diff --git a/ecdsa_key.cpp b/ecdsa_key.cpp
index 4593f7e..5602689 100644
--- a/ecdsa_key.cpp
+++ b/ecdsa_key.cpp
@@ -22,8 +22,6 @@
 
 namespace keymaster {
 
-const uint32_t ECDSA_DEFAULT_KEY_SIZE = 224;
-
 class EcdsaKeyFactory : public AsymmetricKeyFactory {
   public:
     virtual keymaster_algorithm_t registry_key() const { return KM_ALGORITHM_ECDSA; }
@@ -55,9 +53,11 @@
 
     AuthorizationSet authorizations(key_description);
 
-    uint32_t key_size = ECDSA_DEFAULT_KEY_SIZE;
-    if (!authorizations.GetTagValue(TAG_KEY_SIZE, &key_size))
-        authorizations.push_back(Authorization(TAG_KEY_SIZE, key_size));
+    uint32_t key_size;
+    if (!authorizations.GetTagValue(TAG_KEY_SIZE, &key_size)) {
+        LOG_E("%s", "No key size specified for ECDSA key generation");
+        *error = KM_ERROR_UNSUPPORTED_KEY_SIZE;
+    }
 
     UniquePtr<EC_KEY, EcdsaKey::ECDSA_Delete> ecdsa_key(EC_KEY_new());
     UniquePtr<EVP_PKEY, EVP_PKEY_Delete> pkey(EVP_PKEY_new());
diff --git a/google_keymaster_test.cpp b/google_keymaster_test.cpp
index 931a9e1..900db53 100644
--- a/google_keymaster_test.cpp
+++ b/google_keymaster_test.cpp
@@ -273,19 +273,11 @@
 }
 
 TEST_F(NewKeyGeneration, RsaDefaultSize) {
-    ASSERT_EQ(
-        KM_ERROR_OK,
-        GenerateKey(
-            AuthorizationSetBuilder().Authorization(TAG_ALGORITHM, KM_ALGORITHM_RSA).SigningKey()));
-
-    CheckBaseParams();
-
-    // Check specified tags are all present in unenforced characteristics
-    EXPECT_TRUE(contains(sw_enforced(), TAG_ALGORITHM, KM_ALGORITHM_RSA));
-
-    // Now check that unspecified, defaulted tags are correct.
-    EXPECT_TRUE(contains(sw_enforced(), TAG_RSA_PUBLIC_EXPONENT, 65537));
-    EXPECT_TRUE(contains(sw_enforced(), TAG_KEY_SIZE, 2048));
+    ASSERT_EQ(KM_ERROR_UNSUPPORTED_KEY_SIZE,
+              GenerateKey(AuthorizationSetBuilder()
+                              .Authorization(TAG_ALGORITHM, KM_ALGORITHM_RSA)
+                              .Authorization(TAG_RSA_PUBLIC_EXPONENT, 3)
+                              .SigningKey()));
 }
 
 TEST_F(NewKeyGeneration, Ecdsa) {
diff --git a/rsa_key.cpp b/rsa_key.cpp
index 91e1499..e42b9a5 100644
--- a/rsa_key.cpp
+++ b/rsa_key.cpp
@@ -29,9 +29,6 @@
 
 namespace keymaster {
 
-const uint32_t RSA_DEFAULT_KEY_SIZE = 2048;
-const uint64_t RSA_DEFAULT_EXPONENT = 65537;
-
 class RsaKeyFactory : public AsymmetricKeyFactory {
   public:
     virtual keymaster_algorithm_t registry_key() const { return KM_ALGORITHM_RSA; }
@@ -53,18 +50,24 @@
 
     AuthorizationSet authorizations(key_description);
 
-    uint64_t public_exponent = RSA_DEFAULT_EXPONENT;
-    if (!authorizations.GetTagValue(TAG_RSA_PUBLIC_EXPONENT, &public_exponent))
-        authorizations.push_back(Authorization(TAG_RSA_PUBLIC_EXPONENT, public_exponent));
+    uint64_t public_exponent;
+    if (!authorizations.GetTagValue(TAG_RSA_PUBLIC_EXPONENT, &public_exponent)) {
+        LOG_E("%s", "No public exponent specified for RSA key generation");
+        *error = KM_ERROR_INVALID_ARGUMENT;
+        return NULL;
+    }
 
-    uint32_t key_size = RSA_DEFAULT_KEY_SIZE;
-    if (!authorizations.GetTagValue(TAG_KEY_SIZE, &key_size))
-        authorizations.push_back(Authorization(TAG_KEY_SIZE, key_size));
+    uint32_t key_size;
+    if (!authorizations.GetTagValue(TAG_KEY_SIZE, &key_size)) {
+        LOG_E("%s", "No key size specified for RSA key generation");
+        *error = KM_ERROR_UNSUPPORTED_KEY_SIZE;
+        return NULL;
+    }
 
     UniquePtr<BIGNUM, BIGNUM_Delete> exponent(BN_new());
     UniquePtr<RSA, RsaKey::RSA_Delete> rsa_key(RSA_new());
     UniquePtr<EVP_PKEY, EVP_PKEY_Delete> pkey(EVP_PKEY_new());
-    if (rsa_key.get() == NULL || pkey.get() == NULL) {
+    if (exponent.get() == NULL || rsa_key.get() == NULL || pkey.get() == NULL) {
         *error = KM_ERROR_MEMORY_ALLOCATION_FAILED;
         return NULL;
     }