[messaging] MITM-safe communication w/o authentication possible?

Ximin Luo infinity0 at pwned.gg
Mon Nov 30 00:34:53 PST 2015

On 30/11/15 03:09, Karl wrote:
> On 11/29/15, Ximin Luo <infinity0 at pwned.gg> wrote:
>> On 30/11/15 00:53, Ethan Heilman wrote:
>>>> No human user thinks in terms of contacting cryptographic identities.
>>>> [..]
>>> Am I correct in my understanding that .onion addresses work this way?
>> [..]
>> (To put it another way, "self-authenticating" is a joke. My GPG fingerprint
>> is self-authenticating too. Just go talk to 0x1318efac5fbbdbce, it doesn't
>> matter who that is in real life.... what? no takers?)
> It seems reasonable to me that the important part of somebody's
> identity would be their behavior rather than their body or name.  But
> to use fingerprints as identifiers, you'd need a way for humans to
> remember and compare them.  Some way of hashing data into something
> memorable but complex enough to be collision-resistant, like a
> detailed image of a computer-generated human face.
> I wonder if anybody's done something like that.

For an authentication system to actually be safe, it needs to allow me to *distinguish* my contact from any other attacker. For a cryptographic protocol, this means that my contact must know some secret information that attackers do not have. One can generally assume that "behaviour" / "biometrics" do not fit this secrecy requirement since an attacker can just forge it - sometimes literally by copying it as it is generated, as is effectively what happens in MITM.



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