diff --git a/test_libs/pyspec/eth2spec/test/context.py b/test_libs/pyspec/eth2spec/test/context.py
index 4c8ff255b..7a8e959d0 100644
--- a/test_libs/pyspec/eth2spec/test/context.py
+++ b/test_libs/pyspec/eth2spec/test/context.py
@@ -3,12 +3,22 @@ from eth2spec.utils import bls
 
 from .helpers.genesis import create_genesis_state
 
-from .utils import spectest, with_args
+from .utils import spectest, with_args, with_tags
 
 # Provides a genesis state as first argument to the function decorated with this
 with_state = with_args(lambda: [create_genesis_state(spec.SLOTS_PER_EPOCH * 8)])
 
 
+# BLS is turned off by default *for performance purposes during TESTING*.
+# The runner of the test can indicate the preferred setting (test generators prefer BLS to be ON).
+# - Some tests are marked as BLS-requiring, and ignore this setting.
+#    (tests that express differences caused by BLS, e.g. invalid signatures being rejected)
+# - Some other tests are marked as BLS-ignoring, and ignore this setting.
+#    (tests that are heavily performance impacted / require unsigned state transitions)
+# - Most tests respect the BLS setting.
+DEFAULT_BLS_ACTIVE = False
+
+
 # shorthand for decorating @with_state @spectest()
 def spec_state_test(fn):
     return with_state(bls_switch(spectest()(fn)))
@@ -28,6 +38,10 @@ def expect_assertion_error(fn):
         raise AssertionError('expected an assertion error, but got none.')
 
 
+# Tags a test to be ignoring BLS for it to pass.
+bls_ignored = with_tags({'bls_ignored': True})
+
+
 def never_bls(fn):
     """
     Decorator to apply on ``bls_switch`` decorator to force BLS de-activation. Useful to mark tests as BLS-ignorant.
@@ -36,7 +50,11 @@ def never_bls(fn):
         # override bls setting
         kw['bls_active'] = False
         fn(*args, **kw)
-    return entry
+    return bls_ignored(entry)
+
+
+# Tags a test to be requiring BLS for it to pass.
+bls_required = with_tags({'bls_required': True})
 
 
 def always_bls(fn):
@@ -47,7 +65,7 @@ def always_bls(fn):
         # override bls setting
         kw['bls_active'] = True
         fn(*args, **kw)
-    return entry
+    return bls_required(entry)
 
 
 def bls_switch(fn):
@@ -57,7 +75,7 @@ def bls_switch(fn):
     """
     def entry(*args, **kw):
         old_state = bls.bls_active
-        bls.bls_active = kw.pop('bls_active', True)
+        bls.bls_active = kw.pop('bls_active', DEFAULT_BLS_ACTIVE)
         fn(*args, **kw)
         bls.bls_active = old_state
     return entry
diff --git a/test_libs/pyspec/eth2spec/test/helpers/block.py b/test_libs/pyspec/eth2spec/test/helpers/block.py
index 6f1a0fe60..094423ab3 100644
--- a/test_libs/pyspec/eth2spec/test/helpers/block.py
+++ b/test_libs/pyspec/eth2spec/test/helpers/block.py
@@ -4,13 +4,16 @@ from eth2spec.phase0 import spec
 from eth2spec.phase0.spec import get_beacon_proposer_index, slot_to_epoch, get_domain, BeaconBlock
 from eth2spec.phase0.state_transition import state_transition, state_transition_to
 from eth2spec.test.helpers.keys import privkeys
-from eth2spec.utils.bls import bls_sign
+from eth2spec.utils import bls
 from eth2spec.utils.minimal_ssz import signing_root, hash_tree_root
 
 
 def sign_block(state, block, proposer_index=None):
     assert state.slot <= block.slot
 
+    if not bls.bls_active:
+        return
+
     if proposer_index is None:
         if block.slot == state.slot:
             proposer_index = get_beacon_proposer_index(state)
@@ -25,7 +28,7 @@ def sign_block(state, block, proposer_index=None):
 
     privkey = privkeys[proposer_index]
 
-    block.body.randao_reveal = bls_sign(
+    block.body.randao_reveal = bls.bls_sign(
         privkey=privkey,
         message_hash=hash_tree_root(slot_to_epoch(block.slot)),
         domain=get_domain(
@@ -34,7 +37,7 @@ def sign_block(state, block, proposer_index=None):
             domain_type=spec.DOMAIN_RANDAO,
         )
     )
-    block.signature = bls_sign(
+    block.signature = bls.bls_sign(
         message_hash=signing_root(block),
         privkey=privkey,
         domain=get_domain(