PKI doesn't have to be perfect to be worthwhile

Experts say a simpler approach could still yield benefits for security

Nobody ever said implementing a public-key infrastructure would be easy, but a pair of experts at the 2006 International Conference on Network Security said last week that using PKI is often harder than it needs to be.

'We haven't been as successful as I wish we had been,' said Bill Burr of the National Institute of Standards and Technology. 'But I think we've been more successful than we get credit for.'

PKI promises to be a pretty good way to authenticate users, sign documents electronically and secure data. It uses a pair of mathematically related encryption keys to secure data. One key is kept private while the other is made public, allowing communications between individuals without exchanging secret keys. Using a public key, messages can be sent that can only be read by someone possessing the corresponding private key.

Material encrypted with a private key can be decrypted using that individual's public key, validating who sent and 'signed' the message.

The tricky part of PKI is the infrastructure, a system for generating and managing keys and digital certificates that contain them.

'It's much harder than we thought it would be,' Burr said. 'We've backed the wrong horse any number of times.' He said one of these wrong horses was the decision to use a bridge certificate authority rather than a single central certificate authority to issue and manage digital certificates. Burr said that a bridge system between authorities eventually would be needed, but that in retrospect the government should have started by using a single certificate authority within government.

'We are moving to a more hierarchical scheme,' he said. 'We've complicated our life a lot.'

Microsoft Corp.'s Charlie Kaufman said that a primary problem with PKI is finding a common format for carrying and reading the certificates that contain private keys, and a common system for publishing and accessing public keys.

'The technology does exist to solve these problems, but we haven't used [it],' Kaufman said. 'It's a distributed problem. The pieces are all there, but nobody has put them all together.'

'Good enough'

Kaufman and many members of the audience blamed the security industry for feeding the problem.

The industry, they contended, moves on to the next cool thing in security without bothering to simplify the implementation of existing technologies such as PKI.

Kaufman and Burr agreed that, with PKI, the perfect often is the enemy of the good.

People are looking for an infrastructure that would allow universal authentication between strangers.

A simpler and 'good enough' solution would be to simply use public/private key pairs the way passwords now are used, supplying a user's public key to the recipient when an account is set up or a relationship is established. This would be more secure than the current use of passwords for access security, and simpler than a full-blown PKI implementation.

'We don't have to build an eternal, nonreputable PKI for authentication and confidentiality,' Burr said. Although PKI can be used to provide legally binding signatures on documents that can be verified years after signing, this is not necessary. 'That's not our primary problem.'

The primary problem, authenticating users and securing data, can be solved much more simply, he said.

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