diff --git a/crypto/cipher/keyexchange.go b/crypto/cipher/keyexchange.go
new file mode 100644
index 000000000..b55e81302
--- /dev/null
+++ b/crypto/cipher/keyexchange.go
@@ -0,0 +1,13 @@
+package cipher
+
+import (
+	"github.com/mailchain/mailchain/crypto"
+)
+
+type KeyExchange interface {
+	// EphemeralKey generates a private/public key pair.
+	EphemeralKey() (private crypto.PrivateKey, public crypto.PublicKey, err error)
+
+	// SharedSecret computes a secret value from ephemeralKey private key and recipientKey public key.
+	SharedSecret(ephemeralKey crypto.PrivateKey, recipientKey crypto.PublicKey) ([]byte, error)
+}