Tag: air

風扇的出風孔的遮罩，不同形狀產生噪音的差異

前幾天在 Hacker News Daily 上看的文章：「Effects of grill patterns on fan performance/noise (2011) (pugetsystems.com)」，原文在「Effects of Grill Patterns on Fan Performance/Noise」。文章在講電腦風扇的出風口擋板的樣式對噪音的影響。這是一篇 2011 的老文章，但看了一下好像沒有什麼新資料...

出風口的遮罩在有些地區似乎是法律要求，主要是怕小朋友手指戳進去，以及成年人不小心碰到，所以就會有專門的測試項目在跑：

I remember back in 2000 ish I worked in R&D of a PC manufacturer and had to check the new PSUs and cases with a 'Test Finger' to make sure all the holes were small enough. The test finger was really expensive IIRC.

但回到這篇的重點，噪音與風量的差異，所以基準值是拔掉遮罩的部份先測試 (所以可以知道最低的噪音與最大的風量)，然後上各種遮罩測差異。

Mesh 增加的噪音是最少，但風量有點差：

Wire 增加的噪音也很少，風量也達到最高：

從倒數的方向來看，Turbine 是最吵風量也最少的：

發現比較差的遮罩增加的噪音不算少，把很多風的動能變成聲音的能量了...

用 SATA 界面產生的電磁訊號突破 Air Gap 限制傳輸資料

在 Hacker News 首頁上看到「SATAn: Air-Gap Exfiltration Attack via Radio Signals From SATA Cables」這個，透過 SATA 界面產生的電磁訊號突破 Air Gap 限制傳輸資料，對應的討論在「SATAn: Air-Gap Exfiltration Attack via Radio Signals from SATA Cables (arxiv.org)」。

Although air-gap computers have no wireless connectivity, we show that attackers can use the SATA cable as a wireless antenna to transfer radio signals at the 6 GHz frequency band.

翻了一下論文裡面提到的距離，在 PC-1 上測試到 120cm，對應的 SNR 有 9db：

Table IV presents the signal-to-noise ratio (SNR) received with the three transmitting computers. The signal transmitted from PC-1 has a strength of 20 dB at 30 cm to 9 dB at 120 cm apart. The signal generated from PC-1 and PC-2 were significantly weaker, with 15 dB at 60 cm (PC-2) and 7 dB at 30 cm (PC-3).

另外大概是 PoC 的關係，只有簡單測一下是可行的 (對於真的有利用 air gap 的環境當作一種保護機制的威脅就夠大了)，看起來沒有測極限可以跑多快：

We transmitted the data with a bit rate of 1 bit/sec, which is shown to be the minimal time to generate a signal which is strong enough for modulation.

關於反制的部份，這類的技術 (透過電磁訊號) 之前在其他的裝置上都有發生過，目前的 air gap 標準應該都有電磁訊號洩漏的防範了，這篇主要還是在展示 SATA 也可以這樣搞 XD

謠言說蘋果要將蝴蝶鍵盤退役...

9to5Mac 的報導說 Apple 要改用剪刀式的設計：「Kuo: Apple to include new scissor switch keyboard in 2019 MacBook Air and 2020 MacBook Pro」。

取自「File:Scissor switch mechanism.svg」這頁。

Apple is apparently set to ditch the butterfly mechanism used in MacBooks since 2015, which has been the root of reliability issues and its low-travel design has also not been popular with many Mac users.

In a report published today, Ming-Chi Kuo says that Apple will roll out a new keyboard design based on scissor switches, offering durability and longer key travel, starting with the 2019 MacBook Air. The MacBook Pro is also getting the new scissor switch keyboard, but not until 2020.

還沒真的放出來前都不能確認...

愈來愈多無人機捕捉方式被發展出來

愈來愈多捕捉無人機的方式被發展出來，像這個是透過網子與降落傘拉下來：「SkyWall gun stops drones dead, then gives a parachute landing」：

The most important feature of SkyWall is that it not only stops the flight of a drone but, once it captures a drone, it deploys a mini-parachute, bringing the drone back to earth with no damage, allowing authorities to keep it intact for subsequent investigation.

這個 GIF 展示了捕捉的方法與過程：

打破實體隔離限制傳遞資訊

GitHub 上的 fulldecent/system-bus-radio 這個專案可以打破實體隔離限制傳遞資訊：

Some computers are intentionally disconnected from the rest of the world. This includes having their internet, wireless, bluetooth, USB, external file storage and audio capabilities removed. This is called "air gapping". Even in such a situation, this program can transmit radio.

有些電腦因為種種因素而實體隔離 (像是因為安全因素，或是保密因素)，於是就有人研究各種方法傳遞資訊。這隻程式利用 system bus 在 Macbook Air 上產生 AM radio 訊號：

And run it on an Apple MacBook Air (13-inch, Early 2015):

./main

Then use a Sony STR-K670P radio receiver with the included antenna and tune it to 1580 kHz on AM.

這方法好硬... 但也證明了可以藉由這種方法傳遞訊息。

Update：強者我同事 ccn 在 Twitter 上找到一位日本人的 demo 影片：