Start working on de-obfuscating ephemeral keys from remote peers

Makefile

@@ -27,7 +27,7 @@ clean:
 	$(GO) clean -v
 
 fmt:
-	find . -name '*.go' -exec gofmt -w -s {} \;
+	find . -name '*.go' -exec gofumpt -w {} \;
 
 info:
 	echo "GOROOT: ${GOROOT}"

lib/transport/noise/noise_obfs.go

@@ -0,0 +1,44 @@
+package noise
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"encoding/hex"
+
+	"github.com/flynn/noise"
+	"github.com/go-i2p/go-i2p/lib/common/router_address"
+	log "github.com/sirupsen/logrus"
+)
+
+// Noise obfuscation functions used in I2P NTCP2 and SSU2 Handshakes,
+// including obfuscating the ephemeral keys with a known key and IV found
+// in the netDb.
+
+func AESDeObfuscateEphemeralKeys(cipherText string, config noise.Config, bob router_address.RouterAddress) (*noise.DHKey, error) {
+	bobsStaticKey, err := bob.StaticKey()
+	if err != nil {
+		return nil, err
+	}
+	bobsInitializatonVector, err := bob.InitializationVector()
+	if err != nil {
+		return nil, err
+	}
+	log.WithFields(
+		log.Fields{
+			"at": "(noise) AESObfuscateEphemeralKeys",
+		}).Debugf("getting ready to obfuscate our ephemeral keys with bob's static key %s and IV %s", bobsStaticKey, bobsInitializatonVector)
+	cipherTextDecoded, err := hex.DecodeString(cipherText)
+	if err != nil {
+		return nil, err
+	}
+	block, err := aes.NewCipher(bobsStaticKey[:])
+	if err != nil {
+		return nil, err
+	}
+	mode := cipher.NewCBCDecrypter(block, bobsInitializatonVector[:])
+	mode.CryptBlocks([]byte(cipherTextDecoded), []byte(cipherTextDecoded))
+	dhk := &noise.DHKey{
+		Private: cipherTextDecoded,
+	}
+	return dhk, nil
+}