Improve host key scanner, add Ed25519 generator

pkg/ssh/host_scan.go

@@ -4,27 +4,20 @@ import (
 	"encoding/base64"
 	"fmt"
 	"net"
+	"time"
 
 	"golang.org/x/crypto/ssh"
 	"golang.org/x/crypto/ssh/knownhosts"
 )
 
 // ScanHostKey collects the given host's preferred public key for the
-// algorithm of the given key pair. Any errors (e.g. authentication
-// failures) are ignored, except if no key could be collected from the
-// host.
-func ScanHostKey(host string, user string, pair *KeyPair) ([]byte, error) {
-	signer, err := ssh.ParsePrivateKey(pair.PrivateKey)
-	if err != nil {
-		return nil, err
-	}
+// Any errors (e.g. authentication  failures) are ignored, except if
+// no key could be collected from the host.
+func ScanHostKey(host string, timeout time.Duration) ([]byte, error) {
 	col := &collector{}
 	config := &ssh.ClientConfig{
-		User: user,
-		Auth: []ssh.AuthMethod{
-			ssh.PublicKeys(signer),
-		},
-		HostKeyCallback: col.StoreKey(),
+		HostKeyCallback:   col.StoreKey(),
+		Timeout:           timeout,
 	}
 	client, err := ssh.Dial("tcp", host, config)
 	if err == nil {
@@ -40,6 +33,10 @@ type collector struct {
 	knownKeys []byte
 }
 
+// StoreKey stores the public key in bytes as returned by the host.
+// To collect multiple public key types from the host, multiple
+// SSH dials need with the ClientConfig HostKeyAlgorithms set to
+// the algorithm you want to collect.
 func (c *collector) StoreKey() ssh.HostKeyCallback {
 	return func(hostname string, remote net.Addr, key ssh.PublicKey) error {
 		c.knownKeys = append(

pkg/ssh/key_pair.go

@@ -2,6 +2,7 @@ package ssh
 
 import (
 	"crypto/ecdsa"
+	"crypto/ed25519"
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/rsa"
@@ -79,6 +80,31 @@ func (g *ECDSAGenerator) Generate() (*KeyPair, error) {
 	}, nil
 }
 
+type Ed25519Generator struct{}
+
+func NewEd25519Generator() KeyPairGenerator {
+	return &Ed25519Generator{}
+}
+
+func (g *Ed25519Generator) Generate() (*KeyPair, error) {
+	pk, pv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		return nil, err
+	}
+	pub, err := generatePublicKey(pk)
+	if err != nil {
+		return nil, err
+	}
+	priv, err := encodePrivateKeyToPEM(pv)
+	if err != nil {
+		return nil, err
+	}
+	return &KeyPair{
+		PublicKey:  pub,
+		PrivateKey: priv,
+	}, nil
+}
+
 func generatePublicKey(pk interface{}) ([]byte, error) {
 	b, err := ssh.NewPublicKey(pk)
 	if err != nil {