Moving forward with Curve25519

[Werner Koch]

On Wed,  6 Aug 2014 11:20, gniibe at fsij.org said:

> Please clarify: X in MPI?
>
> In draft-josefsson-tls-curve25519-05, it seems that it's in original
> format (little endian).

I would use whatever has been specified for the curve.  Or well in this
case in the software describing the use of the curve.  I have not
checked but I am pretty sure that OpenSSH uses the native (i.e. littel
endian format).  So let's define it as 

   0x41 || X_in_native_format

> And prefix 0x40 for Curve25519 ECDH is in original format?

   0x40 || X_and_Y_in_native_format

If Curve25519 specifies its own compressed format (does it?) that would
be that format.  If it does not define a compressed format it would be
the full point in the format defined for the Curve25519.


Salam-Shalom,

   Werner


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