+++ /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