Technical Terms and Abbreviations Glossary: P
PFS, PGP, Pretty URL
(abbr.): Perfect Forward Secrecy. In cryptography, forward secrecy (FS), also known as perfect forward secrecy (PFS), is a feature of specific key agreement protocols that gives assurances that session keys will not be compromised even if long-term secrets used in the session key exchange are compromised. For HTTPS the long-term secret is typically the private signing key of the server. Forward secrecy protects past sessions against future compromises of keys or passwords. By generating a unique session key for every session a user initiates, the compromise of a single session key will not affect any data other than that exchanged in the specific session protected by that particular key. This by itself is not sufficient for forward secrecy which additionally requires that a long-term secret compromise does not affect the security of past session keys.
Forward secrecy protects data on the transport layer of a network that uses common SSL/TLS protocols, including OpenSSL, when its long-term secret keys are compromised, as with the Heartbleed security bug. If forward secrecy is used, encrypted communications and sessions recorded in the past cannot be retrieved and decrypted should long-term secret keys or passwords be compromised in the future, even if the adversary actively interfered, for example via a man-in-the-middle attack.
The value of forward secrecy is that it protects past communication. This reduces the motivation for attackers to compromise keys. For instance, if an attacker learns a long-term key, but the compromise is detected and the long-term key is revoked and updated, relatively little information is leaked in a forward secure system.
The value of forward secrecy depends on the assumed capabilities of an adversary. Forward secrecy has value if an adversary is assumed to be able to obtain secret keys from a device (read access) but is either detected or unable to modify the way session keys are generated in the device (full compromise). In some cases an adversary who can read long-term keys from a device may also be able to modify the functioning of the session key generator, as in the backdoored Dual Elliptic Curve Deterministic Random Bit Generator. If an adversay can make the random number generator predictable past traffic will be protected but all future traffic will be compromised.
The value of forward secrecy is limited not only by the assumption that an adversary will attack a server by only stealing keys and not modifying the random number generator used by the server but it is also limited by the assumption that the adversary will only passively collect traffic on the communications link and not be active using a Man-in-the-Middle (MITM) attack. Forward secrecy typically uses an ephemeral Diffie-Hellman key exchange to prevent reading past traffic. The ephemeral Diffie-Hellman key exchange is often signed by the server using a static signing key. If an adversary can steal (or obtain through a court order) this static (long term) signing key, the adverary can masqerade as the server to the client and as the client to the server and implement a classic Man-in-the-Middle attack.
is an encryption program that provides cryptographic privacy and authentication for data communication. PGP is used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partitions and to increase the security of e-mail communications. Phil Zimmermann developed PGP in 1991.
also sometimes referred to as Clean URLs, RESTful URLs, user-friendly URLs, or search engine-friendly URLs, are Uniform Resource Locators (URLs) intended to improve the usability and accessibility of a website or web service by being immediately and intuitively meaningful to non-expert users. Such URL schemes tend to reflect the conceptual structure of a collection of information and decouple the user interface from a server's internal representation of information. Other reasons for using clean URLs include search engine optimization (SEO), conforming to the representational state transfer (REST) style of software architecture, and ensuring that individual web resources remain consistently at the same URL. This makes the World Wide Web a more stable and useful system, and allows more durable and reliable bookmarking of web resources.
Pretty URLs also do not contain implementation details of the underlying web application. This carries the benefit of reducing the difficulty of changing the implementation of the resource at a later date. For example, many URLs include the filename of a server-side script, such as example.php, example.asp or cgi-bin. If the underlying implementation of a resource is changed, such URLs would need to change along with it. Likewise, when URLs are not "clean", if the site database is moved or restructured it has the potential to cause broken links, both internally and from external sites, the latter of which can lead to removal from search engine listings. The use of clean URLs presents a consistent location for resources to user-agents regardless of internal structure. A further potential benefit to the use of clean URLs is that the concealment of internal server or application information can improve the security of a system.
Eh? What? Didn't you get it? Here again in simple language:
My personal short explanation for Pretty URL: easy-to-remember web address as «talking name» like these: