--- /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 implements a tamper-evident log
+// used in the Go module go.sum database server.
+//
+// This package follows the design of Certificate Transparency (RFC 6962)
+// and its proofs are compatible with that system.
+// See TestCertificateTransparency.
+//
+package tlog
+
+import (
+ "crypto/sha256"
+ "encoding/base64"
+ "errors"
+ "fmt"
+ "math/bits"
+)
+
+// A Hash is a hash identifying a log record or tree root.
+type Hash [HashSize]byte
+
+// HashSize is the size of a Hash in bytes.
+const HashSize = 32
+
+// String returns a base64 representation of the hash for printing.
+func (h Hash) String() string {
+ return base64.StdEncoding.EncodeToString(h[:])
+}
+
+// MarshalJSON marshals the hash as a JSON string containing the base64-encoded hash.
+func (h Hash) MarshalJSON() ([]byte, error) {
+ return []byte(`"` + h.String() + `"`), nil
+}
+
+// UnmarshalJSON unmarshals a hash from JSON string containing the a base64-encoded hash.
+func (h *Hash) UnmarshalJSON(data []byte) error {
+ if len(data) != 1+44+1 || data[0] != '"' || data[len(data)-2] != '=' || data[len(data)-1] != '"' {
+ return errors.New("cannot decode hash")
+ }
+
+ // As of Go 1.12, base64.StdEncoding.Decode insists on
+ // slicing into target[33:] even when it only writes 32 bytes.
+ // Since we already checked that the hash ends in = above,
+ // we can use base64.RawStdEncoding with the = removed;
+ // RawStdEncoding does not exhibit the same bug.
+ // We decode into a temporary to avoid writing anything to *h
+ // unless the entire input is well-formed.
+ var tmp Hash
+ n, err := base64.RawStdEncoding.Decode(tmp[:], data[1:len(data)-2])
+ if err != nil || n != HashSize {
+ return errors.New("cannot decode hash")
+ }
+ *h = tmp
+ return nil
+}
+
+// ParseHash parses the base64-encoded string form of a hash.
+func ParseHash(s string) (Hash, error) {
+ data, err := base64.StdEncoding.DecodeString(s)
+ if err != nil || len(data) != HashSize {
+ return Hash{}, fmt.Errorf("malformed hash")
+ }
+ var h Hash
+ copy(h[:], data)
+ return h, nil
+}
+
+// maxpow2 returns k, the maximum power of 2 smaller than n,
+// as well as l = log₂ k (so k = 1<<l).
+func maxpow2(n int64) (k int64, l int) {
+ l = 0
+ for 1<<uint(l+1) < n {
+ l++
+ }
+ return 1 << uint(l), l
+}
+
+var zeroPrefix = []byte{0x00}
+
+// RecordHash returns the content hash for the given record data.
+func RecordHash(data []byte) Hash {
+ // SHA256(0x00 || data)
+ // https://tools.ietf.org/html/rfc6962#section-2.1
+ h := sha256.New()
+ h.Write(zeroPrefix)
+ h.Write(data)
+ var h1 Hash
+ h.Sum(h1[:0])
+ return h1
+}
+
+// NodeHash returns the hash for an interior tree node with the given left and right hashes.
+func NodeHash(left, right Hash) Hash {
+ // SHA256(0x01 || left || right)
+ // https://tools.ietf.org/html/rfc6962#section-2.1
+ // We use a stack buffer to assemble the hash input
+ // to avoid allocating a hash struct with sha256.New.
+ var buf [1 + HashSize + HashSize]byte
+ buf[0] = 0x01
+ copy(buf[1:], left[:])
+ copy(buf[1+HashSize:], right[:])
+ return sha256.Sum256(buf[:])
+}
+
+// For information about the stored hash index ordering,
+// see section 3.3 of Crosby and Wallach's paper
+// "Efficient Data Structures for Tamper-Evident Logging".
+// https://www.usenix.org/legacy/event/sec09/tech/full_papers/crosby.pdf
+
+// StoredHashIndex maps the tree coordinates (level, n)
+// to a dense linear ordering that can be used for hash storage.
+// Hash storage implementations that store hashes in sequential
+// storage can use this function to compute where to read or write
+// a given hash.
+func StoredHashIndex(level int, n int64) int64 {
+ // Level L's n'th hash is written right after level L+1's 2n+1'th hash.
+ // Work our way down to the level 0 ordering.
+ // We'll add back the original level count at the end.
+ for l := level; l > 0; l-- {
+ n = 2*n + 1
+ }
+
+ // Level 0's n'th hash is written at n+n/2+n/4+... (eventually n/2ⁱ hits zero).
+ i := int64(0)
+ for ; n > 0; n >>= 1 {
+ i += n
+ }
+
+ return i + int64(level)
+}
+
+// SplitStoredHashIndex is the inverse of StoredHashIndex.
+// That is, SplitStoredHashIndex(StoredHashIndex(level, n)) == level, n.
+func SplitStoredHashIndex(index int64) (level int, n int64) {
+ // Determine level 0 record before index.
+ // StoredHashIndex(0, n) < 2*n,
+ // so the n we want is in [index/2, index/2+log₂(index)].
+ n = index / 2
+ indexN := StoredHashIndex(0, n)
+ if indexN > index {
+ panic("bad math")
+ }
+ for {
+ // Each new record n adds 1 + trailingZeros(n) hashes.
+ x := indexN + 1 + int64(bits.TrailingZeros64(uint64(n+1)))
+ if x > index {
+ break
+ }
+ n++
+ indexN = x
+ }
+ // The hash we want was committed with record n,
+ // meaning it is one of (0, n), (1, n/2), (2, n/4), ...
+ level = int(index - indexN)
+ return level, n >> uint(level)
+}
+
+// StoredHashCount returns the number of stored hashes
+// that are expected for a tree with n records.
+func StoredHashCount(n int64) int64 {
+ if n == 0 {
+ return 0
+ }
+ // The tree will have the hashes up to the last leaf hash.
+ numHash := StoredHashIndex(0, n-1) + 1
+ // And it will have any hashes for subtrees completed by that leaf.
+ for i := uint64(n - 1); i&1 != 0; i >>= 1 {
+ numHash++
+ }
+ return numHash
+}
+
+// StoredHashes returns the hashes that must be stored when writing
+// record n with the given data. The hashes should be stored starting
+// at StoredHashIndex(0, n). The result will have at most 1 + log₂ n hashes,
+// but it will average just under two per call for a sequence of calls for n=1..k.
+//
+// StoredHashes may read up to log n earlier hashes from r
+// in order to compute hashes for completed subtrees.
+func StoredHashes(n int64, data []byte, r HashReader) ([]Hash, error) {
+ return StoredHashesForRecordHash(n, RecordHash(data), r)
+}
+
+// StoredHashesForRecordHash is like StoredHashes but takes
+// as its second argument RecordHash(data) instead of data itself.
+func StoredHashesForRecordHash(n int64, h Hash, r HashReader) ([]Hash, error) {
+ // Start with the record hash.
+ hashes := []Hash{h}
+
+ // Build list of indexes needed for hashes for completed subtrees.
+ // Each trailing 1 bit in the binary representation of n completes a subtree
+ // and consumes a hash from an adjacent subtree.
+ m := int(bits.TrailingZeros64(uint64(n + 1)))
+ indexes := make([]int64, m)
+ for i := 0; i < m; i++ {
+ // We arrange indexes in sorted order.
+ // Note that n>>i is always odd.
+ indexes[m-1-i] = StoredHashIndex(i, n>>uint(i)-1)
+ }
+
+ // Fetch hashes.
+ old, err := r.ReadHashes(indexes)
+ if err != nil {
+ return nil, err
+ }
+ if len(old) != len(indexes) {
+ return nil, fmt.Errorf("tlog: ReadHashes(%d indexes) = %d hashes", len(indexes), len(old))
+ }
+
+ // Build new hashes.
+ for i := 0; i < m; i++ {
+ h = NodeHash(old[m-1-i], h)
+ hashes = append(hashes, h)
+ }
+ return hashes, nil
+}
+
+// A HashReader can read hashes for nodes in the log's tree structure.
+type HashReader interface {
+ // ReadHashes returns the hashes with the given stored hash indexes
+ // (see StoredHashIndex and SplitStoredHashIndex).
+ // ReadHashes must return a slice of hashes the same length as indexes,
+ // or else it must return a non-nil error.
+ // ReadHashes may run faster if indexes is sorted in increasing order.
+ ReadHashes(indexes []int64) ([]Hash, error)
+}
+
+// A HashReaderFunc is a function implementing HashReader.
+type HashReaderFunc func([]int64) ([]Hash, error)
+
+func (f HashReaderFunc) ReadHashes(indexes []int64) ([]Hash, error) {
+ return f(indexes)
+}
+
+// TreeHash computes the hash for the root of the tree with n records,
+// using the HashReader to obtain previously stored hashes
+// (those returned by StoredHashes during the writes of those n records).
+// TreeHash makes a single call to ReadHash requesting at most 1 + log₂ n hashes.
+// The tree of size zero is defined to have an all-zero Hash.
+func TreeHash(n int64, r HashReader) (Hash, error) {
+ if n == 0 {
+ return Hash{}, nil
+ }
+ indexes := subTreeIndex(0, n, nil)
+ hashes, err := r.ReadHashes(indexes)
+ if err != nil {
+ return Hash{}, err
+ }
+ if len(hashes) != len(indexes) {
+ return Hash{}, fmt.Errorf("tlog: ReadHashes(%d indexes) = %d hashes", len(indexes), len(hashes))
+ }
+ hash, hashes := subTreeHash(0, n, hashes)
+ if len(hashes) != 0 {
+ panic("tlog: bad index math in TreeHash")
+ }
+ return hash, nil
+}
+
+// subTreeIndex returns the storage indexes needed to compute
+// the hash for the subtree containing records [lo, hi),
+// appending them to need and returning the result.
+// See https://tools.ietf.org/html/rfc6962#section-2.1
+func subTreeIndex(lo, hi int64, need []int64) []int64 {
+ // See subTreeHash below for commentary.
+ for lo < hi {
+ k, level := maxpow2(hi - lo + 1)
+ if lo&(k-1) != 0 {
+ panic("tlog: bad math in subTreeIndex")
+ }
+ need = append(need, StoredHashIndex(level, lo>>uint(level)))
+ lo += k
+ }
+ return need
+}
+
+// subTreeHash computes the hash for the subtree containing records [lo, hi),
+// assuming that hashes are the hashes corresponding to the indexes
+// returned by subTreeIndex(lo, hi).
+// It returns any leftover hashes.
+func subTreeHash(lo, hi int64, hashes []Hash) (Hash, []Hash) {
+ // Repeatedly partition the tree into a left side with 2^level nodes,
+ // for as large a level as possible, and a right side with the fringe.
+ // The left hash is stored directly and can be read from storage.
+ // The right side needs further computation.
+ numTree := 0
+ for lo < hi {
+ k, _ := maxpow2(hi - lo + 1)
+ if lo&(k-1) != 0 || lo >= hi {
+ panic("tlog: bad math in subTreeHash")
+ }
+ numTree++
+ lo += k
+ }
+
+ if len(hashes) < numTree {
+ panic("tlog: bad index math in subTreeHash")
+ }
+
+ // Reconstruct hash.
+ h := hashes[numTree-1]
+ for i := numTree - 2; i >= 0; i-- {
+ h = NodeHash(hashes[i], h)
+ }
+ return h, hashes[numTree:]
+}
+
+// A RecordProof is a verifiable proof that a particular log root contains a particular record.
+// RFC 6962 calls this a “Merkle audit path.”
+type RecordProof []Hash
+
+// ProveRecord returns the proof that the tree of size t contains the record with index n.
+func ProveRecord(t, n int64, r HashReader) (RecordProof, error) {
+ if t < 0 || n < 0 || n >= t {
+ return nil, fmt.Errorf("tlog: invalid inputs in ProveRecord")
+ }
+ indexes := leafProofIndex(0, t, n, nil)
+ if len(indexes) == 0 {
+ return RecordProof{}, nil
+ }
+ 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))
+ }
+
+ p, hashes := leafProof(0, t, n, hashes)
+ if len(hashes) != 0 {
+ panic("tlog: bad index math in ProveRecord")
+ }
+ return p, nil
+}
+
+// leafProofIndex builds the list of indexes needed to construct the proof
+// that leaf n is contained in the subtree with leaves [lo, hi).
+// It appends those indexes to need and returns the result.
+// See https://tools.ietf.org/html/rfc6962#section-2.1.1
+func leafProofIndex(lo, hi, n int64, need []int64) []int64 {
+ // See leafProof below for commentary.
+ if !(lo <= n && n < hi) {
+ panic("tlog: bad math in leafProofIndex")
+ }
+ if lo+1 == hi {
+ return need
+ }
+ if k, _ := maxpow2(hi - lo); n < lo+k {
+ need = leafProofIndex(lo, lo+k, n, need)
+ need = subTreeIndex(lo+k, hi, need)
+ } else {
+ need = subTreeIndex(lo, lo+k, need)
+ need = leafProofIndex(lo+k, hi, n, need)
+ }
+ return need
+}
+
+// leafProof constructs the proof that leaf n is contained in the subtree with leaves [lo, hi).
+// It returns any leftover hashes as well.
+// See https://tools.ietf.org/html/rfc6962#section-2.1.1
+func leafProof(lo, hi, n int64, hashes []Hash) (RecordProof, []Hash) {
+ // We must have lo <= n < hi or else the code here has a bug.
+ if !(lo <= n && n < hi) {
+ panic("tlog: bad math in leafProof")
+ }
+
+ if lo+1 == hi { // n == lo
+ // Reached the leaf node.
+ // The verifier knows what the leaf hash is, so we don't need to send it.
+ return RecordProof{}, hashes
+ }
+
+ // Walk down the tree toward n.
+ // Record the hash of the path not taken (needed for verifying the proof).
+ var p RecordProof
+ var th Hash
+ if k, _ := maxpow2(hi - lo); n < lo+k {
+ // n is on left side
+ p, hashes = leafProof(lo, lo+k, n, hashes)
+ th, hashes = subTreeHash(lo+k, hi, hashes)
+ } else {
+ // n is on right side
+ th, hashes = subTreeHash(lo, lo+k, hashes)
+ p, hashes = leafProof(lo+k, hi, n, hashes)
+ }
+ return append(p, th), hashes
+}
+
+var errProofFailed = errors.New("invalid transparency proof")
+
+// CheckRecord verifies that p is a valid proof that the tree of size t
+// with hash th has an n'th record with hash h.
+func CheckRecord(p RecordProof, t int64, th Hash, n int64, h Hash) error {
+ if t < 0 || n < 0 || n >= t {
+ return fmt.Errorf("tlog: invalid inputs in CheckRecord")
+ }
+ th2, err := runRecordProof(p, 0, t, n, h)
+ if err != nil {
+ return err
+ }
+ if th2 == th {
+ return nil
+ }
+ return errProofFailed
+}
+
+// runRecordProof runs the proof p that leaf n is contained in the subtree with leaves [lo, hi).
+// Running the proof means constructing and returning the implied hash of that
+// subtree.
+func runRecordProof(p RecordProof, lo, hi, n int64, leafHash Hash) (Hash, error) {
+ // We must have lo <= n < hi or else the code here has a bug.
+ if !(lo <= n && n < hi) {
+ panic("tlog: bad math in runRecordProof")
+ }
+
+ if lo+1 == hi { // m == lo
+ // Reached the leaf node.
+ // The proof must not have any unnecessary hashes.
+ if len(p) != 0 {
+ return Hash{}, errProofFailed
+ }
+ return leafHash, nil
+ }
+
+ if len(p) == 0 {
+ return Hash{}, errProofFailed
+ }
+
+ k, _ := maxpow2(hi - lo)
+ if n < lo+k {
+ th, err := runRecordProof(p[:len(p)-1], lo, lo+k, n, leafHash)
+ if err != nil {
+ return Hash{}, err
+ }
+ return NodeHash(th, p[len(p)-1]), nil
+ } else {
+ th, err := runRecordProof(p[:len(p)-1], lo+k, hi, n, leafHash)
+ if err != nil {
+ return Hash{}, err
+ }
+ return NodeHash(p[len(p)-1], th), nil
+ }
+}
+
+// A TreeProof is a verifiable proof that a particular log tree contains
+// as a prefix all records present in an earlier tree.
+// RFC 6962 calls this a “Merkle consistency proof.”
+type TreeProof []Hash
+
+// ProveTree returns the proof that the tree of size t contains
+// as a prefix all the records from the tree of smaller size n.
+func ProveTree(t, n int64, h HashReader) (TreeProof, error) {
+ if t < 1 || n < 1 || n > t {
+ return nil, fmt.Errorf("tlog: invalid inputs in ProveTree")
+ }
+ indexes := treeProofIndex(0, t, n, nil)
+ if len(indexes) == 0 {
+ return TreeProof{}, nil
+ }
+ hashes, err := h.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))
+ }
+
+ p, hashes := treeProof(0, t, n, hashes)
+ if len(hashes) != 0 {
+ panic("tlog: bad index math in ProveTree")
+ }
+ return p, nil
+}
+
+// treeProofIndex builds the list of indexes needed to construct
+// the sub-proof related to the subtree containing records [lo, hi).
+// See https://tools.ietf.org/html/rfc6962#section-2.1.2.
+func treeProofIndex(lo, hi, n int64, need []int64) []int64 {
+ // See treeProof below for commentary.
+ if !(lo < n && n <= hi) {
+ panic("tlog: bad math in treeProofIndex")
+ }
+
+ if n == hi {
+ if lo == 0 {
+ return need
+ }
+ return subTreeIndex(lo, hi, need)
+ }
+
+ if k, _ := maxpow2(hi - lo); n <= lo+k {
+ need = treeProofIndex(lo, lo+k, n, need)
+ need = subTreeIndex(lo+k, hi, need)
+ } else {
+ need = subTreeIndex(lo, lo+k, need)
+ need = treeProofIndex(lo+k, hi, n, need)
+ }
+ return need
+}
+
+// treeProof constructs the sub-proof related to the subtree containing records [lo, hi).
+// It returns any leftover hashes as well.
+// See https://tools.ietf.org/html/rfc6962#section-2.1.2.
+func treeProof(lo, hi, n int64, hashes []Hash) (TreeProof, []Hash) {
+ // We must have lo < n <= hi or else the code here has a bug.
+ if !(lo < n && n <= hi) {
+ panic("tlog: bad math in treeProof")
+ }
+
+ // Reached common ground.
+ if n == hi {
+ if lo == 0 {
+ // This subtree corresponds exactly to the old tree.
+ // The verifier knows that hash, so we don't need to send it.
+ return TreeProof{}, hashes
+ }
+ th, hashes := subTreeHash(lo, hi, hashes)
+ return TreeProof{th}, hashes
+ }
+
+ // Interior node for the proof.
+ // Decide whether to walk down the left or right side.
+ var p TreeProof
+ var th Hash
+ if k, _ := maxpow2(hi - lo); n <= lo+k {
+ // m is on left side
+ p, hashes = treeProof(lo, lo+k, n, hashes)
+ th, hashes = subTreeHash(lo+k, hi, hashes)
+ } else {
+ // m is on right side
+ th, hashes = subTreeHash(lo, lo+k, hashes)
+ p, hashes = treeProof(lo+k, hi, n, hashes)
+ }
+ return append(p, th), hashes
+}
+
+// CheckTree verifies that p is a valid proof that the tree of size t with hash th
+// contains as a prefix the tree of size n with hash h.
+func CheckTree(p TreeProof, t int64, th Hash, n int64, h Hash) error {
+ if t < 1 || n < 1 || n > t {
+ return fmt.Errorf("tlog: invalid inputs in CheckTree")
+ }
+ h2, th2, err := runTreeProof(p, 0, t, n, h)
+ if err != nil {
+ return err
+ }
+ if th2 == th && h2 == h {
+ return nil
+ }
+ return errProofFailed
+}
+
+// runTreeProof runs the sub-proof p related to the subtree containing records [lo, hi),
+// where old is the hash of the old tree with n records.
+// Running the proof means constructing and returning the implied hashes of that
+// subtree in both the old and new tree.
+func runTreeProof(p TreeProof, lo, hi, n int64, old Hash) (Hash, Hash, error) {
+ // We must have lo < n <= hi or else the code here has a bug.
+ if !(lo < n && n <= hi) {
+ panic("tlog: bad math in runTreeProof")
+ }
+
+ // Reached common ground.
+ if n == hi {
+ if lo == 0 {
+ if len(p) != 0 {
+ return Hash{}, Hash{}, errProofFailed
+ }
+ return old, old, nil
+ }
+ if len(p) != 1 {
+ return Hash{}, Hash{}, errProofFailed
+ }
+ return p[0], p[0], nil
+ }
+
+ if len(p) == 0 {
+ return Hash{}, Hash{}, errProofFailed
+ }
+
+ // Interior node for the proof.
+ k, _ := maxpow2(hi - lo)
+ if n <= lo+k {
+ oh, th, err := runTreeProof(p[:len(p)-1], lo, lo+k, n, old)
+ if err != nil {
+ return Hash{}, Hash{}, err
+ }
+ return oh, NodeHash(th, p[len(p)-1]), nil
+ } else {
+ oh, th, err := runTreeProof(p[:len(p)-1], lo+k, hi, n, old)
+ if err != nil {
+ return Hash{}, Hash{}, err
+ }
+ return NodeHash(p[len(p)-1], oh), NodeHash(p[len(p)-1], th), nil
+ }
+}
projects / dotfiles / .git / blobdiff