3 An alternative

An alternative approach to the problem of authentication of public key information across time and space is the web of trustIn cryptography, a web of trust is a concept used in PGP, GnuPG, and other OpenPGP-compatible systems to establish the authenticity of the binding between a public key and a user. It is, in some respects, an alternative to centralized PKI reliance exclusi scheme, which uses self-signed certificates and third party attestations of those certificates. Examples implementations of this approach are GPG (The GNU Privacy Guard), and PGP (Pretty Good Privacy). Because of PGP's (and clones') extensive use in email, the Web of Trust originally implemented by PGP is the most widely deployed bidirectional PKI extant at this writing ( 2004).

An even newer and rapidly growing alternative is the simple public key infrastructure (SPKI) that grew out of 3 independent efforts to overcome the complexities of X.509 and the anarchy of PGP's web of trust. SPKI binds people/systems directly to keys using a local trust model, similar to PGPs web of trust, with the addition of authorisation integral to its design.

4 History

The public disclosure of both secure key exchange and asymmetric key algorithms in 1976 by Diffie, Hellman, and Rivest, Shamir, and Adleman changed secure communications entirely. With the further development of high speed digital electronic communications (the Internet and its predecessors), a need became evident for ways in which users could securely communicate with each other, and as a further consequence of that, for ways in which users could be sure with whom they were actually interacting. The idea of cryptographically protected certificates binding user identities to public keys was eagerly developed.

Assorted cryptographic protocols were invented and analyzed within which the new cryptographic primitives could be effectively used. With the invention of the World Wide Web and its rapid spread, the need for authentication and secure communication became still more acute. Commercial reasons alone (e.g., e-commerce, on-line access to proprietary databases from Web browsers, etc.) were sufficient. Taher ElGamal and others at Netscape developed the SSL protocol (' https' in Web URLs); it included key establishment, server authentication (prior to v3, one-way only), and so on. A PKI structure was thus created for Web users/sites wishing secure (or more secure) communications.

Vendors and entrepreneurs saw the possibility of a large market, started companies (or new projects at existing companies), and began to agitate for legal recognition and protection from liability. An American Bar Association technology project published an extensive analysis of some of the foreseeable legal aspects of PKI operations (see ABA digital signature guidelines), and shortly thereafter, several US states ( Utah being the first in 1995) and other jurisdictions throughout the world, began to enact laws and adopt regulations. Consumer groups and others raised questions of privacy, access, and liability considerations which were more taken into consideration in some jurisdictions than in others.

The enacted laws and regulations differed, there were technical and operational problems in converting PKI schemes into successful commercial operation, and progress has been far slower than pioneers had imagined it would be.

By the first few years of the 21st century, it had become clear that the underlying cryptographic engineering was not easy to deploy correctly, that operating procedures (manual or automatic) were not easy to correctly design (nor even if so designed, to execute perfectly, which the engineering required), and that such standards as existed were in some respects inadequate to the purposes to which they were being put.

PKI vendors have found a market, but it is not quite the market envisioned in the mid-90s, and it has grown both more slowly and in somewhat different ways than were anticipated. PKIs have not solved some of the problems they were expected to, and several major vendors have gone out of business or been acquired by others.

5 Usage examples

PKIs of one type or another, and from any of several vendors, have many uses, including, providing public keys and bindings to user identities which are used for:

• Encryption and/or sender authentication of Email messages, (e.g., using OpenPGP or S/MIME).
• Encryption and/or authentication of documents, (e.g., the XML Signature * or XML Encryption * standards if documents are encoded as XML).
• Authentication of users to applications, (e.g., smart card logon, client authentication with SSL).
• Bootstrapping secure communication protocols, such as Internet key exchange (IKE) and SSL. In both of these, initial set-up of a secure channel (a " security association ") uses asymmetric key (a.k.a. public key) methods, whereas actual communication uses faster secret key (a.k.a. symmetric key) methods.

6 A few PKI implementations

Some leading certificate authorities, e.g. VeriSign, are not listed, since their software is not available to others.

• Computer Associates eTrust PKI
• Entrust
• Microsoft
• Netscape CMS
• OpenCA (an Open Source movement publicly available PKI scheme including server software)
• RSA Security

7 See also

• Public key cryptography
• Key authentication
• Certificate revocation list

8 External links

• PKI tutorial by Peter Gutmann
• PKIX workgroup
• http://www.pk3i.com/
• http://www.newpki.org/

A detailed explanation of PKI Privacy, Authentication, Integrity and Non-repudiation (PAIN) can be found at: PAIN

• Conclusive Logic (A standards based "website security infrastructure".)
• Betrusted (acquired the Baltimore UniCERT product in early 2004)
• NIST PKI Program, in which the National Institute of Standards and Technology (NIST) is attempting to develop a public key infrastructure
• http://www.mozilla.org/projects/security/pki - Open Source PKI Projects
• PKI Public Key Infrastructure news, information and education from the PKI Forum (pkiforum.com)

Cryptography

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