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One of the killer-features of RISC-V was being backdoor-free, but it appears that chinese companies will produce most of the chips. Back to square one. This is

One of the killer-features of RISC-V was being backdoor-free, but it appears that chinese companies will produce most of the chips. Back to square one. This is a pipe dream, but having self-managed local foundries (à la hackerspace) would be awesome to ensure that RISC-V stays secured, decentralised and competitive.

ClumsyPilot 6y ago
But now consumer can choose who will spy on them!
MaxBarraclough 6y ago
> Back to square one. It's an open source processor, right? (Not just the RISC-V instruction-set, but the specific chip.) Could the chip be compared against that design to check for backdoors?
- progre 6y ago
  Is this chip open hardware? I didn't see that in the article but maybe you have other sources... In that case, you would still need is a electron scanning microscope and a known good reference to verify with.
- nsajko 6y ago
  > It's an open source processor, right? The term open source was used in the article, but did they mean that in an accurate sense, or was it just empty marketing? Also, I can't find the source after a short search. > Could the chip be compared against that design to check for backdoors? Don't know, but I'm sure much expertise, man-hours and expensive equipment would be necessary. Maybe prohibitively so.
- tyingq 6y ago
  Not sure how you would practically do that. You could thwart all that with a microcode layer anyway. I think the closest you're going to get to "verifiably secure" is an FPGA based core.
  - MaxBarraclough 6y ago
    > Not sure how you would practically do that. The idea would be to somehow scan the design of the chip, presumably using an electron microscope as progre said, and compare it against the design's netlist. This isn't something I know much about, so perhaps it's not at all practical, but at least in principle this should be possible for chips with open designs. > You could thwart all that with a microcode layer anyway. I don't see that the particular techniques used in the design, such as microcode, would matter. The question is whether the published netlist matches the one on your chip. > I think the closest you're going to get to "verifiably secure" is an FPGA based core. I agree that's the most practical solution.
    - nsajko 6y ago
      > I don't see that the particular techniques used in the design, such as microcode, would matter. The question is whether the published netlist matches the one on your chip. You're missing the fact that microcode lies between the hardware and the user-supplied machine code. Thus hardware+microcode is what has to be verified.
      - MaxBarraclough 6y ago
        I see what you're saying now, that the microcode would also need to be published and studied, and it would also be necessary to ensure the delivered microcode matched the published microcode. I thought you were saying that the use of microcode would complicate verification of the hardware. If it's open hardware, I presume they'll publish the microcode.
        tyingq 6y ago
        "I thought you were saying that the use of microcode would complicate verification of the hardware." I do think that microcode opens up the possibility of subtle injections to follow code/hardware paths you might not easily predict. A really good talk on reverse engineering an ISA implementation: https://youtu.be/KrksBdWcZgQ https://youtu.be/KrksBdWcZgQ
- pabs3 6y ago
  Check out bunnie's talk on supply chain security: https://www.bunniestudios.com/blog/?p=5519 https://www.bunniestudios.com/blog/?p=5519
nl 6y ago
Thanks to Google you can now do this under some circumstances at the Skywater 130nm foundry https://fossi-foundation.org/2020/06/30/skywater-pdk https://fossi-foundation.org/2020/06/30/skywater-pdk
nsajko 6y ago
> One of the killer-features of RISC-V was being backdoor-free I think you are confused. RISC-V is just an ISA, not a hardware design, so it can't have a backdoor or, on the other hand, be free of them.
- hajile 6y ago
  It's a related idea. With a closed ISA, the only manufacturers are closed-source and I can't verify the chip is secure under any circumstances. With an open ISA, I may not be able to verify all designs are secure, but, I can verify that some are secure and choose one of those.
  - nsajko 6y ago
    No, there is no relation. You are conflating the ISA with its hardware designs. I'm not an expert, but imagine an ISA being like a C library API, in that case the hardware would be the APIs implementation.
throwaway4good 6y ago
Can you give an example of an chip with a hidden backdoor?
- PeCaN 6y ago
  All the Intel CPUs with RDRAND, although I guess that's not exactly hidden anymore.
  - KMag 6y ago
    Do you have any documentation that a back door has been found? I'm aware Ted Ts'o and others were worried of the possibility of backdoors in RDRAND, but I wasn't aware of any being confirmed. Also, the Wikipedia article for RDRAND really needs to be updated if a back door has been confirmed.
- MisterTea 6y ago
  https://en.wikipedia.org/wiki/Clipper_chip https://en.wikipedia.org/wiki/Clipper_chip
  - snvzz 6y ago
    He asked for a Hidden backdoor. That chip is literally an explicit backdoor.
    - KMag 6y ago
      On a side note, there was a workaround found for the backdoor: since it was using DH key agreement without digital signatures, both sides could use proxies that each generated a secret w, raised the outgoing DH public key to the power of w, and raised the incoming DH public key to the same power w. Alice's public key is g^x, where x is known to the government but is otherwise locked away deep in tamper-resistant hardware in the Clipper chip. Alice's proxy raises her (g^x)^w mod p = g^(xw) mod p before it hits the wire. Likewise, Bob's proxy raises (g^y)^v mod p = g^(y v) mod p. Alice's proxy raises Bob's seen public key to her secret exponent g^(y * v)^w mod p = g^(y * v * w) mod p before sending it to her clipper chip, and the tamper-resistant hardware calculates g^(y * v * w) ^ x mod p = g^(x * y * w * v) mod p. Bob's clipper chip likewise is given 9^(x * w)^v mod p and calculates g^(x * w)^v^y mod p = g^(x * y * w * v) mod p. Both chips calculate the same shared secret Skipkack key to encrypt the keystream. A government wiretapper knows x and y and sees g^(xw) and g^(yv), but can't calculate g^(xywv) unless they can compute discrete logarithms mod p. As a bonus, they'd get perfect forward secrecy whereas fixed DH public keys don't provide forward secrecy. Authentication worked by the phone displaying a hash of the session key, and the two users were expected to read the key hash to each other and recognize each other's voices. If they were being MitM'd, they wouldn't have identical session keys. Alice and Bob's authentication procedure would then still work just fine, since they'd still have identical session keys. If the government were wiretapping Alice, they'd of course detect the tampering because they'd be getting garbage data/failed checksums, but otherwise, the tampering would be undetectable, and Alice and Bob get hardware-accelerated 80-bit Skipjack encryption of their data stream, back when 56-bit DES was generally considered reasonably safe and 80-bit symmetric keys were considered sufficient for data classified SECRET and below. (Or maybe the tampering could be detected when the wiretappers went to look up Alice's fixed DH public key and couldn't find it in their escrow database... I forget if the escrow worked by having a database or if the chip encrypted the DH secret key with a master key and transmitted it at the start of every session. In any case, the whole thing wasn't that well thought out. It's also possible the DH exchange was signed using a malleable signature scheme using the same prime as DH, allowing Alice to raise the DH public key to a known-only-to-Alice power and calculate the power needed to raise the signature in order to still get a valid signature on the modified DH public key. Clearly, I forget the exact details.)
cheaprentalyeti 6y ago
Chip-making is material-intensive and needs to be done at a large capital-intensive scale in order to be competitive with other mercantilist states. You can't have a manufacturing-hostile environment here in this country and expect to be able to buy phones that are owned by you instead of President Xi and just on loan to you. Remember the fight over clipper chips? We've rearranged the electronics industry so that everything has a clipper chip, it's just outsourced and you can't see the details. (I say this like all of y'all reading this aren't younger than 35 and _remember_ the clipper chip).
someperson 6y ago
It's worth pointing out that fabless design companies build upon reference designs (whether ARM or RISC V) created by other companies (eg, ARM Holdings or SiFive), and both these kinds of businesses and are distinct from semiconductor fabrication companies like Taiwan's TSMC. Although fabless design companies like Allwinner and fabrication companies like SMIC both exist in China, there is accessible pathways to China-free chips, especially if you're willing to pay the premium for TSMC's high end manufacturing.
trasz 6y ago
Funny that you mention that, since most backdoors found so far were in silicon from US companies, not the Chinese :-)

ClumsyPilot 6y ago

But now consumer can choose who will spy on them!

MaxBarraclough 6y ago

> Back to square one. It's an open source processor, right? (Not just the RISC-V instruction-set, but the specific chip.) Could the chip be compared against that design to check for backdoors?

progre 6y ago
Is this chip open hardware? I didn't see that in the article but maybe you have other sources... In that case, you would still need is a electron scanning microscope and a known good reference to verify with.
nsajko 6y ago
> It's an open source processor, right? The term open source was used in the article, but did they mean that in an accurate sense, or was it just empty marketing? Also, I can't find the source after a short search. > Could the chip be compared against that design to check for backdoors? Don't know, but I'm sure much expertise, man-hours and expensive equipment would be necessary. Maybe prohibitively so.
tyingq 6y ago
Not sure how you would practically do that. You could thwart all that with a microcode layer anyway. I think the closest you're going to get to "verifiably secure" is an FPGA based core.
- MaxBarraclough 6y ago
  > Not sure how you would practically do that. The idea would be to somehow scan the design of the chip, presumably using an electron microscope as progre said, and compare it against the design's netlist. This isn't something I know much about, so perhaps it's not at all practical, but at least in principle this should be possible for chips with open designs. > You could thwart all that with a microcode layer anyway. I don't see that the particular techniques used in the design, such as microcode, would matter. The question is whether the published netlist matches the one on your chip. > I think the closest you're going to get to "verifiably secure" is an FPGA based core. I agree that's the most practical solution.
  - nsajko 6y ago
    > I don't see that the particular techniques used in the design, such as microcode, would matter. The question is whether the published netlist matches the one on your chip. You're missing the fact that microcode lies between the hardware and the user-supplied machine code. Thus hardware+microcode is what has to be verified.
    - MaxBarraclough 6y ago
      I see what you're saying now, that the microcode would also need to be published and studied, and it would also be necessary to ensure the delivered microcode matched the published microcode. I thought you were saying that the use of microcode would complicate verification of the hardware. If it's open hardware, I presume they'll publish the microcode.
      - tyingq 6y ago
        "I thought you were saying that the use of microcode would complicate verification of the hardware." I do think that microcode opens up the possibility of subtle injections to follow code/hardware paths you might not easily predict. A really good talk on reverse engineering an ISA implementation: https://youtu.be/KrksBdWcZgQ https://youtu.be/KrksBdWcZgQ
pabs3 6y ago
Check out bunnie's talk on supply chain security: https://www.bunniestudios.com/blog/?p=5519 https://www.bunniestudios.com/blog/?p=5519

nl 6y ago

Thanks to Google you can now do this under some circumstances at the Skywater 130nm foundry https://fossi-foundation.org/2020/06/30/skywater-pdk https://fossi-foundation.org/2020/06/30/skywater-pdk

nsajko 6y ago

> One of the killer-features of RISC-V was being backdoor-free I think you are confused. RISC-V is just an ISA, not a hardware design, so it can't have a backdoor or, on the other hand, be free of them.

hajile 6y ago
It's a related idea. With a closed ISA, the only manufacturers are closed-source and I can't verify the chip is secure under any circumstances. With an open ISA, I may not be able to verify all designs are secure, but, I can verify that some are secure and choose one of those.
- nsajko 6y ago
  No, there is no relation. You are conflating the ISA with its hardware designs. I'm not an expert, but imagine an ISA being like a C library API, in that case the hardware would be the APIs implementation.

throwaway4good 6y ago

Can you give an example of an chip with a hidden backdoor?

PeCaN 6y ago
All the Intel CPUs with RDRAND, although I guess that's not exactly hidden anymore.
- KMag 6y ago
  Do you have any documentation that a back door has been found? I'm aware Ted Ts'o and others were worried of the possibility of backdoors in RDRAND, but I wasn't aware of any being confirmed. Also, the Wikipedia article for RDRAND really needs to be updated if a back door has been confirmed.
MisterTea 6y ago
https://en.wikipedia.org/wiki/Clipper_chip https://en.wikipedia.org/wiki/Clipper_chip
- snvzz 6y ago
  He asked for a Hidden backdoor. That chip is literally an explicit backdoor.
  - KMag 6y ago
    On a side note, there was a workaround found for the backdoor: since it was using DH key agreement without digital signatures, both sides could use proxies that each generated a secret w, raised the outgoing DH public key to the power of w, and raised the incoming DH public key to the same power w. Alice's public key is g^x, where x is known to the government but is otherwise locked away deep in tamper-resistant hardware in the Clipper chip. Alice's proxy raises her (g^x)^w mod p = g^(xw) mod p before it hits the wire. Likewise, Bob's proxy raises (g^y)^v mod p = g^(y v) mod p. Alice's proxy raises Bob's seen public key to her secret exponent g^(y * v)^w mod p = g^(y * v * w) mod p before sending it to her clipper chip, and the tamper-resistant hardware calculates g^(y * v * w) ^ x mod p = g^(x * y * w * v) mod p. Bob's clipper chip likewise is given 9^(x * w)^v mod p and calculates g^(x * w)^v^y mod p = g^(x * y * w * v) mod p. Both chips calculate the same shared secret Skipkack key to encrypt the keystream. A government wiretapper knows x and y and sees g^(xw) and g^(yv), but can't calculate g^(xywv) unless they can compute discrete logarithms mod p. As a bonus, they'd get perfect forward secrecy whereas fixed DH public keys don't provide forward secrecy. Authentication worked by the phone displaying a hash of the session key, and the two users were expected to read the key hash to each other and recognize each other's voices. If they were being MitM'd, they wouldn't have identical session keys. Alice and Bob's authentication procedure would then still work just fine, since they'd still have identical session keys. If the government were wiretapping Alice, they'd of course detect the tampering because they'd be getting garbage data/failed checksums, but otherwise, the tampering would be undetectable, and Alice and Bob get hardware-accelerated 80-bit Skipjack encryption of their data stream, back when 56-bit DES was generally considered reasonably safe and 80-bit symmetric keys were considered sufficient for data classified SECRET and below. (Or maybe the tampering could be detected when the wiretappers went to look up Alice's fixed DH public key and couldn't find it in their escrow database... I forget if the escrow worked by having a database or if the chip encrypted the DH secret key with a master key and transmitted it at the start of every session. In any case, the whole thing wasn't that well thought out. It's also possible the DH exchange was signed using a malleable signature scheme using the same prime as DH, allowing Alice to raise the DH public key to a known-only-to-Alice power and calculate the power needed to raise the signature in order to still get a valid signature on the modified DH public key. Clearly, I forget the exact details.)

cheaprentalyeti 6y ago

Chip-making is material-intensive and needs to be done at a large capital-intensive scale in order to be competitive with other mercantilist states. You can't have a manufacturing-hostile environment here in this country and expect to be able to buy phones that are owned by you instead of President Xi and just on loan to you. Remember the fight over clipper chips? We've rearranged the electronics industry so that everything has a clipper chip, it's just outsourced and you can't see the details. (I say this like all of y'all reading this aren't younger than 35 and _remember_ the clipper chip).

someperson 6y ago

It's worth pointing out that fabless design companies build upon reference designs (whether ARM or RISC V) created by other companies (eg, ARM Holdings or SiFive), and both these kinds of businesses and are distinct from semiconductor fabrication companies like Taiwan's TSMC. Although fabless design companies like Allwinner and fabrication companies like SMIC both exist in China, there is accessible pathways to China-free chips, especially if you're willing to pay the premium for TSMC's high end manufacturing.

trasz 6y ago

Funny that you mention that, since most backdoors found so far were in silicon from US companies, not the Chinese :-)