+++ /dev/null
-// Copyright (c) 2015-2016 The btcsuite developers
-// Use of this source code is governed by an ISC
-// license that can be found in the LICENSE file.
-
-package txscript
-
-import (
- "sync"
-
- "github.com/btcsuite/btcd/btcec"
- "github.com/btcsuite/btcd/chaincfg/chainhash"
-)
-
-// sigCacheEntry represents an entry in the SigCache. Entries within the
-// SigCache are keyed according to the sigHash of the signature. In the
-// scenario of a cache-hit (according to the sigHash), an additional comparison
-// of the signature, and public key will be executed in order to ensure a complete
-// match. In the occasion that two sigHashes collide, the newer sigHash will
-// simply overwrite the existing entry.
-type sigCacheEntry struct {
- sig *btcec.Signature
- pubKey *btcec.PublicKey
-}
-
-// SigCache implements an ECDSA signature verification cache with a randomized
-// entry eviction policy. Only valid signatures will be added to the cache. The
-// benefits of SigCache are two fold. Firstly, usage of SigCache mitigates a DoS
-// attack wherein an attack causes a victim's client to hang due to worst-case
-// behavior triggered while processing attacker crafted invalid transactions. A
-// detailed description of the mitigated DoS attack can be found here:
-// https://bitslog.wordpress.com/2013/01/23/fixed-bitcoin-vulnerability-explanation-why-the-signature-cache-is-a-dos-protection/.
-// Secondly, usage of the SigCache introduces a signature verification
-// optimization which speeds up the validation of transactions within a block,
-// if they've already been seen and verified within the mempool.
-type SigCache struct {
- sync.RWMutex
- validSigs map[chainhash.Hash]sigCacheEntry
- maxEntries uint
-}
-
-// NewSigCache creates and initializes a new instance of SigCache. Its sole
-// parameter 'maxEntries' represents the maximum number of entries allowed to
-// exist in the SigCache at any particular moment. Random entries are evicted
-// to make room for new entries that would cause the number of entries in the
-// cache to exceed the max.
-func NewSigCache(maxEntries uint) *SigCache {
- return &SigCache{
- validSigs: make(map[chainhash.Hash]sigCacheEntry, maxEntries),
- maxEntries: maxEntries,
- }
-}
-
-// Exists returns true if an existing entry of 'sig' over 'sigHash' for public
-// key 'pubKey' is found within the SigCache. Otherwise, false is returned.
-//
-// NOTE: This function is safe for concurrent access. Readers won't be blocked
-// unless there exists a writer, adding an entry to the SigCache.
-func (s *SigCache) Exists(sigHash chainhash.Hash, sig *btcec.Signature, pubKey *btcec.PublicKey) bool {
- s.RLock()
- entry, ok := s.validSigs[sigHash]
- s.RUnlock()
-
- return ok && entry.pubKey.IsEqual(pubKey) && entry.sig.IsEqual(sig)
-}
-
-// Add adds an entry for a signature over 'sigHash' under public key 'pubKey'
-// to the signature cache. In the event that the SigCache is 'full', an
-// existing entry is randomly chosen to be evicted in order to make space for
-// the new entry.
-//
-// NOTE: This function is safe for concurrent access. Writers will block
-// simultaneous readers until function execution has concluded.
-func (s *SigCache) Add(sigHash chainhash.Hash, sig *btcec.Signature, pubKey *btcec.PublicKey) {
- s.Lock()
- defer s.Unlock()
-
- if s.maxEntries <= 0 {
- return
- }
-
- // If adding this new entry will put us over the max number of allowed
- // entries, then evict an entry.
- if uint(len(s.validSigs)+1) > s.maxEntries {
- // Remove a random entry from the map. Relying on the random
- // starting point of Go's map iteration. It's worth noting that
- // the random iteration starting point is not 100% guaranteed
- // by the spec, however most Go compilers support it.
- // Ultimately, the iteration order isn't important here because
- // in order to manipulate which items are evicted, an adversary
- // would need to be able to execute preimage attacks on the
- // hashing function in order to start eviction at a specific
- // entry.
- for sigEntry := range s.validSigs {
- delete(s.validSigs, sigEntry)
- break
- }
- }
- s.validSigs[sigHash] = sigCacheEntry{sig, pubKey}
-}
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