Use interior mutability for the Client's PRNG; add constructor.

willow/benches/shell_benchmarks.rs

@@ -131,9 +131,7 @@ fn setup_base(args: &Args) -> BaseInputs {
     // Create client.
     let kahe = ShellKahe::new(kahe_config.clone(), CONTEXT_STRING).unwrap();
     let vahe = ShellVahe::new(ahe_config.clone(), CONTEXT_STRING).unwrap();
-    let seed = SingleThreadHkdfPrng::generate_seed().unwrap();
-    let prng = SingleThreadHkdfPrng::create(&seed).unwrap();
-    let client = WillowV1Client { kahe, vahe, prng };
+    let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe).unwrap();
 
     // Create decryptor.
     let vahe = ShellVahe::new(ahe_config.clone(), CONTEXT_STRING).unwrap();
@@ -218,7 +216,7 @@ struct VerifierInputs {
 }
 
 fn setup_verifier_verify_client_message(args: &Args) -> VerifierInputs {
-    let mut inputs = setup_base(args);
+    let inputs = setup_base(args);
     let mut decryption_request_contributions = vec![];
     for _ in 0..args.n_iterations {
         // Generates a plaintext and encrypts.
@@ -257,7 +255,7 @@ fn run_verifier_verify_client_message(inputs: &mut VerifierInputs) {
 }
 
 fn setup_server_handle_client_message(args: &Args) -> ServerInputs {
-    let mut inputs = setup_base(args);
+    let inputs = setup_base(args);
     let mut ciphertext_contributions = vec![];
     for _ in 0..args.n_iterations {
         // Generates a plaintext and encrypts.

willow/src/api/client.rs

@@ -86,9 +86,7 @@ impl WillowShellClient {
         let context_bytes = aggregation_config.compute_context_bytes()?;
         let kahe = ShellKahe::new(kahe_config, &context_bytes)?;
         let vahe = ShellVahe::new(ahe_config, &context_bytes)?;
-        let client_seed = SingleThreadHkdfPrng::generate_seed()?;
-        let prng = SingleThreadHkdfPrng::create(&client_seed)?;
-        let client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe)?;
         Ok(WillowShellClient(client))
     }
 

willow/src/traits/client.rs

@@ -26,7 +26,7 @@ pub trait SecureAggregationClient: HasKahe + HasVahe {
     /// Creates a client message to be sent to the Server.
     /// nonce is used for the VAHE encryption, has to be unique.
     fn create_client_message(
-        &mut self,
+        &self,
         plaintext: &Self::PlaintextSlice<'_>,
         signed_public_key: &DecryptorPublicKey<<Self as HasVahe>::Vahe>,
         nonce: &[u8],

willow/src/willow_v1/client.rs

@@ -15,13 +15,15 @@
 use client_traits::SecureAggregationClient;
 use kahe_traits::{HasKahe, KaheBase, KaheEncrypt, KaheKeygen, TrySecretKeyInto};
 use messages::{ClientMessage, DecryptorPublicKey};
+use prng_traits::SecurePrng;
+use std::cell::RefCell;
 use vahe_traits::{HasVahe, VaheBase, VerifiableEncrypt};
 
 /// Lightweight client directly exposing KAHE/VAHE types.
 pub struct WillowV1Client<Kahe: KaheBase, Vahe: VaheBase> {
     pub kahe: Kahe,
     pub vahe: Vahe,
-    pub prng: Kahe::Rng, // Using a single PRNG for both VAHE and KAHE.
+    pub prng: RefCell<Kahe::Rng>, // Using a single PRNG for both VAHE and KAHE.
 }
 
 impl<Kahe: KaheBase, Vahe: VaheBase> HasKahe for WillowV1Client<Kahe, Vahe> {
@@ -38,6 +40,17 @@ impl<Kahe: KaheBase, Vahe: VaheBase> HasVahe for WillowV1Client<Kahe, Vahe> {
     }
 }
 
+impl<Kahe: KaheBase, Vahe: VaheBase> WillowV1Client<Kahe, Vahe> {
+    pub fn new_with_randomly_generated_seed(
+        kahe: Kahe,
+        vahe: Vahe,
+    ) -> Result<Self, status::StatusError> {
+        let seed = Kahe::Rng::generate_seed()?;
+        let prng = RefCell::new(Kahe::Rng::create(&seed)?);
+        Ok(Self { kahe, vahe, prng })
+    }
+}
+
 /// Implementation of the `SecureAggregationClient` trait for the generic
 /// KAHE/VAHE client, using WillowCommon as the common types (e.g. protocol
 /// messages are directly the AHE public key and ciphertexts).
@@ -51,16 +64,17 @@ where
     type PlaintextSlice<'a> = <Kahe as KaheBase>::PlaintextSlice<'a>;
 
     fn create_client_message(
-        &mut self,
+        &self,
         plaintext: &Self::PlaintextSlice<'_>,
         signed_public_key: &DecryptorPublicKey<Vahe>,
         nonce: &[u8],
     ) -> Result<ClientMessage<Kahe, Vahe>, status::StatusError> {
         // Generate a new KAHE key.
-        let kahe_secret_key = self.kahe.key_gen(&mut self.prng)?;
+        let kahe_secret_key = self.kahe.key_gen(&mut self.prng.borrow_mut())?;
 
         // Encrypt long plaintext with KAHE.
-        let kahe_ciphertext = self.kahe.encrypt(plaintext, &kahe_secret_key, &mut self.prng)?;
+        let kahe_ciphertext =
+            self.kahe.encrypt(plaintext, &kahe_secret_key, &mut self.prng.borrow_mut())?;
 
         // Convert KAHE secret key into short AHE plaintext.
         let ahe_plaintext: Vahe::Plaintext = self.kahe.try_secret_key_into(kahe_secret_key)?;
@@ -70,7 +84,7 @@ where
             &ahe_plaintext,
             signed_public_key,
             nonce,
-            &mut self.prng,
+            &mut self.prng.borrow_mut(),
         )?;
 
         // Keep a copy of the nonce so the message can be forwarded as-is.
@@ -112,9 +126,7 @@ mod test {
         let (kahe_config, ahe_config) = create_shell_configs(&aggregation_config)?;
         let kahe = ShellKahe::new(kahe_config, CONTEXT_STRING)?;
         let vahe = ShellVahe::new(ahe_config, CONTEXT_STRING)?;
-        let client_seed = SingleThreadHkdfPrng::generate_seed()?;
-        let prng = SingleThreadHkdfPrng::create(&client_seed)?;
-        let mut client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe)?;
 
         // Generate AHE keys.
         let mut testing_decryptor =
@@ -153,17 +165,13 @@ mod test {
         let (kahe_config, ahe_config) = create_shell_configs(&aggregation_config)?;
         let kahe = ShellKahe::new(kahe_config, CONTEXT_STRING)?;
         let vahe = ShellVahe::new(ahe_config, CONTEXT_STRING)?;
-        let client1_seed = SingleThreadHkdfPrng::generate_seed()?;
-        let prng = SingleThreadHkdfPrng::create(&client1_seed)?;
-        let mut client1 = WillowV1Client { kahe, vahe, prng };
+        let client1 = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe)?;
 
         // Create a second client.
         let (kahe_config, ahe_config) = create_shell_configs(&aggregation_config)?;
         let kahe = ShellKahe::new(kahe_config, CONTEXT_STRING)?;
         let vahe = ShellVahe::new(ahe_config, CONTEXT_STRING)?;
-        let client2_seed = SingleThreadHkdfPrng::generate_seed()?;
-        let prng = SingleThreadHkdfPrng::create(&client2_seed)?;
-        let mut client2 = WillowV1Client { kahe, vahe, prng };
+        let client2 = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe)?;
 
         // Generate AHE keys.
         let mut testing_decryptor =

willow/src/willow_v1/server.rs

@@ -392,9 +392,7 @@ mod tests {
             CONTEXT_STRING,
         )
         .unwrap();
-        let seed = SingleThreadHkdfPrng::generate_seed()?;
-        let prng = SingleThreadHkdfPrng::create(&seed)?;
-        let mut client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe)?;
 
         // Create decryptor.
         let vahe = ShellVahe::new(

willow/src/willow_v1/verifier.rs

@@ -305,9 +305,7 @@ mod tests {
             CONTEXT_STRING,
         )
         .unwrap();
-        let seed = SingleThreadHkdfPrng::generate_seed()?;
-        let prng = SingleThreadHkdfPrng::create(&seed)?;
-        let mut client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe)?;
 
         // Create decryptor, which needs its own `vahe` (with same public polynomials
         // generated from the seeds) and `prng`.

willow/tests/willow_v1_shell.rs

@@ -57,9 +57,7 @@ fn encrypt_decrypt_one() -> googletest::Result<()> {
     let kahe =
         ShellKahe::new(create_shell_kahe_config(&aggregation_config).unwrap(), CONTEXT_STRING)
             .unwrap();
-    let seed = SingleThreadHkdfPrng::generate_seed().unwrap();
-    let prng = SingleThreadHkdfPrng::create(&seed).unwrap();
-    let mut client = WillowV1Client { kahe, vahe, prng };
+    let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe).unwrap();
 
     // Create decryptor, which needs its own `vahe` (with same public polynomials
     // generated from the seeds) and `prng`.
@@ -147,9 +145,7 @@ fn encrypt_decrypt_one_serialized() -> googletest::Result<()> {
     let vahe =
         ShellVahe::new(create_shell_ahe_config(max_number_of_decryptors).unwrap(), CONTEXT_STRING)
             .unwrap();
-    let seed = SingleThreadHkdfPrng::generate_seed().unwrap();
-    let prng = SingleThreadHkdfPrng::create(&seed).unwrap();
-    let mut client = WillowV1Client { kahe, vahe, prng };
+    let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe).unwrap();
 
     // Create decryptor, which needs its own `vahe` (with same public polynomials
     // generated from the seeds) and `prng`.
@@ -287,9 +283,7 @@ fn encrypt_decrypt_multiple_clients() -> googletest::Result<()> {
         let kahe =
             ShellKahe::new(create_shell_kahe_config(&aggregation_config).unwrap(), CONTEXT_STRING)
                 .unwrap();
-        let seed = SingleThreadHkdfPrng::generate_seed().unwrap();
-        let prng = SingleThreadHkdfPrng::create(&seed).unwrap();
-        let client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe).unwrap();
         clients.push(client);
     }
 
@@ -420,9 +414,7 @@ fn encrypt_decrypt_multiple_clients_including_invalid_proofs() -> googletest::Re
         let kahe =
             ShellKahe::new(create_shell_kahe_config(&aggregation_config).unwrap(), CONTEXT_STRING)
                 .unwrap();
-        let seed = SingleThreadHkdfPrng::generate_seed().unwrap();
-        let prng = SingleThreadHkdfPrng::create(&seed).unwrap();
-        let client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe).unwrap();
         good_clients.push(client);
     }
 
@@ -437,9 +429,7 @@ fn encrypt_decrypt_multiple_clients_including_invalid_proofs() -> googletest::Re
         let kahe =
             ShellKahe::new(create_shell_kahe_config(&aggregation_config).unwrap(), CONTEXT_STRING)
                 .unwrap();
-        let seed = SingleThreadHkdfPrng::generate_seed().unwrap();
-        let prng = SingleThreadHkdfPrng::create(&seed).unwrap();
-        let client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe).unwrap();
         bad_clients.push(client);
     }
 
@@ -652,9 +642,7 @@ fn encrypt_decrypt_many_clients_decryptors() -> googletest::Result<()> {
         let kahe =
             ShellKahe::new(create_shell_kahe_config(&aggregation_config).unwrap(), CONTEXT_STRING)
                 .unwrap();
-        let seed = SingleThreadHkdfPrng::generate_seed().unwrap();
-        let prng = SingleThreadHkdfPrng::create(&seed).unwrap();
-        let mut client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe).unwrap();
 
         let client_input_values =
             generate_random_unsigned_vector(INPUT_LENGTH as usize, INPUT_DOMAIN as u64);
@@ -730,9 +718,7 @@ fn encrypt_decrypt_no_dropout() -> googletest::Result<()> {
         let kahe =
             ShellKahe::new(create_shell_kahe_config(&aggregation_config).unwrap(), CONTEXT_STRING)
                 .unwrap();
-        let seed = SingleThreadHkdfPrng::generate_seed().unwrap();
-        let prng = SingleThreadHkdfPrng::create(&seed).unwrap();
-        let client = WillowV1Client { kahe, vahe, prng };
+        let client = WillowV1Client::new_with_randomly_generated_seed(kahe, vahe).unwrap();
         clients.push(client);
     }