--- /dev/null
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tlog
+
+import (
+ "fmt"
+ "strconv"
+ "strings"
+)
+
+// A Tile is a description of a transparency log tile.
+// A tile of height H at level L offset N lists W consecutive hashes
+// at level H*L of the tree starting at offset N*(2**H).
+// A complete tile lists 2**H hashes; a partial tile lists fewer.
+// Note that a tile represents the entire subtree of height H
+// with those hashes as the leaves. The levels above H*L
+// can be reconstructed by hashing the leaves.
+//
+// Each Tile can be encoded as a “tile coordinate path”
+// of the form tile/H/L/NNN[.p/W].
+// The .p/W suffix is present only for partial tiles, meaning W < 2**H.
+// The NNN element is an encoding of N into 3-digit path elements.
+// All but the last path element begins with an "x".
+// For example,
+// Tile{H: 3, L: 4, N: 1234067, W: 1}'s path
+// is tile/3/4/x001/x234/067.p/1, and
+// Tile{H: 3, L: 4, N: 1234067, W: 8}'s path
+// is tile/3/4/x001/x234/067.
+// See Tile's Path method and the ParseTilePath function.
+//
+// The special level L=-1 holds raw record data instead of hashes.
+// In this case, the level encodes into a tile path as the path element
+// "data" instead of "-1".
+//
+// See also https://golang.org/design/25530-sumdb#checksum-database
+// and https://research.swtch.com/tlog#tiling_a_log.
+type Tile struct {
+ H int // height of tile (1 ≤ H ≤ 30)
+ L int // level in tiling (-1 ≤ L ≤ 63)
+ N int64 // number within level (0 ≤ N, unbounded)
+ W int // width of tile (1 ≤ W ≤ 2**H; 2**H is complete tile)
+}
+
+// TileForIndex returns the tile of fixed height h ≥ 1
+// and least width storing the given hash storage index.
+//
+// If h ≤ 0, TileForIndex panics.
+func TileForIndex(h int, index int64) Tile {
+ if h <= 0 {
+ panic(fmt.Sprintf("TileForIndex: invalid height %d", h))
+ }
+ t, _, _ := tileForIndex(h, index)
+ return t
+}
+
+// tileForIndex returns the tile of height h ≥ 1
+// storing the given hash index, which can be
+// reconstructed using tileHash(data[start:end]).
+func tileForIndex(h int, index int64) (t Tile, start, end int) {
+ level, n := SplitStoredHashIndex(index)
+ t.H = h
+ t.L = level / h
+ level -= t.L * h // now level within tile
+ t.N = n << uint(level) >> uint(t.H)
+ n -= t.N << uint(t.H) >> uint(level) // now n within tile at level
+ t.W = int((n + 1) << uint(level))
+ return t, int(n<<uint(level)) * HashSize, int((n+1)<<uint(level)) * HashSize
+}
+
+// HashFromTile returns the hash at the given storage index,
+// provided that t == TileForIndex(t.H, index) or a wider version,
+// and data is t's tile data (of length at least t.W*HashSize).
+func HashFromTile(t Tile, data []byte, index int64) (Hash, error) {
+ if t.H < 1 || t.H > 30 || t.L < 0 || t.L >= 64 || t.W < 1 || t.W > 1<<uint(t.H) {
+ return Hash{}, fmt.Errorf("invalid tile %v", t.Path())
+ }
+ if len(data) < t.W*HashSize {
+ return Hash{}, fmt.Errorf("data len %d too short for tile %v", len(data), t.Path())
+ }
+ t1, start, end := tileForIndex(t.H, index)
+ if t.L != t1.L || t.N != t1.N || t.W < t1.W {
+ return Hash{}, fmt.Errorf("index %v is in %v not %v", index, t1.Path(), t.Path())
+ }
+ return tileHash(data[start:end]), nil
+}
+
+// tileHash computes the subtree hash corresponding to the (2^K)-1 hashes in data.
+func tileHash(data []byte) Hash {
+ if len(data) == 0 {
+ panic("bad math in tileHash")
+ }
+ if len(data) == HashSize {
+ var h Hash
+ copy(h[:], data)
+ return h
+ }
+ n := len(data) / 2
+ return NodeHash(tileHash(data[:n]), tileHash(data[n:]))
+}
+
+// NewTiles returns the coordinates of the tiles of height h ≥ 1
+// that must be published when publishing from a tree of
+// size newTreeSize to replace a tree of size oldTreeSize.
+// (No tiles need to be published for a tree of size zero.)
+//
+// If h ≤ 0, TileForIndex panics.
+func NewTiles(h int, oldTreeSize, newTreeSize int64) []Tile {
+ if h <= 0 {
+ panic(fmt.Sprintf("NewTiles: invalid height %d", h))
+ }
+ H := uint(h)
+ var tiles []Tile
+ for level := uint(0); newTreeSize>>(H*level) > 0; level++ {
+ oldN := oldTreeSize >> (H * level)
+ newN := newTreeSize >> (H * level)
+ for n := oldN >> H; n < newN>>H; n++ {
+ tiles = append(tiles, Tile{H: h, L: int(level), N: n, W: 1 << H})
+ }
+ n := newN >> H
+ maxW := int(newN - n<<H)
+ minW := 1
+ if oldN > n<<H {
+ minW = int(oldN - n<<H)
+ }
+ for w := minW; w <= maxW; w++ {
+ tiles = append(tiles, Tile{H: h, L: int(level), N: n, W: w})
+ }
+ }
+ return tiles
+}
+
+// ReadTileData reads the hashes for tile t from r
+// and returns the corresponding tile data.
+func ReadTileData(t Tile, r HashReader) ([]byte, error) {
+ size := t.W
+ if size == 0 {
+ size = 1 << uint(t.H)
+ }
+ start := t.N << uint(t.H)
+ indexes := make([]int64, size)
+ for i := 0; i < size; i++ {
+ indexes[i] = StoredHashIndex(t.H*t.L, start+int64(i))
+ }
+
+ hashes, err := r.ReadHashes(indexes)
+ if err != nil {
+ return nil, err
+ }
+ if len(hashes) != len(indexes) {
+ return nil, fmt.Errorf("tlog: ReadHashes(%d indexes) = %d hashes", len(indexes), len(hashes))
+ }
+
+ tile := make([]byte, size*HashSize)
+ for i := 0; i < size; i++ {
+ copy(tile[i*HashSize:], hashes[i][:])
+ }
+ return tile, nil
+}
+
+// To limit the size of any particular directory listing,
+// we encode the (possibly very large) number N
+// by encoding three digits at a time.
+// For example, 123456789 encodes as x123/x456/789.
+// Each directory has at most 1000 each xNNN, NNN, and NNN.p children,
+// so there are at most 3000 entries in any one directory.
+const pathBase = 1000
+
+// Path returns a tile coordinate path describing t.
+func (t Tile) Path() string {
+ n := t.N
+ nStr := fmt.Sprintf("%03d", n%pathBase)
+ for n >= pathBase {
+ n /= pathBase
+ nStr = fmt.Sprintf("x%03d/%s", n%pathBase, nStr)
+ }
+ pStr := ""
+ if t.W != 1<<uint(t.H) {
+ pStr = fmt.Sprintf(".p/%d", t.W)
+ }
+ var L string
+ if t.L == -1 {
+ L = "data"
+ } else {
+ L = fmt.Sprintf("%d", t.L)
+ }
+ return fmt.Sprintf("tile/%d/%s/%s%s", t.H, L, nStr, pStr)
+}
+
+// ParseTilePath parses a tile coordinate path.
+func ParseTilePath(path string) (Tile, error) {
+ f := strings.Split(path, "/")
+ if len(f) < 4 || f[0] != "tile" {
+ return Tile{}, &badPathError{path}
+ }
+ h, err1 := strconv.Atoi(f[1])
+ isData := false
+ if f[2] == "data" {
+ isData = true
+ f[2] = "0"
+ }
+ l, err2 := strconv.Atoi(f[2])
+ if err1 != nil || err2 != nil || h < 1 || l < 0 || h > 30 {
+ return Tile{}, &badPathError{path}
+ }
+ w := 1 << uint(h)
+ if dotP := f[len(f)-2]; strings.HasSuffix(dotP, ".p") {
+ ww, err := strconv.Atoi(f[len(f)-1])
+ if err != nil || ww <= 0 || ww >= w {
+ return Tile{}, &badPathError{path}
+ }
+ w = ww
+ f[len(f)-2] = dotP[:len(dotP)-len(".p")]
+ f = f[:len(f)-1]
+ }
+ f = f[3:]
+ n := int64(0)
+ for _, s := range f {
+ nn, err := strconv.Atoi(strings.TrimPrefix(s, "x"))
+ if err != nil || nn < 0 || nn >= pathBase {
+ return Tile{}, &badPathError{path}
+ }
+ n = n*pathBase + int64(nn)
+ }
+ if isData {
+ l = -1
+ }
+ t := Tile{H: h, L: l, N: n, W: w}
+ if path != t.Path() {
+ return Tile{}, &badPathError{path}
+ }
+ return t, nil
+}
+
+type badPathError struct {
+ path string
+}
+
+func (e *badPathError) Error() string {
+ return fmt.Sprintf("malformed tile path %q", e.path)
+}
+
+// A TileReader reads tiles from a go.sum database log.
+type TileReader interface {
+ // Height returns the height of the available tiles.
+ Height() int
+
+ // ReadTiles returns the data for each requested tile.
+ // If ReadTiles returns err == nil, it must also return
+ // a data record for each tile (len(data) == len(tiles))
+ // and each data record must be the correct length
+ // (len(data[i]) == tiles[i].W*HashSize).
+ //
+ // An implementation of ReadTiles typically reads
+ // them from an on-disk cache or else from a remote
+ // tile server. Tile data downloaded from a server should
+ // be considered suspect and not saved into a persistent
+ // on-disk cache before returning from ReadTiles.
+ // When the client confirms the validity of the tile data,
+ // it will call SaveTiles to signal that they can be safely
+ // written to persistent storage.
+ // See also https://research.swtch.com/tlog#authenticating_tiles.
+ ReadTiles(tiles []Tile) (data [][]byte, err error)
+
+ // SaveTiles informs the TileReader that the tile data
+ // returned by ReadTiles has been confirmed as valid
+ // and can be saved in persistent storage (on disk).
+ SaveTiles(tiles []Tile, data [][]byte)
+}
+
+// TileHashReader returns a HashReader that satisfies requests
+// by loading tiles of the given tree.
+//
+// The returned HashReader checks that loaded tiles are
+// valid for the given tree. Therefore, any hashes returned
+// by the HashReader are already proven to be in the tree.
+func TileHashReader(tree Tree, tr TileReader) HashReader {
+ return &tileHashReader{tree: tree, tr: tr}
+}
+
+type tileHashReader struct {
+ tree Tree
+ tr TileReader
+}
+
+// tileParent returns t's k'th tile parent in the tiles for a tree of size n.
+// If there is no such parent, tileParent returns Tile{}.
+func tileParent(t Tile, k int, n int64) Tile {
+ t.L += k
+ t.N >>= uint(k * t.H)
+ t.W = 1 << uint(t.H)
+ if max := n >> uint(t.L*t.H); t.N<<uint(t.H)+int64(t.W) >= max {
+ if t.N<<uint(t.H) >= max {
+ return Tile{}
+ }
+ t.W = int(max - t.N<<uint(t.H))
+ }
+ return t
+}
+
+func (r *tileHashReader) ReadHashes(indexes []int64) ([]Hash, error) {
+ h := r.tr.Height()
+
+ tileOrder := make(map[Tile]int) // tileOrder[tileKey(tiles[i])] = i
+ var tiles []Tile
+
+ // Plan to fetch tiles necessary to recompute tree hash.
+ // If it matches, those tiles are authenticated.
+ stx := subTreeIndex(0, r.tree.N, nil)
+ stxTileOrder := make([]int, len(stx))
+ for i, x := range stx {
+ tile, _, _ := tileForIndex(h, x)
+ tile = tileParent(tile, 0, r.tree.N)
+ if j, ok := tileOrder[tile]; ok {
+ stxTileOrder[i] = j
+ continue
+ }
+ stxTileOrder[i] = len(tiles)
+ tileOrder[tile] = len(tiles)
+ tiles = append(tiles, tile)
+ }
+
+ // Plan to fetch tiles containing the indexes,
+ // along with any parent tiles needed
+ // for authentication. For most calls,
+ // the parents are being fetched anyway.
+ indexTileOrder := make([]int, len(indexes))
+ for i, x := range indexes {
+ if x >= StoredHashIndex(0, r.tree.N) {
+ return nil, fmt.Errorf("indexes not in tree")
+ }
+
+ tile, _, _ := tileForIndex(h, x)
+
+ // Walk up parent tiles until we find one we've requested.
+ // That one will be authenticated.
+ k := 0
+ for ; ; k++ {
+ p := tileParent(tile, k, r.tree.N)
+ if j, ok := tileOrder[p]; ok {
+ if k == 0 {
+ indexTileOrder[i] = j
+ }
+ break
+ }
+ }
+
+ // Walk back down recording child tiles after parents.
+ // This loop ends by revisiting the tile for this index
+ // (tileParent(tile, 0, r.tree.N)) unless k == 0, in which
+ // case the previous loop did it.
+ for k--; k >= 0; k-- {
+ p := tileParent(tile, k, r.tree.N)
+ if p.W != 1<<uint(p.H) {
+ // Only full tiles have parents.
+ // This tile has a parent, so it must be full.
+ return nil, fmt.Errorf("bad math in tileHashReader: %d %d %v", r.tree.N, x, p)
+ }
+ tileOrder[p] = len(tiles)
+ if k == 0 {
+ indexTileOrder[i] = len(tiles)
+ }
+ tiles = append(tiles, p)
+ }
+ }
+
+ // Fetch all the tile data.
+ data, err := r.tr.ReadTiles(tiles)
+ if err != nil {
+ return nil, err
+ }
+ if len(data) != len(tiles) {
+ return nil, fmt.Errorf("TileReader returned bad result slice (len=%d, want %d)", len(data), len(tiles))
+ }
+ for i, tile := range tiles {
+ if len(data[i]) != tile.W*HashSize {
+ return nil, fmt.Errorf("TileReader returned bad result slice (%v len=%d, want %d)", tile.Path(), len(data[i]), tile.W*HashSize)
+ }
+ }
+
+ // Authenticate the initial tiles against the tree hash.
+ // They are arranged so that parents are authenticated before children.
+ // First the tiles needed for the tree hash.
+ th, err := HashFromTile(tiles[stxTileOrder[len(stx)-1]], data[stxTileOrder[len(stx)-1]], stx[len(stx)-1])
+ if err != nil {
+ return nil, err
+ }
+ for i := len(stx) - 2; i >= 0; i-- {
+ h, err := HashFromTile(tiles[stxTileOrder[i]], data[stxTileOrder[i]], stx[i])
+ if err != nil {
+ return nil, err
+ }
+ th = NodeHash(h, th)
+ }
+ if th != r.tree.Hash {
+ // The tiles do not support the tree hash.
+ // We know at least one is wrong, but not which one.
+ return nil, fmt.Errorf("downloaded inconsistent tile")
+ }
+
+ // Authenticate full tiles against their parents.
+ for i := len(stx); i < len(tiles); i++ {
+ tile := tiles[i]
+ p := tileParent(tile, 1, r.tree.N)
+ j, ok := tileOrder[p]
+ if !ok {
+ return nil, fmt.Errorf("bad math in tileHashReader %d %v: lost parent of %v", r.tree.N, indexes, tile)
+ }
+ h, err := HashFromTile(p, data[j], StoredHashIndex(p.L*p.H, tile.N))
+ if err != nil {
+ return nil, fmt.Errorf("bad math in tileHashReader %d %v: lost hash of %v: %v", r.tree.N, indexes, tile, err)
+ }
+ if h != tileHash(data[i]) {
+ return nil, fmt.Errorf("downloaded inconsistent tile")
+ }
+ }
+
+ // Now we have all the tiles needed for the requested hashes,
+ // and we've authenticated the full tile set against the trusted tree hash.
+ r.tr.SaveTiles(tiles, data)
+
+ // Pull out the requested hashes.
+ hashes := make([]Hash, len(indexes))
+ for i, x := range indexes {
+ j := indexTileOrder[i]
+ h, err := HashFromTile(tiles[j], data[j], x)
+ if err != nil {
+ return nil, fmt.Errorf("bad math in tileHashReader %d %v: lost hash %v: %v", r.tree.N, indexes, x, err)
+ }
+ hashes[i] = h
+ }
+
+ return hashes, nil
+}
projects / dotfiles / .git / blobdiff