add keypair derivation

zk-token-sdk/src/encryption/elgamal.rs

@@ -57,6 +57,14 @@ impl ElGamal {
         }
     }
 
+    #[cfg(not(target_arch = "bpf"))]
+    #[allow(non_snake_case)]
+    pub fn from_signing_key(signing_key: &SigningKey, label: &'static [u8]) -> Self {
+        let secret = ElGamalSecretKey::new(signing_key, label);
+        let public = ElGamalPubkey::new(&secret);
+        Self {secret, public}
+    }
+
     /// On input a public key and a message to be encrypted, the function
     /// returns an ElGamal ciphertext of the message under the public key.
     #[cfg(not(target_arch = "bpf"))]