Privacy Badger 預設關閉學習功能

Privacy Badger 是一個自動學習的 extension,可以學習 tracker 並且予以阻擋:

Privacy Badger automatically learns to block invisible trackers.

而這個自動學習功能在剛剛看到公告說明預設會關閉:「Privacy Badger Is Changing to Protect You Better」,主要是因為這個自動學習功能可以變成 fingerprint 資訊的一環:

The team also alerted us to a class of attacks that were enabled by Privacy Badger’s learning. Essentially, since Privacy Badger adapts its behavior based on the way that sites you visit behave, a dedicated attacker could manipulate the way Privacy Badger acts: what it blocks and what it allows. In theory, this can be used to identify users (a form of fingerprinting) or to extract some kinds of information from the pages they visit. This is similar to the set of vulnerabilities that Safari’s Intelligent Tracking Prevention feature disclosed and patched late last year.

所以現在變成會固定更新 pre-train ruleset 了:

From now on, Privacy Badger will rely solely on its “Badger Sett” pre-trained list of tracking domains to perform blocking by default. Furthermore, Privacy Badger’s tracker database will be refreshed periodically with the latest pre-trained definitions. This means, moving forward, all Privacy Badgers will default to relying on the same learned list of trackers for blocking.

當然這個功能還是可以手動開,但就有可能會被拿去 fingerprint 了,要開的人可以自己想一下... 不過不開的話就只是一個 ruleset 了 XD

有用的人可以自己考慮一下 XD

Google 用 x-client-data 追蹤使用者的問題

前陣子 Chromium 團隊在研究要移除 User-Agent 字串的事情 (參考「User-Agent 的淘汰提案」),結果 kiwibrowser 就直接炸下去,Google 很久前就會針對自家網站送出 x-client-data 這個 HTTP header,裡面足以辨識使用者瀏覽器的單一性:「Partial freezing of the User-Agent string#467」。

Google 的白皮書裡面是說用在 server 的試驗:

We want to build features that users want, so a subset of users may get a sneak peek at new functionality being tested before it’s launched to the world at large. A list of field trials that are currently active on your installation of Chrome will be included in all requests sent to Google. This Chrome-Variations header (X-Client-Data) will not contain any personally identifiable information, and will only describe the state of the installation of Chrome itself, including active variations, as well as server-side experiments that may affect the installation.

The variations active for a given installation are determined by a seed number which is randomly selected on first run. If usage statistics and crash reports are disabled, this number is chosen between 0 and 7999 (13 bits of entropy). If you would like to reset your variations seed, run Chrome with the command line flag “--reset-variation-state”. Experiments may be further limited by country (determined by your IP address), operating system, Chrome version and other parameters.

但因為這個預設值開啟的關係,就算關掉後也足以把使用者再分類到另外一個區塊,仍然具有高度辨識性,不是你 Google 說無法辨識就算數。

另外如果看 source code 裡的說明:

    // Note the criteria for attaching client experiment headers:
    // 1. We only transmit to Google owned domains which can evaluate
    // experiments.
    //    1a. These include hosts which have a standard postfix such as:
    //         *.doubleclick.net or *.googlesyndication.com or
    //         exactly www.googleadservices.com or
    //         international TLD domains *.google. or *.youtube..
    // 2. Only transmit for non-Incognito profiles.
    // 3. For the X-Client-Data header, only include non-empty variation IDs.

可以看到 *.doubleclick.net*.googlesyndication.comwww.googleadservices.com 全部都是廣告相關,另外 Google 自家搜尋引擎是直接提供廣告 (不透過前面提到的網域),YouTube 也是一樣的情況,所以完全可以猜測 x-client-data 這個資料就是用在廣告相關的系統上。

The Register 在「Is Chrome really secretly stalking you across Google sites using per-install ID numbers? We reveal the truth」這邊用粗體的 Update 提到了 GDPR 的問題,不確定是不是開始有單位在調查了:

Updated Google is potentially facing a massive privacy and GDPR row over Chrome sending per-installation ID numbers to the mothership.

在這個問題沒修正之前,只能暫時用操作 HTTP header 的 extension 移掉這個欄位。

利用 Sensor 校正資訊產生 Device Fingerprint 的隱私攻擊

看到「Fingerprinting iPhones」這篇提出的攻擊,標題雖然是提到 iPhone,但實際上攻擊包括了 Android 的手機:

You are affected by this fingerprinting attack if you are using any iOS devices with the iOS version below 12.2, including the latest iPhone XS, iPhone XS Max, and iPhone XR. You are also likely to be affected if you are using a Pixel 2/3 device, although we hypothesise the generated fingerprint has less entropy and is unlikely to be globally unique. A SensorID can be generated by both apps and mobile websites and requires no user interaction.

目前 iPhone 升級到 12.2 之後可以緩解這個問題,Android 看起來還不清楚...

攻擊的方式是透過手機在出場前會使用外部的校正工具,找出手機內 sensor 所偵測到的值與實際值的差異,然後把這些資訊燒到韌體裡,當呼叫 API 時就可以修正給出比較正確的值。

而因為這些校正資訊幾乎每一隻手機都不一樣,而且不會因為重裝而變更 (即使 factory reset),加上還可以跨 app 與 web 追蹤,就成為這次攻擊的目標:

In the context of mobile devices, the main benefit of per-device calibration is that it allows more accurate attitude estimation.

資訊量其實相當大,透過 app 分析可以得到 67 bits entropy,透過網頁也有 42 bits entropy,而且不怎麼會變:

In general, it is difficult to create a unique fingerprint for iOS devices due to strict sandboxing and device homogeneity. However, we demonstrated that our approach can produce globally unique fingerprints for iOS devices from an installed app -- around 67 bits of entropy for the iPhone 6S. Calibration fingerprints generated by a website are less unique (~42 bits of entropy for the iPhone 6S), but they are orthogonal to existing fingerprinting techniques and together they are likely to form a globally unique fingerprint for iOS devices.

We have not observed any change in the SensorID of our test devices in the past half year. Our dataset includes devices running iOS 9/10/11/12. We have tested compass calibration, factory reset, and updating iOS (up until iOS 12.1); the SensorID always stays the same. We have also tried measuring the sensor data at different locations and under different temperatures; we confirm that these factors do not change the SensorID either.

目前提出來的解法是加入隨機值的噪音 (iOS 的作法),不過作者有建議預設應該要關閉 js 存取 sensor 的權限:

To mitigate this calibration fingerprint attack, vendors can add uniformly distributed random noise to ADC outputs before calibration is applied. Alternatively, vendors could round the sensor outputs to the nearest multiple of the nominal gain. Please refer to our paper for more details. In addition, we recommend privacy-focused mobile browsers add an option to disable the access to motion sensors via JavaScript. This could help protect Android devices and iOS devices that no longer receive updates from Apple.

不過當初這群人怎麼會注意到的...

解鎖 iPhone 的 Diper ID...

Twitter 上看到 Diper ID 這個糟糕的東西:

查了資料,操作方式可以從這個影片看到:

這明顯有資安問題啊 XDDD

Facebook 的智障防範措施...

Facebook 新的防範報復性照片計畫不少媒體都有報導了,我拿 Bruce Schneier 這篇來引用好了:「Facebook Fingerprinting Photos to Prevent Revenge Porn」。

重點是:

According to a Facebook spokesperson, Facebook workers will have to review full, uncensored versions of nude images first, volunteered by the user, to determine if malicious posts by other users qualify as revenge porn.

智障... 結果裸照從這些管道先傳出去?

偵測 Chrome Headless

作者因為種種原因,想要偵測 Headless 模式的 Google Chrome:「Detecting Chrome Headless」。

之前因為主要是 PhantomJS,有很多地方跟一般的瀏覽器不同,可以利用這些不同的地方來判斷出是不是 PhantomJS:

Until now, one of the most popular headless browser was PhantomJS. Since it is built on the Qt framework, it exhibits many differences compared to most popular browsers. As presented in this post, it is possible to detect it using some browser fingerprinting techniques.

但從 Google Chrome 59 以後因為支援 Headless,使得大多數的判斷的失效:

Since version 59, Google released a headless version of its Chrome browser. Unlike PhantomJS, it is based on a vanilla Chrome, and not on an external framework, making its presence more difficult to detect.

所以作者找了不少方式想要判斷兩者的相異之處... 不過這些方式看起來不太穩定,加上 Firefox 也在準備了,之後只會愈來愈困難吧 :o

分析聲音模擬其他人講話...

這種黑科技愈來愈成熟啦:「Lyrebird - An API to copy the voice of anyone」。

Record 1 minute from someone's voice and Lyrebird can compress her/his voice's DNA into a unique key. Use this key to generate anything with its corresponding voice.

Demo 的地方直接拿這三個人惡搞:(這樣做沒問題嗎 XDDD)

Please note that those are artificial voices and they do not convey the opinions of Donald Trump, Barack Obama and Hillary Clinton.

而且是有能力做到即時轉換:

Our GPU clusters generate 1000 sentences in less than half a second.

Uber 戰火蔓延到 Unroll

最近 Uber 的 CEO 被 Tim Cook 叫去喝咖啡的事情被報導出來:「Uber’s C.E.O. Plays With Fire」,裡面提到了 Uber 試著要「辨別」使用者的 iPhone,而這違反蘋果的政策:

To halt the activity, Uber engineers assigned a persistent identity to iPhones with a small piece of code, a practice called “fingerprinting.” Uber could then identify an iPhone and prevent itself from being fooled even after the device was erased of its contents.

There was one problem: Fingerprinting iPhones broke Apple’s rules. Mr. Cook believed that wiping an iPhone should ensure that no trace of the owner’s identity remained on the device.

而 Uber 的搞法是針對蘋果總部所在地點屏蔽這個功能:

So Mr. Kalanick told his engineers to “geofence” Apple’s headquarters in Cupertino, Calif., a way to digitally identify people reviewing Uber’s software in a specific location. Uber would then obfuscate its code for people within that geofenced area, essentially drawing a digital lasso around those it wanted to keep in the dark. Apple employees at its headquarters were unable to see Uber’s fingerprinting.

然後被蘋果工程師抓到,於是 Tim Cook 把人叫來喝咖啡:

The ruse did not last. Apple engineers outside of Cupertino caught on to Uber’s methods, prompting Mr. Cook to call Mr. Kalanick to his office.

另外提到了 Uber 從 Unroll.me 買來 Lyft 的帳單資料當作分析:

Using an email digest service it owns named Unroll.me, Slice collected its customers’ emailed Lyft receipts from their inboxes and sold the anonymized data to Uber. Uber used the data as a proxy for the health of Lyft’s business. (Lyft, too, operates a competitive intelligence team.)

而更精彩的在 Hacker News 上的這串爆了不少料,提到 Unroll 會把所有信件掃下來,丟到 S3 上面:

I worked for a company that nearly acquired unroll.me. At the time, which was over three years ago, they had kept a copy of every single email of yours that you sent or received while a part of their service. Those emails were kept in a series of poorly secured S3 buckets. A large part of Slice buying unroll.me was for access to those email archives. Specifically, they wanted to look for keyword trends and for receipts from online purchases.

The founders of unroll.me were pretty dishonest, which is a large part of why the company I worked for declined to purchase the company. As an example, one of the problems was how the founders had valued and then diluted equity shares that employees held. To make a long story short, there weren't any circumstances in which employees who held options or an equity stake would see any money.

I hope you weren't emailed any legal documents or passwords written in the clear.

而在 FAQ 的「If I delete my Unroll.Me account, what will happen to all of my previously rolled up emails?」裡則是說我們沒有存你的信件:

這爆米花要多買一些了...

利用 Side-channel 資訊判斷被 HTTPS 保護的 Netflix 影片資訊

在「Netflix found to leak information on HTTPS-protected videos」這篇看到了研究員透過 VBR 所透露出的 side channel 資訊,成功的取得了被 HTTPS 保護的 Netflix 影片資訊。這對於美國的 ISP 是個大利多 (加上之前通過的法案),但對於個人隱私則是嚴重的打擊。

這項研究的準確率非常高:

To support our analysis, we created a fingerprint database comprised of 42,027 Netflix videos. Given this collection of fingerprints, we show that our system can differentiate between videos with greater than 99.99% accuracy. Moreover, when tested against 200 random 20-minute video streams, our system identified 99.5% of the videos with the majority of the identifications occurring less than two and a half minutes into the video stream.

而且他們居然是用這樣的單機分析:

null

苦啊...

Bitcoin.org 對於接下來的 release 發出警告

Bitcoin.org 發出了有點摸不著頭緒的警告:「0.13.0 Binary Safety Warning」。

Bitcoin.org has reason to suspect that the binaries for the upcoming Bitcoin Core release will likely be targeted by state sponsored attackers. As a website, Bitcoin.org does not have the necessary technical resources to guarantee that we can defend ourselves from attackers of this calibre.

而且直接是點名可能是針對中國區的用戶:

We ask the Bitcoin community, and in particular the Chinese Bitcoin community to be extra vigilant when downloading binaries from our website.

由於 Bitcoin.org 全站走 HTTPS,這是在暗示會出現「不小心發出 Bitcoin.org 的 SSL certificate」的事情?另外官方也建議使用 PGP public key 驗證:

We strongly recommend that you download that key, which should have a fingerprint of 01EA5486DE18A882D4C2684590C8019E36C2E964. You should securely verify the signature and hashes before running any Bitcoin Core binaries. This is the safest and most secure way of being confident that the binaries you’re running are the same ones created by the Core Developers.

來拿板凳蹲著看,順便拉一張目前 certificate 看到的資訊,目前是從 RapidSSL SHA256 CA - G3 簽出來: