src: Get random authvalues locally instead of from the TPM

Currently, the TPM itself is the root of trust for randomness in
authvalues used for creating Primary Keys.
This is susceptible to physical attacks over the TPM bus.

 * Get authvalues via the 'getrandom' crate

getrandom retrieves random data from the (operating) system sources
and assumes "that the system always provides high-quality
cryptographically secure random data, ideally backed by hardware
entropy sources", so the administrator of the platfrom should take
this into account.

Note: This change may slow down the tests as accessing random values
from the OS instead of the TPM may be slower.

Signed-off-by: Tomás González <tomasagustin.gonzalezorlando@arm.com>

Author: tgonzalezorlandoarm

tss-esapi/Cargo.toml

@@ -34,6 +34,7 @@ cfg-if = "1.0.0"
 strum = { version = "0.25.0", optional = true }
 strum_macros = { version = "0.25.0", optional = true }
 paste = "1.0.14"
+getrandom = "0.2.11"
 
 [dev-dependencies]
 env_logger = "0.9.0"

tss-esapi/src/abstraction/transient/mod.rs

@@ -137,6 +137,7 @@ impl TransientKeyContext {
     ///
     /// # Errors
     /// * if the authentication size is larger than 32 a `WrongParamSize` wrapper error is returned
+    /// * if there is an error when obtaining random numbers from the local machine
     pub fn create_key(
         &mut self,
         key_params: KeyParams,
@@ -147,8 +148,12 @@ impl TransientKeyContext {
         }
         let key_auth = if auth_size > 0 {
             self.set_session_attrs()?;
-            let random_bytes = self.context.get_random(auth_size)?;
-            Some(Auth::from_bytes(random_bytes.as_bytes())?)
+            let mut random_bytes = vec![0u8; auth_size];
+            getrandom::getrandom(&mut random_bytes).map_err(|_| {
+                log::error!("Failed to obtain a random authvalue for key creation");
+                Error::WrapperError(ErrorKind::InternalError)
+            })?;
+            Some(Auth::from_bytes(random_bytes.as_slice())?)
         } else {
             None
         };
@@ -630,7 +635,7 @@ impl TransientKeyContextBuilder {
     /// Bootstrap the TransientKeyContext.
     ///
     /// The root key is created as a primary key in the provided hierarchy and thus authentication is
-    /// needed for said hierarchy. The authentication value for the key is generated by the TPM itself,
+    /// needed for said hierarchy. The authentication value for the key is generated locally in the machine,
     /// with a configurable length, and never exposed outside the context.
     ///
     /// # Warning
@@ -643,9 +648,9 @@ impl TransientKeyContextBuilder {
     /// * `root_key_auth_size` must be at most 32
     ///
     /// # Errors
-    /// * errors are returned if any method calls return an error: `Context::get_random`,
-    /// `Context::start_auth_session`, `Context::create_primary`, `Context::flush_context`,
-    /// `Context::set_handle_auth`
+    /// * errors are returned if any method calls return an error: `Context::start_auth_session`
+    /// `Context::create_primary`, `Context::flush_context`, `Context::set_handle_auth`
+    /// or if an internal error occurs when getting random numbers from the local machine
     /// * if the root key authentication size is given greater than 32 or if the root key size is
     /// not 1024, 2048, 3072 or 4096, a `InvalidParam` wrapper error is returned
     pub fn build(mut self) -> Result<TransientKeyContext> {
@@ -658,8 +663,12 @@ impl TransientKeyContextBuilder {
         let mut context = Context::new(self.tcti_name_conf)?;
 
         let root_key_auth = if self.root_key_auth_size > 0 {
-            let random = context.get_random(self.root_key_auth_size)?;
-            Some(Auth::from_bytes(random.as_bytes())?)
+            let mut random = vec![0u8; self.root_key_auth_size];
+            getrandom::getrandom(&mut random).map_err(|_| {
+                log::error!("Failed to obtain a random value for root key authentication");
+                Error::WrapperError(ErrorKind::InternalError)
+            })?;
+            Some(Auth::from_bytes(random.as_slice())?)
         } else {
             None
         };

tss-esapi/src/context/tpm_commands/asymmetric_primitives.rs

@@ -127,8 +127,9 @@ impl Context {
     /// # context.tr_sess_set_attributes(session, session_attributes, session_attributes_mask)
     /// #     .expect("Failed to set attributes on session");
     /// # context.set_sessions((Some(session), None, None));
-    /// # let random_digest = context.get_random(16).unwrap();
-    /// # let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+    /// # let mut random_digest = vec![0u8; 16];
+    /// # getrandom::getrandom(&mut random_digest).unwrap();
+    /// # let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
     /// #
     /// // Create a key suitable for ECDH key generation
     /// let ecc_parms = PublicEccParametersBuilder::new()
@@ -262,8 +263,9 @@ impl Context {
     /// # context.tr_sess_set_attributes(session, session_attributes, session_attributes_mask)
     /// #     .expect("Failed to set attributes on session");
     /// # context.set_sessions((Some(session), None, None));
-    /// # let random_digest = context.get_random(16).unwrap();
-    /// # let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+    /// # let mut random_digest = vec![0u8; 16];
+    /// # getrandom::getrandom(&mut random_digest).unwrap();
+    /// # let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
     /// #
     /// // Create a key suitable for ECDH key generation
     /// let ecc_parms = PublicEccParametersBuilder::new()

tss-esapi/src/context/tpm_commands/context_management.rs

@@ -112,10 +112,9 @@ impl Context {
     ///
     /// // Execute context methods using the session
     /// context.execute_with_session(Some(session), |ctx| {
-    ///     let random_digest = ctx.get_random(16)
-    ///         .expect("Call to get_random failed");
-    ///     let key_auth = Auth::from_bytes(random_digest.as_bytes())
-    ///         .expect("Failed to create Auth");
+    ///     let mut random_digest = vec![0u8; 16];
+    ///     getrandom::getrandom(&mut random_digest).expect("Call to getrandom failed");
+    ///     let key_auth = Auth::from_bytes(random_digest.as_slice()).expect("Failed to create Auth");
     ///     let key_handle = ctx
     ///         .create_primary(
     ///             Hierarchy::Owner,

tss-esapi/src/context/tpm_commands/symmetric_primitives.rs

@@ -56,12 +56,11 @@ impl Context {
     /// #     .tr_set_auth(tss_esapi::interface_types::reserved_handles::Hierarchy::Owner.into(), Auth::default())
     /// #     .expect("Failed to set auth to empty for owner");
     /// # // Create primary key auth
-    /// # let primary_key_auth = Auth::try_from(
-    /// #     context
-    /// #         .get_random(16)
-    /// #         .expect("get_rand call failed")
-    /// #         .as_bytes()
-    /// #         .to_vec(),
+    /// # let mut random_digest = vec![0u8; 16];
+    /// # getrandom::getrandom(&mut random_digest).expect("get_rand call failed");
+    /// # let primary_key_auth = Auth::from_bytes(
+    /// #     random_digest
+    /// #         .as_slice()
     /// # )
     /// # .expect("Failed to create primary key auth");
     /// # // Create primary key
@@ -103,12 +102,11 @@ impl Context {
     /// #     .build()
     /// #     .expect("Failed to create public for symmetric key public");
     /// # // Create auth for the symmetric key
-    /// # let symmetric_key_auth = Auth::try_from(
-    /// #     context
-    /// #         .get_random(16)
-    /// #         .expect("get_rand call failed")
-    /// #         .as_bytes()
-    /// #         .to_vec(),
+    /// # let mut random_digest = vec![0u8; 16];
+    /// # getrandom::getrandom(&mut random_digest).expect("get_rand call failed");
+    /// # let symmetric_key_auth = Auth::from_bytes(
+    /// #     random_digest
+    /// #         .as_slice()
     /// # )
     /// # .expect("Failed to create symmetric key auth");
     /// # // Create symmetric key data

tss-esapi/tests/integration_tests/abstraction_tests/transient_key_context_tests.rs

@@ -502,8 +502,9 @@ fn ctx_migration_test() {
     // Create two key contexts using `Context`, one for an RSA keypair,
     // one for just the public part of the key
     let mut basic_ctx = crate::common::create_ctx_with_session();
-    let random_digest = basic_ctx.get_random(16).unwrap();
-    let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+    let mut random_digest = vec![0u8; 16];
+    getrandom::getrandom(&mut random_digest).unwrap();
+    let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
     let prim_key_handle = basic_ctx
         .create_primary(
             Hierarchy::Owner,

tss-esapi/tests/integration_tests/context_tests/tpm_commands/asymmetric_primitives_tests.rs

@@ -19,8 +19,9 @@ mod test_rsa_encrypt_decrypt {
     #[test]
     fn test_encrypt_decrypt() {
         let mut context = create_ctx_with_session();
-        let random_digest = context.get_random(16).unwrap();
-        let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let key_handle = context
             .create_primary(
@@ -59,8 +60,9 @@ mod test_rsa_encrypt_decrypt {
     #[test]
     fn test_ecdh() {
         let mut context = create_ctx_with_session();
-        let random_digest = context.get_random(16).unwrap();
-        let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let ecc_parms = PublicEccParametersBuilder::new()
             .with_ecc_scheme(EccScheme::EcDh(HashScheme::new(HashingAlgorithm::Sha256)))

tss-esapi/tests/integration_tests/context_tests/tpm_commands/context_management_tests.rs

@@ -7,8 +7,9 @@ mod test_ctx_save {
     #[test]
     fn test_ctx_save() {
         let mut context = create_ctx_with_session();
-        let random_digest = context.get_random(16).unwrap();
-        let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let key_handle = context
             .create_primary(
@@ -27,8 +28,9 @@ mod test_ctx_save {
     #[test]
     fn test_ctx_save_leaf() {
         let mut context = create_ctx_with_session();
-        let random_digest = context.get_random(16).unwrap();
-        let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let prim_key_handle = context
             .create_primary(
@@ -70,13 +72,14 @@ mod test_ctx_load {
     #[test]
     fn test_ctx_load() {
         let mut context = create_ctx_with_session();
-        let key_auth = context.get_random(16).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
 
         let prim_key_handle = context
             .create_primary(
                 Hierarchy::Owner,
                 decryption_key_pub(),
-                Some(Auth::from_bytes(key_auth.as_bytes()).unwrap()),
+                Some(Auth::from_bytes(random_digest.as_slice()).unwrap()),
                 None,
                 None,
                 None,
@@ -88,7 +91,7 @@ mod test_ctx_load {
             .create(
                 prim_key_handle,
                 signing_key_pub(),
-                Some(Auth::from_bytes(key_auth.as_bytes()).unwrap()),
+                Some(Auth::from_bytes(random_digest.as_slice()).unwrap()),
                 None,
                 None,
                 None,
@@ -112,8 +115,9 @@ mod test_flush_context {
     #[test]
     fn test_flush_ctx() {
         let mut context = create_ctx_with_session();
-        let random_digest = context.get_random(16).unwrap();
-        let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let key_handle = context
             .create_primary(
@@ -133,8 +137,9 @@ mod test_flush_context {
     #[test]
     fn test_flush_parent_ctx() {
         let mut context = create_ctx_with_session();
-        let random_digest = context.get_random(16).unwrap();
-        let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let prim_key_handle = context
             .create_primary(

tss-esapi/tests/integration_tests/context_tests/tpm_commands/enhanced_authorization_ea_commands_tests.rs

@@ -536,8 +536,9 @@ mod test_policy_authorize {
     #[test]
     fn test_policy_authorize() {
         let mut context = create_ctx_with_session();
-        let random_digest = context.get_random(16).unwrap();
-        let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let key_handle = context
             .create_primary(

tss-esapi/tests/integration_tests/context_tests/tpm_commands/hierarchy_commands_tests.rs

@@ -9,8 +9,9 @@ mod test_create_primary {
     #[test]
     fn test_create_primary() {
         let mut context = create_ctx_with_session();
-        let random_digest = context.get_random(16).unwrap();
-        let key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let key_handle = context
             .create_primary(
@@ -93,8 +94,9 @@ mod test_change_auth {
             )
             .unwrap();
 
-        let random_digest = context.get_random(16).unwrap();
-        let new_key_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let new_key_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         let new_private = context
             .object_change_auth(loaded_key.into(), prim_key_handle.into(), new_key_auth)
@@ -108,8 +110,9 @@ mod test_change_auth {
     fn test_hierarchy_change_auth() {
         let mut context = create_ctx_with_session();
 
-        let random_digest = context.get_random(16).unwrap();
-        let new_auth = Auth::from_bytes(random_digest.as_bytes()).unwrap();
+        let mut random_digest = vec![0u8; 16];
+        getrandom::getrandom(&mut random_digest).unwrap();
+        let new_auth = Auth::from_bytes(random_digest.as_slice()).unwrap();
 
         // NOTE: If this test failed on your system, you are probably running it against a
         //  real (hardware) TPM or one that is provisioned. This hierarchy is supposed to be