Ubuntu 改變放掉 i386 的計畫

先前在「Ubuntu 19.10 要放掉 i386 架構」這邊提到 Ubuntu 要放掉 i386 的計畫,因為造成的迴響很大,現在官方決定修改本來的結論:「Statement on 32-bit i386 packages for Ubuntu 19.10 and 20.04 LTS」。

在本來的計畫裡,是完全放生 i386 架構 (完全不管):

While this means we will not provide 32-bit builds of new upstream versions of libraries, there are a number of ways that 32-bit applications can continue to be made available to users of later Ubuntu releases, as detailed in [4]. We will be working to polish the 32-bit support story over the course of the 19.10 development cycle. To follow the evolution of this support, you can participate in the discourse thread at [5].

現在則是打算透過 container 技術支援 32-bit library & binary,算是某種緩衝方式:

We will also work with the WINE, Ubuntu Studio and gaming communities to use container technology to address the ultimate end of life of 32-bit libraries; it should stay possible to run old applications on newer versions of Ubuntu. Snaps and LXD enable us both to have complete 32-bit environments, and bundled libraries, to solve these issues in the long term.

但應該還是會有程式沒辦法在 container 環境裡跑,看起來官方決定放掉了...

WebKit 對 HSTS Super Cookie 提出的改法

Twitter 上看到 WebKitHSTS 所產生的 Super Cookie 提出的改善方案:

拿原文的例子來說明,先指定一個隨機數給 user,像是 8396804 (二進位是 100000000010000000000100),所以就存取下面的網址:


在存取這些 HTTPS 網址時都會指定 HSTS,所以之後連到這三個網址的 HTTP request 就不會觸發到 HTTP 版本,會因為 HSTS 被轉到 HTTPS 版本。於是就可以用 32 個 HTTP request 測試 32bits 而判斷出身份。(當然你可以用更多)

WebKit 提出的改善方案大概有幾種,主要是就觀察到的現象來限制。

第一種解法「Mitigation 1: Limit HSTS State to the Hostname, or the Top Level Domain + 1」是因為會看到這樣的設計:


所以提出的方案是只有目前網站的 domain 以及 top domain + 1 (像是 example.com) 可以被設定 HSTS:

Telemetry showed that attackers would set HSTS across a wide range of sub-domains at once. Because using HSTS in this way does not benefit legitimate use cases, but does facilitate tracking, we revised our network stack to only permit HSTS state to be set for the loaded hostname (e.g., “https://a.a.a.a.a.a.a.a.a.a.a.a.a.example.com”), or the Top Level Domain + 1 (TLD+1) (e.g., “https://example.com”).

但其實廣告主只需要註冊 32 domains (或是 64) 就可以避開這個問題。

第二種是「Mitigation 2: Ignore HSTS State for Subresource Requests to Blocked Domains」,如果在 HTTPS 頁面上,某個 domain 的 cookie 已經因為某些原因被阻擋 (像是手動設定),那麼就忽略掉 HSTS 的設計:

We modified WebKit so that when an insecure third-party subresource load from a domain for which we block cookies (such as an invisible tracking pixel) had been upgraded to an authenticated connection because of dynamic HSTS, we ignore the HSTS upgrade request and just use the original URL. This causes HSTS super cookies to become a bit string consisting only of zeroes.

後面這點在現在因為 SEO 設計而使得各大網站都往 HTTPS 方向走,應該會有些幫助吧...

NSA 付錢給 RSA 放後門的事件...

Edward Snowden 再次丟出 NSA 內部文件,表示 NSA 付錢給 RSA 在演算法裡面放後門:「Exclusive: Secret contract tied NSA and security industry pioneer」。

RSA 的回應則是完全不想提到這筆錢是做什麼用的:「RSA Response to Media Claims Regarding NSA Relationship」。

現在一般在猜測,這個後門應該就是 RSA BSAFE 的預設偽隨機數產生器 Dual_EC_DRBG

對於 Dual_EC_DRBG 的攻擊,2006 年的「Cryptanalysis of the Dual Elliptic Curve Pseudorandom Generator」就這樣寫:

Our experimental results and also empirical argument show that the DEC PRG is insecure. The attack does not imply solving the ECDLP for the corresponding elliptic curve. The attack is very efficient.

在 2007 年,Bruce Schneier 寫了一篇「Did NSA Put a Secret Backdoor in New Encryption Standard?」,提到這個弱點並沒有大到使得這個演算法不堪用,但看了總是不爽:

Problems with Dual_EC_DRBG were first described in early 2006. The math is complicated, but the general point is that the random numbers it produces have a small bias. The problem isn't large enough to make the algorithm unusable -- and Appendix E of the NIST standard describes an optional work-around to avoid the issue -- but it's cause for concern. Cryptographers are a conservative bunch: We don't like to use algorithms that have even a whiff of a problem.

並且建議不要用 Dual_EC_DRBG:

My recommendation, if you're in need of a random-number generator, is not to use Dual_EC_DRBG under any circumstances. If you have to use something in SP 800-90, use CTR_DRBG or Hash_DRBG.

現在回頭看這件事情... hmmm...