fix up elg crypto parts

lib/crypto/decrypt.go

@@ -0,0 +1,15 @@
+package crypto
+
+// decrypts data
+type Decrypter interface {
+  // decrypt a block of data
+  // return decrypted block or nil and error if error happens
+  Decrypt(data []byte) ([]byte, error)
+}
+
+type PrivateEncryptionKey interface {
+
+  // create a new decryption object for this private key to decrypt data encrypted to our public key
+  // returns decrypter or nil and error if the private key is in a bad format
+  NewDecrypter() (Decrypter, error)
+}