Trusted Platform Module 2.0

Connect to a TPM 2.0 Device

Install TPM 2.0 Software Stack and Tools

In order to connect to a TPM 2.0 hardware or firmware device a software stack implementing the TCG TSS 2.0 System Level API is needed. An excellent open source tpm2-tss library is available from the tpm2-software project that also offers a set of tpm2-tools using the TCG TSS 2.0 Enhanced System Level API.

Figure 1. TPM 2.0 implemented as a hardware device

When using a strongSwan version newer than 5.9.0 with Linux 5.4 kernel or newer, we recommend these latest versions:

tpm2-tss version 3.2.0: https://github.com/tpm2-software/tpm2-tss/releases/tag/3.2.0
tpm2-tools version 5.2: https://github.com/tpm2-software/tpm2-tools/releases/tag/5.2

Fedora 36 and Ubuntu 22.04 come with version 3.2.0 of the tpm2-tss library and version 5.2 of the tpm2-tools, whereas Debian 11 supports the slightly older tpm2-tss 3.0.3 and tpm2-tools 5.0 versions, so that for these Linux distributions no manual compilation of the two packages is necessary. For older Linux releases it is recommended to download and install the latest tarballs from the tpm2-software site.

In order to test if we can connect to the TPM 2.0 device, we list all persistent keys stored in the Non-Volatile (NV) RAM:

$ tpm2_getcap handles-persistent

- 0x81000001
- 0x81000002
- 0x81010001

The man pages of all tpm2-tools functions with their arguments can be found here. The access to the /dev/tpmrm0 TPM resource manager device requires root rights on most Linux platforms. But e.g. with Ubuntu, adding the user to the tss group enables direct access to the TPM device:

$ sudo usermod -a -G tss <username>

Enable the strongSwan tpm Plugin

The strongSwan libtpmtss tpm plugin and the TSS2 interface are enabled and built with the following options

$ ./configure --enable-tss-tss2 --enable-tpm  ...

With the strongSwan pki tool we can now list the persistent key stored under the handle 0x81010001

$ pki --print --type priv --keyid 0x81010001 --debug 2

With debug level 2 some basic information on the TPM device is shown. A second generation Intel firmware TPM running on the Intel Management Engine is employed. Both SHA1 and SHA256 PCR banks are available:

TPM 2.0 - manufacturer: INTC (Intel) rev: 01.38 2018
TPM 2.0 - algorithms: RSA SHA1 HMAC AES MGF1 KEYEDHASH XOR SHA256 RSASSA RSAES RSAPSS OAEP ECDSA ECDH ECDAA ECSCHNORR KDF1_SP800_56A KDF1_SP800_108 ECC SYMCIPHER CTR OFB CBC CFB ECB
TPM 2.0 - ECC curves: NIST_P256 BN_P256
TPM 2.0 - PCR banks: SHA1 SHA256

Apparently the analyzed persistent key can be used for encryption only:

TPM 2.0 via TSS2 v2 available
encryption algorithm is AES-CFB with 128 bits

Debug level 2 shows that pki extracts the public key from the TPM and converts it into a standard PKCS#1 format:

L0 - subjectPublicKeyInfo:
L1 - algorithm:
L2 - algorithmIdentifier:
L3 - algorithm:
  'rsaEncryption'
L1 - subjectPublicKey:
-- > --
L0 - RSAPublicKey:
L1 - modulus:
L1 - publicExponent:
-- < --

At the end of the output the fingerprint of the 2048 bit RSA key is listed:

  privkey:   RSA 2048 bits
  keyid:     ee:c7:bf:5a:de:0f:11:84:2c:86:2b:69:84:ba:65:b9:81:d2:a9:45
  subjkey:   df:f2:e9:e7:79:98:f0:d2:0b:62:db:c0:5c:2c:eb:45:73:85:e9:79

Derive Persistent Endorsement Keys

RSA Endorsement Key

The tpm2_createek command derives a 2048 bit RSA Endorsement Key (EK) in a deterministic way from the secret Endorsement Primary Seed unique to each TPM device and makes the key persistent in the non-volatile memory of the TPM under the object handle 0x81010002

$ tpm2_createek -G rsa -c 0x81010002

Using the tpm2_getcap command we can check that the newly derived Endorsement Key has been persisted in the NV RAM

$ tpm2_getcap handles-persistent

- 0x81000001
- 0x81000002
- 0x81010001
- 0x81010002

Listing the key properties shows that the 2048 bit Endorsement Key already exists under the handle 0x81010001 analyzed in the previous section

$ pki --print --type priv --keyid 0x81010002

TPM 2.0 via TSS2 v2 available
encryption algorithm is AES-CFB with 128 bits
  privkey:   RSA 2048 bits
  keyid:     ee:c7:bf:5a:de:0f:11:84:2c:86:2b:69:84:ba:65:b9:81:d2:a9:45
  subjkey:   df:f2:e9:e7:79:98:f0:d2:0b:62:db:c0:5c:2c:eb:45:73:85:e9:79

Delete Persisted Keys

We therefore delete the duplicate key with the following tpm2_evictcontrol command

$ tpm2_evictcontrol -c 0x81010002

persistent-handle: 0x81010002
action: evicted

The key removal can be verified with

$ tpm2_getcap handles-persistent

- 0x81000001
- 0x81000002
- 0x81010001

ECC Endorsement Key

Again using the tpm2_createek command we derive a 256 bit ECC Endorsement Key (EK) in a deterministic way from the secret Endorsement Primary Seed unique to each TPM device and make the key persistent in the non-volatile memory of the TPM under the object handle 0x81010002:

$ tpm2_createek -G ecc -c 0x81010002 -u ek_ecc.pub

Optionally we saved the public key in a TPM 2.0 proprietary format in the file ek_ecc.pub. The fingerprint of the ECC EK private key can be directly displayed with the command

$ pki --print --type priv --keyid 0x81010002

TPM 2.0 via TSS2 v2 available
encryption algorithm is AES-CFB with 128 bits
  privkey:   ECDSA 256 bits
  keyid:     25:db:73:13:0f:c9:c8:91:68:30:8e:02:89:c1:0d:65:bd:ad:69:2a
  subjkey:   9c:b9:fb:b0:32:81:24:82:a7:07:b2:bd:bd:d3:7c:2b:22:7f:74:bf

Endorsement Key Certificates

Fetched via URL

Endorsement Key certificates issued for Intel firmware TPMs can be automatically downloaded from an Intel web server using the tpm2_getcertificate command:

$ tpm2_getekcertificate -o ek_ecc.crt -u ek_ecc.pub

For successful retrieval the public key ek_ecc.pub in the TPM 2.0 proprietary format is required. Using the pki tool we can list the downloaded EK certificate belonging to the ECC key:

$ pki --print --type x509 --in ek_ecc.crt

  subject:  ""
  issuer:   "C=US, ST=CA, L=Santa Clara, O=Intel Corporation, OU=TPM EK intermediate for CNL_EPID_POST_B1LP_PROD_2 pid:9, CN=www.intel.com"
  validity:  not before Sep 04 02:00:00 2019, ok
             not after  Jan 01 00:59:59 2050, ok (expires in 10600 days)
  serial:    07:99:3b:c6:88:aa:7d:72:b0:24:24:05:09:01:bb:42:55:70:1a:43
  altNames:  tcg-at-tpmManufacturer=id:494E5443, tcg-at-tpmModel=CNL, tcg-at-tpmVersion=id:00020000
  CRL URIs:  https://trustedservices.intel.com/content/CRL/ekcert/CNLEPIDPOSTB1LPPROD2_EK_Device.crl
  certificatePolicies:
             1.2.840.113741.1.5.2.1
             CPS: https://trustedservices.intel.com/content/CRL/ekcert/EKcertPolicyStatement.pdf
  authkeyId: 17:a0:05:75:d0:5e:58:e3:88:12:10:bb:98:b1:04:5b:b4:c3:06:39
  subjkeyId: 9c:b9:fb:b0:32:81:24:82:a7:07:b2:bd:bd:d3:7c:2b:22:7f:74:bf
  pubkey:    ECDSA 256 bits
  keyid:     25:db:73:13:0f:c9:c8:91:68:30:8e:02:89:c1:0d:65:bd:ad:69:2a
  subjkey:   9c:b9:fb:b0:32:81:24:82:a7:07:b2:bd:bd:d3:7c:2b:22:7f:74:bf

For the RSA 2048 Endorsement Key we first have to extract the public keyfile ek_rsa.pub in the TPM 2.0 proprietary format using the tpm2_readpublic command because we forgot to do this in the first place:

$ tpm2_readpublic -Q -c 0x81010001 -o ek_rsa.pub

Now we can retrieve the RSA EK certificate, too:

$ tpm2_getekcertificate -o ek_rsa.crt -u ek_rsa.pub

and view the contents with the pki --print command

$ pki --print --type x509 --in ek_rsa.crt

  subject:  ""
  issuer:   "C=US, ST=CA, L=Santa Clara, O=Intel Corporation, OU=TPM EK intermediate for CNL_EPID_POST_B1LP_PROD_2 pid:9, CN=www.intel.com"
  validity:  not before Sep 04 02:00:00 2019, ok
             not after  Jan 01 00:59:59 2050, ok (expires in 10600 days)
  serial:    14:26:0b:eb:12:a2:82:87:af:3b:75:e0:a1:a4:87:60:72:95:55:92
  altNames:  tcg-at-tpmManufacturer=id:494E5443, tcg-at-tpmModel=CNL, tcg-at-tpmVersion=id:00020000
  CRL URIs:  https://trustedservices.intel.com/content/CRL/ekcert/CNLEPIDPOSTB1LPPROD2_EK_Device.crl
  certificatePolicies:
             1.2.840.113741.1.5.2.1
             CPS: https://trustedservices.intel.com/content/CRL/ekcert/EKcertPolicyStatement.pdf
  authkeyId: 17:a0:05:75:d0:5e:58:e3:88:12:10:bb:98:b1:04:5b:b4:c3:06:39
  subjkeyId: df:f2:e9:e7:79:98:f0:d2:0b:62:db:c0:5c:2c:eb:45:73:85:e9:79
  pubkey:    RSA 2048 bits
  keyid:     ee:c7:bf:5a:de:0f:11:84:2c:86:2b:69:84:ba:65:b9:81:d2:a9:45
  subjkey:   df:f2:e9:e7:79:98:f0:d2:0b:62:db:c0:5c:2c:eb:45:73:85:e9:79

We can easily check that in both EK certificates the key fingerprints (keyid and subjkey match with those of the EK keys persisted in the TPM.

Stored in Non-Volatile RAM

Most hardware TPMs are shipped with their Endorsement Key Certificates stored in NV RAM. E.g. on an STMicroelectronics TPM device the following data objects are stored in an NV index:

$ tpm2_getcap handles-nv-index

- 0x1410001
- 0x1410002
- 0x1410004
- 0x1880001
- 0x1880011
- 0x1C00002
- 0x1C0000A
- 0x1C00012
- 0x1C10102
- 0x1C10103
- 0x1C10104
- 0x1C101C0

Using the tpm2_nvreadpublic command we can look for large data objects which are prime candidates for X.509 certificates:

$ tpm2_nvreadpublic

  ...
0x1c00002:
  name: 000b5c112bd5f410d0abe96a50e94ff721a005c32567e4b1112ab0a8fb7e0289b7f2
  hash algorithm:
    friendly: sha256
    value: 0xB
  attributes:
    friendly: ppwrite|writedefine|write_stclear|ppread|ownerread|authread|no_da|written|platformcreate
    value: 0x1600762
  size: 1033

0x1c0000a:
  name: 000b1948300e66afad594b7a8e8368d53ddd36908fb2b46dd7b5a88051b50e4047ab
  hash algorithm:
    friendly: sha256
    value: 0xB
  attributes:
    friendly: ppwrite|writedefine|write_stclear|ppread|ownerread|authread|no_da|written|platformcreate
    value: 0x1600762
  size: 639

0x1c00012:
  name: 000cde411e123085083eedb1c9312e08dd8d229df6a5e16996035a2e3000d860b372c924de0354a6af4c7886656d2065814f
  hash algorithm:
    friendly: sha384
    value: 0xC
  attributes:
    friendly: ppwrite|writedefine|write_stclear|ppread|ownerread|authread|no_da|written|platformcreate
    value: 0x1600762
  size: 707
  ...

We can use pki --print command to directly list the properties of the EK certificates:

$ pki --print --type x509 --keyid 0x01c00002

TPM 2.0 via TSS2 v2 available
loaded certificate from TPM NV index 0x01c00002
  subject:  ""
  issuer:   "C=CH, O=STMicroelectronics NV, CN=STM TPM EK Intermediate CA 06"
  validity:  not before Feb 11 01:00:00 2020, ok
             not after  Jan 01 01:00:00 2031, ok (expires in 3650 days)
  serial:    72:78:a1:2c:87:b6:aa:45:c4:1f:57:ff:d1:3d:cf:93:42:34:b9:c9
  altNames:  tcg-at-tpmManufacturer=id:53544D20, tcg-at-tpmModel=ST33HTPHAHD4, tcg-at-tpmVersion=id:00010101
  authkeyId: fb:17:d7:0d:73:48:70:e9:19:c4:e8:e6:03:97:5e:66:4e:0e:43:de
  subjkeyId: e9:3d:51:32:04:42:73:3e:fc:bb:9e:f8:0c:21:9a:53:ec:73:80:94
  pubkey:    RSA 2048 bits
  keyid:     d3:e3:71:79:df:32:53:34:60:0f:1f:38:dc:d4:6d:53:59:1b:c5:3c
  subjkey:   e9:3d:51:32:04:42:73:3e:fc:bb:9e:f8:0c:21:9a:53:ec:73:80:94

$ pki --print --type x509 --keyid 0x01c0000a

TPM 2.0 via TSS2 v2 available
loaded certificate from TPM NV index 0x01c0000a
  subject:  ""
  issuer:   "C=CH, O=STMicroelectronics NV, CN=STM TPM ECC Intermediate CA 02"
  validity:  not before Mar 09 01:00:00 2020, ok
             not after  Jan 01 01:00:00 2031, ok (expires in 3650 days)
  serial:    51:e8:fc:b2:64:8d:1d:36:a5:bc:d7:c9:63:c1:d6:de:e7:25:09:a4
  altNames:  tcg-at-tpmManufacturer=id:53544D20, tcg-at-tpmModel=ST33HTPHAHD4, tcg-at-tpmVersion=id:00010101
  authkeyId: 66:2d:8f:1c:ec:df:f1:47:a8:b6:f0:ea:29:6a:f7:f2:4c:ad:f9:cf
  subjkeyId: d1:e8:fc:b2:64:8d:1d:36:a5:bc:d7:c9:63:c1:d6:de:e7:25:09:a4
  pubkey:    ECDSA 256 bits
  keyid:     8b:62:31:bf:08:9d:39:74:6d:05:fd:35:eb:2e:13:64:12:86:03:16
  subjkey:   d1:e8:fc:b2:64:8d:1d:36:a5:bc:d7:c9:63:c1:d6:de:e7:25:09:a4

or we can first retrieve the binary certificate blob from the NV RAM using the tpm2_nvread command:

$ tpm2_nvread 0x01c00012 -C o -o ek_ecc384.crt

and then list the properties of the EK certificate file:

$ pki --print --type x509 --in ek_ecc384.crt

  subject:  ""
  issuer:   "C=CH, O=STMicroelectronics NV, CN=STM TPM ECC384 Intermediate CA 01"
  validity:  not before Feb 08 01:00:00 2020, ok
             not after  Jan 01 01:00:00 2031, ok (expires in 3650 days)
  serial:    39:ed:ae:d4:89:9e:52:08:9f:42:8a:f5:d5:58:7b:50:a6:24:f3:63
  altNames:  tcg-at-tpmManufacturer=id:53544D20, tcg-at-tpmModel=ST33HTPHAHD4, tcg-at-tpmVersion=id:00010101
  authkeyId: bd:96:3e:9a:d5:74:aa:d9:4f:ad:6c:bf:41:6d:d8:5b:4a:55:99:42
  subjkeyId: b9:ed:ae:d4:89:9e:52:08:9f:42:8a:f5:d5:58:7b:50:a6:24:f3:63
  pubkey:    ECDSA 384 bits
  keyid:     04:68:52:c4:00:ab:10:75:82:57:99:45:1e:7c:12:01:5a:8e:50:c9
  subjkey:   b9:ed:ae:d4:89:9e:52:08:9f:42:8a:f5:d5:58:7b:50:a6:24:f3:63

We see that the STMicroelectronics device apparently supports 384 bit ECC keys

TPM 2.0 - manufacturer: STM  () rev: 01.38 2018 FIPS 140-2
TPM 2.0 - algorithms: RSA SHA1 HMAC AES MGF1 KEYEDHASH XOR SHA256 SHA384 RSASSA RSAES RSAPSS OAEP ECDSA ECDH ECDAA ECSCHNORR KDF1_SP800_56A KDF1_SP800_108 ECC SYMCIPHER SHA3_256 SHA3_384 CTR OFB CBC CFB ECB
TPM 2.0 - ECC curves: NIST_P256 NIST_P384 BN_P256
TPM 2.0 - PCR banks: SHA1 SHA256

Generate Persistent Attestation Keys

RSA Attestation Key

A 2048 bit RSA Attestation Key (AK) bound to the RSA EK with handle 0x81010001 can be created with the tpm2_createak command:

$ tpm2_createak -C 0x81010001 -G rsa -g sha256 -s rsassa -c ak_rsa.ctx -u ak_rsa.pub -n ak_rsa.name

and made persistent under the handle 0x81010003 with the tpm2_evictcontrol command:

$ tpm2_evictcontrol -C o -c ak_rsa.ctx 0x81010003

persistent-handle: 0x81010003
action: persisted

The properties of the RSA AK which is a signing key can be displayed with the command

$ pki --print --type priv --keyid 0x81010003

TPM 2.0 via TSS2 v2 available
signature algorithm is RSASSA with SHA256 hash
  privkey:   RSA 2048 bits
  keyid:     df:b7:8f:95:61:8f:70:84:f4:03:e8:7e:83:a6:dd:5f:c5:ff:72:b5
  subjkey:   48:82:62:15:74:a2:10:c5:75:70:c2:d6:7d:59:9f:22:d9:4f:9c:07

ECC Attestation Key

A 256 bit ECC Attestation Key (AK) bound to the ECC EK with handle 0x81010002 can be created with the tpm2_createak command:

$ tpm2_createak -C 0x81010002 -G ecc -g sha256 -s ecdsa -c ak_ecc.ctx -u ak_ecc.pub -n ak_ecc.name

and made persistent under the handle 0x81010004 with the tpm2_evictcontrol command:

$ tpm2_evictcontrol -C o -c ak_ecc.ctx 0x81010004

persistent-handle: 0x81010004
action: persisted

The properties of the ECC AK which is a signing key can be displayed with the command

$ pki --print --type priv --keyid 0x81010004

TPM 2.0 via TSS2 v2 available
signature algorithm is ECDSA with SHA256 hash
  privkey:   ECDSA 256 bits
  keyid:     ba:64:37:a4:0e:c8:42:67:8c:55:5a:f9:1b:2a:eb:ff:5f:40:c3:e3
  subjkey:   cc:83:49:87:2b:9e:f3:cb:b8:35:12:02:87:ff:14:89:28:44:a6:04

Generate PKCS#10 Certificate Requests

RSA Certificate Request

The pki --req tool can directly generate a PKCS#10 certificate request self-signed by the TPM 2.0 private key and containing the corresponding public key as well as the desired end entity identity:

$ pki --req --type priv --keyid 0x81010003 --dn "C=CH, O=strongSec GmbH, OU=AK RSA, CN=edu.strongsec.com" --san edu.strongsec.com --outform pem > ak_rsa_req.pem

TPM 2.0 via TSS2 v2 available
signature algorithm is RSASSA with SHA256 hash
Smartcard PIN: <return>

Since we didn’t configure a password when creating the AK, just press <return> when prompted for the PIN. With openssl we can verify the contents of the generated certificate request:

$ openssl req -in ak_rsa_req.pem -noout -text

Certificate Request:
    Data:
        Version: 1 (0x0)
        Subject: C = CH, O = strongSec GmbH, OU = AK RSA, CN = edu.strongsec.com
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                RSA Public-Key: (2048 bit)
                Modulus:
                    00:9e:cc:3c:be:0a:37:86:db:ab:a5:01:49:a4:be:
                    0f:10:0e:32:50:12:27:64:52:85:0f:21:5e:c7:14:
                    f4:d9:7f:95:0a:22:91:73:9f:60:07:45:d3:8e:4b:
                    6d:94:00:83:44:ed:9c:f2:c0:14:9c:33:01:46:d0:
                    78:e4:10:ae:51:3a:9c:c2:b7:a0:c7:04:66:80:bb:
                    c2:bc:02:5b:d6:de:da:93:98:de:a7:cd:a5:5d:c1:
                    8a:bb:13:8b:d9:21:88:c0:61:40:d2:30:eb:0d:dd:
                    63:8d:a4:e0:b0:1a:bb:18:7f:6e:62:e1:bf:b3:39:
                    fa:c2:80:32:88:6a:da:f0:24:90:5c:16:b6:bb:30:
                    5d:96:25:24:cf:f2:03:19:0f:56:58:f2:32:00:51:
                    8b:0a:c3:15:81:db:34:ee:a4:64:5b:b6:3c:e6:d3:
                    df:e3:16:80:07:0e:13:91:4d:18:9c:b3:fd:ca:72:
                    78:72:56:e9:13:4c:1d:a2:03:f0:e1:8d:cd:54:1c:
                    68:ea:46:47:1c:f9:f9:97:7a:f1:59:96:58:6c:d8:
                    8e:a9:15:fc:4d:93:5d:fa:51:5d:33:5a:bb:77:59:
                    18:3e:6b:f6:45:f7:92:c2:12:0a:bb:64:af:0b:ff:
                    0d:08:7a:18:90:d9:10:63:b1:6a:19:78:da:9d:ab:
                    7a:87
                Exponent: 65537 (0x10001)
        Attributes:
        Requested Extensions:
            X509v3 Subject Alternative Name:
                DNS:edu.strongsec.com
    Signature Algorithm: sha256WithRSAEncryption
         35:89:16:59:fc:ab:64:a9:a1:89:cc:d0:e6:a9:06:19:e1:5e:
         11:98:20:ea:ca:f0:5f:06:3c:11:ff:72:98:96:92:08:91:68:
         d8:bd:e6:05:ed:ef:49:cf:22:6d:da:ab:2c:10:a7:df:59:a3:
         0e:e4:bf:f6:8a:62:0b:28:eb:62:89:d0:50:d0:df:2f:5a:2d:
         39:c6:7b:ac:34:6c:85:93:be:0d:9b:70:15:47:73:2f:00:da:
         52:e3:65:c2:02:f9:88:0f:b8:f5:24:dc:db:43:15:fe:bc:8c:
         98:96:81:aa:6d:aa:4c:6e:38:a2:89:27:5c:8d:27:5d:16:1a:
         fa:3b:e7:81:69:58:db:a9:9a:c7:ea:06:d2:1c:13:ba:ee:92:
         a4:8a:64:e3:5f:19:2c:d3:54:4f:3c:da:52:fc:9a:35:72:5c:
         a9:d4:93:7c:e3:69:08:2b:fb:4e:35:84:7e:e3:eb:95:86:2e:
         5b:e5:01:c1:69:53:86:f9:6b:38:31:83:97:76:8b:ba:3d:9c:
         28:5b:84:b0:9b:e9:91:8b:db:9e:4d:3b:03:db:f4:84:a6:8d:
         b2:18:9f:3a:3e:f9:36:64:15:98:4f:69:37:6b:9e:b2:92:a0:
         9c:ab:05:35:65:28:b8:df:92:4b:fe:d1:40:6d:05:e2:4f:4e:
         75:15:8c:22

ECC Certificate Request

We repeat the same for the ECC Attestation Key:

$ pki --req --type priv --keyid 0x81010004 --dn "C=CH, O=strongSec GmbH, OU=AK ECC, CN=edu.strongsec.com" --san edu.strongsec.com --outform pem > ak_ecc_req.pem

TPM 2.0 via TSS2 v2 available
signature algorithm is ECDSA with SHA256 hash
Smartcard PIN: <return>

and verify that the certificate request has been self-signed by the ECC AK private-key:

$ openssl req -in ak_ecc_req.pem -noout -text

Certificate Request:
    Data:
        Version: 1 (0x0)
        Subject: C = CH, O = strongSec GmbH, OU = AK ECC, CN = edu.strongsec.com
        Subject Public Key Info:
            Public Key Algorithm: id-ecPublicKey
                Public-Key: (256 bit)
                pub:
                    04:80:e7:cd:47:9e:c7:71:08:98:82:22:ed:99:1f:
                    40:50:bd:44:da:a1:ca:ac:0b:e2:13:7f:f3:ae:63:
                    99:61:74:a2:b6:15:ae:5c:27:9e:bd:f2:27:91:95:
                    d1:ee:8f:99:93:ca:7b:4e:4e:87:a1:00:9e:94:24:
                    b1:13:d1:11:2c
                ASN1 OID: prime256v1
                NIST CURVE: P-256
        Attributes:
        Requested Extensions:
            X509v3 Subject Alternative Name:
                DNS:edu.strongsec.com
    Signature Algorithm: ecdsa-with-SHA256
         30:46:02:21:00:a0:3a:98:28:79:4b:bf:bd:90:92:d0:86:a2:
         69:34:9c:61:6b:87:8e:d0:30:8b:69:b0:94:bd:20:1a:c2:d8:
         e8:02:21:00:8e:e1:3d:5a:84:69:a1:dc:eb:c3:68:7d:80:7c:
         3b:73:c8:40:08:a2:88:56:94:03:9f:49:52:60:40:a1:9a:9f

Issuing Attestion Key Certificates

Certification Authority

X.509 end entity certificates have to be signed by an in-house or official external Certification Authority (CA). In our example we are using the strongSec 2016 Root CA which was generated in 2016 with the pki --gen command

$ pki --gen --type rsa --size 4096 --outform pem > cakey.pem

creating a 4096 bit RSA key pair and then creating a self-signed CA certificate with a lifetime of 10 years

$ pki --self --ca --type rsa --in cakey.pem --dn="C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA" --lifetime 3652 --outform pem > cacert.pem

as the following listing shows:

$ pki --print --type x509 --in cacert.pem

  subject:  "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
  issuer:   "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
  validity:  not before Sep 02 10:25:01 2016, ok
             not after  Sep 02 10:25:01 2026, ok (expires in 2067 days)
  serial:    7c:24:43:4b:b7:dc:ef:7e
  flags:     CA CRLSign self-signed
  subjkeyId: 6d:c2:af:37:49:41:b9:fd:f4:45:8b:aa:e0:03:3b:b9:e5:7b:9c:b5
  pubkey:    RSA 4096 bits
  keyid:     6c:79:f3:7a:b0:df:ac:69:03:b2:ac:6a:ed:82:3a:d2:66:93:b1:21
  subjkey:   6d:c2:af:37:49:41:b9:fd:f4:45:8b:aa:e0:03:3b:b9:e5:7b:9c:b5

RSA Attestation Key Certificate

The PKCS#10 certificate request exported from the TPM is used to generate an RSA Attestation Key certificate signed by the Root CA:

$ pki --issue --cacert cacert.pem --cakey cakey.pem -type pkcs10 --in ak_rsa_req.pem --dn "C=CH, O=strongSec GmbH, OU=AK RSA, CN=edu.strongsec.com" --san "edu.strongsec.com" --crl http://www.strongsec.com/ca/strongsec.crl --flag serverAuth --lifetime 1827 > ak_rsa_cert.der

having the following content

$ pki --print --type x509 --in ak_rsa_cert.der

  subject:  "C=CH, O=strongSec GmbH, OU=AK RSA, CN=edu.strongsec.com"
  issuer:   "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
  validity:  not before Dec 23 15:26:22 2020, ok
             not after  Dec 23 15:26:22 2025, ok (expires in 1814 days)
  serial:    79:e5:74:2f:a4:df:b8:d2
  altNames:  edu.strongsec.com
  flags:     serverAuth
  CRL URIs:  http://www.strongsec.com/ca/strongsec.crl
  authkeyId: 6d:c2:af:37:49:41:b9:fd:f4:45:8b:aa:e0:03:3b:b9:e5:7b:9c:b5
  subjkeyId: 48:82:62:15:74:a2:10:c5:75:70:c2:d6:7d:59:9f:22:d9:4f:9c:07
  pubkey:    RSA 2048 bits
  keyid:     df:b7:8f:95:61:8f:70:84:f4:03:e8:7e:83:a6:dd:5f:c5:ff:72:b5
  subjkey:   48:82:62:15:74:a2:10:c5:75:70:c2:d6:7d:59:9f:22:d9:4f:9c:07

ECC Attestation Key Certificate

The second PKCS#10 certificate request exported from the TPM is used to generate an ECC Attestation Key certificate signed by the Root CA:

$ pki --issue --cacert cacert.pem --cakey cakey.pem -type pkcs10 --in ak_ecc_req.pem --dn "C=CH, O=strongSec GmbH, OU=AK ECC, CN=edu.strongsec.com" --san "edu.strongsec.com" --crl http://www.strongsec.com/ca/strongsec.crl --flag serverAuth --lifetime 1827 > ak_ecc_cert.der

having the following content

$ pki --print --type x509 --in ak_ecc_cert.der

  subject:  "C=CH, O=strongSec GmbH, OU=AK ECC, CN=edu.strongsec.com"
  issuer:   "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
  validity:  not before Dec 23 15:27:40 2020, ok
             not after  Dec 23 15:27:40 2025, ok (expires in 1814 days)
  serial:    65:fd:5b:98:47:11:f6:45
  altNames:  edu.strongsec.com
  flags:     serverAuth
  CRL URIs:  http://www.strongsec.com/ca/strongsec.crl
  authkeyId: 6d:c2:af:37:49:41:b9:fd:f4:45:8b:aa:e0:03:3b:b9:e5:7b:9c:b5
  subjkeyId: cc:83:49:87:2b:9e:f3:cb:b8:35:12:02:87:ff:14:89:28:44:a6:04
  pubkey:    ECDSA 256 bits
  keyid:     ba:64:37:a4:0e:c8:42:67:8c:55:5a:f9:1b:2a:eb:ff:5f:40:c3:e3
  subjkey:   cc:83:49:87:2b:9e:f3:cb:b8:35:12:02:87:ff:14:89:28:44:a6:04

Storing Certificates in the NV RAM

A TPM 2.0 has a certain amount of Non Volatile Random Access Memory (NV RAM) that can be used to store arbitrary data, e.g. the X.509 certificates matching the persistent keys. If both the certificates and keys are persisted in the TPM then the system disk of the host can be reformatted at any time without loosing the machine or user credentials.As with smartcards the needed amount of memory must be reserved first so we check the size of the X.509 ECC certificate

$ ls -l ak_ecc_cert.der

-rw-rw-r-- 1 andi andi 1001 Dez 23 15:31 ak_ecc_cert.der

The tpm2_nvdefine command allocates a memory location with a size of 1001 bytes that can be accessed via the handle 0x01800004 which is also called the NV index

$ tpm2_nvdefine 0x01800004 -C o -s 1001 -a 0x2000A

nv-index: 0x1800004

Then we write the certificate file to the NV RAM destination using the tpm2_nvwrite command:

$ tpm2_nvwrite 0x01800004 -C o -i ak_ecc_cert.der

Removing Certificates from NV RAM

First we store the RSA AK certificate in the NV RAM under the handle 0x0180003, again by first determining the size of the object to be persisted:

$ ls -l ak_rsa_cert.der

-rw-rw-r-- 1 andi andi 1204 Dez 23 15:30 ak_rsa_cert.der

allocating space for it

$ tpm2_nvdefine 0x01800003 -C o -s 1204 -a 0x2000A

nv-index: 0x1800003

and finally storing the certificate

$ tpm2_nvwrite 0x01800003 -C o -i ak_rsa_cert.der

We decide to use the RSA AK certificate externally, though. Thus we release the memory assigned to NV index 0x01800003 via the tpm2_nvundefine command:

$ tpm2_nvundefine 0x01800003 -C o

Using TPM 2.0 Keys with strongSwan

Configure Private Key Access

Configuration of TPM 2.0 private key access as tokens in the secrets section of swanctl.conf

secrets {
    token_ak_rsa {
       handle = 0x81010003
    }
    token_ak_ecc {
       handle = 0x81010004
    }
}

Define IPsec Connection

This connection configuration in swanctl.conf references the ECC AK certificate used for client authentication via its handle, i.e. the NV index

connections {
   host {
      remote_addrs = 10.10.1.43

      local {
         auth = pubkey
         certs-tpm {
            handle = 0x01800004
         }
         id = edu.strongsec.com
      }
      remote {
         auth = pubkey
         id = mijas.strongsec.com
      }
      children {
         host {
            esp_proposals = aes256gcm128-x25519
         }
      }
      version = 2
      proposals = aes256-sha256-x25519
   }
}

Starting the strongSwan Daemon

The strongSwan IKEv2 charon-systemd daemon is started via systemd:

$ sudo systemctl start strongswan

Jan 04 15:18:38 systemd[1]: Starting strongSwan IPsec IKEv1/IKEv2 daemon using swanctl...
Jan 04 15:18:38 edu charon-systemd[648407]: loaded plugins: charon-systemd random nonce drbg x509 revocation constraints pubkey pkcs1 pkcs8 pkcs12 pem openssl curl tpm kernel-netl>
Jan 04 15:18:38 edu charon-systemd[648407]: spawning 16 worker threads
Jan 04 15:18:38 edu charon-systemd[648407]: loaded certificate 'C=CH, O=strongSec GmbH, OU=AK RSA, CN=edu.strongsec.com'
Jan 04 15:18:38 edu charon-systemd[648407]: loaded certificate 'C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA'

The RSA AK private key is attached to the charon-systemd daemon via the TPM 2.0 TSS interface

Jan 04 15:18:38 edu charon-systemd[648407]: TPM 2.0 via TSS2 v2 available
Jan 04 15:18:38 edu charon-systemd[648407]: signature algorithm is RSASSA with SHA256 hash
Jan 04 15:18:38 edu charon-systemd[648407]: loaded RSA private key from token

The ECC AK private key is attached to the charon-systemd daemon via the TPM 2.0 TSS interface

Jan 04 15:18:38 edu charon-systemd[648407]: TPM 2.0 via TSS2 v2 available
Jan 04 15:18:38 edu charon-systemd[648407]: signature algorithm is ECDSA with SHA256 hash
Jan 04 15:18:38 edu charon-systemd[648407]: loaded ECDSA private key from token

The ECC AK certificate is loaded by the charon-systemd daemon via the TPM 2.0 TSS interface

Jan 04 15:18:38 edu charon-systemd[648407]: TPM 2.0 via TSS2 v2 available
Jan 04 15:18:38 edu charon-systemd[648407]: loaded certificate from TPM NV index 0x01800004

The connection definition is received by the charon-systemd daemon triggered by the swanctl --load-conns command via the VICI interface

Jan 04 15:18:38 edu charon-systemd[648407]: added vici connection: host

The swanctl command line tool reports its actions

Jan 04 15:18:38 edu swanctl[648429]: loaded certificate from '/etc/swanctl/x509/ak_rsa_cert.der'
Jan 04 15:18:38 edu swanctl[648429]: loaded certificate from '/etc/swanctl/x509ca/cacert.pem'
Jan 04 15:18:38 edu swanctl[648429]: loaded key token_ak_rsa from token [keyid: 4882621574a210c57570c2d67d599f22d94f9c07]
Jan 04 15:18:38 edu swanctl[648429]: loaded key token_ak_ecc from token [keyid: cc8349872b9ef3cbb835120287ff14892844a604]
Jan 04 15:18:38 edu swanctl[648429]: loaded connection 'host'
Jan 04 15:18:38 edu swanctl[648429]: successfully loaded 1 connections, 0 unloaded

Jan 04 15:18:38 edu systemd[1]: Started strongSwan IPsec IKEv1/IKEv2 daemon using swanctl.

The swanctl --list-conns command allows to list the loaded connection definitions

$ swanctl --list-conns

host: IKEv2, no reauthentication, rekeying every 14400s
  local:  %any
  remote: 10.10.1.43
  local public key authentication:
    id: edu.strongsec.com
    certs: C=CH, O=strongSec GmbH, OU=AK ECC, CN=edu.strongsec.com
  remote public key authentication:
    id: mijas.strongsec.com
  host: TUNNEL, rekeying every 3600s
    local:  dynamic
    remote: dynamic

The loaded certificates can also be displayed

$ swanctl --list-certs

You can clearly see that the connection between the AK certificates and their matching AK private key has been established (…, has private key)

List of X.509 End Entity Certificates

  subject:  "C=CH, O=strongSec GmbH, OU=AK ECC, CN=edu.strongsec.com"
  issuer:   "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
  validity:  not before Dec 23 15:27:40 2020, ok
             not after  Dec 23 15:27:40 2025, ok (expires in 1814 days)
  serial:    65:fd:5b:98:47:11:f6:45
  altNames:  edu.strongsec.com
  flags:     serverAuth
  CRL URIs:  http://www.strongsec.com/ca/strongsec.crl
  authkeyId: 6d:c2:af:37:49:41:b9:fd:f4:45:8b:aa:e0:03:3b:b9:e5:7b:9c:b5
  subjkeyId: cc:83:49:87:2b:9e:f3:cb:b8:35:12:02:87:ff:14:89:28:44:a6:04
  pubkey:    ECDSA 256 bits, has private key
  keyid:     ba:64:37:a4:0e:c8:42:67:8c:55:5a:f9:1b:2a:eb:ff:5f:40:c3:e3
  subjkey:   cc:83:49:87:2b:9e:f3:cb:b8:35:12:02:87:ff:14:89:28:44:a6:04

  subject:  "C=CH, O=strongSec GmbH, OU=AK RSA, CN=edu.strongsec.com"
  issuer:   "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
  validity:  not before Dec 23 15:26:22 2020, ok
             not after  Dec 23 15:26:22 2025, ok (expires in 1813 days)
  serial:    79:e5:74:2f:a4:df:b8:d2
  altNames:  edu.strongsec.com
  flags:     serverAuth
  CRL URIs:  http://www.strongsec.com/ca/strongsec.crl
  authkeyId: 6d:c2:af:37:49:41:b9:fd:f4:45:8b:aa:e0:03:3b:b9:e5:7b:9c:b5
  subjkeyId: 48:82:62:15:74:a2:10:c5:75:70:c2:d6:7d:59:9f:22:d9:4f:9c:07
  pubkey:    RSA 2048 bits, has private key
  keyid:     df:b7:8f:95:61:8f:70:84:f4:03:e8:7e:83:a6:dd:5f:c5:ff:72:b5
  subjkey:   48:82:62:15:74:a2:10:c5:75:70:c2:d6:7d:59:9f:22:d9:4f:9c:07

List of X.509 CA Certificates

  subject:  "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
  issuer:   "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
  validity:  not before Sep 02 10:25:01 2016, ok
             not after  Sep 02 10:25:01 2026, ok (expires in 2066 days)
  serial:    7c:24:43:4b:b7:dc:ef:7e
  flags:     CA CRLSign self-signed
  subjkeyId: 6d:c2:af:37:49:41:b9:fd:f4:45:8b:aa:e0:03:3b:b9:e5:7b:9c:b5
  pubkey:    RSA 4096 bits
  keyid:     6c:79:f3:7a:b0:df:ac:69:03:b2:ac:6a:ed:82:3a:d2:66:93:b1:21
  subjkey:   6d:c2:af:37:49:41:b9:fd:f4:45:8b:aa:e0:03:3b:b9:e5:7b:9c:b5

Initiating IKEv2 Connection

Next we initiate the "host" connection

$ swanctl --initiate --child host

[IKE] initiating IKE_SA host[1] to 10.10.1.43
[ENC] generating IKE_SA_INIT request 0 [ SA KE No N(NATD_S_IP) N(NATD_D_IP) N(FRAG_SUP) N(HASH_ALG) N(REDIR_SUP) ]
[NET] sending packet: from 10.10.1.33[500] to 10.10.1.43[500] (240 bytes)
[NET] received packet: from 10.10.1.43[500] to 10.10.1.33[500] (293 bytes)
[ENC] parsed IKE_SA_INIT response 0 [ SA KE No N(NATD_S_IP) N(NATD_D_IP) CERTREQ N(FRAG_SUP) N(HASH_ALG) N(CHDLESS_SUP) N(MULT_AUTH) ]
[CFG] selected proposal: IKE:AES_CBC_256/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/CURVE_25519
[IKE] received cert request for "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
[IKE] sending cert request for "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"

The ECC AK private key stored in the TPM 2.0 is used to generate an ECDSA_WITH_SHA256_DER signature which is sent in the AUTH payload of the IKE_AUTH request. The matching client certificate is sent int the CERT payload.

[IKE] authentication of 'edu.strongsec.com' (myself) with ECDSA_WITH_SHA256_DER successful
[IKE] sending end entity cert "C=CH, O=strongSec GmbH, OU=AK ECC, CN=edu.strongsec.com"

[IKE] establishing CHILD_SA host{1}
[ENC] generating IKE_AUTH request 1 [ IDi CERT N(INIT_CONTACT) CERTREQ IDr AUTH SA TSi TSr N(MOBIKE_SUP) N(ADD_6_ADDR) N(MULT_AUTH) N(EAP_ONLY) N(MSG_ID_SYN_SUP) ]
[NET] sending packet: from 10.10.1.33[4500] to 10.10.1.43[4500] (1392 bytes)
[NET] received packet: from 10.10.1.43[4500] to 10.10.1.33[4500] (1236 bytes)
[ENC] parsed IKE_AUTH response 1 [ EF(1/2) ]
[ENC] received fragment #1 of 2, waiting for complete IKE message
[NET] received packet: from 10.10.1.43[4500] to 10.10.1.33[4500] (132 bytes)
[ENC] parsed IKE_AUTH response 1 [ EF(2/2) ]
[ENC] received fragment #2 of 2, reassembled fragmented IKE message (1296 bytes)
[ENC] parsed IKE_AUTH response 1 [ IDr CERT AUTH SA TSi TSr N(AUTH_LFT) N(MOBIKE_SUP) N(ADD_4_ADDR) N(ADD_6_ADDR) ]
[IKE] received end entity cert "C=CH, O=strongSec GmbH, CN=mijas.strongsec.com"
[CFG]   using certificate "C=CH, O=strongSec GmbH, CN=mijas.strongsec.com"
[CFG]   using trusted ca certificate "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"

The status of the received peer certificate is verified using CRLs:

[CFG] checking certificate status of "C=CH, O=strongSec GmbH, CN=mijas.strongsec.com"
[CFG]   fetching crl from 'http://www.strongsec.com/ca/strongsec.crl' ...
[CFG]   using trusted certificate "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
[CFG]   crl correctly signed by "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
[CFG]   crl is valid: until Jan 10 10:00:01 2021
[CFG]   fetching crl from 'http://www.strongsec.net/ca/strongsec_delta.crl' ...
[CFG]   using trusted certificate "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
[CFG]   crl correctly signed by "C=CH, O=strongSec GmbH, CN=strongSec 2016 Root CA"
[CFG]   crl is valid: until Jan 05 10:00:01 2021
[CFG] certificate status is good

[CFG]   reached self-signed root ca with a path length of 0
[IKE] authentication of 'mijas.strongsec.com' with ECDSA_WITH_SHA256_DER successful
[IKE] IKE_SA host[1] established between 10.10.1.33[edu.strongsec.com]...10.10.1.43[mijas.strongsec.com]
[IKE] scheduling rekeying in 13703s
[IKE] maximum IKE_SA lifetime 15143s
[CFG] selected proposal: ESP:AES_GCM_16_256/NO_EXT_SEQ
[IKE] CHILD_SA host{1} established with SPIs c585d49f_i c1630769_o and TS 10.10.1.33/32 === 10.10.1.43/32
[IKE] received AUTH_LIFETIME of 9777s, scheduling reauthentication in 8337s
initiate completed successfully

The established IKE and CHILD SAs can be displayed

$ swanctl --list-sas

host: #1, ESTABLISHED, IKEv2, 4ef1452bda258a1b_i* a8508d872adadc84_r
  local  'edu.strongsec.com' @ 10.10.1.33[4500]
  remote 'mijas.strongsec.com' @ 10.10.1.43[4500]
  AES_CBC-256/HMAC_SHA2_256_128/PRF_HMAC_SHA2_256/CURVE_25519
  established 60s ago, rekeying in 13643s, reauth in 8277s
  host: #1, reqid 1, INSTALLED, TUNNEL, ESP:AES_GCM_16-256
    installed 62s ago, rekeying in 3271s, expires in 3900s
    in  c585d49f,  15168 bytes,   172 packets,     0s ago
    out c1630769,  25184 bytes,   113 packets,    60s ago
    local  10.10.1.33/32
    remote 10.10.1.43/32

Terminating IKEv2 Connection

The IKE and CHILD SAs are terminated

$ swanctl --terminate --ike host

[IKE] deleting IKE_SA host[1] between 10.10.1.33[edu.strongsec.com]...10.10.1.43[mijas.strongsec.com]
[IKE] sending DELETE for IKE_SA host[1]
[ENC] generating INFORMATIONAL request 2 [ D ]
[NET] sending packet: from 10.10.1.33[4500] to 10.10.1.43[4500] (80 bytes)
[NET] received packet: from 10.10.1.43[4500] to 10.10.1.33[4500] (80 bytes)
[ENC] parsed INFORMATIONAL response 2 [ ]
[IKE] IKE_SA deleted
terminate completed successfully

Publications

TCG Developer Blog April 2018: Easy TPM 2.0 Access with the strongSwan VPN Solution.