curve25519

curve25519-donna plus curve25519 signing and verifying as Erlang NIFs.

Install

This is only tested on i386 and X86_64 Debian. It might very well work on other platforms as well.

$ cd curve25519/
$ rebar3 clean compile eunit doc

Usage

Generate a curve25519 keypair. The function returns a tuple with the private and public key.

$ rebar3 shell
Erlang/OTP 22 [erts-10.4] [source] [64-bit] [smp:2:2] [ds:2:2:10] [async-threads:1]

Eshell V10.4  (abort with ^G)
1> {Private_key, Public_key} = curve25519:key_pair().
{<<248,145,8,249,68,34,194,102,57,70,243,15,115,45,100,
   103,228,117,122,129,128,34,221,61,134,185,211,174,...>>,
 <<194,212,123,58,151,194,124,83,9,213,64,100,20,201,164,
   59,115,179,32,58,37,153,44,114,115,98,253,...>>}
2> {Private_key_1, Public_key_1} = curve25519:key_pair(<<0:256>>).
{<<0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
   0,...>>,
 <<47,229,125,163,71,205,98,67,21,40,218,172,95,187,41,7,
   48,255,246,132,175,196,207,194,237,144,153,...>>}

Do DH.

show_me_how() ->
    Secret_A = <<"01234567890123456789012345678901">>,
    Private_key_A = make_private(Secret_A),
    Public_key_A = make_public(Private_key_A),

    Secret_B = <<"abcdefghijklmnopqrstuvwxyz012345">>,
    Private_key_B = make_private(Secret_B),
    Public_key_B = make_public(Private_key_B),
    
    Shared_key_A = make_shared(Public_key_B, Private_key_A),
    Shared_key_B = make_shared(Public_key_A, Private_key_B),
    
    Shared_key_A == Shared_key_B.

Now sign and verify:

9> l(curve25519).                  
{module,curve25519}
10> Csk = curve25519:make_private().
<<128,231,156,248,52,34,71,100,187,134,147,59,96,169,184,
  170,126,38,111,68,125,149,90,52,37,55,15,127,139,...>>
11> Cpk = curve25519:make_public(Csk).       
<<182,42,23,82,131,51,198,210,30,63,237,171,191,136,86,
  254,27,255,29,205,8,244,47,86,204,98,201,30,255,...>>
12> M = "Stupid message".              
"Stupid message"
13> Sig = curve25519:sign(Csk, M).     
<<214,205,244,91,4,136,155,160,13,146,224,109,111,21,109,
  38,28,118,159,101,149,208,249,74,121,153,174,150,178,...>>
14> curve25519:verify(Cpk, M, Sig).    
true
15> curve25519:verify(Cpk, "forged message", Sig).
false