Web Of Trust
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cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...
, a web of trust is a concept used in
PGP PGP or Pgp may refer to: Science and technology * P-glycoprotein, a type of protein * Pelvic girdle pain, a pregnancy discomfort * Personal Genome Project, to sequence genomes and medical records * Pretty Good Privacy, a computer program for the ...
,
GnuPG GNU Privacy Guard (GnuPG or GPG) is a free-software replacement for Symantec's PGP cryptographic software suite. The software is compliant with RFC 4880, the IETF standards-track specification of OpenPGP. Modern versions of PGP are interoperabl ...
, and other
OpenPGP Pretty Good Privacy (PGP) 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 partiti ...
-compatible systems to establish the
authenticity Authenticity or authentic may refer to: * Authentication, the act of confirming the truth of an attribute Arts and entertainment * Authenticity in art, ways in which a work of art or an artistic performance may be considered authentic Music * A ...
of the binding between a
public key Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic al ...
and its owner. Its decentralized trust model is an alternative to the centralized trust model of a public key infrastructure (PKI), which relies exclusively on a
certificate authority In cryptography, a certificate authority or certification authority (CA) is an entity that stores, signs, and issues digital certificates. A digital certificate certifies the ownership of a public key by the named subject of the certificate. Thi ...
(or a hierarchy of such). As with computer networks, there are many independent webs of trust, and any user (through their
public key certificate In cryptography, a public key certificate, also known as a digital certificate or identity certificate, is an electronic document used to prove the validity of a public key. The certificate includes information about the key, information about the ...
) can be a part of, and a link between, multiple webs. The web of trust concept was first put forth by PGP creator
Phil Zimmermann Philip R. Zimmermann (born 1954) is an American computer scientist and Cryptography, cryptographer. He is the creator of Pretty Good Privacy (PGP), the most widely used email encryption software in the world. He is also known for his work in VoI ...
in 1992 in the manual for PGP version 2.0: Note the use of the word
emergence In philosophy, systems theory, science, and art, emergence occurs when an entity is observed to have properties its parts do not have on their own, properties or behaviors that emerge only when the parts interact in a wider whole. Emergence ...
in this context. The web of trust makes use of the concept of emergence.


Operation of a web of trust

All OpenPGP-compliant implementations include a certificate
vetting Vetting is the process of performing a background check on someone before offering them employment, conferring an award, or doing fact-checking prior to making any decision. In addition, in intelligence gathering, assets are vetted to determine th ...
scheme to assist with this; its operation has been termed a web of trust. OpenPGP certificates (which include one or more public keys along with owner information) can be digitally signed by other users who, by that act, endorse the association of that public key with the person or entity listed in the certificate. This is commonly done at
key signing parties In public-key cryptography, a key signing party is an event at which people present their public keys to others in person, who, if they are confident the key actually belongs to the person who claims it, digitally sign the certificate containin ...
. OpenPGP-compliant implementations also include a vote counting scheme which can be used to determine which public key – owner association a user will trust while using PGP. For instance, if three partially trusted endorsers have vouched for a certificate (and so its included public key – owner binding), or if one fully trusted endorser has done so, the association between owner and public key in that certificate will be trusted to be correct. The parameters are user-adjustable (e.g., no partials at all, or perhaps six partials) and can be completely bypassed if desired. The scheme is flexible, unlike most public key infrastructure designs, and leaves trust decisions in the hands of individual users. It is not perfect and requires both caution and intelligent supervision by users. Essentially all PKI designs are less flexible and require users to follow the trust endorsement of the PKI generated, certificate authority (CA)-signed, certificates.


Simplified explanation

There are two keys pertaining to a person: a public key which is shared openly and a private key that is withheld by the owner. The owner's private key will decrypt any information encrypted with its public key. In the web of trust, each user has a key ring with other people's public keys. Senders encrypt their information with the recipient's public key, and only the recipient's private key will decrypt it. Each sender then digitally signs the encrypted information with their private key. When the recipient verifies the received encrypted information against the sender's public key, they can confirm that it is from the sender. Doing this will ensure that the encrypted information came from the specific user and has not been tampered with, and only the intended recipient can decrypt the information (because only they know their private key).


Contrast with typical PKI

Unlike WOT, a typical
X.509 In cryptography, X.509 is an International Telecommunication Union (ITU) standard defining the format of public key certificates. X.509 certificates are used in many Internet protocols, including TLS/SSL, which is the basis for HTTPS, the secu ...
PKI enables each certificate to be signed by a single party: a
certificate authority In cryptography, a certificate authority or certification authority (CA) is an entity that stores, signs, and issues digital certificates. A digital certificate certifies the ownership of a public key by the named subject of the certificate. Thi ...
(CA). The CA's certificate may itself be signed by a different CA, all the way up to a 'self-signed'
root certificate In cryptography and computer security, a root certificate is a public key certificate that identifies a root certificate authority (CA). Root certificates are self-signed (and it is possible for a certificate to have multiple trust paths, say if ...
. Root certificates must be available to those who use a lower-level CA certificate and so are typically distributed widely. They are for instance, distributed with such applications as browsers and email clients. In this way SSL/TLS-protected Web pages, email messages, etc. can be authenticated without requiring users to manually install root certificates. Applications commonly include over one hundred root certificates from dozens of PKIs, thus by default bestowing trust throughout the hierarchy of certificates which lead back to them. WOT favors the decentralization of trust anchors to prevent a single point of failure from compromising the CA hierarchy. A notable project that uses WOT against PKI to provide a framework for authentication in other areas of Internet is Monkeysphere utilities.


Problems


Loss of private keys

The OpenPGP web of trust is essentially unaffected by such things as company failures, and has continued to function with little change. However, a related problem does occur: users, whether individuals or organizations, who lose track of a private key can no longer decrypt messages sent to them produced using the matching public key found in an OpenPGP certificate. Early PGP certificates did not include expiry dates, and those certificates had unlimited lives. Users had to prepare a signed cancellation certificate against the time when the matching private key was lost or compromised. One very prominent cryptographer is still getting messages encrypted using a public key for which he long ago lost track of the private key. They can't do much with those messages except discard them after notifying the sender that they were unreadable and requesting resending with a public key for which they still have the matching private key. Later PGP, and all OpenPGP compliant certificates include expiry dates which automatically preclude such troubles (eventually) when used sensibly. This problem can also be easily avoided by the use of "designated revokers", which were introduced in the early 1990s. A key owner may designate a third party that has permission to revoke the key owner's key (in case the key owner loses his own private key and thus loses the ability to revoke his own public key).


Public key authenticity check

A non-technical, social difficulty with a Web of Trust like the one built into PGP/OpenPGP type systems is that every web of trust without a central controller (e.g., a CA) depends on other users for trust. Those with new certificates (i.e., produced in the process of generating a new key pair) will not likely be readily trusted by other users' systems, that is by those they have not personally met, until they find enough endorsements for the new certificate. This is because many other Web of Trust users will have their certificate vetting set to require one or more fully trusted endorsers of an otherwise unknown certificate (or perhaps several partial endorsers) before using the public key in that certificate to prepare messages, believe signatures, etc. Despite the wide use of OpenPGP compliant systems and easy availability of on-line multiple key servers, it is possible in practice to be unable to readily find someone (or several people) to endorse a new certificate (e.g., by comparing physical identification to key owner information and then digitally signing the new certificate). Users in remote areas or undeveloped ones, for instance, may find other users scarce. And, if the other's certificate is also new (and with no or few endorsements from others), then its signature on any new certificate can offer only marginal benefit toward becoming trusted by still other parties' systems and so able to securely exchange messages with them.
Key signing parties In public-key cryptography, a key signing party is an event at which people present their public keys to others in person, who, if they are confident the key actually belongs to the person who claims it, digitally sign the certificate containin ...
are a relatively popular mechanism to resolve this problem of finding other users who can install one's certificate in existing webs of trust by endorsing it. Websites also exist to facilitate the location of other OpenPGP users to arrange keysignings. Th
Gossamer Spider Web of Trust
also makes key verification easier by linking OpenPGP users via a hierarchical style web of trust where end users can benefit by coincidental or determined trust of someone who is endorsed as an introducer, or by explicitly trusting GSWoT's top-level key minimally as a level 2 introducer (the top-level key endorses level 1 introducers). The possibility of finding chains of certificates is often justified by the "
small world phenomenon The small-world experiment comprised several experiments conducted by Stanley Milgram and other researchers examining the average path length for social networks of people in the United States. The research was groundbreaking in that it suggeste ...
": given two individuals, it is often possible to find a short chain of people between them such that each person in the chain knows the preceding and following links. However, such a chain is not necessarily useful: the person encrypting an email or verifying a signature not only has to find a chain of signatures from their private key to their correspondent's, but also to trust each person of the chain to be honest and competent about signing keys (that is, they have to judge whether these people are likely to honestly follow the guidelines about verifying the identity of people before signing keys). This is a much stronger constraint. Another obstacle is the requirement to physically meet with someone (for example, at a
key signing party In public-key cryptography, a key signing party is an event at which people present their public keys to others in person, who, if they are confident the key actually belongs to the person who claims it, digitally sign the certificate containing ...
) to verify their identity and ownership of a public key and email address, which may involve travel expenses and scheduling constraints affecting both sides. A software user may need to verify hundreds of software components produced by thousands of developers located around the world. As the general population of software users cannot meet in person with all software developers to establish direct trust, they must instead rely on the comparatively slower propagation of indirect trust. Obtaining the PGP/GPG key of an author (or developer, publisher, etc.) from a public key server also presents risks, since the key server is a third-party middle-man, itself vulnerable to abuse or attacks. To avoid this risk, an author can instead choose to publish their public key on their own key server (i.e., a web server accessible through a domain name owned by them, and securely located in their private office or home) and require the use of HKPS-encrypted connections for the transmission of their public key. For details, see
WOT Assisting Solutions Wot, WOT, WoT or wot may refer to: Acronyms * War on Terror * Weak operator topology in functional analysis * Web of trust, a mechanism for authenticating cryptographic keys * WOT Services, an online reputation service * ''The Wheel of Time'', ...
below.


Strong set

The strong set refers to the largest collection of
strongly connected In the mathematical theory of directed graphs, a graph is said to be strongly connected if every vertex is reachable from every other vertex. The strongly connected components of an arbitrary directed graph form a partition into subgraphs that ...
PGP PGP or Pgp may refer to: Science and technology * P-glycoprotein, a type of protein * Pelvic girdle pain, a pregnancy discomfort * Personal Genome Project, to sequence genomes and medical records * Pretty Good Privacy, a computer program for the ...
keys. This forms the basis for the global web of trust. Any two keys in the strong set have a path between them; while islands of sets of keys that only sign each other in a disconnected group can and do exist, only one member of that group needs to exchange signatures with the strong set for that group to also become a part of the strong set. The strong set had a size of about 55000 Keys at the beginning of the year 2015.


Mean shortest distance

In statistical analysis of the
PGP PGP or Pgp may refer to: Science and technology * P-glycoprotein, a type of protein * Pelvic girdle pain, a pregnancy discomfort * Personal Genome Project, to sequence genomes and medical records * Pretty Good Privacy, a computer program for the ...
/
GnuPG GNU Privacy Guard (GnuPG or GPG) is a free-software replacement for Symantec's PGP cryptographic software suite. The software is compliant with RFC 4880, the IETF standards-track specification of OpenPGP. Modern versions of PGP are interoperabl ...
/
OpenPGP Pretty Good Privacy (PGP) 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 partiti ...
Web of trust the mean shortest distance (MSD) is one measurement of how "trusted" a given PGP key is within the strongly connected set of PGP keys that make up the Web of trust. MSD has become a common metric for analysis of sets of PGP keys. Very often you will see the MSD being calculated for a given subset of keys and compared with the ''global MSD'' which generally refers to the keys ranking within one of the larger key analyses of the global Web of trust.


WOT assisting solutions

Physically meeting with original developer or author, is always the best way to obtain and distribute and verify and trust PGP/GPG Keys with highest trust level, and will remain as the best level of best trustworthy way. Publishing of GPG/PGP full Key or full Key fingerprint on/with widely known (physical/paper-material based) book, by the original author/developer, is the 2nd best form of sharing trustworthy key with and for users. Before meeting a developer or author, users should research on their own on the developer or author in book library and via internet, and aware of developer's or author's photo, work, pub-key fingerprint, email-address, etc. However, it is not practical for millions of users who want to communicate or message securely to physically meet with each recipient users, and it is also not practical for millions of software users who need to physically meet with hundreds of software developers or authors, whose software or file signing
PGP PGP or Pgp may refer to: Science and technology * P-glycoprotein, a type of protein * Pelvic girdle pain, a pregnancy discomfort * Personal Genome Project, to sequence genomes and medical records * Pretty Good Privacy, a computer program for the ...
/ GPG public Key they want to verify and trust and ultimately use in their computers. Therefore, one or more trusted third-party authority (TTPA) type of entity or group need to be available for users and be usable by users, and such entity/group need to be capable of providing trusted-
verification Verify or verification may refer to: General * Verification and validation, in engineering or quality management systems, is the act of reviewing, inspecting or testing, in order to establish and document that a product, service or system meets ...
or trust- delegation services for millions of users around the world, at any time. Practically, to verify any downloaded or received content or data or email or file's
authenticity Authenticity or authentic may refer to: * Authentication, the act of confirming the truth of an attribute Arts and entertainment * Authenticity in art, ways in which a work of art or an artistic performance may be considered authentic Music * A ...
, a user need to verify their downloaded main content or main data/email or main file's PGP/GPG
signature A signature (; from la, signare, "to sign") is a handwritten (and often stylized) depiction of someone's name, nickname, or even a simple "X" or other mark that a person writes on documents as a proof of identity and intent. The writer of a ...
code/file (ASC, SIG). So users would need to use original developer's or original author's trustworthy and verified public-key, or users would need to use trustworthy file-signing public-key trusted-by the original owner of that public-key. And to really trust a specific PGP/GPG key, users would need to physically meet with every specific original author or developer, or users would need to physically meet with the original-releaser of file-signing pub-key, or, users would need to find another alternative trustworthy user, who is in trusted-chain of WOT (aka, another user or another developer or another author, who is trusted by that very specific original author or developer), and then physically meet with that person, to verify their real ID with his/her PGP/GPG key (and also provide your own ID and key to the other user, so that both side can sign/certify and trust each other's PGP/GPG key). Whether a software is popular or not, software users are usually located around the world in different locations. It is physically not possible for an original author or developer or file-releaser to provide public-key or trust or ID verification services to millions of users. Neither is it practical for millions of software users to physically meet with each and every software or every software-library or every piece of code's developer or author or releaser, which they will (use or) need to use in their computers. Even with multiple trusted people/person (by original-author) in trusted-chain from WOT, its still not physically or practically possible for every developer or author to meet with every other users, and it is also not possible for every users to meet with hundreds of developers whose software they will be using or working on. When this decentralized hierarchy based WoT chain model will become popular and used by most nearby users, only then physical meeting and pub-key certify and sign procedure of WoT will be easier. A few solutions are: original author/developer need to first set a trust-level to sign/certify their own file-signing key. Then updated public-keys and updated file-signing public-keys must also have to be published and distributed (or made accessible) to users, via online secure and encrypted mediums, so that any user from any location in world, can get the correct and trusted and unmodified public-key. To make sure that each users are getting the correct and trusted public-keys and signed-code/file, original dev/author or original-releaser must publish their updated public-keys on their own key server and force HKPS encrypted connection usage, or publish their updated and full public-keys (and signed-code/file) on their own
HTTPS Hypertext Transfer Protocol Secure (HTTPS) is an extension of the Hypertext Transfer Protocol (HTTP). It is used for secure communication over a computer network, and is widely used on the Internet. In HTTPS, the communication protocol is enc ...
encrypted webpage, under their own web server, from their own primary domain website, (not-from any sub-domains which are located in external-servers, not-from any mirror, not-from any external/shared forum/wiki etc website servers, not-from any public or external/shared cloud or hosting service servers), and must have to be located and kept securely inside their own premises: own-home, own-home-office, or own-office. In that way, those small pieces of original keys/code, will travel intact through internet and will remain unmodified during transit (because of encrypted connection) and will reach destination without being eavesdropped or modified, into user's side, and can be treated as trustworthy public-keys because of single or multi channel TTPA based verification. When a public-key is obtained (from original developer's own web-server) via more than one
TTPA Alpha-tocopherol transfer protein (α-TTP) is a protein that in humans is encoded by the ''TTPA'' gene. See also * Familial isolated vitamin E deficiency Familial isolated vitamin E deficiency or Ataxia with vitamin E deficiency (AVED) is a rar ...
(trusted third party authority) based secured, verified and encrypted connection, then it is more trustworthy. When original public-keys/signed-codes are shown in original dev's or author's own web server or key server, over encrypted connection or encrypted webpage, then any other files, data or content can be transferred over any type of non-encrypted connection, like: HTTP/FTP etc from any sub-domain server or from any mirror or from any shared cloud/hosting servers, because, non-encrypted connection based downloaded items/data/files can be authenticated later, by using the original public-keys/signed-codes, which were obtained from the original author's/developer's own server over secured, encrypted, and trusted (aka, verified) connection/channels. Using encrypted connection to transfer keys or signed/signature code/files, allow software users to delegate their trust with a
PKI PKI may refer to: * Partai Komunis Indonesia, the Communist Party of Indonesia * Peter Kiewit Institute The Peter Kiewit Institute is a facility in Omaha, Nebraska, United States which houses academic programs from the University of Nebraska ...
TTPA Alpha-tocopherol transfer protein (α-TTP) is a protein that in humans is encoded by the ''TTPA'' gene. See also * Familial isolated vitamin E deficiency Familial isolated vitamin E deficiency or Ataxia with vitamin E deficiency (AVED) is a rar ...
(trusted third party authority), like public CA (Certificate Authority), to help in providing trusted connection in between the original developer/author's web server, and millions of worldwide users' computers, at any time. When the original author/developer's domain-name and name-server is signed by
DNSSEC The Domain Name System Security Extensions (DNSSEC) are a suite of extension specifications by the Internet Engineering Task Force (IETF) for securing data exchanged in the Domain Name System (DNS) in Internet Protocol (IP) networks. The protocol ...
, and when used SSL/TLS public certificate is declared/shown in TLSA/
DANE Dane or Danes may refer to: People Pertaining to Denmark * Dane, somebody from Denmark * Danes, an ethnic group native to Denmark * Danes (Germanic tribe) Other people * Dane (name), a surname and a given name (and a list of people with the nam ...
DNSSec DNS resource-record, (and when SSL/TLS Certs in the trust chain are pinned and used via HPKP technique by web servers), then a web-server's webpage or data can also be verified via another PKI
TTPA Alpha-tocopherol transfer protein (α-TTP) is a protein that in humans is encoded by the ''TTPA'' gene. See also * Familial isolated vitamin E deficiency Familial isolated vitamin E deficiency or Ataxia with vitamin E deficiency (AVED) is a rar ...
: DNSSEC and DNS namespace maintainer ICANN, other than a public CA. DNSSEC is another form of PGP/GPG WOT but for name-servers; it creates a trusted-chain for name-servers first (instead of people/person), and then people/person's PGP/GPG Keys and fingerprints can also be added into a server's DNSSEC DNS records. So any users who want to communicate securely (or any software users), can effectively get/receive their data/key/code/webpage etc. verified (aka, authenticated) via two (aka, dual/double) trusted PKI TTPAs/Channels at the same time: ICANN (DNSSEC) and CA ( SSL/TLS Certificate). So PGP/GPG key/signed-code data (or file) can be trusted, when such solutions and techniques are used: HKPS, HKPS+DNSSEC+DANE, HTTPS, HTTPS+HPKP or HTTPS+HPKP+DNSSEC+DANE. If a vast number of user's group create their own new
DLV The DLV (DataLog with Disjunction, where the logical disjunction symbol V is used) system is a disjunctive logic programming system, implementing the stable model semantics under the answer set programming paradigm. It extends the Datalog ...
based DNSSEC
registry Registry may refer to: Computing * Container registry, an operating-system-level virtualization registry * Domain name registry, a database of top-level internet domain names * Local Internet registry * Metadata registry, information system for re ...
, and if users use that new DLV (along with ICANN-DNSSEC) root-key in their own local DNSSEC-based DNS Resolver/Server, and if domain-owners also use it for additional signing of their own domain-names, then there can be a new third TTPA. In such case, any PGP/GPG Key/signed-code data or a webpage or web data can be three/triple-channel verified.
ISC #REDIRECT ISC {{redirect category shell, {{R from other capitalisation{{R from ambiguous page ...
's DLV itself can be used as a third TTPA as its still used widely and active, so availability of another new DLV will become fourth TTPA.


See also

*
Friend-to-friend A friend-to-friend (or F2F) computer network is a type of peer-to-peer network in which users only make direct connections with people they know. Passwords or digital signatures can be used for authentication. Unlike other kinds of private P2P ...
(F2F) computer network. *
Self-sovereign identity Self-sovereign identity (SSI) is an approach to digital identity that gives individuals control over the information they use to prove who they are to websites, services, and applications across the web. Without SSI, individuals with persistent ...
*
Thawte Thawte Consulting (pronounced "thought") is a certificate authority (CA) for X.509 certificates. Thawte was founded in 1995 by Mark Shuttleworth in South Africa. As of December 30, 2016, its then-parent company, Symantec Group, was collectivel ...
stopped signing OpenPGP keys many years ago and now only issues X.509 certificates. *
Virtual community A virtual community is a social network of individuals who connect through specific social media, potentially crossing geographical and political boundaries in order to pursue mutual interests or goals. Some of the most pervasive virtual communi ...


References


Further reading

*


External links


An explanation of the PGP Web of Trustanalysis of the ''strong set'' in the PGP web of trust
no longer maintained; last archived link from August 2020. {{DEFAULTSORT:Web Of Trust Key management Public key infrastructure OpenPGP Authentication Computational trust Identity management ja:公開鍵基盤#信用の輪(Web of Trust)