golang-jwt library for PKCS11

2021-11-28

Another extension for go-jwt that allows creating and verifying JWT tokens where the private key is embedded inside Hardware like HSM, TPM or Yubikeys. Unlike the following:

This library abstracts the interface away to those devices by using PKCS11.

for reference, see

this is just a proof of concept/alpha quality! caveat emptor. I also find PKCS11 support pretty inconsistent. Its better to use the native integrations

Supported Algorithms

  • RSA-2048

(i just didn’t’’ have the time to account for the additional types)

Setup (softHSM)

First install softHSM.

Then make create a key and generate a JWT

sudo apt-get install libsofthsm2-dev opensc

mkdir -p $HOME/soft_hsm/tokens

$ cat /path/to/softhsm.conf 
log.level = DEBUG
objectstore.backend = file
directories.tokendir = /path/to/soft_hsm/tokens
slots.removable = true

export SOFTHSM2_CONF=/path/to/softhsm.conf

$ pkcs11-tool --module /usr/lib/x86_64-linux-gnu/softhsm/libsofthsm2.so --slot-index=0 --init-token --label="token1" --so-pin="123456"
$ pkcs11-tool --module /usr/lib/x86_64-linux-gnu/softhsm/libsofthsm2.so  --label="token1" --init-pin --so-pin "123456" --pin mynewpin
$ pkcs11-tool --module /usr/lib/x86_64-linux-gnu/softhsm/libsofthsm2.so --list-mechanisms --slot-index 0

$ pkcs11-tool --module /usr/lib/x86_64-linux-gnu/softhsm/libsofthsm2.so --list-token-slots
      Available slots:
      Slot 0 (0x54349ba6): SoftHSM slot ID 0x54349ba6
        token label        : token1
        token manufacturer : SoftHSM project
        token model        : SoftHSM v2
        token flags        : login required, rng, token initialized, PIN initialized, other flags=0x20
        hardware version   : 2.6
        firmware version   : 2.6
        serial num         : bae0cdf454349ba6
        pin min/max        : 4/255
      Slot 1 (0x1): SoftHSM slot ID 0x1
        token state:   uninitialized


$ softhsm2-util --show-slots
      Available slots:
      Slot 859281362
          Slot info:
              Description:      SoftHSM slot ID 0x333797d2                                      
              Manufacturer ID:  SoftHSM project                 
              Hardware version: 2.6
              Firmware version: 2.6
              Token present:    yes
          Token info:
              Manufacturer ID:  SoftHSM project                 
              Model:            SoftHSM v2      
              Hardware version: 2.6
              Firmware version: 2.6
              Serial number:    0c1edf42333797d2
              Initialized:      yes
              User PIN init.:   yes
              Label:            token1                          
      Slot 1
          Slot info:
              Description:      SoftHSM slot ID 0x1                                             
              Manufacturer ID:  SoftHSM project                 
              Hardware version: 2.6
              Firmware version: 2.6
              Token present:    yes
          Token info:
              Manufacturer ID:  SoftHSM project                 
              Model:            SoftHSM v2      
              Hardware version: 2.6
              Firmware version: 2.6
              Serial number:                    
              Initialized:      no
              User PIN init.:   no
              Label:               

$ pkcs11-tool --module /usr/lib/x86_64-linux-gnu/softhsm/libsofthsm2.so -l -k --key-type rsa:2048 --id 4142 --label keylabel1 --pin mynewpin
      Using slot 0 with a present token (0x1ccdc205)
      Key pair generated:
      Private Key Object; RSA 
        label:      keylabel1
        ID:         4142
        Usage:      decrypt, sign, unwrap
        Access:     sensitive, always sensitive, never extractable, local
      Public Key Object; RSA 2048 bits
        label:      keylabel1
        ID:         4142
        Usage:      encrypt, verify, wrap
        Access:     local


      Using slot 0 with a present token (0x1ccdc205)
      Public Key Object; RSA 2048 bits
        label:      keylabel1
        ID:         4142
        Usage:      encrypt, verify, wrap
        Access:     local


    $ pkcs11-tool --module /usr/lib/x86_64-linux-gnu/softhsm/libsofthsm2.so  --list-objects
      Using slot 0 with a present token (0x333797d2)
      Public Key Object; RSA 2048 bits
        label:      keylabel1
        ID:         4142
        Usage:      encrypt, verify, wrap
        Access:     local

# cd examples/
$ go run main.go 
  2021/12/05 12:46:13 Token: eyJhbGciOiJSUzI1NiIsImtpZCI6IjFiOTk1YmVkOGFmY2JlZDhkZTEzOTIyMzgxOTUzNmYxYjdiOGY1YzRjZmUzMDk1ZDE5OTRmYzdjODUyMDYzNzgiLCJ0eXAiOiJKV1QifQ.eyJleHAiOjE2Mzg3MjY0MzMsImlzcyI6InRlc3QifQ.OxfU7sX4URX_VAVsEkjiS0hs8xHrygB6lZC950FFdmzD8LDu5ArSJ1HY-geS2Cscyvo5bbQLAFb0GcTk_UvW8bslLOiPWbPTXRY1a6DsXi4zCfdj939HkmAkkuS017Onk0JuPNYcT2TNRZIW8UCgNFcyfYS3cUyjf-ZgEjwh2-Y18iIQbDGXSZuFDB1aERpGhlgt-7ZMKIa_62TmcRYjcdXrJozycLy48fKviIAus6Z9PkvbIzk_Le8kSC5GwN5UTfK8obHTTVx-_6iyXOq6ZKKzrlXnpYuwnoZrWeHQOUf8Den1ibSbclnyQcIFCWp3D6p4oK1lsq3RJ3n3n2ZTJA
  2021/12/05 12:46:13      verified with YK PublicKey
  2021/12/05 12:46:13      verified with exported PubicKey

The JWT is formatted as:

{
  "alg": "RS256",
  "kid": "1b995bed8afcbed8de139223819536f1b7b8f5c4cfe3095d1994fc7c85206378",
  "typ": "JWT"
}
{
  "exp": 1638726433,
  "iss": "test"
}

Note for SoftHSM, the keyID: 1b995bed8afcbed8de139223819536f1b7b8f5c4cfe3095d1994fc7c85206378…is the sha256Hash of the publicKey

to use, just import the library ("github.com/salrashid123/golang-jwt-pkcs11") configure the Yubikey wiht the pin. Remember to set the override so that the correct alg is defined in the JWT header

package main

import (
	"context"
	"log"
	"time"

	"github.com/golang-jwt/jwt"
	pk "github.com/salrashid123/golang-jwt-pkcs11"
)

var ()

func main() {

	ctx := context.Background()

	var keyctx interface{}
	claims := &jwt.StandardClaims{
		ExpiresAt: time.Now().Add(time.Minute * 1).Unix(),
		Issuer:    "test",
	}

	pk.SigningMethodPKRS256.Override()
	token := jwt.NewWithClaims(pk.SigningMethodPKRS256, claims)

	var slotNum = new(int)
	var err error
	// export SOFTHSM2_CONF=/path/to/softhsm.conf
	//
	// SoftHSM
	// *slotNum = 859281362 // softhsm2-util --show-slots
	// hex_id, err := hex.DecodeString("4142")
	// if err != nil {
	// 	log.Fatalf("Unable to create hex+id: %v", err)
	// }
	config := &pk.PKConfig{
		Pin:        "mynewpin",
		TokenLabel: "token1",
		KeyLabel:   "keylabel1",
		//PKCS_ID:    hex_id,
		//SlotNumber: slotNum,
		Path: "/usr/lib/x86_64-linux-gnu/softhsm/libsofthsm2.so",
	}

	// Yubikey
	// *slotNum = 0
	// config := &pk.PKConfig{
	// 	Pin:        "123456",
	// 	TokenLabel: "YubiKey PIV #13981219",
	// 	PKCS_ID:    []byte{1},
	// 	//SlotNumber: slotNum,
	// 	Path: "/usr/local/lib/libykcs11.so.2",
	// }

	// config := &pk.PKConfig{
	// 	Pin:        "123456",
	// 	TokenLabel: "user1_esodemoapp2_com",
	// 	PKCS_ID:    []byte{1},
	// 	//SlotNumber: slotNum,
	// 	Path: "/usr/lib/x86_64-linux-gnu/opensc-pkcs11.so",
	// }

	// TPM

	// config := &pk.PKConfig{
	// 	Pin:        "mynewpin",
	// 	TokenLabel: "token1",
	// 	//SlotNumber: slotNum,
	// 	Path: "/usr/local/lib/libtpm2_pkcs11.so",
	// }

	keyctx, err = pk.NewPKContext(ctx, config)
	if err != nil {
		log.Fatalf("Unable to initialize pkcsJWT: %v", err)
	}

	token.Header["kid"] = config.GetKeyID()
	tokenString, err := token.SignedString(keyctx)
	if err != nil {
		log.Fatalf("Error signing %v", err)
	}

	log.Printf("Token: %s", tokenString)

	// verify with TPM based publicKey
	keyFunc, err := pk.YKVerfiyKeyfunc(ctx, config)
	if err != nil {
		log.Fatalf("could not get keyFunc: %v", err)
	}

	vtoken, err := jwt.Parse(tokenString, keyFunc)
	if err != nil {
		log.Fatalf("Error verifying token %v", err)
	}
	if vtoken.Valid {
		log.Println("     verified with YK PublicKey")
	}

	// verify with provided RSAPublic key
	pubKey := config.GetPublicKey()

	v, err := jwt.Parse(vtoken.Raw, func(token *jwt.Token) (interface{}, error) {
		return pubKey, nil
	})
	if err != nil {
		log.Println("     Error Parsing %v", err)
	}
	if v.Valid {
		log.Println("     verified with exported PubicKey")
	}

}

Setup (Yubikey)

To enable PKCS with Yubikey, you need a specific type of Yubikey that allows you to embed a certificate. For more information for the type of keys, see:

Once you installed ykcs11, specify the path to the module and either generate a key or get the key specifications. The snippet below shows a key that was already generated earlier.

  • Using libykcs11.so.2:
export PKCS_MODULE=/usr/local/lib/libykcs11.so.2

$  pkcs11-tool --module $PKCS_MODULE --list-token-slots
Available slots:
Slot 0 (0x0): Yubico YubiKey OTP+FIDO+CCID 00 00
  token label        : YubiKey PIV #13981219
  token manufacturer : Yubico (www.yubico.com)
  token model        : YubiKey YK5
  token flags        : login required, rng, token initialized, PIN initialized
  hardware version   : 1.0
  firmware version   : 5.27
  serial num         : 13981219
  pin min/max        : 6/48


$ pkcs11-tool --module $PKCS_MODULE  --list-objects

Certificate Object; type = X.509 cert
  label:      X.509 Certificate for PIV Authentication
  subject:    DN: C=US, O=Google, OU=Enterprise, CN=user1_esodemoapp2_com
  ID:         01
Public Key Object; RSA 2048 bits
  label:      Public key for PIV Authentication
  ID:         01
  Usage:      encrypt, verify
  Access:     local
  • Using generic opensc-pkcs11.so
export PKCS_MODULE=/usr/lib/x86_64-linux-gnu/opensc-pkcs11.so

$ pkcs11-tool --module $PKCS_MODULE --list-token-slots
    Available slots:
    Slot 0 (0x0): Yubico YubiKey OTP+FIDO+CCID 00 00
      token label        : user1_esodemoapp2_com
      token manufacturer : piv_II
      token model        : PKCS#15 emulated
      token flags        : login required, rng, token initialized, PIN initialized
      hardware version   : 0.0
      firmware version   : 0.0
      serial num         : 993084513cb2a39d
      pin min/max        : 4/8


$ pkcs11-tool --module $PKCS_MODULE --slot-index=0 --list-objects
    Using slot with index 0 (0x0)
    Public Key Object; RSA 2048 bits
      label:      PIV AUTH pubkey
      ID:         01
      Usage:      encrypt, verify, wrap
      Access:     none
    Certificate Object; type = X.509 cert
      label:      Certificate for PIV Authentication
      subject:    DN: C=US, O=Google, OU=Enterprise, CN=user1_esodemoapp2_com
      ID:         01
    Public Key Object; RSA 2048 bits
      label:      SIGN pubkey
      ID:         02
      Usage:      encrypt, verify, wrap
      Access:     none

The corresponding configuration for the setting above may look like

	config := &pk.PKConfig{
		Pin:        "123456",
		TokenLabel: "YubiKey PIV #13981219",
		PKCS_ID:    []byte{1},
		Path: "/usr/local/lib/libykcs11.so.2",
	}

TPM

TO use PKCS with Trusted Platform Modules, first install

tpm2-pkcs11 as described here

Then install a certificate (if you have one already configured, you would just need to bootstrap pkcs11 + tpm to reference it)

export PKCS_MODULE=/usr/local/lib/libtpm2_pkcs11.so

pkcs11-tool --module $PKCS_MODULE --slot-index=0 --list-objects
pkcs11-tool --module $PKCS_MODULE --list-token-slots
pkcs11-tool --module $PKCS_MODULE --slot-index=0 --init-token --label="token1" --so-pin="123456"
pkcs11-tool --module $PKCS_MODULE --label="token1" --init-pin --so-pin "123456" --pin mynewpin
pkcs11-tool --module $PKCS_MODULE --list-token-slots
pkcs11-tool --module $PKCS_MODULE -l -k --key-type rsa:2048 --id 0 --label keylabel1 --pin mynewpin
pkcs11-tool --module $PKCS_MODULE --label="keylabel1" --pin mynewpin --generate-random 50 | xxd -p
pkcs11-tool --module $PKCS_MODULE --list-token-slots
pkcs11-tool --module $PKCS_MODULE --slot-index=0 --list-objects

	config := &pk.PKConfig{
		Pin:        "mynewpin",
		TokenLabel: "token1",
		//SlotNumber: slotNum,
		Path: "/usr/local/lib/libtpm2_pkcs11.so",
	}

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