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Add ability to generate a certificate from an existing key. #1416

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39cf202
Add ability to generate a certificate from an existing key.
SohamG May 28, 2025
cefc65f
Add ability to keygen public key from private key.
SohamG May 30, 2025
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42 changes: 35 additions & 7 deletions cmd/nebula-cert/ca.go
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@ import (
"strings"
"time"

ed25519_std "crypto/ed25519"
"github.com/skip2/go-qrcode"
"github.com/slackhq/nebula/cert"
"github.com/slackhq/nebula/pkclient"
Expand All @@ -24,6 +25,7 @@ type caFlags struct {
name *string
duration *time.Duration
outKeyPath *string
inKeyPath *string
outCertPath *string
outQRPath *string
groups *string
Expand All @@ -50,6 +52,7 @@ func newCaFlags() *caFlags {
cf.version = cf.set.Uint("version", uint(cert.Version2), "Optional: version of the certificate format to use")
cf.duration = cf.set.Duration("duration", time.Duration(time.Hour*8760), "Optional: amount of time the certificate should be valid for. Valid time units are seconds: \"s\", minutes: \"m\", hours: \"h\"")
cf.outKeyPath = cf.set.String("out-key", "ca.key", "Optional: path to write the private key to")
cf.inKeyPath = cf.set.String("in-key", "", "Optional: path to read private key for the new certificate")
cf.outCertPath = cf.set.String("out-crt", "ca.crt", "Optional: path to write the certificate to")
cf.outQRPath = cf.set.String("out-qr", "", "Optional: output a qr code image (png) of the certificate")
cf.groups = cf.set.String("groups", "", "Optional: comma separated list of groups. This will limit which groups subordinate certs can use")
Expand Down Expand Up @@ -95,6 +98,9 @@ func ca(args []string, out io.Writer, errOut io.Writer, pr PasswordReader) error
}
if !isP11 {
if err = mustFlagString("out-key", cf.outKeyPath); err != nil {
if err = mustFlagString("in-key", cf.outKeyPath); err != nil {
return err
}
return err
}
}
Expand Down Expand Up @@ -220,9 +226,25 @@ func ca(args []string, out io.Writer, errOut io.Writer, pr PasswordReader) error
switch *cf.curve {
case "25519", "X25519", "Curve25519", "CURVE25519":
curve = cert.Curve_CURVE25519
pub, rawPriv, err = ed25519.GenerateKey(rand.Reader)
if err != nil {
return fmt.Errorf("error while generating ed25519 keys: %s", err)
if *cf.inKeyPath == "" {
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@JackDoan JackDoan Jun 9, 2025

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I'd really like to have this feature, but I think if we're going to add it, we need to support P256 as well.

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@SohamG SohamG Jun 9, 2025

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On it. My particular use case was Curve25519 but I don't see too much trouble adding this for P256 too.

pub, rawPriv, err = ed25519.GenerateKey(rand.Reader)
if err != nil {
return fmt.Errorf("error while generating ed25519 keys: %s", err)
}
} else {
var err error
rawPrivFile, err := os.ReadFile(*cf.inKeyPath)
if err != nil {
return err
}
rawPriv, _, _, err = cert.UnmarshalSigningPrivateKeyFromPEM(rawPrivFile)

// type ed25519.PrivateKey
privEd25519 := ed25519_std.PrivateKey(rawPriv)
// .Public returns a crypto.PublicKey which is
// an alias for any
pub = privEd25519.Public().(ed25519.PublicKey)

}
case "P256":
var key *ecdsa.PrivateKey
Expand Down Expand Up @@ -260,7 +282,10 @@ func ca(args []string, out io.Writer, errOut io.Writer, pr PasswordReader) error

if !isP11 {
if _, err := os.Stat(*cf.outKeyPath); err == nil {
return fmt.Errorf("refusing to overwrite existing CA key: %s", *cf.outKeyPath)
// Check if we already have a private key
if *cf.inKeyPath == "" {
return fmt.Errorf("refusing to overwrite existing CA key: %s", *cf.outKeyPath)
}
}
}

Expand Down Expand Up @@ -291,9 +316,12 @@ func ca(args []string, out io.Writer, errOut io.Writer, pr PasswordReader) error
b = cert.MarshalSigningPrivateKeyToPEM(curve, rawPriv)
}

err = os.WriteFile(*cf.outKeyPath, b, 0600)
if err != nil {
return fmt.Errorf("error while writing out-key: %s", err)
// Do not write private key if one was provided
if *cf.inKeyPath != "" {
err = os.WriteFile(*cf.outKeyPath, b, 0600)
if err != nil {
return fmt.Errorf("error while writing out-key: %s", err)
}
}
}

Expand Down
26 changes: 22 additions & 4 deletions cmd/nebula-cert/keygen.go
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ type keygenFlags struct {
set *flag.FlagSet
outKeyPath *string
outPubPath *string
inKeyPath *string
curve *string
p11url *string
}
Expand All @@ -24,6 +25,7 @@ func newKeygenFlags() *keygenFlags {
cf.set.Usage = func() {}
cf.outPubPath = cf.set.String("out-pub", "", "Required: path to write the public key to")
cf.outKeyPath = cf.set.String("out-key", "", "Required: path to write the private key to")
cf.inKeyPath = cf.set.String("in-key", "", "Optional: Path to existing private key")
cf.curve = cf.set.String("curve", "25519", "ECDH Curve (25519, P256)")
cf.p11url = p11Flag(cf.set)
return &cf
Expand All @@ -40,7 +42,9 @@ func keygen(args []string, out io.Writer, errOut io.Writer) error {

if !isP11 {
if err = mustFlagString("out-key", cf.outKeyPath); err != nil {
return err
if *cf.inKeyPath == "" {
return err
}
}
}
if err = mustFlagString("out-pub", cf.outPubPath); err != nil {
Expand All @@ -59,8 +63,22 @@ func keygen(args []string, out io.Writer, errOut io.Writer) error {
} else {
switch *cf.curve {
case "25519", "X25519", "Curve25519", "CURVE25519":
pub, rawPriv = x25519Keypair()
curve = cert.Curve_CURVE25519
if *cf.inKeyPath == "" {
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@JackDoan JackDoan Jun 9, 2025

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Do you think this ought to be it's own "command"? Making this a bonus feature of keygen is potentially confusing.

Also, many users encrypt their private keys, we may need to support that. I think there's a helper function for this.... somewhere?

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@SohamG SohamG Jun 9, 2025

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Yes, I did spot the helper, I threw this together as a Proof-Of-Concept and without knowing if this feature was desired. I'll add encrypted keys and a new subcommand.

pub, rawPriv = x25519Keypair()
curve = cert.Curve_CURVE25519
} else {
rawBytes, err := os.ReadFile(*cf.inKeyPath)
if err != nil {
return err
}

rawPriv, _, _, err = cert.UnmarshalPrivateKeyFromPEM(rawBytes)
if err != nil {
return err
}
pub, _ = x25519KeyFromPriv(rawPriv)

}
case "P256":
pub, rawPriv = p256Keypair()
curve = cert.Curve_P256
Expand All @@ -81,7 +99,7 @@ func keygen(args []string, out io.Writer, errOut io.Writer) error {
if err != nil {
return fmt.Errorf("error while getting public key: %w", err)
}
} else {
} else if *cf.inKeyPath == "" {
err = os.WriteFile(*cf.outKeyPath, cert.MarshalPrivateKeyToPEM(curve, rawPriv), 0600)
if err != nil {
return fmt.Errorf("error while writing out-key: %s", err)
Expand Down
8 changes: 8 additions & 0 deletions cmd/nebula-cert/sign.go
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Expand Up @@ -404,6 +404,14 @@ func newKeypair(curve cert.Curve) ([]byte, []byte) {
}
}

func x25519KeyFromPriv(priv []byte) ([]byte, []byte) {
pubkey, err := curve25519.X25519(priv, curve25519.Basepoint)
if err != nil {
panic(err)
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@JackDoan JackDoan Jun 9, 2025

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In most cases, I prefer to bubble the error back up and let the caller decide to panic

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@SohamG SohamG Jun 9, 2025

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Well the original function I modeled this one from (similar name in the same file) didn't bubble err, so I didn't do it either. That being said its a relatively minor fix, which I will implement.

}
return pubkey, priv
}

func x25519Keypair() ([]byte, []byte) {
privkey := make([]byte, 32)
if _, err := io.ReadFull(rand.Reader, privkey); err != nil {
Expand Down