diff --git a/.gitignore b/.gitignore
index df3807d50..c5f192e57 100644
--- a/.gitignore
+++ b/.gitignore
@@ -49,6 +49,7 @@ build/
 /local_testnet*_data*/
 
 test_keymanager_api
+test_sim
 
 /libnfuzz_linkerArgs.txt
 
diff --git a/research/simutils.nim b/research/simutils.nim
index c261920d7..e03c117e1 100644
--- a/research/simutils.nim
+++ b/research/simutils.nim
@@ -1,5 +1,5 @@
 # beacon_chain
-# Copyright (c) 2020-2022 Status Research & Development GmbH
+# Copyright (c) 2020-2023 Status Research & Development GmbH
 # Licensed and distributed under either of
 #   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
 #   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
@@ -8,7 +8,7 @@
 import
   stats, strformat, times,
   ../tests/testblockutil, ../tests/consensus_spec/os_ops,
-  ../beacon_chain/beacon_chain_db,
+  ../beacon_chain/[beacon_chain_db, filepath],
   ../beacon_chain/spec/datatypes/[phase0, altair],
   ../beacon_chain/spec/[beaconstate, deposit_snapshots, forks, helpers],
   ../beacon_chain/consensus_object_pools/[blockchain_dag, block_pools_types]
@@ -68,10 +68,16 @@ func verifyConsensus*(state: ForkedHashedBeaconState, attesterRatio: auto) =
 
 proc loadGenesis*(validators: Natural, validate: bool):
                  (ref ForkedHashedBeaconState, DepositTreeSnapshot) =
+  const genesisDir = "test_sim"
+  if (let res = secureCreatePath(genesisDir); res.isErr):
+    fatal "Could not create directory",
+      path = genesisDir, err = ioErrorMsg(res.error)
+    quit 1
+
   let
-    genesisFn =
+    genesisFn = genesisDir /
       &"genesis_{const_preset}_{validators}_{SPEC_VERSION}.ssz"
-    contractSnapshotFn =
+    contractSnapshotFn = genesisDir /
       &"deposit_contract_snapshot_{const_preset}_{validators}_{SPEC_VERSION}.ssz"
     cfg = defaultRuntimeConfig
 
@@ -89,7 +95,7 @@ proc loadGenesis*(validators: Natural, validate: bool):
 
       echo &"Loaded {genesisFn}..."
 
-      # TODO check that the private keys are interop keys
+      # TODO check that the private keys are EF test keys
 
       let contractSnapshot = SSZ.loadFile(contractSnapshotFn,
                                           DepositTreeSnapshot)
diff --git a/tests/testblockutil.nim b/tests/testblockutil.nim
index bfcaf252e..7d5ee0d00 100644
--- a/tests/testblockutil.nim
+++ b/tests/testblockutil.nim
@@ -30,9 +30,7 @@ const
 
 # https://github.com/ethereum/consensus-specs/blob/v1.3.0/tests/core/pyspec/eth2spec/test/helpers/keys.py
 func `[]`*(_: MockPrivKeysT, index: ValidatorIndex|uint64): ValidatorPrivKey =
-  # 0 is not a valid BLS private key - 1000 helps interop with rust BLS library,
-  # lighthouse. EF tests use 1 instead of 1000.
-  var bytes = (index.uint64 + 1000'u64).toBytesLE()
+  var bytes = (index.uint64 + 1'u64).toBytesLE()  # Consistent with EF tests
   static: doAssert sizeof(bytes) <= sizeof(result)
   copyMem(addr result, addr bytes, sizeof(bytes))