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Do not generate RSA key for runner sshd #3926

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Merged
r4victor merged 1 commit into from
Jun 2, 2026
+20 −14
Merged

Do not generate RSA key for runner sshd #3926

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34 changes: 20 additions & 14 deletions runner/internal/runner/ssh/sshd.go
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Original file line number Diff line number Diff line change
Expand Up @@ -23,10 +23,16 @@ type SshdManager interface {
AddAuthorizedKeys(context.Context, ...string) error
}

var hostKeys = [...]string{
"ssh_host_rsa_key",
"ssh_host_ecdsa_key",
"ssh_host_ed25519_key",
// Host keys generated and configured for sshd. RSA is intentionally omitted:
// ssh-keygen -A's RSA-3072 generation dominates runner startup (~1000ms vs
// <50ms for ECDSA + Ed25519 combined). Both ECDSA and Ed25519 are
// universally supported by modern SSH clients (OpenSSH >= 6.5).
var hostKeys = [...]struct {
name string
keyType string
}{
{name: "ssh_host_ecdsa_key", keyType: "ecdsa"},
{name: "ssh_host_ed25519_key", keyType: "ed25519"},
}

// Implements SshdManager
Expand Down Expand Up @@ -163,14 +169,14 @@ func generateHostKeys(ctx context.Context, confDir string) error {
return err
}

// TODO: specify the full path if a custom OpenSSH build is used
cmd := exec.CommandContext(ctx, "ssh-keygen", "-A", "-f", tmpDir)
if err := cmd.Run(); err != nil {
return err
}

for _, key := range hostKeys {
if err := copyHostKey(keyDir, confDir, key); err != nil {
for _, k := range hostKeys {
// TODO: specify the full path if a custom OpenSSH build is used
cmd := exec.CommandContext(ctx, "ssh-keygen",
"-t", k.keyType, "-q", "-N", "", "-f", path.Join(keyDir, k.name))
if err := cmd.Run(); err != nil {
return fmt.Errorf("generate %s host key: %w", k.keyType, err)
}
if err := copyHostKey(keyDir, confDir, k.name); err != nil {
return err
}
}
Expand Down Expand Up @@ -251,8 +257,8 @@ func createSshdConfig(ctx context.Context, confDir string, port int, logLevel st
"ClientAliveInterval 30",
"ClientAliveCountMax 4",
}
for _, hostKey := range hostKeys {
lines = append(lines, fmt.Sprintf("HostKey %s/%s", confDir, hostKey))
for _, k := range hostKeys {
lines = append(lines, fmt.Sprintf("HostKey %s/%s", confDir, k.name))
}
for _, line := range lines {
if _, err := fmt.Fprintln(file, line); err != nil {
Expand Down
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