1 files changed, 66 insertions, 0 deletions
diff --git a/vendor/go.mau.fi/libsignal/keys/root/RootKey.go b/vendor/go.mau.fi/libsignal/keys/root/RootKey.go
new file mode 100644
index 00000000..e925bc76
--- /dev/null
+++ b/vendor/go.mau.fi/libsignal/keys/root/RootKey.go
@@ -0,0 +1,66 @@
+// Package root provides root keys which are used to derive new chain and
+// root keys in a ratcheting session.
+package root
+
+import (
+	"go.mau.fi/libsignal/ecc"
+	"go.mau.fi/libsignal/kdf"
+	"go.mau.fi/libsignal/keys/chain"
+	"go.mau.fi/libsignal/keys/session"
+)
+
+// DerivedSecretsSize is the size of the derived secrets for root keys.
+const DerivedSecretsSize = 64
+
+// KdfInfo is used as the info for message keys to derive secrets using a Key Derivation Function
+const KdfInfo string = "WhisperRatchet"
+
+// NewKey returns a new RootKey given the key derivation function and bytes.
+func NewKey(kdf kdf.HKDF, key []byte) *Key {
+	rootKey := Key{
+		kdf: kdf,
+		key: key,
+	}
+
+	return &rootKey
+}
+
+// Key is a structure for RootKeys, which are used to derive a new set of chain and root
+// keys for every round trip of messages.
+type Key struct {
+	kdf kdf.HKDF
+	key []byte
+}
+
+// Bytes returns the RootKey in bytes.
+func (k *Key) Bytes() []byte {
+	return k.key
+}
+
+// CreateChain creates a new RootKey and ChainKey from the recipient's ratchet key and our private key.
+func (k *Key) CreateChain(theirRatchetKey ecc.ECPublicKeyable, ourRatchetKey *ecc.ECKeyPair) (*session.KeyPair, error) {
+	theirPublicKey := theirRatchetKey.PublicKey()
+	ourPrivateKey := ourRatchetKey.PrivateKey().Serialize()
+
+	// Use our key derivation function to calculate a shared secret.
+	sharedSecret := kdf.CalculateSharedSecret(theirPublicKey, ourPrivateKey)
+	derivedSecretBytes, err := kdf.DeriveSecrets(sharedSecret[:], k.key, []byte(KdfInfo), DerivedSecretsSize)
+	if err != nil {
+		return nil, err
+	}
+
+	// Split the derived secret bytes in half, using one half for the root key and the second for the chain key.
+	derivedSecrets := session.NewDerivedSecrets(derivedSecretBytes)
+
+	// Create new root and chain key structures from the derived secrets.
+	rootKey := NewKey(k.kdf, derivedSecrets.RootKey())
+	chainKey := chain.NewKey(k.kdf, derivedSecrets.ChainKey(), 0)
+
+	// Create a session keypair with the generated root and chain keys.
+	keyPair := session.NewKeyPair(
+		rootKey,
+		chainKey,
+	)
+
+	return keyPair, nil
+}