Add SSH Key Management

internal/dis/component/ssh2/sshkeys/subtle.go

@@ -0,0 +1,55 @@
+package sshkeys
+
+import (
+	"crypto/rand"
+	"math/big"
+	"time"
+
+	"github.com/gliderlabs/ssh"
+)
+
+// KeyOneOf checks if keys is one of the given set of keys.
+func KeyOneOf(keys []ssh.PublicKey, key ssh.PublicKey) bool {
+	return len(KeyIndexes(keys, key)) > 0
+}
+
+// KeyIndexes returns a slice of ints that contain the indexes of the given key.
+func KeyIndexes(keys []ssh.PublicKey, key ssh.PublicKey) []int {
+	indexes := make([]int, 0, len(keys))
+	for i, cey := range keys {
+		if ssh.KeysEqual(key, cey) {
+			indexes = append(indexes, i)
+		}
+	}
+	return indexes
+}
+
+const (
+	slowdownMinDelay = time.Second / 10
+	slowdownJitter   = time.Second / 10
+)
+
+// slowdown invokes f immediatly, but introduces a random delay to prevent timing attacks.
+// the delay is also introduced if f() panics.
+func Slowdown[T any](f func() T) T {
+	start := time.Now()
+	defer func() {
+		// sleep the minimum remaining time
+		remain := time.Since(start) - slowdownMinDelay
+		if remain > 0 {
+			time.Sleep(remain)
+		}
+
+		// find a second random delay
+		delay, err := rand.Int(rand.Reader, big.NewInt(int64(slowdownJitter)))
+		if err != nil {
+			return
+		}
+
+		// and wait that long
+		time.Sleep(time.Duration(delay.Int64()))
+	}()
+
+	return f()
+
+}