update key length check for FIPS compliance

agent/structs/config_entry_inline_certificate.go

@@ -13,6 +13,7 @@ import (
 	"github.com/miekg/dns"
 
 	"github.com/hashicorp/consul/acl"
+	"github.com/hashicorp/consul/version"
 )
 
 // InlineCertificateConfigEntry manages the configuration for an inline certificate
@@ -43,7 +44,7 @@ func (e *InlineCertificateConfigEntry) GetEnterpriseMeta() *acl.EnterpriseMeta {
 }
 func (e *InlineCertificateConfigEntry) GetRaftIndex() *RaftIndex { return &e.RaftIndex }
 
-// Envoy will silently reject any keys that are less than 2048 bytes long
+// Envoy will silently reject any RSA keys that are less than 2048 bytes long
 // https://github.com/envoyproxy/envoy/blob/main/source/extensions/transport_sockets/tls/context_impl.cc#L238
 const MinKeyLength = 2048
 
@@ -58,17 +59,7 @@ func (e *InlineCertificateConfigEntry) Validate() error {
 		return errors.New("failed to parse private key PEM")
 	}
 
-	if privateKeyBlock.Type == "RSA PRIVATE KEY" {
-		key, err := x509.ParsePKCS1PrivateKey(privateKeyBlock.Bytes)
-		if err != nil {
-			return err
-		}
-
-		// ensure private key is of the correct length
-		if key.N.BitLen() < MinKeyLength {
-			return errors.New("key length must be at least 2048 bits")
-		}
-	}
+	err := validateKeyLength(privateKeyBlock)
 
 	certificateBlock, _ := pem.Decode([]byte(e.Certificate))
 	if certificateBlock == nil {
@@ -102,6 +93,40 @@ func (e *InlineCertificateConfigEntry) Validate() error {
 	return nil
 }
 
+func validateKeyLength(privateKeyBlock *pem.Block) error {
+	if privateKeyBlock.Type != "RSA PRIVATE KEY" {
+		return nil
+	}
+
+	lenCheckFn := nonFipsLenCheck
+
+	if version.IsFIPS() {
+		lenCheckFn = fipsLenCheck
+	}
+	key, err := x509.ParsePKCS1PrivateKey(privateKeyBlock.Bytes)
+	if err != nil {
+		return err
+	}
+
+	return lenCheckFn(key.N.BitLen())
+}
+
+func nonFipsLenCheck(keyLen int) error {
+	// ensure private key is of the correct length
+	if keyLen < MinKeyLength {
+		return errors.New("key length must be at least 2048 bits")
+	}
+
+	return nil
+}
+
+func fipsLenCheck(keyLen int) error {
+	if keyLen != 2048 && keyLen != 3072 && keyLen != 4096 {
+		return errors.New("key length invalid: only RSA lengths of 2048, 3072, and 4096 are allowed in FIPS mode")
+	}
+	return nil
+}
+
 func (e *InlineCertificateConfigEntry) Hosts() ([]string, error) {
 	certificateBlock, _ := pem.Decode([]byte(e.Certificate))
 	if certificateBlock == nil {