Check for enough unwrapped shares before combining

PiperOrigin-RevId: 583109015
Change-Id: Ib84b11c072c95b983c3bcc0eb73c165e777a1968

client/client.go

@@ -325,21 +325,21 @@ func (c *StetClient) unwrapAndValidateShares(ctx context.Context, wrappedShares
 	// implementation handle the subset of shares.
 	var unwrappedShares []shares.UnwrappedShare
 	for i, wrapped := range wrappedShares {
-		glog.Infof("Attempting to unwrap share #%v", i+1)
 		unwrapped := shares.UnwrappedShare{}
 		kek := opts.kekInfos[i]
+		glog.Infof("Attempting to unwrap share #%v, URI %v", i+1, kek.GetKekUri())
 
 		switch x := kek.KekType.(type) {
 		case *configpb.KekInfo_RsaFingerprint:
 			key, err := PrivateKeyForRSAFingerprint(kek, opts.asymmetricKeys)
 			if err != nil {
-				glog.Warningf("Failed to find public key for RSA fingerprint: %v", err)
+				glog.Errorf("Failed to find private key for RSA fingerprint: %v", err)
 				continue
 			}
 
 			unwrapped.Share, err = rsa.DecryptOAEP(sha256.New(), rand.Reader, key, wrapped.GetShare(), nil)
 			if err != nil {
-				glog.Warningf("Error unwrapping key share: %v", err)
+				glog.Errorf("Error unwrapping key share for %v: %v", kek.GetKekUri(), err)
 				continue
 			}
 
@@ -352,12 +352,14 @@ func (c *StetClient) unwrapAndValidateShares(ctx context.Context, wrappedShares
 
 			kmsClient, err := kmsClients.Client(ctx, creds)
 			if err != nil {
-				return nil, fmt.Errorf("error initializing Cloud KMS Client with credentials \"%v\": %v", creds, err)
+				glog.Errorf("Error initializing Cloud KMS Client with credentials \"%v\" for %v: %v", creds, kek.GetKekUri(), err)
+				continue
 			}
 
 			kmd, err := getKekURIMetadata(ctx, kmsClient, kek)
 			if err != nil {
-				return nil, fmt.Errorf("Error retrieving KEK Metadata: %v", err)
+				glog.Errorf("Error retrieving KEK Metadata for %v: %v", kek.GetKekUri(), err)
+				continue
 			}
 
 			// Unwrap share via KMS.
@@ -369,17 +371,17 @@ func (c *StetClient) unwrapAndValidateShares(ctx context.Context, wrappedShares
 				}
 				unwrapped.Share, err = cloudkms.UnwrapShare(ctx, kmsClient, unwrapOpts)
 				if err != nil {
-					glog.Warningf("Error unwrapping key share: %v", err)
+					glog.Errorf("Error unwrapping key sharefor %v: %v", kmd.uri, err)
 					continue
 				}
 			case rpb.ProtectionLevel_EXTERNAL:
 				unwrapped.Share, err = c.ekmSecureSessionUnwrap(ctx, wrapped.GetShare(), *kmd)
 				if err != nil {
-					glog.Warningf("Error unwrapping with external EKM for %v: %v", kmd.uri, err)
+					glog.Errorf("Error unwrapping with external EKM for %v: %v", kmd.uri, err)
 					continue
 				}
 			default:
-				glog.Warningf("Unsupported protection level %v", pl)
+				glog.Errorf("Unsupported protection level for %v: %v", kek.GetKekUri(), pl)
 				continue
 			}
 
@@ -388,16 +390,16 @@ func (c *StetClient) unwrapAndValidateShares(ctx context.Context, wrappedShares
 			unwrapped.URI = kmd.uri
 
 		default:
-			glog.Warningf("Unsupported KekInfo type: %v", x)
+			glog.Errorf("Unsupported KekInfo type for %v: %v", kek.GetKekUri(), x)
 			continue
 		}
 
 		if !shares.ValidateShare(unwrapped.Share, wrapped.GetHash()) {
-			glog.Warningf("Unwrapped share %v does not have the expected hash", i)
+			glog.Errorf("Unwrapped share %v does not have the expected hash", i)
 			continue
 		}
 
-		glog.Infof("Successfully unwrapped share #%v", i+1)
+		glog.Infof("Successfully unwrapped share %v", unwrapped.URI)
 		unwrappedShares = append(unwrappedShares, unwrapped)
 	}
 
@@ -483,6 +485,26 @@ func (c *StetClient) Encrypt(ctx context.Context, input io.Reader, output io.Wri
 
 }
 
+// Returns whether the number of unwrapped shares is sufficient for combining the DEK based
+// on the splitting
+func enoughUnwrappedShares(shares []shares.UnwrappedShare, config *configpb.KeyConfig) error {
+	numShares := len(shares)
+
+	// Return error if no unwrapped shares found.
+	if numShares == 0 {
+		return fmt.Errorf("no unwrapped shares")
+	}
+
+	// Otherwise, verify the number of shares is enough for the specified shamir threshold.
+	if _, ok := config.GetKeySplittingAlgorithm().(*configpb.KeyConfig_Shamir); ok {
+		if int64(numShares) < config.GetShamir().GetThreshold() {
+			return fmt.Errorf("number of unwrapped shares %v is less than threshold needed %v", numShares, config.GetShamir().GetThreshold())
+		}
+	}
+
+	return nil
+}
+
 // Decrypt writes the decrypted data to the `output` writer, and returns the
 // key URIs used during decryption and the blob ID decrypted.
 func (c *StetClient) Decrypt(ctx context.Context, input io.Reader, output io.Writer, stetConfig *configpb.StetConfig) (*StetMetadata, error) {
@@ -522,6 +544,13 @@ func (c *StetClient) Decrypt(ctx context.Context, input io.Reader, output io.Wri
 		return nil, fmt.Errorf("error unwrapping and validating shares: %v", err)
 	}
 
+	// Verify we have enough unwrapped shares for the key config.
+	if err := enoughUnwrappedShares(unwrappedShares, matchingKeyConfig); err != nil {
+		return nil, fmt.Errorf("not enough unwrapped shares to recombine DEK, see logs for unwrap details: %v", err)
+	} else if len(unwrappedShares) < len(matchingKeyConfig.GetKekInfos()) {
+		glog.Warningf("Recieved enough unwrapped shares to recombine DEK, but not all shares unwrapped successfully: %v of %v unwrapped, see logs for unwrap details.", len(unwrappedShares), len(matchingKeyConfig.GetKekInfos()))
+	}
+
 	combinedShares, err := shares.CombineUnwrappedShares(matchingKeyConfig, unwrappedShares)
 	if err != nil {
 		return nil, fmt.Errorf("error combining unwrapped shares: %v", err)

client/client_test.go

@@ -1772,3 +1772,54 @@ func TestNewConfspaceConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestEnoughUnwrappedShares(t *testing.T) {
+	testShare := shares.UnwrappedShare{[]byte("test share"), "test hash"}
+	testcases := []struct {
+		name      string
+		shares    []shares.UnwrappedShare
+		config    *configpb.KeyConfig
+		expectErr bool
+	}{
+		{
+			name:   "With no split",
+			shares: []shares.UnwrappedShare{testShare},
+			config: &configpb.KeyConfig{
+				KeySplittingAlgorithm: &configpb.KeyConfig_NoSplit{true},
+			},
+		},
+		{
+			name:   "With shamir config",
+			shares: []shares.UnwrappedShare{testShare, testShare},
+			config: &configpb.KeyConfig{
+				KeySplittingAlgorithm: &configpb.KeyConfig_Shamir{&configpb.ShamirConfig{Threshold: 2, Shares: 2}},
+			},
+		},
+		{
+			name:   "Zero shares",
+			shares: []shares.UnwrappedShare{},
+			config: &configpb.KeyConfig{
+				KeySplittingAlgorithm: &configpb.KeyConfig_NoSplit{true},
+			},
+			expectErr: true,
+		},
+		{
+			name:   "Less shares than shamir threshold",
+			shares: []shares.UnwrappedShare{testShare},
+			config: &configpb.KeyConfig{
+				KeySplittingAlgorithm: &configpb.KeyConfig_Shamir{&configpb.ShamirConfig{Threshold: 2, Shares: 2}},
+			},
+			expectErr: true,
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := enoughUnwrappedShares(tc.shares, tc.config)
+
+			if (err != nil) != tc.expectErr {
+				t.Errorf("enoughWrappedShares did not return expected output: want (err == nil) == %v, got %v", tc.expectErr, err)
+			}
+		})
+	}
+}