diff --git a/vfs/adiantum/adiantum.go b/vfs/adiantum/adiantum.go
index 13d1bdd..39e45bb 100644
--- a/vfs/adiantum/adiantum.go
+++ b/vfs/adiantum/adiantum.go
@@ -13,6 +13,9 @@ const pepper = "github.com/ncruces/go-sqlite3/vfs/adiantum"
 type adiantumCreator struct{}
 
 func (adiantumCreator) HBSH(key []byte) *hbsh.HBSH {
+	if len(key) != 32 {
+		return nil
+	}
 	return adiantum.New(key)
 }
 
diff --git a/vfs/adiantum/hbsh.go b/vfs/adiantum/hbsh.go
index 8d40d33..6b40e41 100644
--- a/vfs/adiantum/hbsh.go
+++ b/vfs/adiantum/hbsh.go
@@ -22,29 +22,41 @@ func (h *hbshVFS) Open(name string, flags vfs.OpenFlag) (vfs.File, vfs.OpenFlag,
 }
 
 func (h *hbshVFS) OpenParams(name string, flags vfs.OpenFlag, params url.Values) (file vfs.File, _ vfs.OpenFlag, err error) {
+	encrypt := flags&(0|
+		vfs.OPEN_MAIN_DB|
+		vfs.OPEN_MAIN_JOURNAL|
+		vfs.OPEN_SUBJOURNAL|
+		vfs.OPEN_WAL) != 0
+
+	var hbsh *hbsh.HBSH
+	if encrypt {
+		var key []byte
+		if t, ok := params["key"]; ok {
+			key = []byte(t[0])
+		} else if t, ok := params["hexkey"]; ok {
+			key, _ = hex.DecodeString(t[0])
+		} else if t, ok := params["textkey"]; ok {
+			key = h.hbsh.KDF(t[0])
+		}
+
+		if hbsh = h.hbsh.HBSH(key); hbsh == nil {
+			return nil, flags, sqlite3.NOTADB
+		}
+	}
+
 	if h, ok := h.VFS.(vfs.VFSParams); ok {
+		delete(params, "vfs")
+		delete(params, "key")
+		delete(params, "hexkey")
+		delete(params, "textkey")
 		file, flags, err = h.OpenParams(name, flags, params)
 	} else {
 		file, flags, err = h.Open(name, flags)
 	}
-	if err != nil || flags&(0|
-		vfs.OPEN_MAIN_DB|
-		vfs.OPEN_MAIN_JOURNAL|
-		vfs.OPEN_SUBJOURNAL|
-		vfs.OPEN_WAL) == 0 {
+	if err != nil || hbsh == nil {
 		return file, flags, err
 	}
-
-	var key []byte
-	if t, ok := params["key"]; ok {
-		key = []byte(t[0])
-	} else if t, ok := params["hexkey"]; ok {
-		key, err = hex.DecodeString(t[0])
-	} else if t, ok := params["textkey"]; ok {
-		key = h.hbsh.KDF(t[0])
-	}
-
-	return &hbshFile{File: file, hbsh: h.hbsh.HBSH(key)}, flags, err
+	return &hbshFile{File: file, hbsh: hbsh}, flags, err
 }
 
 const (
@@ -93,20 +105,22 @@ func (h *hbshFile) WriteAt(p []byte, off int64) (n int, err error) {
 		binary.LittleEndian.PutUint64(h.tweak[:], uint64(min))
 		data := h.block[:]
 
-		if min < off || len(p[n:]) < blockSize {
+		if off > min || len(p[n:]) < blockSize {
 			// Read full block.
 			m, err := h.File.ReadAt(h.block[:], min)
-			switch {
-			case m == 0 && err == io.EOF:
-				clear(data)
-			case m != blockSize:
-				return n, err
-			default:
-				// Partial update.
-				data = h.hbsh.Decrypt(h.block[:], h.tweak[:])
-				if off > min {
-					data = data[off-min:]
+			if m != blockSize {
+				if err != io.EOF {
+					return n, err
 				}
+				// Writing past the EOF.
+				// A partially written block is corrupt,
+				// and also considered to be past the EOF.
+				clear(data)
+			}
+
+			data = h.hbsh.Decrypt(h.block[:], h.tweak[:])
+			if off > min {
+				data = data[off-min:]
 			}
 		}