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You can proof that a digital file existed at a given time and hasn't been altered since. It is something that I use on a daily basis.

woodruffw 4y ago
We've been able to do this for decades. It's a core part of our PKI ecosystem.
- WFHRenaissance 4y ago
  Surely, but PKI still relies on cert authorities which have been compromised before
  - woodruffw 4y ago
    DeFi is, after all, notably devoid of serious compromises :-) More seriously: there are cryptographically sound schemes (like CT) that address CA compromise.
    - WFHRenaissance 4y ago
      CT is cool, but who is writing/submitting those logs?
      - woodruffw 4y ago
        There are multiple, independent entities both maintaining and submitting to the logs. The short answer: CAs submit precertificates to the logs; the logs respond with signed certificate timestamps that are embedded within the ultimate certificate rendered to the user. User agents (i.e., browsers) cross-check against the logs using the SCTs. Third parties ("monitors") additionally watch the logs for suspicious events (unexpected issuances, unusual certificates being signed for, etc.) There's a nice visualization here[1]. [1]: https://certificate.transparency.dev/howctworks/#stepby https://certificate.transparency.dev/howctworks/#stepby
- razemio 4y ago
  Not without a middlemen that we trust (cert authority in this case).
  - vlovich123 4y ago
    That's certainly not true. P2P file transfer systems have long provided cryptographic guarantees that the file you receive hasn't been modified by anyone, even though you're fetching it from multiple untrusted sources simultaneously. Merkle trees have made this more efficient and offered maybe more guarantees, but being able to have files be transferred in a distributed fashion but impervious to corruption is not a new invention. The one thing cryptocurrencies have not figured out how to solve is the root problem of all PKI systems, which is establishing trust of identity.
    - razemio 4y ago
      That is different use case. How would I prove that a file existed without a middlemen? I would gladly switch since the method I am currently using isn't exactly cheap.
      - joshstrange 4y ago
        Could you share you use-case and current method? I have no advice for you I'm just interested in how this is being used and who is providing said services.
      - woodruffw 4y ago
        > How would I prove that a file existed without a middlemen? How are you defining "middleman"? You can do this with any basic commitment scheme: take a cryptographically secure hash of your file and publish it somewhere that's either (1) trivially copyable, or (2) difficult to tamper with. Alternatively, you could do an online scheme where someone asks you for your proof and you present them with your hash after being challenged. That's a gross oversimplification, but it's the general idea. (In general, "prove that a file existed" is not something that you often want to do in the real world. What is it you're actually trying to accomplish?)
- onionisafruit 4y ago
  PKI is cryptography.
  - woodruffw 4y ago
    Where was it implied that it wasn't? Of course it's cryptography.
    - onionisafruit 4y ago
      Nevermind me. I was being an idiot thinking crypto was cryptography.
      - orwin 4y ago
        For 30+ year olds who learned by cracking video games, used eMule/limewire and partipated in crypto CTF, crypto is still cryptography, but let's be honest, this usage is loosing.
mrow84 4y ago
How do you use it, out of interest?

woodruffw 4y ago

We've been able to do this for decades. It's a core part of our PKI ecosystem.

WFHRenaissance 4y ago
Surely, but PKI still relies on cert authorities which have been compromised before
- woodruffw 4y ago
  DeFi is, after all, notably devoid of serious compromises :-) More seriously: there are cryptographically sound schemes (like CT) that address CA compromise.
  - WFHRenaissance 4y ago
    CT is cool, but who is writing/submitting those logs?
    - woodruffw 4y ago
      There are multiple, independent entities both maintaining and submitting to the logs. The short answer: CAs submit precertificates to the logs; the logs respond with signed certificate timestamps that are embedded within the ultimate certificate rendered to the user. User agents (i.e., browsers) cross-check against the logs using the SCTs. Third parties ("monitors") additionally watch the logs for suspicious events (unexpected issuances, unusual certificates being signed for, etc.) There's a nice visualization here[1]. [1]: https://certificate.transparency.dev/howctworks/#stepby https://certificate.transparency.dev/howctworks/#stepby
razemio 4y ago
Not without a middlemen that we trust (cert authority in this case).
- vlovich123 4y ago
  That's certainly not true. P2P file transfer systems have long provided cryptographic guarantees that the file you receive hasn't been modified by anyone, even though you're fetching it from multiple untrusted sources simultaneously. Merkle trees have made this more efficient and offered maybe more guarantees, but being able to have files be transferred in a distributed fashion but impervious to corruption is not a new invention. The one thing cryptocurrencies have not figured out how to solve is the root problem of all PKI systems, which is establishing trust of identity.
  - razemio 4y ago
    That is different use case. How would I prove that a file existed without a middlemen? I would gladly switch since the method I am currently using isn't exactly cheap.
    - joshstrange 4y ago
      Could you share you use-case and current method? I have no advice for you I'm just interested in how this is being used and who is providing said services.
    - woodruffw 4y ago
      > How would I prove that a file existed without a middlemen? How are you defining "middleman"? You can do this with any basic commitment scheme: take a cryptographically secure hash of your file and publish it somewhere that's either (1) trivially copyable, or (2) difficult to tamper with. Alternatively, you could do an online scheme where someone asks you for your proof and you present them with your hash after being challenged. That's a gross oversimplification, but it's the general idea. (In general, "prove that a file existed" is not something that you often want to do in the real world. What is it you're actually trying to accomplish?)
onionisafruit 4y ago
PKI is cryptography.
- woodruffw 4y ago
  Where was it implied that it wasn't? Of course it's cryptography.
  - onionisafruit 4y ago
    Nevermind me. I was being an idiot thinking crypto was cryptography.
    - orwin 4y ago
      For 30+ year olds who learned by cracking video games, used eMule/limewire and partipated in crypto CTF, crypto is still cryptography, but let's be honest, this usage is loosing.

mrow84 4y ago

How do you use it, out of interest?