wsddn / go-ecdh Goto Github PK

In the curve25519.go have the following code:

priv[0] &= 248
priv[31] &= 127
priv[31] |= 64

It's already done in the golang.org/x/crypto/curve25519.

I cannot find 'code.google.com/p/go.crypto/curve25519', where is it?

Function GenerateKey returns 32 random bytes. It does not apply further steps, described here:

     mysecret[0] &= 248;
     mysecret[31] &= 127;
     mysecret[31] |= 64;

I think you need to check that the public key you've been given (the other party's key, that is) is actually on the curve, otherwise it's possible for an attacker to derive your private key. See Practical Invalid Curve Attacks on TLS-ECDH.

It's this kind of thing, of course, that makes implementing cryptographic algorithms tricky.

It might also be worth reading this paper about security issues in Diffie-Hellman. Some of the things in there don't apply, as far as I can tell, to elliptic curve Diffie-Hellman because of properties of the group (having the identity at infinity, in particular, appears to rule out attacks that choose the identity as the public key), but it seems a decent overview of things you'd need to pay attention to to make a genuinely secure DH implementation.

I have a current project that uses ECDH from this embedded library and was hoping to get your library to talk to it.

https://github.com/kmackay/micro-ecc
It uses different key sizes, where it looks like yours uses 32,32 public,private

Public Key (64 bytes)
Private Key (32 bytes)

I believe it's due to the way the referenced github library defaulted, but i cannot make changes to the embedded device that has it implemented using library above.

I am not familiar enough with the algorithm to know, in all the places you have a hard coded in size, how much would get corrupted by making the change and if the hash etc belongs to one of the key sizes.

Is it possible to wrap your sizes in a const () at the top, and make it easily changeable ?

Structure curve25519ECDH has anonymous member ECDH. It is not needed there. An interface is implemented implicitly.