Fix secret value showing up in logs

Signed-off-by: Matheus Pimenta <[email protected]>

internal/decryptor/decryptor.go

@@ -292,7 +292,7 @@ func (d *Decryptor) SopsDecryptWithFormat(data []byte, inputFormat, outputFormat
 	}
 
 	cipher := aes.NewCipher()
-	mac, err := tree.Decrypt(metadataKey, cipher)
+	mac, err := safeDecrypt(tree.Decrypt(metadataKey, cipher))
 	if err != nil {
 		return nil, sopsUserErr("error decrypting sops tree", err)
 	}
@@ -302,11 +302,11 @@ func (d *Decryptor) SopsDecryptWithFormat(data []byte, inputFormat, outputFormat
 		// the one that was stored in the document. If they match,
 		// integrity was preserved
 		// Ref: github.com/getsops/sops/v3/decrypt/decrypt.go
-		originalMac, err := cipher.Decrypt(
+		originalMac, err := safeDecrypt(cipher.Decrypt(
 			tree.Metadata.MessageAuthenticationCode,
 			metadataKey,
 			tree.Metadata.LastModified.Format(time.RFC3339),
-		)
+		))
 		if err != nil {
 			return nil, sopsUserErr("failed to verify sops data integrity", err)
 		}
@@ -811,3 +811,33 @@ func detectFormatFromMarkerBytes(b []byte) formats.Format {
 	}
 	return unsupportedFormat
 }
+
+// safeDecrypt redacts secret values in sops error messages.
+func safeDecrypt[T any](mac T, err error) (T, error) {
+	const (
+		prefix = "Input string "
+		suffix = " does not match sops' data format"
+	)
+
+	if err == nil {
+		return mac, nil
+	}
+
+	var buf strings.Builder
+
+	e := err.Error()
+	prefIdx := strings.Index(e, prefix)
+	suffIdx := strings.Index(e, suffix)
+
+	var zero T
+	if prefIdx == -1 || suffIdx == -1 {
+		return zero, err
+	}
+
+	buf.WriteString(e[:prefIdx])
+	buf.WriteString(prefix)
+	buf.WriteString("<redacted>")
+	buf.WriteString(suffix)
+
+	return zero, errors.New(buf.String())
+}

internal/decryptor/decryptor_test.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"io/fs"
 	"os"
@@ -1598,3 +1599,54 @@ func TestDecryptor_detectFormatFromMarkerBytes(t *testing.T) {
 		})
 	}
 }
+
+func TestSafeDecrypt(t *testing.T) {
+	for _, tt := range []struct {
+		name        string
+		mac         string
+		err         string
+		expectedMac string
+		expectedErr string
+	}{
+		{
+			name:        "no error",
+			mac:         "some mac",
+			expectedMac: "some mac",
+		},
+		{
+			name:        "only prefix",
+			err:         "Input string was not in a correct format",
+			expectedErr: "Input string was not in a correct format",
+		},
+		{
+			name:        "only suffix",
+			err:         "The value does not match sops' data format",
+			expectedErr: "The value does not match sops' data format",
+		},
+		{
+			name:        "redacted value",
+			err:         "Input string 1234567897 does not match sops' data format",
+			expectedErr: "Input string <redacted> does not match sops' data format",
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			g := NewWithT(t)
+
+			var err error
+			if tt.err != "" {
+				err = errors.New(tt.err)
+			}
+
+			mac, err := safeDecrypt(tt.mac, err)
+
+			g.Expect(mac).To(Equal(tt.expectedMac))
+
+			if tt.expectedErr == "" {
+				g.Expect(err).To(Not(HaveOccurred()))
+			} else {
+				g.Expect(err).To(HaveOccurred())
+				g.Expect(err.Error()).To(Equal(tt.expectedErr))
+			}
+		})
+	}
+}