fix: hint people to changing from RSA peer ids

cmd/ipfs/daemon.go

@@ -30,6 +30,7 @@ import (
 	fsrepo "github.com/ipfs/kubo/repo/fsrepo"
 	"github.com/ipfs/kubo/repo/fsrepo/migrations"
 	"github.com/ipfs/kubo/repo/fsrepo/migrations/ipfsfetcher"
+	p2pcrypto "github.com/libp2p/go-libp2p/core/crypto"
 	pnet "github.com/libp2p/go-libp2p/core/pnet"
 	sockets "github.com/libp2p/go-socket-activation"
 
@@ -459,6 +460,22 @@ func daemonFunc(req *cmds.Request, re cmds.ResponseEmitter, env cmds.Environment
 
 	printSwarmAddrs(node)
 
+	if node.PrivateKey.Type() == p2pcrypto.RSA {
+		fmt.Print(`
+Warning: You are using an RSA Peer ID, which was replaced by Ed25519
+as the default recommended in Kubo since September 2020. Signing with
+RSA Peer IDs is more CPU-intensive than with other key types.
+It is recommended that you change your public key type to ed25519
+by using the following command:
+
+  ipfs key rotate -o rsa-key-backup -t ed25519
+
+After changing your key type, restart your node for the changes to
+take effect.
+
+`)
+	}
+
 	defer func() {
 		// We wait for the node to close first, as the node has children
 		// that it will wait for before closing, such as the API server.

docs/changelogs/v0.18.md

@@ -159,7 +159,7 @@ To support QUICv1 and WebTransport by default a new config migration (`v13`) is
 To help protect nodes from DoS (resource exhaustion) and eclipse attacks,
 Kubo enabled the [go-libp2p Network Resource Manager](https://github.com/libp2p/go-libp2p/tree/master/p2p/host/resource-manager)
 by default in [Kubo 0.17](https://github.com/ipfs/kubo/blob/master/docs/changelogs/v0.17.md#libp2p-resource-management-enabled-by-default).
- 
+
 Introducing limits like this by default after the fact is tricky,
 and various improvements have been made to improve the UX including:
 1. [Dedicated docs concerning the resource manager integration](https://github.com/ipfs/kubo/blob/master/docs/libp2p-resource-management.md).  This is a great place to go to learn more or get your FAQs answered.