Public key infrastructure
From Wikipedia, the free encyclopedia.
In computing, a PKI (Public Key Infrastructure) is an arrangement, usually carried out by software at a central location and other coordinated software at distributed locations, which provides for third party (often termed a Trusted Third Party) vetting and vouching for user identities and for binding of public keys to users and vice versa. The term is used to mean both the Certificate Authority and related arrangements as well as, more broadly and somewhat confusingly, to mean use of public key algorithms in electronic communications. The later sense is erroneous since PKI methods are not necessary to use public key algorithms.
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2 Typical use 3 An alternative 4 History 5 Usage examples 6 A few PKI implementations 7 See also 8 External links |
Purpose and function
PKI arrangements enable users to be authenticated to each other, and to use the information in identity certificatess (i.e., each others' public keys) to encrypt and decrypt messages traveling to and fro. In general, a PKI consists of client software, server software such as a certificate authority, hardware (e.g. smart cards) and operational procedures. A user may digitally sign messages using his private key, and (using the public key contained in that user's certificate issued by a Certificate Authority within the PKI) another user can check that signature. This enables two (or more) communicating parties to establish confidentiality, message integrity and user authentication without having to exchange any secret information in advance.
Typical use
Most enterprise PKI systems rely on certificate chains to establish a party's identity, as a certificate may have been issued by a Certificate Authority computer whose 'legitimacy' is established for such purposes by a certificate issued by a higher level Certificate Authority, and so on. This produces a certificate hierarchy composed of, at a minimum, several computers, often more than one organization, and often assorted interoperating software packages from several sources. Standards are critical to PKI operation, and public standards are critical to PKIs intended for extensive operation. Much of the standardization in this area is done by the IETF PKIX workgroup.
Enterprise PKI systems are often closely tied to the enterprise directory, in which each employee's public key is often stored (embedded in a certificate), together with other personal details (phone number, email address, location, department, ...). Today's leading directory technology is LDAP and in fact, the most common certificate format (X.509) stems from its use in LDAP's predecessor, the X.500 directory schema.
An alternative
An alternative approach to the problem of authentication of public key information across time and space is the Web of trust scheme, which uses self-signed certificates. Examples of implementations 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).
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 early 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 more acute. Commercial reasons alone (e.g., e-commerce, on-line access to proprietary databases from Web browsers, etc.) were sufficient. Taher El-Gamal and others at Netscape developed the SSL protocol (flagged as '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 entrepenuers 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, and 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 jurisdications and less 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.
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, (eg, using PGP or S/MIME).
- Encryption and/or authentication of documents, (e.g., the XMLDSIG standard if documents are encoded as XML).
- Authentication of users to applications, (e.g., smart card logon, and client authentication with SSL).
- Bootstrapping secure communication protocols, such as 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.
A few PKI implementations
Some leading certificate authorities, e.g. VeriSign, are not listed, since their software is not available to others.
- Entrust
- RSA Security
- Microsoft
- Betrusted (acquired the Baltimore UniCERT product in early 2004)
- OpenCA
- Computer Associates eTrust PKI
See also
External links
A detailed explanation of PKI Privacy, Authentication, Integrity and Non-repudiation (PAIN) can be found at: PAIN