ssl - Pre-master secret mistmatched when implementing Diffie-Hellman key exchange

Question

I am trying to implement DHE_DSS into go's crypto/tls package. Unfortunately I can not seem to get the PreMasterSecret (Z) to be the same, my basic workflow is:

Receive Server Key Exchange Message

• Extract P, G, Ys
• Verify using the digital signature provided

Prepare Client Key Exchange Message

• Create client's Xc
• Generate Yc (Yc = G^Xc % P)
• Generate Z (Z = Ys^Xc % P)
• Send back Yc, packed like so:

ckx := make([]byte, len(yC)+2)
ckx[0] = byte(len(Yc)>>8)
ckx[1] = byte(len(Yc))
copy(ckx[2:], yBytes)

However, when I am debugging this with gnutls-serv the two PreMasterSecrets (Z) are different. Do I need to sign the returned Yc, or perhaps pack it in another way? I can not see anything in RFC 5246 to suggest this.

<-- EDIT -->

Here is a patch of my changes:

https://08766345559465695203.googlegroups.com/attach/48587532c74b4348/crypto.patch?part=4&view=1&vt=ANaJVrHbwydqEZc3zjUWqQ5C8Q5zEkWXZLdL0w6JJG3HYntOlBurUTY7mc9xR9OTfE0bJxs4eeL5a5SGd2jj9eIfXcwJQgLvJchXOgkYKBBynbPfshY8kuQ

question from:https://stackoverflow.com/questions/12422908/pre-master-secret-mistmatched-when-implementing-diffie-hellman-key-exchange

Answer 1

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