diff --git a/prf/hkdf_prf_key_manager.go b/prf/hkdf_prf_key_manager.go
index fc149f8..c2ff225 100644
--- a/prf/hkdf_prf_key_manager.go
+++ b/prf/hkdf_prf_key_manager.go
@@ -57,8 +57,8 @@ func (km *hkdfprfKeyManager) Primitive(serializedKey []byte) (interface{}, error
 	if err := km.validateKey(key); err != nil {
 		return nil, err
 	}
-	hash := commonpb.HashType_name[int32(key.Params.Hash)]
-	hkdf, err := subtle.NewHKDFPRF(hash, key.KeyValue, key.Params.Salt)
+	hash := commonpb.HashType_name[int32(key.GetParams().GetHash())]
+	hkdf, err := subtle.NewHKDFPRF(hash, key.GetKeyValue(), key.GetParams().GetSalt())
 	if err != nil {
 		return nil, err
 	}
@@ -77,10 +77,10 @@ func (km *hkdfprfKeyManager) NewKey(serializedKeyFormat []byte) (proto.Message,
 	if err := km.validateKeyFormat(keyFormat); err != nil {
 		return nil, fmt.Errorf("hkdf_prf_key_manager: invalid key format: %s", err)
 	}
-	keyValue := random.GetRandomBytes(keyFormat.KeySize)
+	keyValue := random.GetRandomBytes(keyFormat.GetKeySize())
 	return &hkdfpb.HkdfPrfKey{
 		Version:  hkdfprfKeyVersion,
-		Params:   keyFormat.Params,
+		Params:   keyFormat.GetParams(),
 		KeyValue: keyValue,
 	}, nil
 }
@@ -142,7 +142,7 @@ func (km *hkdfprfKeyManager) DeriveKey(serializedKeyFormat []byte, pseudorandomn
 
 	return &hkdfpb.HkdfPrfKey{
 		Version:  hkdfprfKeyVersion,
-		Params:   keyFormat.Params,
+		Params:   keyFormat.GetParams(),
 		KeyValue: keyValue,
 	}, nil
 }
@@ -150,20 +150,16 @@ func (km *hkdfprfKeyManager) DeriveKey(serializedKeyFormat []byte, pseudorandomn
 // validateKey validates the given HKDFPRFKey. It only validates the version of the
 // key because other parameters will be validated in primitive construction.
 func (km *hkdfprfKeyManager) validateKey(key *hkdfpb.HkdfPrfKey) error {
-	err := keyset.ValidateKeyVersion(key.Version, hkdfprfKeyVersion)
-	if err != nil {
+	if err := keyset.ValidateKeyVersion(key.GetVersion(), hkdfprfKeyVersion); err != nil {
 		return fmt.Errorf("hkdf_prf_key_manager: invalid version: %s", err)
 	}
-	keySize := uint32(len(key.KeyValue))
-	hash := commonpb.HashType_name[int32(key.Params.Hash)]
-	return subtle.ValidateHKDFPRFParams(hash, keySize, key.Params.Salt)
+	keySize := uint32(len(key.GetKeyValue()))
+	hash := commonpb.HashType_name[int32(key.GetParams().GetHash())]
+	return subtle.ValidateHKDFPRFParams(hash, keySize, key.GetParams().GetSalt())
 }
 
 // validateKeyFormat validates the given HKDFKeyFormat
 func (km *hkdfprfKeyManager) validateKeyFormat(format *hkdfpb.HkdfPrfKeyFormat) error {
-	if format.Params == nil {
-		return fmt.Errorf("null HKDF params")
-	}
-	hash := commonpb.HashType_name[int32(format.Params.Hash)]
-	return subtle.ValidateHKDFPRFParams(hash, format.KeySize, format.Params.Salt)
+	hash := commonpb.HashType_name[int32(format.GetParams().GetHash())]
+	return subtle.ValidateHKDFPRFParams(hash, format.GetKeySize(), format.GetParams().GetSalt())
 }
diff --git a/prf/hkdf_prf_key_manager_test.go b/prf/hkdf_prf_key_manager_test.go
index b2b5de0..0b668f6 100644
--- a/prf/hkdf_prf_key_manager_test.go
+++ b/prf/hkdf_prf_key_manager_test.go
@@ -421,6 +421,8 @@ func genInvalidHKDFKeys() []proto.Message {
 	badVersionKey.Version++
 	shortKey := testutil.NewHKDFPRFKey(commonpb.HashType_SHA256, make([]byte, 0))
 	shortKey.KeyValue = []byte{1, 1}
+	nilParams := testutil.NewHKDFPRFKey(commonpb.HashType_SHA256, make([]byte, 0))
+	nilParams.Params = nil
 	return []proto.Message{
 		// not a HKDFPRFKey
 		testutil.NewHKDFPRFParams(commonpb.HashType_SHA256, make([]byte, 0)),
@@ -432,12 +434,16 @@ func genInvalidHKDFKeys() []proto.Message {
 		testutil.NewHKDFPRFKey(commonpb.HashType_SHA1, make([]byte, 0)),
 		// unknown hash type
 		testutil.NewHKDFPRFKey(commonpb.HashType_UNKNOWN_HASH, make([]byte, 0)),
+		// params field is unset
+		nilParams,
 	}
 }
 
 func genInvalidHKDFKeyFormats() []proto.Message {
 	shortKeyFormat := testutil.NewHKDFPRFKeyFormat(commonpb.HashType_SHA256, make([]byte, 0))
 	shortKeyFormat.KeySize = 1
+	nilParams := testutil.NewHKDFPRFKeyFormat(commonpb.HashType_SHA256, make([]byte, 0))
+	nilParams.Params = nil
 	return []proto.Message{
 		// not a HKDFPRFKeyFormat
 		testutil.NewHMACParams(commonpb.HashType_SHA256, 32),
@@ -447,6 +453,8 @@ func genInvalidHKDFKeyFormats() []proto.Message {
 		testutil.NewHKDFPRFKeyFormat(commonpb.HashType_SHA1, make([]byte, 0)),
 		// unknown hash type
 		testutil.NewHKDFPRFKeyFormat(commonpb.HashType_UNKNOWN_HASH, make([]byte, 0)),
+		// params field is unset
+		nilParams,
 	}
 }
 
diff --git a/prf/hmac_prf_key_manager.go b/prf/hmac_prf_key_manager.go
index 74e21d8..c9e6569 100644
--- a/prf/hmac_prf_key_manager.go
+++ b/prf/hmac_prf_key_manager.go
@@ -53,8 +53,8 @@ func (km *hmacprfKeyManager) Primitive(serializedKey []byte) (interface{}, error
 	if err := km.validateKey(key); err != nil {
 		return nil, err
 	}
-	hash := commonpb.HashType_name[int32(key.Params.Hash)]
-	hmac, err := subtle.NewHMACPRF(hash, key.KeyValue)
+	hash := commonpb.HashType_name[int32(key.GetParams().GetHash())]
+	hmac, err := subtle.NewHMACPRF(hash, key.GetKeyValue())
 	if err != nil {
 		return nil, err
 	}
@@ -75,8 +75,8 @@ func (km *hmacprfKeyManager) NewKey(serializedKeyFormat []byte) (proto.Message,
 	}
 	return &hmacpb.HmacPrfKey{
 		Version:  hmacprfKeyVersion,
-		Params:   keyFormat.Params,
-		KeyValue: random.GetRandomBytes(keyFormat.KeySize),
+		Params:   keyFormat.GetParams(),
+		KeyValue: random.GetRandomBytes(keyFormat.GetKeySize()),
 	}, nil
 }
 
@@ -112,12 +112,11 @@ func (km *hmacprfKeyManager) TypeURL() string {
 // validateKey validates the given HMACPRFKey. It only validates the version of the
 // key because other parameters will be validated in primitive construction.
 func (km *hmacprfKeyManager) validateKey(key *hmacpb.HmacPrfKey) error {
-	err := keyset.ValidateKeyVersion(key.Version, hmacprfKeyVersion)
-	if err != nil {
+	if err := keyset.ValidateKeyVersion(key.GetVersion(), hmacprfKeyVersion); err != nil {
 		return fmt.Errorf("hmac_prf_key_manager: invalid version: %s", err)
 	}
-	keySize := uint32(len(key.KeyValue))
-	hash := commonpb.HashType_name[int32(key.Params.Hash)]
+	keySize := uint32(len(key.GetKeyValue()))
+	hash := commonpb.HashType_name[int32(key.GetParams().GetHash())]
 	return subtle.ValidateHMACPRFParams(hash, keySize)
 }
 
@@ -155,9 +154,6 @@ func (km *hmacprfKeyManager) DeriveKey(serializedKeyFormat []byte, pseudorandomn
 
 // validateKeyFormat validates the given HMACKeyFormat
 func (km *hmacprfKeyManager) validateKeyFormat(format *hmacpb.HmacPrfKeyFormat) error {
-	if format.Params == nil {
-		return fmt.Errorf("null HMAC params")
-	}
-	hash := commonpb.HashType_name[int32(format.Params.Hash)]
-	return subtle.ValidateHMACPRFParams(hash, format.KeySize)
+	hash := commonpb.HashType_name[int32(format.GetParams().GetHash())]
+	return subtle.ValidateHMACPRFParams(hash, format.GetKeySize())
 }
diff --git a/prf/hmac_prf_key_manager_test.go b/prf/hmac_prf_key_manager_test.go
index 7c6c505..ad16d34 100644
--- a/prf/hmac_prf_key_manager_test.go
+++ b/prf/hmac_prf_key_manager_test.go
@@ -400,6 +400,8 @@ func genInvalidHMACPRFKeys() []proto.Message {
 	badVersionKey.Version++
 	shortKey := testutil.NewHMACPRFKey(commonpb.HashType_SHA256)
 	shortKey.KeyValue = []byte{1, 1}
+	nilParams := testutil.NewHMACPRFKey(commonpb.HashType_SHA256)
+	nilParams.Params = nil
 	return []proto.Message{
 		// not a HMACPRFKey
 		testutil.NewHMACParams(commonpb.HashType_SHA256, 32),
@@ -409,12 +411,16 @@ func genInvalidHMACPRFKeys() []proto.Message {
 		shortKey,
 		// unknown hash type
 		testutil.NewHMACPRFKey(commonpb.HashType_UNKNOWN_HASH),
+		// params field is unset
+		nilParams,
 	}
 }
 
 func genInvalidHMACPRFKeyFormats() []proto.Message {
 	shortKeyFormat := testutil.NewHMACPRFKeyFormat(commonpb.HashType_SHA256)
 	shortKeyFormat.KeySize = 1
+	nilParams := testutil.NewHMACPRFKey(commonpb.HashType_SHA256)
+	nilParams.Params = nil
 	return []proto.Message{
 		// not a HMACPRFKeyFormat
 		testutil.NewHMACParams(commonpb.HashType_SHA256, 32),
@@ -422,6 +428,8 @@ func genInvalidHMACPRFKeyFormats() []proto.Message {
 		shortKeyFormat,
 		// unknown hash type
 		testutil.NewHMACPRFKeyFormat(commonpb.HashType_UNKNOWN_HASH),
+		// params field is unset
+		nilParams,
 	}
 }