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Yep, secret derivation checks it out sage math

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* Meaning the way we calculate the shared secret
* They get M = (G * x_us) * b_0, they calc the secret with M * x_them
   * M * x_them = G * x_us * b_ * x_them
* We have H = (G * x_them), we calc with H * (x_us * b_0 mod n))
  * H * (x_us * b_0) = G * x_them * x_us * b_0
This commit is contained in:
Olaoluwa Osuntokun 2015-10-08 17:19:11 -07:00
parent 032c24824a
commit 90316e6426
1 changed files with 5 additions and 5 deletions
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10
sphinx.go
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@ -49,22 +49,22 @@ func GenerateSphinxHeader(dest LnAddr, identifier wire.ShaHash, paymentPath []No
hopSharedSecret[0] = sha256.Sum256(btcec.GenerateSharedSecret(sessionKey, paymentPath[0]))
hopBlindingFactors[0] = computeBlindingFactor(hopEphemeralPubKeys[0], hopSharedSecret[0][:])
// x * b_{0} mod n
// x * b_{0} mod n. Becomes x * b_{0} * b_{1} * ..... * b_{n} mod curve_order, etc.
cummulativeBlind := new(big.Int).Mul(sessionKey.X, new(big.Int).SetBytes(hopBlindingFactors[0][:]))
cummulativeBlind.Mod(cummulativeBlind, btcec.S256().N)
// Now recursively compute the ephemeral ECDH pub keys, the shared
// secret, and blinding factor for each hop.
for i := 1; i < numHops-1; i++ {
// a_{n} = a_{n-1} x c_{n-1}
// hopEphemeralPubKeys[i] = ScalarBaseMult(cummulativeBlind.Bytes())
hopEphemeralPubKeys[i] = blindGroupElement(hopEphemeralPubKeys[i-1], cummulativeBlind.Bytes())
// a_{n} = a_{n-1} x c_{n-1} -> (Y_prev_pub_key x prevBlindingFactor)
hopEphemeralPubKeys[i] = blindGroupElement(hopEphemeralPubKeys[i-1], hopBlindingFactors[i-1][:])
// s_{n} = sha256( y_{n} x c_{n-1} )
// s_{n} = sha256( y_{n} x c_{n-1} ) -> Y_their_pub_key x (x_our_priv * all prev blinding factors mod curve_order)
hopSharedSecret[i] = sha256.Sum256(blindGroupElement(paymentPath[i], cummulativeBlind.Bytes()).X.Bytes())
// b_{n} = sha256(a_{n} || s_{n})
hopBlindingFactors[i] = computeBlindingFactor(hopEphemeralPubKeys[i], hopSharedSecret[i][:])
// TODO(roasbeef): prob don't need to store all blinding factors, only the prev...
// c_{n} = c_{n-1} * b_{n} mod curve_order
cummulativeBlind.Mul(cummulativeBlind, new(big.Int).SetBytes(hopBlindingFactors[i][:]))