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71-481: S/MIME provides the following cryptographic security services for electronic messaging applications: S/MIME specifies the MIME type application/pkcs7-mime (smime-type "enveloped-data") for data enveloping (encrypting) where the whole (prepared) MIME entity to be enveloped is encrypted and packed into an object which subsequently is inserted into an application/pkcs7-mime MIME entity. Before S/MIME can be used in any of

142-417: A key ceremony when generating signing keys, in order to ensure that the keys are not tampered with or copied. The critical weakness in the way that the current X.509 scheme is implemented is that any CA trusted by a particular party can then issue certificates for any domain they choose. Such certificates will be accepted as valid by the trusting party whether they are legitimate and authorized or not. This

213-462: A CA are server supervisors who call for a certificate that their servers will bestow to users. Commercial CAs charge money to issue certificates, and their customers anticipate the CA's certificate to be contained within the majority of web browsers, so that safe connections to the certified servers work efficiently out-of-the-box. The quantity of internet browsers, other devices and applications which trust

284-517: A California nonprofit recognized as federally tax-exempt. According to Netcraft in May 2015, the industry standard for monitoring active TLS certificates, "Although the global [TLS] ecosystem is competitive, it is dominated by a handful of major CAs — three certificate authorities (Symantec, Comodo, GoDaddy) account for three-quarters of all issued [TLS] certificates on public-facing web servers. The top spot has been held by Symantec (or VeriSign before it

355-420: A certificate that claims to represent Alice. That is, the certificate would publicly state that it represents Alice, and might include other information about Alice. Some of the information about Alice, such as her employer name, might be true, increasing the certificate's credibility. Eve, however, would have the all-important private key associated with the certificate. Eve could then use the certificate to send

426-600: A certificate which can in turn be used by external relying parties. Notaries are required in some cases to personally know the party whose signature is being notarized; this is a higher standard than is reached by many CAs. According to the American Bar Association outline on Online Transaction Management the primary points of US Federal and State statutes enacted regarding digital signatures has been to "prevent conflicting and overly burdensome local regulation and to establish that electronic writings satisfy

497-430: A communication trusts this organization (and knows its public key). When the user's web browser receives the public key from www.bank.example it also receives a digital signature of the key (with some more information, in a so-called X.509 certificate). The browser already possesses the public key of the CA and consequently can verify the signature, trust the certificate and the public key in it: since www.bank.example uses

568-443: A digitally signed email to Bob, tricking Bob into believing that the email was from Alice. Bob might even respond with encrypted email, believing that it could only be read by Alice, when Eve is actually able to decrypt it using the private key. A notable case of CA subversion like this occurred in 2001, when the certificate authority VeriSign issued two certificates to a person claiming to represent Microsoft. The certificates have

639-504: A domain validated certificate for the victim domain, and deploy it during an attack; if that occurred, the difference observable to the victim user would be the absence of a green bar with the company name. There is some question as to whether users would be likely to recognise this absence as indicative of an attack being in progress: a test using Internet Explorer 7 in 2009 showed that the absence of IE7's EV warnings were not noticed by users, however Microsoft's current browser, Edge , shows

710-486: A group of companies and nonprofit organizations, including the Electronic Frontier Foundation , Mozilla, Cisco, and Akamai, announced Let's Encrypt , a nonprofit certificate authority that provides free domain validated X.509 certificates as well as software to enable installation and maintenance of certificates. Let's Encrypt is operated by the newly formed Internet Security Research Group ,

781-517: A hierarchy or mesh of CAs and CA certificates. A certificate may be revoked before it expires, which signals that it is no longer valid. Without revocation, an attacker would be able to exploit such a compromised or misissued certificate until expiry. Hence, revocation is an important part of a public key infrastructure . Revocation is performed by the issuing CA, which produces a cryptographically authenticated statement of revocation. For distributing revocation information to clients, timeliness of

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852-478: A key exchange protocol can be enciphered with the bank's public key in such a way that only the bank server has the private key to read them. The rest of the communication then proceeds using the new (disposable) symmetric key, so when the user enters some information to the bank's page and submits the page (sends the information back to the bank) then the data the user has entered to the page will be encrypted by their web browser. Therefore, even if someone can access

923-487: A key, but generally prevent extraction of that key with both physical and software controls. CAs typically take the further precaution of keeping the key for their long-term root certificates in an HSM that is kept offline , except when it is needed to sign shorter-lived intermediate certificates. The intermediate certificates, stored in an online HSM, can do the day-to-day work of signing end-entity certificates and keeping revocation information up to date. CAs sometimes use

994-629: A minimum, is mandatory to uphold the integrity of the public key infrastructure. In 2020, the S/MIME Certificate Working Group of the CA/Browser Forum was chartered to create a baseline requirement applicable to CAs that issue S/MIME certificates used to sign, verify, encrypt, and decrypt email. That effort is intended to create standards including: Version 1 of the Baseline Requirements for

1065-459: A more rigorous alternative to domain validated certificates. Extended validation is intended to verify not only control of a domain name, but additional identity information to be included in the certificate. Some browsers display this additional identity information in a green box in the URL bar. One limitation of EV as a solution to the weaknesses of domain validation is that attackers could still obtain

1136-1122: A particular certificate authority is referred to as ubiquity. Mozilla , which is a non-profit business, issues several commercial CA certificates with its products. While Mozilla developed their own policy, the CA/Browser Forum developed similar guidelines for CA trust. A single CA certificate may be shared among multiple CAs or their resellers . A root CA certificate may be the base to issue multiple intermediate CA certificates with varying validation requirements. In addition to commercial CAs, some non-profits issue publicly-trusted digital certificates without charge, for example Let's Encrypt . Some large cloud computing and web hosting companies are also publicly-trusted CAs and issue certificates to services hosted on their infrastructure, for example IBM Cloud , Amazon Web Services , Cloudflare , and Google Cloud Platform . Large organizations or government bodies may have their own PKIs ( public key infrastructure ), each containing their own CAs. Any site using self-signed certificates acts as its own CA. Commercial banks that issue EMV payment cards are governed by

1207-416: A public key that the certification authority certifies, a fake www.bank.example can only use the same public key. Since the fake www.bank.example does not know the corresponding private key, it cannot create the signature needed to verify its authenticity. It is difficult to assure correctness of match between data and entity when the data are presented to the CA (perhaps over an electronic network), and when

1278-473: A significantly greater difference between EV and domain validated certificates, with domain validated certificates having a hollow, grey lock. Domain validation suffers from certain structural security limitations. In particular, it is always vulnerable to attacks that allow an adversary to observe the domain validation probes that CAs send. These can include attacks against the DNS, TCP, or BGP protocols (which lack

1349-454: A source of security vulnerabilities. In one instance, security researchers showed that attackers could obtain certificates for webmail sites because a CA was willing to use an email address like ssladmin@domain.com for domain.com, but not all webmail systems had reserved the "ssladmin" username to prevent attackers from registering it. Prior to 2011, there was no standard list of email addresses that could be used for domain validation, so it

1420-565: A trusted root by a web browser or operating system. As of 24 August 2020 , 147 root certificates, representing 52 organizations, are trusted in the Mozilla Firefox web browser, 168 root certificates, representing 60 organizations, are trusted by macOS , and 255 root certificates, representing 101 organizations, are trusted by Microsoft Windows . As of Android 4.2 (Jelly Bean), Android currently contains over 100 CAs that are updated with each release. On November 18, 2014,

1491-425: A valid certificate issued by a Microsoft Terminal Server licensing certificate that used the broken MD5 hash algorithm. The authors thus was able to conduct a collision attack with the hash listed in the certificate. In 2015, a Chinese certificate authority named MCS Holdings and affiliated with China's central domain registry issued unauthorized certificates for Google domains. Google thus removed both MCS and

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1562-499: Is a serious shortcoming given that the most commonly encountered technology employing X.509 and trusted third parties is the HTTPS protocol. As all major web browsers are distributed to their end-users pre-configured with a list of trusted CAs that numbers in the dozens this means that any one of these pre-approved trusted CAs can issue a valid certificate for any domain whatsoever. The industry response to this has been muted. Given that

1633-511: Is commonly referred to as a man-in-the-middle attack . The client uses the CA certificate to authenticate the CA signature on the server certificate, as part of the authorizations before launching a secure connection. Usually, client software—for example, browsers—include a set of trusted CA certificates. This makes sense, as many users need to trust their client software. A malicious or compromised client can skip any security check and still fool its users into believing otherwise. The clients of

1704-578: Is evidence that the fraudulent DigiNotar certificates were used in a man-in-the-middle attack in Iran. In 2012, it became known that Trustwave issued a subordinate root certificate that was used for transparent traffic management (man-in-the-middle) which effectively permitted an enterprise to sniff SSL internal network traffic using the subordinate certificate. In 2012, the Flame malware (also known as SkyWiper) contained modules that had an MD5 collision with

1775-445: Is less error-prone importing and trusting the CA issued, rather than confirm a security exemption each time the server's certificate is renewed. Less often, trustworthy certificates are used for encrypting or signing messages. CAs dispense end-user certificates too, which can be used with S/MIME . However, encryption entails the receiver's public key and, since authors and receivers of encrypted messages, apparently, know one another,

1846-472: Is necessary so the message can be encrypted for both, recipient and sender, and a copy of the message can be kept (in the sent folder) and be readable for the sender. A typical basic ("class 1") personal certificate verifies the owner's "identity" only insofar as it declares that the sender is the owner of the "From:" email address in the sense that the sender can receive email sent to that address, and so merely proves that an email received really did come from

1917-655: Is the world's largest high-assurance certificate authority, commanding 60% of the Extended Validation Certificate market, and 96% of organization-validated certificates globally. As of July 2024 the survey company W3Techs, which collects statistics on certificate authority usage among the Alexa top 10 million and the Tranco top 1 million websites, lists the six largest authorities by absolute usage share as below. The commercial CAs that issue

1988-460: The certificate transparency initiative proposes auditing all certificates in a public unforgeable log, which could help in the prevention of phishing . In large-scale deployments, Alice may not be familiar with Bob's certificate authority (perhaps they each have a different CA server), so Bob's certificate may also include his CA's public key signed by a different CA 2 , which is presumably recognizable by Alice. This process typically leads to

2059-412: The Electronic Frontier Foundation (EFF) recommended to stop using any PGP plugins in email programs even though the vulnerability does not directly relate to PGP but to the configuration of an email program. A coordinated publication was originally scheduled for the 15 May. The EFF was criticized for ignoring this by various parties. As a consequence of this, Robert Hansen recommended to establish

2130-412: The email encryption systems OpenPGP and S/MIME . An attacker needs access to the attacked email message in its encrypted form, as well as the ability to send an email to at least one regular recipient of this original email. To exploit the security gap, the attacker modifies the encrypted email, causing the recipient's email program to send the decrypted content of the email to the attacker. To access

2201-427: The "From:" address given. It does not verify the person's name or business name. If a sender wishes to enable email recipients to verify the sender's identity in the sense that a received certificate name carries the sender's name or an organization's name, the sender needs to obtain a certificate ("class 2") from a CA, who carries out a more in-depth identity verification process, and this involves making inquiries about

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2272-401: The (encrypted) data that was communicated from the user to www.bank.example, such eavesdropper cannot read or decipher it. This mechanism is only safe if the user can be sure that it is the bank that they see in their web browser. If the user types in www.bank.example, but their communication is hijacked and a fake website (that pretends to be the bank website) sends the page information back to

2343-407: The Baseline Requirements, a list of policies and technical requirements for CAs to follow. These are a requirement for inclusion in the certificate stores of Firefox and Safari. If the CA can be subverted, then the security of the entire system is lost, potentially subverting all the entities that trust the compromised CA. For example, suppose an attacker, Eve, manages to get a CA to issue to her

2414-490: The CA, certify that". If the user trusts the CA and can verify the CA's signature, then they can also assume that a certain public key does indeed belong to whoever is identified in the certificate. Public-key cryptography can be used to encrypt data communicated between two parties. This can typically happen when a user logs on to any site that implements the HTTP Secure protocol. In this example let us suppose that

2485-621: The EMV Certificate Authority, payment schemes that route payment transactions initiated at Point of Sale Terminals ( POS ) to a Card Issuing Bank to transfer the funds from the card holder's bank account to the payment recipient's bank account. Each payment card presents along with its card data also the Card Issuer Certificate to the POS. The Issuer Certificate is signed by EMV CA Certificate. The POS retrieves

2556-554: The Issuance and Management of Publicly‐Trusted S/MIME Certificates was published on January 1, 2023 by the CA/Browser Forum. It defined four types of S/MIME certificate standards. Mailbox‐validated, Organization‐validated, Sponsor‐validated and Individual‐validated. Any message that an S/MIME email client stores encrypted cannot be decrypted if the applicable key pair's private key is unavailable or otherwise unusable (e.g.,

2627-527: The World Wide Web. Another common use is in issuing identity cards by national governments for use in electronically signing documents. Trusted certificates can be used to create secure connections to a server via the Internet. A certificate is essential in order to circumvent a malicious party which happens to be on the route to a target server which acts as if it were the target. Such a scenario

2698-432: The above applications, one must obtain and install an individual key/certificate either from one's in-house certificate authority (CA) or from a public CA. The accepted best practice is to use separate private keys (and associated certificates) for signature and for encryption, as this permits escrow of the encryption key without compromise to the non-repudiation property of the signature key. Encryption requires having

2769-471: The bulk of certificates for HTTPS servers typically use a technique called " domain validation " to authenticate the recipient of the certificate. The techniques used for domain validation vary between CAs, but in general domain validation techniques are meant to prove that the certificate applicant controls a given domain name , not any information about the applicant's identity. Many Certificate Authorities also offer Extended Validation (EV) certificates as

2840-430: The certificate belongs to the person, organization, server or other entity noted in the certificate. A CA's obligation in such schemes is to verify an applicant's credentials, so that users and relying parties can trust the information in the issued certificate. CAs use a variety of standards and tests to do so. In essence, the certificate authority is responsible for saying "yes, this person is who they say they are, and we,

2911-505: The certificate has been deleted or lost or the private key's password has been forgotten). However, an expired, revoked, or untrusted certificate will remain usable for cryptographic purposes. Indexing of encrypted messages' clear text may not be possible with all email clients. Neither of these potential dilemmas is specific to S/MIME but rather cipher text in general and do not apply to S/MIME messages that are only signed and not encrypted. S/MIME signatures are usually "detached signatures":

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2982-690: The contents of a browser's pre-configured trusted CA list is determined independently by the party that is distributing or causing to be installed the browser application there is really nothing that the CAs themselves can do. This issue is the driving impetus behind the development of the DNS-based Authentication of Named Entities (DANE) protocol. If adopted in conjunction with Domain Name System Security Extensions (DNSSEC) DANE will greatly reduce if not eliminate

3053-596: The cost of revocation checks and the availability impact from potentially-unreliable remote services, Web browsers limit the revocation checks they will perform, and will fail-soft where they do. Certificate revocation lists are too bandwidth-costly for routine use, and the Online Certificate Status Protocol presents connection latency and privacy issues. Other schemes have been proposed but have not yet been successfully deployed to enable fail-hard checking. The CA/Browser Forum publishes

3124-404: The credentials of the person/company/program asking for a certificate are likewise presented. This is why commercial CAs often use a combination of authentication techniques including leveraging government bureaus, the payment infrastructure, third parties' databases and services, and custom heuristics. In some enterprise systems, local forms of authentication such as Kerberos can be used to obtain

3195-436: The cryptographic protections of TLS/SSL), or the compromise of routers. Such attacks are possible either on the network near a CA, or near the victim domain itself. One of the most common domain validation techniques involves sending an email containing an authentication token or link to an email address that is likely to be administratively responsible for the domain. This could be the technical contact email address listed in

3266-411: The decrypted content of an encrypted email, the attacker modifies the email to be attacked to contain text prepared by the attacker in a specific way. The attacker then sends the changed email to one of the regular recipients. The attacker inserts additional text before and after the encrypted text in the encrypted email, thereby changing the message so that a multipart/mixed (MIME) message is created and

3337-497: The decrypted content of the email in the src= attribute of the <img> tag and is passed by the email program as URL to the web server attacker.chosen.url controlled by the attacker, when this content is requested. The attacker can now retrieve the content of the encrypted message from its web server logs. In a variant of the attack, the attacker uses a vulnerability in the CBC (S/MIME) and CFB (OpenPGP) operating modes of

3408-493: The destination party's certificate on store (which is typically automatic upon receiving a message from the party with a valid signing certificate). While it is technically possible to send a message encrypted (using the destination party certificate) without having one's own certificate to digitally sign, in practice, the S/MIME clients will require the user to install their own certificate before they allow encrypting to others. This

3479-491: The discovery of revocation (and hence the window for an attacker to exploit a compromised certificate) trades off against resource usage in querying revocation statuses and privacy concerns. If revocation information is unavailable (either due to accident or an attack), clients must decide whether to fail-hard and treat a certificate as if it is revoked (and so degrade availability ) or to fail-soft and treat it as unrevoked (and allow attackers to sidestep revocation). Due to

3550-482: The domain's WHOIS entry, or an administrative email like admin@ , administrator@ , webmaster@ , hostmaster@ or postmaster@ the domain. Some Certificate Authorities may accept confirmation using root@ , info@ , or support@ in the domain. The theory behind domain validation is that only the legitimate owner of a domain would be able to read emails sent to these administrative addresses. Domain validation implementations have sometimes been

3621-427: The encrypted part of the message appears together with the limit marks of the MIME message as a parameter value of an HTML tag. Example of a modified S/MIME mail: The email client first breaks down the multipart message into its individual parts using the --BOUNDARY tag and then decrypts the encrypted parts. It then reassembles the multipart message, and receives the message in this way: This message now contains

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3692-478: The encryption algorithms used. This allows him to change the ciphertext by inserting gadgets . As a side effect of this manipulation, the originally contained plain text becomes illegible. If this was known, the attacker can correct this by inserting additional gadgets. The attacker can hide unknown plain text by inserting certain HTML tags . The result is a message with a similar structure as described above. Since

3763-517: The market for globally trusted TLS/SSL server certificates is largely held by a small number of multinational companies. This market has significant barriers to entry due to the technical requirements. While not legally required, new providers may choose to undergo annual security audits (such as WebTrust for certificate authorities in North America and ETSI in Europe ) to be included as

3834-525: The name "Microsoft Corporation", so they could be used to spoof someone into believing that updates to Microsoft software came from Microsoft when they actually did not. The fraud was detected in early 2001. Microsoft and VeriSign took steps to limit the impact of the problem. In 2008, Comodo reseller Certstar sold a certificate for mozilla.com to Eddy Nigg, who had no authority to represent Mozilla. In 2011 fraudulent certificates were obtained from Comodo and DigiNotar , allegedly by Iranian hackers. There

3905-462: The private key that corresponds to the certified public key. A CA acts as a trusted third party—trusted both by the subject (owner) of the certificate and by the party relying upon the certificate. The format of these certificates is specified by the X.509 or EMV standard. One particularly common use for certificate authorities is to sign certificates used in HTTPS , the secure browsing protocol for

3976-507: The public key of EMV CA from its storage, validates the Issuer Certificate and authenticity of the payment card before sending the payment request to the payment scheme. Browsers and other clients of sorts characteristically allow users to add or do away with CA certificates at will. While server certificates regularly last for a relatively short period, CA certificates are further extended, so, for repeatedly visited servers, it

4047-617: The role of trusted third parties in a domain's PKI. EFAIL Efail , also written EFAIL , is a security hole in email systems with which content can be transmitted in encrypted form. This gap allows attackers to access the decrypted content of an email if it contains active content like HTML or JavaScript , or if loading of external content has been enabled in the client. Affected email clients include Gmail , Apple Mail , and Microsoft Outlook . Two related Common Vulnerabilities and Exposures IDs, CVE - 2017-17688 and CVE- 2017-17689 , have been issued. The security gap

4118-465: The root certificate authority from Chrome and have revoked the certificates. An attacker who steals a certificate authority's private keys is able to forge certificates as if they were CA, without needed ongoing access to the CA's systems. Key theft is therefore one of the main risks certificate authorities defend against. Publicly trusted CAs almost always store their keys on a hardware security module (HSM), which allows them to sign certificates with

4189-437: The security considerations section of RFC   8551 . 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. This allows others (relying parties) to rely upon signatures or on assertions made about

4260-406: The signature information is separate from the text being signed. The MIME type for this is multipart/signed with the second part having a MIME subtype of application/(x-)pkcs7-signature . Mailing list software is notorious for changing the textual part of a message and thereby invalidating the signature; however, this problem is not specific to S/MIME, and a digital signature only reveals that

4331-399: The signed content has been changed. On May 13, 2018, the Electronic Frontier Foundation (EFF) announced critical vulnerabilities in S/MIME, together with an obsolete form of PGP that is still used, in many email clients. Dubbed EFAIL , the bug required significant coordinated effort by many email client vendors to fix. Mitigations for both Efail vulnerabilities have since been addressed in

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4402-523: The traditional requirements associated with paper documents." Further the US E-Sign statute and the suggested UETA code help ensure that: Despite the security measures undertaken to correctly verify the identities of people and companies, there is a risk of a single CA issuing a bogus certificate to an imposter. It is also possible to register individuals and companies with the same or very similar names, which may lead to confusion. To minimize this hazard,

4473-461: The usefulness of a trusted third party remains confined to the signature verification of messages sent to public mailing lists. Worldwide, the certificate authority business is fragmented, with national or regional providers dominating their home market. This is because many uses of digital certificates, such as for legally binding digital signatures, are linked to local law, regulations, and accreditation schemes for certificate authorities. However,

4544-413: The user logs on to their bank's homepage www.bank.example to do online banking. When the user opens www.bank.example homepage, they receive a public key along with all the data that their web-browser displays. The public key could be used to encrypt data from the client to the server but the safe procedure is to use it in a protocol that determines a temporary shared symmetric encryption key; messages in such

4615-453: The user's browser, the fake web-page can send a fake public key to the user (for which the fake site owns a matching private key). The user will fill the form with their personal data and will submit the page. The fake web-page will then get access to the user's data. This is what the certificate authority mechanism is intended to prevent. A certificate authority (CA) is an organization that stores public keys and their owners, and every party in

4686-433: The vulnerability is directed against the content of the email and not against the recipient, it is necessary that all recipients implement the countermeasures. These include: To what extent even the senders of encrypted content can reduce the vulnerability, e.g. by electronic signatures or the limitation to a subset of MIME formats, has not yet been conclusively clarified. Announcing the security vulnerability on 13 May 2018

4757-438: The would-be certificate holder. For more detail on authentication, see digital signature . Depending on the policy of the CA, the certificate and all its contents may be posted publicly for reference and verification. This makes the name and email address available for all to see and possibly search for. Other CAs only post serial numbers and revocation status, which does not include any of the personal information. The latter, at

4828-420: Was able to obtain a domain-validated certificate for live.fi, despite not being the owner of the domain name. A CA issues digital certificates that contain a public key and the identity of the owner. The matching private key is not made available publicly, but kept secret by the end user who generated the key pair. The certificate is also a confirmation or validation by the CA that the public key contained in

4899-534: Was made public on 13 May 2018 by Damian Poddebniak, Christian Dresen, Jens Müller, Fabian Ising, Sebastian Schinzel, Simon Friedberger, Juraj Somorovsky and Jörg Schwenk as part of a contribution to the 27th USENIX Security Symposium, Baltimore, August 2018. As a result of the vulnerability, the content of an attacked encrypted email can be transmitted to the attacker in plain text by a vulnerable email client. The used encryption keys are not disclosed. The security gap concerns many common email programs when used with

4970-591: Was not clear to email administrators which addresses needed to be reserved. The first version of the CA/Browser Forum Baseline Requirements, adopted November 2011, specified a list of such addresses. This allowed mail hosts to reserve those addresses for administrative use, though such precautions are still not universal. In January 2015, a Finnish man registered the username "hostmaster" at the Finnish version of Microsoft Live and

5041-406: Was purchased by Symantec) ever since [our] survey began, with it currently accounting for just under a third of all certificates. To illustrate the effect of differing methodologies, amongst the million busiest sites Symantec issued 44% of the valid, trusted certificates in use — significantly more than its overall market share." In 2020, according to independent survey company Netcraft , "DigiCert

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