id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	launchpad_bug
217	Ed25519-based mutable files -- fast file creation, possibly smaller URLs	zooko	zooko	"Mole2 and The_8472 and I had a conversation on IRC which leads to the following ideas.  These are late-night-sleepy and fresh ideas, so they may be holey.

To create a new mutable file choose a random seed ''r'', and use it to produce a public/private key pair (for concreteness, think [http://en.wikipedia.org/wiki/Digital_Signature_Algorithm DSA], so your private key is a just the random 256-bit number ''r'' and the public key is just ''g''^''r''^ mod a big prime, let's say maybe 4096-bits).

Now let the symmetric encryption key ''k'' be the secure hash of the public key!

Now encrypt the file and upload it.  Now encrypt the public key and upload it.  Now if you give someone ''k'' they can read and verify.  If you give them ''r'' they can read and write (sign).

Let the ""location index"" be derived from the read-capability.


To squeeze ''r'' you can pick a smaller random number for ''r'', maybe 128-bits and use a secure hash to expand it to 256-bits.  This is cryptographically questionable, but it may be worth asking those questions in order to get really nice ""printable capability"" lengths, as well as a pleasing simplicity of crypto structure."	enhancement	assigned	major		code-mutable	0.7.0		mutable crypto newcaps performance research	tahoe-dev@…