feat: add input encryption for validators

CHANGELOG.md

@@ -3,7 +3,6 @@
 ## Unreleased
 
 - [BREAKING] Updated `miden-protocol` dependencies to use the `next` branch (v0.16). Block and transaction account updates now use the absolute `AccountPatch` representation instead of the relative `AccountDelta`, and the `miden-tx-batch-prover` crate was renamed to `miden-tx-batch` ([#2282](https://github.com/0xMiden/node/pull/2282)).
-
 ## v0.15.0 (2026-06-10)
 
 - Fixed the store dropping a fungible asset's callback flag when applying partial account deltas ([#2222](https://github.com/0xMiden/node/pull/2222)).

bin/validator/Cargo.toml

@@ -47,5 +47,6 @@ miden-node-db = { workspace = true }
 miden-node-store = { workspace = true }
 miden-node-utils = { features = ["testing"], workspace = true }
 miden-protocol   = { default-features = true, features = ["testing"], workspace = true }
+rand             = { workspace = true }
 tempfile         = { workspace = true }
 tokio            = { features = ["macros", "rt-multi-thread"], workspace = true }

bin/validator/src/commands/bootstrap.rs

@@ -68,7 +68,7 @@ async fn build_and_write_genesis(
         .into_unsigned_block()
         .context("failed to build the unsigned genesis block")?;
     let signature = signer
-        .sign(unsigned_genesis_block.header())
+        .sign_commitment(unsigned_genesis_block.header().commitment())
         .await
         .context("failed to sign the genesis block")?;
     let genesis_block = unsigned_genesis_block

bin/validator/src/commands/mod.rs

@@ -3,27 +3,40 @@ mod start;
 
 use std::num::NonZeroUsize;
 use std::path::PathBuf;
+use std::sync::Arc;
 
 use anyhow::Context;
 use clap::Parser;
 use miden_node_utils::clap::GrpcOptionsInternal;
 use miden_node_utils::logging::OpenTelemetry;
 use miden_node_utils::shutdown::CancellationToken;
 use miden_protocol::crypto::dsa::ecdsa_k256_keccak::SigningKey;
+use miden_protocol::crypto::dsa::eddsa_25519_sha512::KeyExchangeKey;
 use miden_protocol::utils::serde::Deserializable;
-use miden_validator::{DataDirectory, ValidatorSigner};
+use miden_validator::{
+    DataDirectory,
+    LOG_TARGET,
+    LocalX25519TransactionInputDecryptor,
+    TransactionInputDecryptor,
+    ValidatorSigner,
+};
 
 const ENV_DATA_DIRECTORY: &str = "MIDEN_VALIDATOR_DATA_DIRECTORY";
 const ENV_LISTEN: &str = "MIDEN_VALIDATOR_LISTEN";
 const ENV_KEY: &str = "MIDEN_VALIDATOR_KEY";
 const ENV_KMS_KEY_ID: &str = "MIDEN_VALIDATOR_KMS_KEY_ID";
+const ENV_ENCRYPTION_KEY: &str = "MIDEN_VALIDATOR_ENCRYPTION_KEY";
 const ENV_GENESIS_CONFIG_FILE: &str = "MIDEN_VALIDATOR_GENESIS_CONFIG_FILE";
 const ENV_SQLITE_CONNECTION_POOL_SIZE: &str = "MIDEN_VALIDATOR_SQLITE_CONNECTION_POOL_SIZE";
 
 /// A predefined, insecure validator key for development purposes.
 pub(crate) const INSECURE_KEY_HEX: &str =
     "0101010101010101010101010101010101010101010101010101010101010101";
 
+/// A predefined, insecure shared transaction encryption key for development purposes.
+pub(crate) const INSECURE_ENCRYPTION_KEY_HEX: &str =
+    "0202020202020202020202020202020202020202020202020202020202020202";
+
 // VALIDATOR COMMAND
 // ================================================================================================
 
@@ -116,6 +129,20 @@ pub enum ValidatorCommand {
             group = "key"
         )]
         kms_key_id: Option<String>,
+
+        /// Hex-encoded shared secret of the transaction encryption key.
+        ///
+        /// Unlike the per-validator signing key, this value must be identical across every
+        /// validator in the set.
+        ///
+        /// If not provided, a predefined insecure key is used.
+        #[arg(
+            long = "encryption-key.hex",
+            env = ENV_ENCRYPTION_KEY,
+            value_name = "VALIDATOR_ENCRYPTION_KEY",
+            default_value = INSECURE_ENCRYPTION_KEY_HEX
+        )]
+        encryption_key: String,
     },
 }
 
@@ -154,34 +181,46 @@ impl ValidatorCommand {
                 data_directory,
                 kms_key_id,
                 sqlite_connection_pool_size,
+                encryption_key,
                 ..
             } => {
                 let address = listen;
 
-                if let Some(kms_key_id) = kms_key_id {
-                    let signer = ValidatorSigner::new_kms(kms_key_id).await?;
-                    start::start(
-                        address,
-                        grpc_options,
-                        signer,
-                        data_directory,
-                        sqlite_connection_pool_size,
-                        shutdown,
-                    )
-                    .await
+                // Unlike the signing key, whose insecure default is caught at startup against the
+                // chain's committed validator key, nothing cross-checks the encryption key. Warn
+                // loudly so the default never runs in production unnoticed.
+                if encryption_key == INSECURE_ENCRYPTION_KEY_HEX {
+                    tracing::warn!(
+                        target: LOG_TARGET,
+                        "Using the predefined, insecure transaction encryption key, configure \
+                         --encryption-key.hex for production deployments"
+                    );
+                }
+
+                let encryption_key_bytes = hex::decode(encryption_key)
+                    .context("failed to decode the encryption key hex")?;
+                let encryption_key = KeyExchangeKey::read_from_bytes(&encryption_key_bytes)
+                    .context("failed to construct the encryption key")?;
+                let decryptor: Arc<dyn TransactionInputDecryptor> =
+                    Arc::new(LocalX25519TransactionInputDecryptor::new(encryption_key));
+
+                let signer = if let Some(kms_key_id) = kms_key_id {
+                    ValidatorSigner::new_kms(kms_key_id).await?
                 } else {
                     let signer = SigningKey::read_from_bytes(hex::decode(validator_key)?.as_ref())?;
-                    let signer = ValidatorSigner::new_local(signer);
-                    start::start(
-                        address,
-                        grpc_options,
-                        signer,
-                        data_directory,
-                        sqlite_connection_pool_size,
-                        shutdown,
-                    )
-                    .await
-                }
+                    ValidatorSigner::new_local(signer)
+                };
+
+                start::start(
+                    address,
+                    grpc_options,
+                    signer,
+                    decryptor,
+                    data_directory,
+                    sqlite_connection_pool_size,
+                    shutdown,
+                )
+                .await
             },
         }
     }

bin/validator/src/commands/start.rs

@@ -1,17 +1,19 @@
 use std::net::SocketAddr;
 use std::num::NonZeroUsize;
 use std::path::PathBuf;
+use std::sync::Arc;
 
 use anyhow::Context;
 use miden_node_utils::clap::GrpcOptionsInternal;
 use miden_node_utils::shutdown::CancellationToken;
-use miden_validator::{DataDirectory, ValidatorServer, ValidatorSigner};
+use miden_validator::{DataDirectory, TransactionInputDecryptor, ValidatorServer, ValidatorSigner};
 
 // Starts the validator component.
 pub async fn start(
     address: SocketAddr,
     grpc_options: GrpcOptionsInternal,
     signer: ValidatorSigner,
+    decryptor: Arc<dyn TransactionInputDecryptor>,
     data_directory: PathBuf,
     sqlite_connection_pool_size: NonZeroUsize,
     shutdown: CancellationToken,
@@ -22,6 +24,7 @@ pub async fn start(
         address,
         grpc_options,
         signer,
+        decryptor,
         data_directory,
         sqlite_connection_pool_size,
     }

bin/validator/src/lib.rs

@@ -6,7 +6,14 @@ mod tx_validation;
 
 pub use data_directory::DataDirectory;
 pub use server::ValidatorServer;
-pub use signers::{KmsSigner, ValidatorSigner};
+pub use signers::{
+    KmsSigner,
+    LocalX25519TransactionInputDecryptor,
+    TransactionEncryptionKeyInfo,
+    TransactionInputDecryptor,
+    ValidatorSigner,
+    attestation_commitment,
+};
 
 // CONSTANTS
 // =================================================================================================

bin/validator/src/server/mod.rs

@@ -20,7 +20,7 @@ use crate::db::{
     load_chain_tip,
     load_with_pool_size,
 };
-use crate::{DataDirectory, LOG_TARGET, ValidatorSigner};
+use crate::{DataDirectory, LOG_TARGET, TransactionInputDecryptor, ValidatorSigner};
 
 mod validator_service;
 
@@ -43,6 +43,10 @@ pub struct ValidatorServer {
     /// The signer used to sign blocks.
     pub signer: ValidatorSigner,
 
+    /// The decryptor for the shared transaction encryption key, used to unseal encrypted
+    /// transaction inputs.
+    pub decryptor: std::sync::Arc<dyn TransactionInputDecryptor>,
+
     /// The data directory for the validator component's database files.
     pub data_directory: DataDirectory,
 
@@ -98,6 +102,7 @@ impl ValidatorServer {
             .add_service(validator_api::service(
                 ValidatorService::new(
                     self.signer,
+                    self.decryptor,
                     db,
                     block_store,
                     initial_chain_tip,

bin/validator/src/server/validator_service/get_transaction_encryption_key.rs

@@ -0,0 +1,42 @@
+use miden_node_proto::generated as grpc;
+use miden_node_utils::tracing::miden_instrument;
+use miden_tx::utils::serde::Serializable;
+
+use super::ValidatorService;
+use crate::COMPONENT;
+
+#[tonic::async_trait]
+impl grpc::server::validator_api::GetTransactionEncryptionKey for ValidatorService {
+    type Input = ();
+    type Output = grpc::transaction::TransactionEncryptionKey;
+
+    fn decode(request: ()) -> tonic::Result<Self::Input> {
+        Ok(request)
+    }
+
+    fn encode(output: Self::Output) -> tonic::Result<grpc::transaction::TransactionEncryptionKey> {
+        Ok(output)
+    }
+
+    #[miden_instrument(
+        target = COMPONENT,
+        name = "get_transaction_encryption_key",
+        skip_all,
+        err,
+    )]
+    async fn handle(
+        &self,
+        _input: Self::Input,
+        _metadata: &tonic::metadata::MetadataMap,
+        _extensions: &tonic::codegen::http::Extensions,
+    ) -> tonic::Result<Self::Output> {
+        // Built entirely from state fixed at construction, so the endpoint stays available while a
+        // backup subscription holds the serve lock.
+        Ok(grpc::transaction::TransactionEncryptionKey {
+            scheme: self.encryption_key_info.scheme,
+            key_id: self.encryption_key_info.key_id.clone(),
+            public_key: self.encryption_key_info.public_key.clone(),
+            signature: self.encryption_key_attestation.to_bytes(),
+        })
+    }
+}

bin/validator/src/server/validator_service/mod.rs

@@ -19,12 +19,14 @@ use miden_protocol::transaction::{TransactionHeader, TransactionId};
 use tokio::sync::{Semaphore, watch};
 
 use crate::db::{find_unvalidated_transactions, load_block_header, load_chain_tip};
-use crate::{COMPONENT, ValidatorSigner};
+use crate::signers::TransactionEncryptionKeyInfo;
+use crate::{COMPONENT, TransactionInputDecryptor, ValidatorSigner};
 
 #[cfg(test)]
 mod tests;
 
 mod block_subscription;
+mod get_transaction_encryption_key;
 mod sign_block;
 mod status;
 mod submit_proven_transaction;
@@ -61,6 +63,10 @@ pub enum ValidatorError {
     BlockBackupFailed(#[source] std::io::Error),
     #[error("expected a single-key validator set, got {actual} keys")]
     UnexpectedValidatorSetSize { actual: usize },
+    #[error("no genesis block header exists")]
+    NoGenesisHeader,
+    #[error("failed to attest the transaction encryption key: {0}")]
+    EncryptionKeyAttestationFailed(String),
 }
 
 // VALIDATOR SERVICE
@@ -71,6 +77,14 @@ pub enum ValidatorError {
 /// Implements the gRPC API for the validator.
 pub(crate) struct ValidatorService {
     signer: ValidatorSigner,
+    /// Decryptor for transaction inputs sealed against the shared encryption key.
+    #[expect(dead_code, reason = "used by the submit path in a follow-up PR")]
+    decryptor: Arc<dyn TransactionInputDecryptor>,
+    /// Public metadata of the shared encryption key, fetched once at construction.
+    encryption_key_info: TransactionEncryptionKeyInfo,
+    /// Signature by this validator's own signing key over the encryption key attestation
+    /// commitment, computed once at construction.
+    encryption_key_attestation: Signature,
     db: Arc<Database>,
     block_store: BlockStore,
     /// Enforces mutual exclusion between backup block subscriptions and all other RPCs. Regular
@@ -93,6 +107,7 @@ pub(crate) struct ValidatorService {
 impl ValidatorService {
     pub(crate) async fn new(
         signer: ValidatorSigner,
+        decryptor: Arc<dyn TransactionInputDecryptor>,
         db: Database,
         block_store: BlockStore,
         initial_chain_tip: u32,
@@ -121,8 +136,28 @@ impl ValidatorService {
             });
         }
 
+        // Both keys are fixed for the process lifetime, so the attestation is computed once. This
+        // also keeps KMS-backed signers to a single signing call.
+        let genesis_commitment = db
+            .read("load_genesis_header", |tx| load_block_header(tx, BlockNumber::GENESIS))
+            .await
+            .map_err(ValidatorError::DatabaseError)?
+            .ok_or(ValidatorError::NoGenesisHeader)?
+            .commitment();
+        let encryption_key_info = decryptor
+            .encryption_key()
+            .await
+            .map_err(|err| ValidatorError::EncryptionKeyAttestationFailed(err.to_string()))?;
+        let encryption_key_attestation = signer
+            .sign_commitment(encryption_key_info.attestation_commitment(genesis_commitment))
+            .await
+            .map_err(|err| ValidatorError::EncryptionKeyAttestationFailed(err.to_string()))?;
+
         Ok(Self {
             signer,
+            decryptor,
+            encryption_key_info,
+            encryption_key_attestation,
             serve_lock: Arc::new(tokio::sync::RwLock::new(())),
             db: db.into(),
             block_store,
@@ -254,7 +289,7 @@ impl ValidatorService {
     )]
     async fn sign_header(&self, header: &BlockHeader) -> Result<Signature, ValidatorError> {
         self.signer
-            .sign(header)
+            .sign_commitment(header.commitment())
             .await
             .map_err(|err| ValidatorError::BlockSigningFailed(err.to_string()))
     }