Add signature caching for individual keys

config/config.go

@@ -70,6 +70,7 @@ type KeyConfig struct {
 	Timestamp       bool     // If true, attach a timestamped countersignature when possible
 	Timestamper     string   // If set, use the named timestamper to countersign
 	Hide            bool     // If true, then omit this key from 'remote list-keys'
+	Memcache        []string // host:port of memcached to use for caching signatures
 
 	name  string
 	token *TokenConfig

doc/relic.yml

@@ -96,6 +96,10 @@ keys:
     # see `namedurls` below. Implies "timestamp: true".
     #timestamper: apple
 
+    # Optional memcache servers for memoizing signing requests
+    #memcache:
+    # - 127.0.0.1:11211
+
     # Clients with any of these roles can utilize this key
     roles: ["somegroup"]
 

internal/signinit/signinit.go

@@ -29,6 +29,7 @@ import (
 	"github.com/sassoftware/relic/v8/signers"
 	"github.com/sassoftware/relic/v8/signers/sigerrors"
 	"github.com/sassoftware/relic/v8/token"
+	"github.com/sassoftware/relic/v8/token/signaturecache"
 )
 
 // InitKey loads the cert chain for a key
@@ -85,6 +86,15 @@ func Init(ctx context.Context, mod *signers.Signer, tok token.Token, keyName str
 		Audit: auditInfo,
 		Flags: flags,
 	}
+
+	// Use signature cache if configured
+	if len(kconf.Memcache) > 0 {
+		cert.PrivateKey, err = signaturecache.New(kconf, &opts, cert.PrivateKey.(crypto.Signer))
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+
 	opts = opts.WithContext(ctx)
 	return cert, &opts, nil
 }

token/signaturecache/signaturecache.go

@@ -0,0 +1,80 @@
+// Copyright © Leonhard Oelke
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package signaturecache
+
+import (
+	"crypto"
+	"fmt"
+	"io"
+	"time"
+
+	"github.com/bradfitz/gomemcache/memcache"
+	"github.com/sassoftware/relic/v8/config"
+	"github.com/sassoftware/relic/v8/signers"
+)
+
+const (
+	// Settings for now are the same as the timestamp cache settings
+	memcacheTimeout = 1 * time.Second
+	memcacheExpiry  = 7 * 24 * time.Hour
+)
+
+type SignatureCache interface {
+	crypto.Signer
+}
+
+type signatureCache struct {
+	keyConf  *config.KeyConfig
+	opts     *signers.SignOpts
+	signer   crypto.Signer
+	Memcache *memcache.Client
+}
+
+func New(keyConf *config.KeyConfig, opts *signers.SignOpts, signer crypto.Signer) (SignatureCache, error) {
+	selector := new(memcache.ServerList)
+	if err := selector.SetServers(keyConf.Memcache...); err != nil {
+		return nil, fmt.Errorf("parsing memcache servers: %w", err)
+	}
+	mc := memcache.NewFromSelector(selector)
+	mc.Timeout = memcacheTimeout
+	return &signatureCache{keyConf, opts, signer, mc}, nil
+}
+
+func (c *signatureCache) Public() crypto.PublicKey {
+	return c.signer.Public()
+}
+
+func (c *signatureCache) Sign(rand io.Reader, digest []byte, opts crypto.SignerOpts) ([]byte, error) {
+	cacheKey := fmt.Sprintf("sig-%s-%x", c.keyConf.Name(), digest)
+
+	item, err := c.Memcache.Get(cacheKey)
+	if err == nil && item != nil {
+		c.opts.Audit.Attributes["sig.cache"] = "hit"
+		return item.Value, nil
+	}
+
+	signature, err := c.signer.Sign(rand, digest, opts)
+	if err != nil {
+		return nil, err
+	}
+
+	_ = c.Memcache.Set(&memcache.Item{
+		Key:        cacheKey,
+		Value:      signature,
+		Expiration: int32(memcacheExpiry / time.Second),
+	})
+
+	c.opts.Audit.Attributes["sig.cache"] = "miss"
+	return signature, nil
+}