改善するing Authentication On The Internet
見解／翻訳／版 0.4 - 2005-05-12
Introduction
The 現在の system for 安全な・保証するing end-使用者 処理／取引s over the Internet consists of （警察などへの）密告，告訴（状） 移転 経由で HTTP over SSL, with 信用 設立するd using server-based 証明書s. The 構成要素s of this system need re-診察するing in the light of the 現在の 脅しs to Internet-based 商業.
脅し 分析
There are three classes of 脅し to 安全な・保証する 処理／取引s over the internet, which are within the domain of this paper. (脅しs such as server 妥協, company 従業員 dishonesty, trojaned （弁護士の）依頼人s and so on are outside its 範囲.) They are:
- Eavesdropping (someone is listening to my conversation)
- Impersonation (I'm not conversing with who I think I am)
- Scamming (I'm conversing with who I think I am, but they are dishonest)
The difference between impersonation and scamming is as follows. Impersonation is where I think I'm conversing with Barclays Bank, but 現実に I'm knowingly conversing with www.安全な・保証する-barclays.co.uk, who I assume are Barclays but are not. Scamming is where I am conversing with what appears to be a 合法的 organisation such as a 商売／仕事, but they misuse the （警察などへの）密告，告訴（状） I give them.
Is "scamming" the best word here? It needs to be 明確な／細部 enough not to 含む those items covered under impersonation, so words like "dishonesty", "詐欺" and so on don't work. "Misrepresentation"? "誤った pretences"?
現在の 脅しs
If we look at which of the 脅しs is most 流布している in May 2005, the answer is 明確に impersonation, in the form of "phishing". Phishing is the setting-up of 偽の websites 趣旨ing to be those of 存在するing 井戸／弁護士席-known （独立の）存在s, with the 目的（とする） of 収穫ing 価値のある （警察などへの）密告，告訴（状） such as bank login 詳細（に述べる）s or credit card numbers. The 存在 of the 300-member Anti Phishing Working Group is 証拠 of 産業 関心 over this 問題／発行する.
No-one is 割れ目ing the encryption on 安全な・保証する 関係s because the value of the data 安全な・保証するd by a 選び出す／独身 処理／取引 is 一般に far too low. This is ありそうもない to change; as 割れ目ing 金物類／武器類 gets cheaper, 重要な lengths get longer and 割れ目ing gets harder. But the 推論する／理由 that there are not so many コンビナート／複合体 scamming attacks is not technical but pragmatic - impersonation 作品, and it is so much easier and cheaper. As impersonation gets harder, scamming will rise.
Today, almost all phishing is 行為／行うd over 非，不，無-安全な・保証する channels, putting the combatting of it outside the 範囲 of the model. (That is to say, we have an important 仕事 to 運動 phishers の上に SSL, but that how to do it is outside the 範囲 of this paper.) However, as 使用者 認識／意識性 and education 改善するs, phishers will look to 追加する extra legitimacy to their 場所／位置s by 供給するing a "安全な・保証する" 関係 to better ape 合法的 場所／位置s. Then, the 脅しs of impersonation and scamming will start to 衝撃 the SSL model. It is useful to 診察する how 井戸／弁護士席 it 保護するs against these 脅しs.
Privacy, Validation and Authentication
To 戦闘 the three 指名するd 脅しs, the model must 供給する the に引き続いて 所有物／資産／財産s:
- Privacy - stopping people listening in - 戦闘s eavesdropping.
- (Domain) Validation - knowing that you are talking to www.good.com and not www.evil.com - 戦闘s impersonation.
- (場所／位置 操作者) Authentication - knowing that the police can find the owners of www.good.com if they turn out to be crooks - 戦闘s scamming.
For our 目的s, privacy from eavesdropping remains unchallenged. Privacy is 供給するd by encryption, and any variation is a 機能（する）／行事 of the strength of the encryption used. However, using high-grade encryption for all 処理／取引s is technically 平易な and financially 比較して 安価な. Notwithstanding the enormous 成果／努力s some go to for small successes, no-one 本気で argues that e.g. the 前進するd AES-256 algorithm can be broken by an eavesdropping 攻撃者.
Validation, at least of domain 支配（する）／統制する, is also not 現在／一般に an 問題／発行する. Assuming the method of 接触するing a domain owner is 安全な・保証する, domain validation can also be 供給するd with 親族 緩和する.
Authentication, on the other 手渡す, is much more of a continuum, because it 伴う／関わるs those tricky real-world 概念s of 身元, 信用, honesty and so on. It's also hard to 手段, and the methods for 確実にするing it change over time. Authentication is needed partly for 予防 (攻撃者s will be 気が進まない to 明らかにする／漏らす （警察などへの）密告，告訴（状） about themselves) and partly for after-the-fact accountability. As Bruce Schneier points out, we can never be 100% successful in 妨げるing attacks, and so enabling （犯罪，病気などの）発見 and 返答 need to be a part of the 解答.
I therefore 示唆する that privacy, validation and authentication are 関係のある as shown by the diagram to the 権利.
Normal web 関係s over HTTP have no privacy except that accidentally 供給するd by 網状組織 topology, no validation except for that 供給するd at domain 登録 or IP-発行 time, and no 重要な authentication. It therefore 落ちるs into the 最高の，を越す left square.
A 安全 model which 供給するd only privacy (底（に届く） left square) would be like SSH - when you connect to a 場所／位置 for the first time it 供給するs you with a 重要な 指紋. You then need to use 外部の means to make sure that 重要な 指紋 belongs to the person you think you are talking to. Only after that can you 保証（人） you are always talking to the same person. While this model has worked 井戸／弁護士席 in those areas where SSH is used, the 公正に／かなり obvious unlikelihood of millions of end-使用者s going through this 過程 for each 安全な・保証する 場所／位置 they visit means that it's not appropriate for SSL. The distinction between the 最高の，を越す left and 底（に届く） left squares is not 関連した to an end-使用者.
A model which 供給するd only validation (最高の，を越す 権利 square) would be one which made sure you were connected to the 場所／位置 you thought you were, but 許すd anyone to listen in. The use of 安全な・保証する DNS with HTTP is in this 部類.
A model which 供給するd only privacy and validation (底（に届く） 権利 square, base of arrow) would mean that you connect to a 場所／位置, and you are 確かな you've connected to that 場所／位置, but you have to use means 外部の to the SSL model to get authentication - i.e. to make sure the 場所／位置 is owned by who you think it is, and that the 場所／位置 owners are 信頼できる. Examples might be "Personal Computer World recommended them", "My brother bought something last month and it went 罰金", or a browser plugin from a 信用d provider which 言及／関連d a 名簿（に載せる）／表（にあげる） of 信用d 場所／位置s for you and showed its findings.
Privacy and validation are prerequistes for authentication. If you have no privacy, the 恐らく-authenticated （独立の）存在 could （人命などを）奪う，主張する "we were eavesdropped". If you have no validation, they could （人命などを）奪う，主張する "you weren't 現実に talking to me". Therefore, the authentication continuum is rooted only in the 底（に届く） 権利 square, and proceeds from there.
How 安全な・保証する 処理／取引s Work Now
The 現在の model 作品 as follows. Web browsers 含む a number of "root 証明書s", which belong to 証明書 当局 (CAs) and are 分配するd with '信用 bits' 始める，決める by default. Browser 製造業者s choose whose root 証明書s to 含む; their methods of choosing 変化させる. A number of 井戸／弁護士席-known CAs, such as Verisign and Geotrust, have their root 証明書s in all major browsers.
When someone comes to a CA with a request for a 証明書 ("cert") for a particular 場所／位置, they do some 立証 to check that the person asking is 許すd to have that 証明書. Validation is 供給するd by checking that the person asking for the 証明書 現実に 支配（する）／統制するs that domain. Beyond that, different levels of authentication can be reached by doing different sorts of checks. The 量 of authentication 変化させるs from CA to CA, and even between different 製品s of the same CA. After 立証, the CA uses its root 証明書 to 調印する a server 証明書 for that 場所／位置, and 手渡すs it over to the requestor.
The 手続きs of a CA, 含むing the 量 of 立証 done, are 始める，決める 負かす／撃墜する in a 文書 called the 証明書 Pratice 声明 (CPS), 利用できる from the CA's website. A CA's 同意／服従 with their CPS is 持続するd 経由で 独立した・無所属 audit.
When a browser visits a 安全な・保証する website, it 陳列する，発揮するs a 警告 if it is not able to 実証する the 証明書 - that is, if it is not 調印するd by one of the root 証明書s. Thereafter, the browser's "安全な・保証する" UI is 陳列する，発揮するd as normal. For that 場所／位置, it 代表するs secrecy only, even if the 使用者 chooses "don't 警告する me again". If the 証明書 is 調印するd by a root 証明書, the UI appears automatically, but this time 代表するing secrecy, validation and some unknown level of authentication.
消費者s are 一般に not aware of these 罰金 distinctions. Those who look for the UI (usually a lock icon) at all consider it a binary 調印する of "安全", and are encouraged to do so by banks, merchants, browser vendors and CAs. The presence of the lock is 扱う／治療するd as a 肯定的な answer to the question "can I 安全に use my credit card number or do online banking on this 場所／位置?"
If a 証明書 is incorrectly 問題／発行するd or the 私的な 重要な is 妥協d and the problem is discovered, the CA 取り消すs the 証明書 by publishing its 詳細（に述べる）s in a 証明書 Revocation 名簿（に載せる）／表（にあげる） (CRL). If a CA suddenly 問題／発行するs a 十分な number of fraudulent certs, the browser 製造業者 could produce a 安全 update to their ソフトウェア which 除去するs that CAs root cerificates from the 蓄える／店.
Shortcomings Of The 現在の Model
No 保証（人） of Authentication
The 現在の SSL model, as used in browsers today, 供給するs good privacy and validation, but 供給するs no 保証（人）d authentication. The level of authentication 変化させるs from CA to CA, but there is no 客観的な 手段 and so the level is not encoded in any 基準 way into the 証明書, and cannot be 陳列する，発揮するd to the 使用者. Even though validation alone is insufficient to 戦闘 phishing - a 実証するd 関係 to www.paypal-支払い（額）s.com is just as 危険な as an insecure one to 12.34.56.78 - 最近の changes in the market show some CAs having to 減ずる the 量 of checking they do ーするために compete with other CAs who do not 供給する authentication. Some CAs already expressly advertise and sell 証明書s with almost no authentication at all.
The audits a CA を受けるs 単に make sure that the 手続きs they follow are those in their CPS. The audit makes no comment on whether the 手続きs are 適する for 設立するing a particular level of authentication. A CPS which said "we 問題／発行する 証明書s to everyone with no checking at all" would pass audit if the CA did what it 約束d.
No Revocation
A 証明書, once 問題／発行するd, can't be 取り消すd - at least, not 事実上. No browser looks at CRLs by default, because they can run to hundreds of K in size and would have to be downloaded on the 飛行機で行く. A 議定書 called Online 証明書 Status 議定書 (OCSP) was invented to get around this 問題／発行する - it 許すs checking the 明言する／公表する of a 選び出す／独身 証明書 in real time. However, for さまざまな technical 推論する／理由s only one browser (オペラ 8) 成し遂げるs this check by default.
No (Practical) 除去
If a CA started 問題／発行するing certs with no 立証 at all as a 事柄 of 商売／仕事 practice, the only 頼みの綱 a browser 製造業者 has is to 除去する their root cert. This then 原因（となる）s error popups and 警告s for each 使用者 who visits a 場所／位置 安全な・保証するd with a cerificate 調印するd by that cert. For large 証明書 当局 who 問題／発行する the certs for many popular 場所／位置s, this would be 事実上 almost impossible. To date, I know of no instance where such a 除去 has ever happened.
Some Things Worse Than Nothing
Using a self-調印するd 証明書, or one 調印するd by an unknown CA, 現在／一般に pops up a 警告 dialog, which appears more scary to the 使用者 than plain unencrypted HTTP. The two are 現実に 同等（の） from an end-使用者 point of 見解（をとる）. In some browsers, connecting to a server 供給するing only 40-bit encryption is also scarier than nothing.
経済的なs of Phishing
Before I 示唆する some 解答s to the aforementioned problems, it is useful here to take a quick look at the 経済的なs of phishing, and how they might 影響する／感情 our choice of 活動／戦闘s.
What 運動s phishers to be so 積極的な - the 願望（する） for money - is also their Achilles heel. Phishers will stop phishing when it's no longer economically sensible to do so. 現在／一般に, 試みる／企てるing an SSL phish can cost next to nothing, and the 伸び（る）s are 潜在的に 広大な／多数の／重要な. We need to 逆転する this. There are two things you can do to make 得るing 証明書 to use for fraudulent 目的s financially unviable. You can 増加する the cost, or 可能性のある cost, of 得るing the 証明書, and you can 減少（する） the 伸び（る） possible after the 証明書 has been 得るd.
It would be hard to 増加する the 財政上の cost of 得るing a 証明書 十分に to 阻止する phishing without also deterring a lot of 合法的 uses. Therefore, the 増加するd cost has to be ーに関して／ーの点でs of 明らかにする／漏らすd （警察などへの）密告，告訴（状） (useful to 法律 施行) rather than money - i.e. in greater authentication.
Once a 証明書 has been 問題／発行するd, the only way to 減少（する） the 伸び（る） possible using it is to make it useful for いっそう少なく long. This would 伴う／関わる 設立するing and using a real-time 証明書 revocation 組織／基盤／下部構造.
提案するd Changes
Separate 安全, Validation and Authentication
The browser UI should separate the 陳列する，発揮する of 安全, validation and level of authentication. This 許すs the 使用者 to know more 正確に／まさに what level of 保護 they have against 詐欺. It is hoped that browser 製造業者s could 共同製作する on defining the form of this UI, as it is important that all browsers 持続する UI consistency ーするために make it possible to define a simple 消費者 message. Some 固める／コンクリート suggestions are in 虫垂 A; they are separated out because people may wish to agree with my 結論 here but 同意しない with my suggestions.
Define Authentication Levels
We should define a number of authentication levels that the UI should show, ーに関して／ーの点でs which a 消費者 can understand and which can be 言及／関連d in the simple 消費者 message. The number of levels should be as low as can be got away with. Again, a 固める／コンクリート suggestion is in 虫垂 A.
By 問題／発行するing 証明書s with 非，不，無-無 authentication levels, the CA would be assuming some level of 義務／負債 for any losses 原因（となる）d by a 失敗 to 審査する out fraudsters. 正確に／まさに what 義務／負債 they are assuming is again beyond the 範囲 of this paper, but it would need to be such that this whole 演習 isn't 単に "安全 theatre". The costs of 証明書s at each level would probably 反映する the level of 義務／負債 the CA assumes.
正規の／正選手 独立した・無所属 audits of 立証 手続きs should be 要求するd for all CAs. The results of each audit, and the nature of the 立証 手続きs, must be public. These audits should check that the 量 of 立証 done for each type of cert 問題／発行するd is 十分な for the authentication level for the root it is 問題／発行するd under. If the authentication level is "非，不，無", the audit 単に needs to ascertain that the CA's method of 接触するing a domain owner is 安全な・保証する. Beyond that, 正確に／まさに what checking should be done for each level is (thankfully) 井戸／弁護士席 beyond the 範囲 of this paper, and is a 事柄 for the CAs, 信用 専門家s and the auditor to work out between them.
Of course, browser 製造業者s have the final say about which authentication level they 示す each root cert with, and would reserve the 権利 to alter the 示唆するd level downwards should there be 重要な levels of nefarious activity associated with 証明書s 問題／発行するd from that root. This 許すs for finer-穀物d 支配（する）／統制する than 単に 除去するing 証明書s altogether.
Ideally, 証明書s with different 量s of 立証 should be 問題／発行するd from different roots or sub-roots. The browser can 蓄える／店 all of these in its 証明書 蓄える／店, and 示す them with its 現在の 見解（をとる） of their authentication level. (In practice, some root-cert-明確な／細部 heuristics may be necessary for 遺産／遺物 roots.) For 証明書s with authentication, the fields (OU, O, C etc.) should be filled in with data that is 訂正する によれば the CA's knowledge, suitable for 陳列する，発揮する to the 使用者. For 証明書s with no authentication, the values should either be blank or 明確に 反映する the CA's 欠如（する） of knowledge of the 訂正する values.
Enable Revocation
For authentication levels above "非，不，無", quick 証明書 revocation is needed to 減ずる the value of fraudulently-得るd 証明書s. The only game in town for this, technically, is OCSP. Therefore, it should be a 必要物／必要条件 that 証明書s 問題／発行するd under roots 示すd for such authentication levels must have embedded OCSP URLs, pointing at a working OCSP responder.
Make All Insecure 関係s The Same
SSL 関係s which do not 供給する 十分な privacy or validation should be shown in the browser UI as plain HTTP 関係s, with the exception that it must be possible to 伸び（る） 接近 to the 詳細（に述べる）s of the 証明書, and it may be necessary to 供給する an explanation why this "https" 関係 is not 示すd as 安全な・保証する. 非，不，無 of the UI used for 私的な/実証するd/authenticated 関係s should be used.
Into this 部類 of "同等（の） to plain HTTP" I would put:
- Self-調印するd 証明書s
- 証明書s 調印するd by unknown CAs
- 関係s 供給するing only 40-bit encryption
Define A Simple 消費者 Message
We should define a simple 消費者 message, which can be spread by CAs, browser 製造業者s, banks and merchants. What the message is, depends on the UI used to separate 安全, validation and authentication. A suggestion for a message is given in 虫垂 A.
There will need to be a period of 移行 when moving from the old to the new 手はず／準備. Authentication levels need to be 始める，決める, 手続きs need to be 工夫するd, audits need to be 成し遂げるd and new 証明書s need to be 問題／発行するd. To 避ける 混乱させるing the 消費者 message with 過度期の （警察などへの）密告，告訴（状）, we may want to have a 旗 day, such that browsers have タイミング code to turn on the new UI all at once when the other 手はず／準備 are in place. This could be …を伴ってd by a 一致した publicity （選挙などの）運動をする around the 消費者 message that explains that UI.
虫垂 A: 固める／コンクリート Suggestions
Authentication Levels
I 示唆する there should be three authentication levels, 指名するd around the most 一般的に-成し遂げるd activites by 使用者s over 安全な・保証する 関係s. I am conscious that this does perhaps 現在の an 極端に e-商業-centric 見解（をとる） of SSL, but it's difficult to balance 完全にする 正確 with having a simple 消費者 message. The levels I 示唆する are:
- 非，不，無
- Shopping
- Banking
The "非，不，無" level must 存在する, because there are 合法的 uses for 証明書s which show no more than domain 支配（する）／統制する.
The "shopping" level would be the most ありふれた, and used on 場所／位置s where 妥協 of （警察などへの）密告，告訴（状） 普通は put into that 場所／位置 would lead to the loss of a 選び出す／独身 credit card number, or 同等（の）.
The "banking" level would be a 賞与金 製品 suitable for companies or organisations for which a very high level of 信用 is needed. If 妥協 of （警察などへの）密告，告訴（状） 普通は put into that 場所／位置 would lead to an 攻撃者 having 接近 to a 使用者's bank accounts or 財政上の 記録，記録的な／記録するs, the 場所／位置 should have a 証明書 at this level. Of course, there's nothing to 妨げる shops buying these 証明書s, but I 嫌疑者，容疑者／疑う that they would be 意味ありげに more expensive and inconvenient to 得る than "shop" level 証明書s.
Browser UI
Unlike the 残り／休憩（する） of this paper, this 虫垂 is based around UI for Mozilla Firefox, although I am 示唆するing it as the UI to be 可決する・採択するd 終始一貫して across all browsers. The に引き続いて discussion is based on the 設立するd Firefox 安全 UI 原則 that there should be a piece of ever-現在の and reliable UI from which 使用者s can make 安全 決定／判定勝ち（する）s. After much discussion, it was decided that using the status 妨げる／法廷，弁護士業 for this 目的 was the best 妥協 between making the 安全 状況 （疑いを）晴らす, and permitting believable and rich web 使用／適用s to be written.
Any discussion of how the UI should work for the new model has, unfortunately, to take account of history, in the 形態／調整 of the question "what do we use the lock icon to 代表する?". There are two main schools of thought here.
The first 見解（をとる） is that which says that, in the real world, a lock is all about privacy (in the colloquial sense), and so we should use the lock icon for all SSL 関係s which 供給する privacy and validation (in their meanings I have used them in this paper). This 基本的に means that it would be used for all SSL 関係s except self-調印するd. The validation UI would then be a separate 指示する人（物）.
The 代案／選択肢 見解（をとる） is that the lock is 現在／一般に associated in a 使用者's mind with some level of authentication, even if that's not 現在／一般に true in practice. And therefore the lock should appear when some 非，不，無-無 authentication level has been reached.
I believe that the first 見解（をとる） is より望ましい, both ーに関して／ーの点でs of making it 平易な to define a simple 消費者 message and ーに関して／ーの点でs of 最小限 change to its 現在の de facto meaning and the meaning one could assume from its form. I therefore 提案する a separate UI for authentication level - with the 底（に届く） level 存在 単独で the lock, and then 追加するing extra symbols as authentication 増加するs.
The simple symbol most closely associated with money around the world is the dollar 調印する, which is the 通貨 symbol in many countries. This is the best 候補者 for a 世界的な symbol. Another suggestion is a pile of coins.
For 場所／位置s 接近d over SSL, Firefox 現在／一般に shows a domain 指示する人（物） in the status 妨げる／法廷，弁護士業. This is an anti-phishing 手段 to を取り引きする URL 妨げる／法廷，弁護士業 複雑さ, and has the meaning "we are sure that this is the 指名する of the 場所／位置 you are on". This fits very 井戸／弁護士席 with the 概念 of validation, and should be used to 代表する that.
I would therefore 提案する a 始める，決める of UIs something like those given in the diagram to the 権利 (with 陳謝s for my poor artistic 技術s.)
The use of 付加 UI to 示す authentication level 許すs the 消費者 message in general to be more a 事例／患者 of "Hey! Look what browser 製造業者s and CAs have done together to 改善する your safety!" rather than "Hey! The lock now means this level of 信用, but this something else means this other level..."
Simple 消費者 Message
My suggestion for the Simple 消費者 Message would be something like (with suitable illustrations or （映画の）フィート数 of the dollar 調印する UI) "When cash is at 火刑／賭ける, check for the money! One for shopping, two for banking!". This てこ入れ／借入資本s the small number of levels, the fact that they are defined in a way 使用者s can understand, and the novel nature of the UI.
虫垂 B: Changes Not Recommended
陳列する，発揮する of CA 指名する
It has been 示唆するd that the browser show the 指名する and/or logo of the 証明書 当局 in the 安全 UI. The idea is that this 許すs the 使用者 to make a 裁判／判断 as to the 安全 of the 関係 based upon their knowledge of the 評判 of the CA in question. There are a number of excellent arguments against this; I will 制限する myself to two main ones.
The brandable space 利用できる in the UI for such an 指示する人（物）, if it is to be 陳列する，発揮するd at all times, is probably about 15px high by 100px long - a 部分 of the status 妨げる／法廷，弁護士業. There is 基本的に enough room for the company 指名する/logo, and little else.
にもかかわらず, in order for a "信用 market" to be 設立するd, the 使用者 needs an 極端に 深い understanding of CA brands. 使用者s would need to 購入（する） or not 購入（する） based on their 見解（をとる） of the 信用 of the CA brand 保護するing the 場所／位置. In other words, the に引き続いて シナリオ would need to take place 定期的に. A 使用者 visits a web shop, spends half an hour filling up their basket with a number of goods, goes to the 安全な・保証する checkout and then, on the basis of their perception of the 信用 of the CA who 調印するd the cert 保護するing the checkout page, abandons that basket of goods and goes and shops どこかよそで. I 示唆する that this is 完全に unrealistic. You are pitting the CA branding 設立するd by a small rectangle in the browser UI against the multi-million dollar advertising （選挙などの）運動をするs of Gap or IBM, 連合させるd with the 使用者's 願望（する） for the goods they are about to buy. It's no contest.
Secondly, there are 35 CAs with root 証明書s in Firefox 1.0, with more in the 列 for later 解放（する）s, and 52 in IE on Windows XP. A 使用者 would need to be aware of, and have opinions on the 信用 of all of them. さもなければ, what should he be advised to do when 遭遇（する）ing a 場所／位置 安全な・保証するd using a 証明書 from a CA he does not know?
Sensible 安全 practice would 示唆する "don't use the 場所／位置"; however this advice, if universally followed, would have a 本気で detrimental 影響 on the 量 of web 商業 and, if 固執するd with, 減ずる the CA market to a small handful of players with big marketing 予算s. Even in that 事例／患者, the value of the total 証明書 market is probably not 十分な to 許す CAs to do 消費者-oriented marketing in all the countries of the world with Internet 接近. On the other 手渡す, the advice "use the 場所／位置 anyway" destroys most of the point of the branding in the first place. CAs would have an incentive to make sure their brand and logo was not known!
It's important that 安全 UI is stable - that is, it should be the same on every visit to a 合法的 場所／位置, and different on any visit to a dodgy 場所／位置. If a CA 信用 market were in 操作／手術, a switch from Just-Gone-Dodgy CA to More-信頼できる-CA would be a good change (場所／位置 昇格ing its 安全), but a change in the 逆転する direction would be a bad change (possible phishing attack). A 使用者 would need very 深い knowledge of the CA market ーするために distinguish the two changes.
These factors and others together mean that 現在のing the CA logo in the UI would 混乱させる the 使用者 far more than it 改善するd 安全, and （問題を）取り上げる 審査する space that could be used for other, more useful 指示する人（物）s.