Cross-certification still needs a personnel touch

Human involvement is still essential to the Federal Bridge Certification Authority's cross-certification efforts, said Tim Polk, the public-key infrastructure program manager at the National Institute of Standards and Technology.

Polk helped set up the cross-certification of digital certificates issued by the Agriculture Department's National Finance Center, the Defense and Treasury departments, and NASA.

If a DOD agency wants to set up secure communications with Treasury, for example, the agency must first send someone with a federal identification card and a floppy disk containing the agency's public key, plus some paperwork, to the bridge's operational authority at the General Services Administration.

Floppy swap

After checking the ID and paperwork, the bridge representative physically swaps the agency public-key floppy for one containing the bridge's public key.

The 1,024-bit public encryption key stored on the floppy disk can open a message or file to read and verify certificates. Both sending and receiving agencies must put their public keys into their messages. The messages identify the senders and verify that the contents were not corrupted in transfer.

'This has integrity checks on it,' Polk said, 'but the real security comes from in-person identity proofing' when the paperwork is first examined.

After an exchange of messages, the Treasury and DOD can use the information they've received to generate a certificate with each other's public keys.

The certificate is stored in their respective databases to make future transactions automatic, as well as in the bridge's directory.

The agencies' private keys are never exposed or exchanged, and the digitally signed messages can be e-mailed over the Internet without fear of tampering, Polk said.

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