Snapshot length and hashes fields are optional in TUF-1.0
TUF-1.0 in section 4.4.4 no longer requires the `length` and
`hashes` fields to be present on the metadata contained in the
snapshot role. This patch makes those fields optional by
only using them for equality if they are listed in the
`expected` object.
Change-Id: I42b9a26fb9b1c5115cd0005a3c489c97f7eb328e
diff --git a/util/util.go b/util/util.go
index bf6f403..18f788f 100644
--- a/util/util.go
+++ b/util/util.go
@@ -76,9 +76,18 @@
if actual.Length != expected.Length {
return ErrWrongLength{expected.Length, actual.Length}
}
+
+ if err := hashEqual(actual.Hashes, expected.Hashes); err != nil {
+ return err
+ }
+
+ return nil
+}
+
+func hashEqual(actual data.Hashes, expected data.Hashes) error {
hashChecked := false
- for typ, hash := range expected.Hashes {
- if h, ok := actual.Hashes[typ]; ok {
+ for typ, hash := range expected {
+ if h, ok := actual[typ]; ok {
hashChecked = true
if !hmac.Equal(h, hash) {
return ErrWrongHash{typ, hash, h}
@@ -86,7 +95,7 @@
}
}
if !hashChecked {
- return ErrNoCommonHash{expected.Hashes, actual.Hashes}
+ return ErrNoCommonHash{expected, actual}
}
return nil
}
@@ -102,8 +111,19 @@
}
func SnapshotFileMetaEqual(actual data.SnapshotFileMeta, expected data.SnapshotFileMeta) error {
- if err := FileMetaEqual(actual.FileMeta, expected.FileMeta); err != nil {
- return err
+ // TUF-1.0 no longer considers the length and hashes to be a required
+ // member of snapshots. However they are considering requiring hashes
+ // for delegated roles to avoid an attack described in Section 5.6 of
+ // the Mercury paper:
+ // https://github.com/theupdateframework/specification/pull/40
+ if expected.Length != 0 && actual.Length != expected.Length {
+ return ErrWrongLength{expected.Length, actual.Length}
+ }
+
+ if len(expected.Hashes) != 0 {
+ if err := hashEqual(actual.Hashes, expected.Hashes); err != nil {
+ return err
+ }
}
if err := versionEqual(actual.Version, expected.Version); err != nil {
@@ -118,6 +138,9 @@
}
func TimestampFileMetaEqual(actual data.TimestampFileMeta, expected data.TimestampFileMeta) error {
+ // As opposed to snapshots, the length and hashes are still required in
+ // TUF-1.0. See:
+ // https://github.com/theupdateframework/specification/issues/38
if err := FileMetaEqual(actual.FileMeta, expected.FileMeta); err != nil {
return err
}
