7 ms·

This also has side-channel implications, and is a reason why eDP is recommended in voting applications. https://www.eerstekamer.nl/nonav/overig/20160428/richtli

by madars 3y ago

This also has side-channel implications, and is a reason why eDP is recommended in voting applications. https://www.eerstekamer.nl/nonav/overig/20160428/richtlijnen_ter_voorkoming_van/document https://www.eerstekamer.nl/nonav/overig/20160428/richtlijnen... >DisplayPort uses a scrambler as part of its line encoding in order to flatten the Fourier spectrum of its emissions and suppress spectral peaks caused by particular image contents. This reduces the chances of any particular image content causing a problem spectral peak during SDIP-27 and EMI spectrum measurements. According to the standard, the scrambler reduces spectral peaks by about 7 dB. As a side effect, the scrambler also makes it far more difficult, probably even impractical, for an attacker to reconstruct any information about the displayed image from the DisplayPort emissions. [..] DisplayPort uses a small number of fixed bit rates, independent of the video mode used. Unlike with most other digital interfaces, video data is transmitted in data packets with header and padding bytes, and not continuously with a television-like timing. As a result, DisplayPort cables are not a common source of van-Eckstyle video emanations and this again will make it very hard for an eavesdropper to synchronize to the transmitted data. Speaking of which: how does one force HDCP (say, in Linux)? That would transform this technology from a DRM nuisance (strippers easily available on AliExpress) into a Van Eck-countermeasure.

angry_octet 3y ago
HDCP can't really be stripped, if it's on then something is an HDCP receiver. For v1.4 signals you can probably get something with the leaked key, but not for v2.2 as yet. HDCP itself needs to be licensed in order to generate it, and that licence is only available to HDMI Adopter companies. However there is code to get some chipsets to turn it on: https://github.com/intel/hdcp https://github.com/intel/hdcp Grab it now before Intel deletes it completely. HDCP is really a very ugly protocol designed just for anti-copying, I wouldn't build anything relying on it, and everything is harder with HDCP from an AV integration perspective. If you have long links that you want to secure, use something like SDVoE with encryption and authentication (bits are easily flipped in HDCP).
- madars 3y ago
  There are devices that will give you HDCP 2.3->1.4 conversion for compatibility reasons (or maybe wink-wink reasons), and after that you can use a HDCP 1.4 stripper. There are also devices that will strip 2.2 outright (they are marketed as HDMI splitters but, oops, one of the two outputs has unencrypted signal, an honest mistake); not sure about 2.3 though. Completely agree that HDCP makes everything harder, but in this scenario it would also make attacker's job of descrambling the eavesdropped signal harder. And this is after they have overcome packetization and spread spectrum hurdles, which the paper suggests is very challenging to do, so would be a (hacky) defense-in-depth for DisplayPort. Even more important for HDMI/DVI which lacks the aforementioned hurdles.
  - zorgmonkey 3y ago
    My understanding is that the downside of those downgrade devices is HDCP 1.4 will leave you stuck without 4k and HDR for content that uses HDCP.
    - angry_octet 3y ago
      Yes you can extract plaintext 1080p but not 4k HDR.
gsich 3y ago
Voting computers are not recommended anyways.
- girvo 3y ago
  It's still shocking to me that they're used widely, and also pains me that my 15+ years of railing against digital voting computers is now looked upon the same way as the hard-right-wing's complaints (made up ones, but in a semi-related space to my complaints) about said computers.
- unixhero 3y ago
  It should be a national citizen identity logon system, which a voting web site uses, everyone can vote from home or from a laptop provided by the independent voting facility.
  - gsich 3y ago
    No.
  - loup-vaillant 3y ago
    Sounds nice, but computer based voting systems, no matter how secure, clean or simple, are fundamentally opaque to the average citizen. That alone undermines the very democracy it tries to support. Paper based voting systems may be bloody tedious but they’re simple, and anyone can participate. As a programmer myself, I have to say no to electronic voting systems. We need to keep it low tech.
    - kaashif 3y ago
      Also, they may be opaque even to software engineers, it's not like we have magic powers to look at a physical computer and know what code is running. Even if the code is released: (1) Who can read and understand tens or hundreds of thousands of lines of probably not very comprehensible code? Not many people can and even fewer will. (2) Is the code running on the machines the same as the published code? I don't even know what code is running on my phone or laptop right now.
ddingus 3y ago
You mean election type voting? Screen scraping is the least of the problems. Voting machines are simply not trustworthy given these requirements for a free and fair election: 0. Freedom to vote or not 1. Anonymity in that no vote may be associated with the voter who cast it (These two are most of why e-voting is not trustworthy and are what differentiates banking from voting.) 2. Transparency. The law, means, methods must all be known to the voting public. It is their election. In particular, seeing how a cast vote moves through the entire process and into the final tally is necessary. 3. Oversight. The first two of these foundation requirements necessary for free and fair public elections have an important ratification: The record of votes cast must be human readable and said record must be used directly to realize the final tally of all votes cast. There is a chain of trust between voter intent and the vote cast. When one casts a vote on physical media, that is a direct record of voter intent. The voter can be sure their intent adds to the tally because they can directly verify their votes cast. Electronic votes are a vote by proxy. The direct expression of intent is not kept and exists as a bit of skin residue left on the machine interface. Put simply, we ask people to vote and then we discard their expression! What gets used instead is whatever the machine thought the voter intent was! Consider this: You have a machine in front of you with two buttons. One brings the world into harmony, the other casts it into war, grief and darkness. You can: A. Submit a paper form you fill out manually indicating your choice , or B. Press one of the buttons and get a receipt for your records. Say this machine has an indicator showing your choice and a third "approval" button you use when you feel good about the machine getting your choice right. How do you the voter know the receipt and or indicators match what the proxy machine says your choice was. What happens when we have a dispute? We know the machine can't be trusted to match receipts. With the direct expression of intent lost, what do we bring to court? We can and have brought paper ballots into court to resolve and election facing genuine ambiguity. I submit to you we can't really be sure who wins an electronic election, unless we also associate your identity with the vote. Say a bunch of people get to choose the fate of the world this way. What is your confidence level? How do we know the machines tallied up the winning choices correctly? What do the tests for that look like and how do they get around the forced trust problem we have with all electronic inputs today? There is a lot more trouble to discuss. What I put here is the core trouble and computers have always had this problem too. It just does not present any real difficulty, until elections are brought into the discussion. Display trust issues are well above the core tech trust issues we face today.

by madars 3y ago

angry_octet 3y ago

HDCP can't really be stripped, if it's on then something is an HDCP receiver. For v1.4 signals you can probably get something with the leaked key, but not for v2.2 as yet. HDCP itself needs to be licensed in order to generate it, and that licence is only available to HDMI Adopter companies. However there is code to get some chipsets to turn it on: https://github.com/intel/hdcp https://github.com/intel/hdcp Grab it now before Intel deletes it completely. HDCP is really a very ugly protocol designed just for anti-copying, I wouldn't build anything relying on it, and everything is harder with HDCP from an AV integration perspective. If you have long links that you want to secure, use something like SDVoE with encryption and authentication (bits are easily flipped in HDCP).

madars 3y ago
There are devices that will give you HDCP 2.3->1.4 conversion for compatibility reasons (or maybe wink-wink reasons), and after that you can use a HDCP 1.4 stripper. There are also devices that will strip 2.2 outright (they are marketed as HDMI splitters but, oops, one of the two outputs has unencrypted signal, an honest mistake); not sure about 2.3 though. Completely agree that HDCP makes everything harder, but in this scenario it would also make attacker's job of descrambling the eavesdropped signal harder. And this is after they have overcome packetization and spread spectrum hurdles, which the paper suggests is very challenging to do, so would be a (hacky) defense-in-depth for DisplayPort. Even more important for HDMI/DVI which lacks the aforementioned hurdles.
- zorgmonkey 3y ago
  My understanding is that the downside of those downgrade devices is HDCP 1.4 will leave you stuck without 4k and HDR for content that uses HDCP.
  - angry_octet 3y ago
    Yes you can extract plaintext 1080p but not 4k HDR.

gsich 3y ago

Voting computers are not recommended anyways.

girvo 3y ago
It's still shocking to me that they're used widely, and also pains me that my 15+ years of railing against digital voting computers is now looked upon the same way as the hard-right-wing's complaints (made up ones, but in a semi-related space to my complaints) about said computers.
unixhero 3y ago
It should be a national citizen identity logon system, which a voting web site uses, everyone can vote from home or from a laptop provided by the independent voting facility.
- gsich 3y ago
  No.
- loup-vaillant 3y ago
  Sounds nice, but computer based voting systems, no matter how secure, clean or simple, are fundamentally opaque to the average citizen. That alone undermines the very democracy it tries to support. Paper based voting systems may be bloody tedious but they’re simple, and anyone can participate. As a programmer myself, I have to say no to electronic voting systems. We need to keep it low tech.
  - kaashif 3y ago
    Also, they may be opaque even to software engineers, it's not like we have magic powers to look at a physical computer and know what code is running. Even if the code is released: (1) Who can read and understand tens or hundreds of thousands of lines of probably not very comprehensible code? Not many people can and even fewer will. (2) Is the code running on the machines the same as the published code? I don't even know what code is running on my phone or laptop right now.

ddingus 3y ago

You mean election type voting? Screen scraping is the least of the problems. Voting machines are simply not trustworthy given these requirements for a free and fair election: 0. Freedom to vote or not 1. Anonymity in that no vote may be associated with the voter who cast it (These two are most of why e-voting is not trustworthy and are what differentiates banking from voting.) 2. Transparency. The law, means, methods must all be known to the voting public. It is their election. In particular, seeing how a cast vote moves through the entire process and into the final tally is necessary. 3. Oversight. The first two of these foundation requirements necessary for free and fair public elections have an important ratification: The record of votes cast must be human readable and said record must be used directly to realize the final tally of all votes cast. There is a chain of trust between voter intent and the vote cast. When one casts a vote on physical media, that is a direct record of voter intent. The voter can be sure their intent adds to the tally because they can directly verify their votes cast. Electronic votes are a vote by proxy. The direct expression of intent is not kept and exists as a bit of skin residue left on the machine interface. Put simply, we ask people to vote and then we discard their expression! What gets used instead is whatever the machine thought the voter intent was! Consider this: You have a machine in front of you with two buttons. One brings the world into harmony, the other casts it into war, grief and darkness. You can: A. Submit a paper form you fill out manually indicating your choice , or B. Press one of the buttons and get a receipt for your records. Say this machine has an indicator showing your choice and a third "approval" button you use when you feel good about the machine getting your choice right. How do you the voter know the receipt and or indicators match what the proxy machine says your choice was. What happens when we have a dispute? We know the machine can't be trusted to match receipts. With the direct expression of intent lost, what do we bring to court? We can and have brought paper ballots into court to resolve and election facing genuine ambiguity. I submit to you we can't really be sure who wins an electronic election, unless we also associate your identity with the vote. Say a bunch of people get to choose the fate of the world this way. What is your confidence level? How do we know the machines tallied up the winning choices correctly? What do the tests for that look like and how do they get around the forced trust problem we have with all electronic inputs today? There is a lot more trouble to discuss. What I put here is the core trouble and computers have always had this problem too. It just does not present any real difficulty, until elections are brought into the discussion. Display trust issues are well above the core tech trust issues we face today.