On 27/06/14 08:59, Ben Laurie wrote: > On 26 June 2014 21:53, Guy K. Kloss <[email protected]> wrote: >> On 27/06/14 12:28, Daniel Kahn Gillmor wrote: >>> But as for courts, I think many transcripts from unencrypted, >>> non-cryptographically-bound communications that are presented to judges >>> and juries are in the form of word documents -- pretty much the >>> layperson's classic example of an editable document. And people still >>> get convicted with those documents, even if there was no attempt to >>> claim cryptographic proof-of-origin. >> >> Yes, that's very sad, indeed. Especially when viewing the fact that >> there are web sites that can help you "digitally sign" documents by >> pasting either a scanned signature or "Your Name" in a chosen font under >> the document. And these are deemed to be legally valid ... > > Signatures, at least in UK law, are about intent. See > http://www.apache-ssl.org/tech-legal.pdf ("Signatures: an Interface > between Law and Technology").
I see ciphertext deniability as a necessary-not-sufficient property to build
systems that might eventually give physical plausible deniability in court.
Ciphertext deniability gives you the ability to deny "the bits-and-bytes" of
the communication, but not the real physical fact "witness W observed these
bits on this physical medium, from address A to address B". People are building
other communications systems that leak less information than this, and this
would improve physical plausible deniability.
Compared to a non-deniable ciphertext, where it doesn't matter where I got the
bits-and-bytes from - it's hard to argue your signature was made by someone
else, even if I presented the bits-and-bytes on my own usb stick and refused to
tell anyone where I got it. I don't need to invoke the ISP here ("a trusted
party" in the judge's eyes); but with a deniable ciphertext, I do need to
invoke other parties.
X
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