part of the IKE negotiation - the two entities may exchange certificates at the beginning of the IKE negotiation. Alternatively, this may be done independent of the IKE

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