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Trusted Platform Module 2.0 » History » Version 24

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Andreas Steffen, 18.02.2017 19:43

Trusted Platform Module 2.0

Connect to a TPM 2.0 device

In order to connect to a TPM 2.0 hardware or firmware device, the TSS2 software stack developed by Intel is needed. Because the official Ubuntu tpm2-tss package is rather outdated (e.g. since version 0.98 the TCTI interface to the TPM 2.0 resource manager has changed several times), strongSwan is currently based on a recent version directly drawn from the TPM2-TSS git repository https://github.com/01org/TPM2.0-TSS. Avoid any TCTI interface incompatibilities by fetching the latest tpm2-tools version from https://github.com/01org/tpm2.0-tools as well.

Build and install both the tpm2-tss stack and the tpm2.0-tools, start the tpm2-resourcemgr as a service in the background and try to connect to the TPM 2.0 by listing e.g. the contents of the SHA-1 bank of PCR registers

tpm2_listpcrs -g 0x0004
Bank/Algorithm: TPM_ALG_SHA1(0x0004)
PCR_00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_01: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_02: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_03: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_04: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_05: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_06: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_07: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_08: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_09: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_10: a9 45 e7 0f 42 a2 79 f0 78 ca d4 64 60 39 39 da 9d 6a d1 a5
PCR_11: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_12: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_13: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_14: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_15: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_16: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
PCR_17: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
PCR_18: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
PCR_19: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
PCR_20: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
PCR_21: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
PCR_22: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
PCR_23: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

A manual showing all tpm2-tools functions with their arguments can be found here.

TPM 2.0 Algorithm IDs

Hash Algorithms

0x0004 SHA-1
0x000B SHA-2_256
0x000C SHA-2_384
0x000D SHA-2_512

Currently available TPM 2.0 devices like the Infineon Optiga SLB 9670 VQ2.0 hardware TPM or Intel's PTT firmware TPM support the SHA-1 and SHA-2_256 algorithms.

Public Key Types

0x0001 RSA
0x0023 ECC

Currently RSA keys have a modulus size of 2048 bits and ECC keys are based on the 256 bit NIST curve.

Signature Schemes

0x0014 RSASSA
0x0016 RSAPSS
0x0018 ECDSA

Derive a Persistent RSA Endorsement Key

The following tpm2-tools command derives a 2048 bit RSA Endorsement Key (EK) in a deterministic way from the secret Endorsement Seed unique to each TPM device and makes the key persistent in the non-volatile memory of the TPM under the object handle 0x81010001

tpm2_getpubek -H 0x81010001 -g 0x0001 -f ek_rsa.pub

The EK public key can be exported in PKCS#1 format from the TPM using the pki tool

pki --pub --keyid 81010001 --outform pem > ek_rsa_pub.pem

The fingerprint of the RSA EK public key can be displayed with the command

pki --print --type pub --in ek_rsa_pub.pem
  pubkey:    RSA 2048 bits
  keyid:     d1:f1:49:84:36:44:e6:8c:d2:a6:69:ee:fd:b5:7d:56:2f:39:ff:58
  subjkey:   c1:1b:8e:f1:c7:f8:8a:1e:9a:dd:7e:82:2f:7a:a3:f5:c0:e2:4d:7d

Generate a Persistent RSA Attestation Key

A 2048 bit RSA Attestation Key (AK) bound to the EK with handle 0x81010001 can be created and made persistent under the handle 0x81010002 with the following tpm2-tools command

tpm2_getpubak -E 0x81010001 -g 0x0001 -D 0x000B -s 0x0014 -k 0x81010002 -f ak_rsa2.pub -n ak_rsa2.name

The AK public key can be exported in PKCS#1 format from the TPM using the pki tool

pki --pub --keyid 81010002 --outform pem > ak_rsa_pub.pem

The fingerprint of the RSA AK public key can be displayed with the command

pki --print --type pub --in ak_rsa_pub.pem
  pubkey:    RSA 2048 bits
  keyid:     71:21:f5:d4:7e:59:4a:88:16:ca:57:85:98:3d:36:a7:b1:d5:75:fa
  subjkey:   f4:9e:85:7d:de:4e:67:f5:fb:87:03:98:67:3f:20:7c:f3:3f:2b:66

Derive a Persistent ECC Endorsement Key

The following tpm2-tools command derives a 256 bit ECC Endorsement Key (EK) in a deterministic way from the secret Endorsement Seed unique to each TPM device and makes the key persistent in the non-volatile memory of the TPM under the object handle 0x81010003:

tpm2_getpubek -H 0x81010003 -g 0x0023 -f ek_ecc.pub

The EK public key can be exported in PKCS#1 format from the TPM using the pki tool:

pki --pub --keyid 81010003 > ek_ecc_pub.der

The fingerprint of the ECC EK public key can be displayed with the command

pki --print --type pub --in ek_ecc_pub.der
  pubkey:    ECDSA 256 bits
  keyid:     7f:39:ca:e6:83:9b:a9:06:97:40:27:6a:e1:bf:8f:f5:9f:d3:a5:31
  subjkey:   8b:43:4d:5e:5e:7b:ff:c2:54:4d:ef:88:cb:0c:7c:47:75:28:4d:09

Generate a Persistent ECC Attestation Key

A 256 bit ECC Attestation Key (AK) bound to the EK with handle 0x81010003 can be created and made persistent under the handle 0x81010004 with the following tpm2-tools command

tpm2_getpubak -E 0x81010003 -g 0x0023 -D 0x000B -s 0x0018 -k 0x81010004 -f ak_ecc4.pub -n ak_ecc4.name

The AK public key can be exported in PKCS#1 format from the TPM using the pki tool

pki --pub --keyid 81010004 > ak_ecc_pub.der

The fingerprint of the RSA AK public key can be displayed with the command

pki --print --type pub --in ak_ecc_pub.der
  pubkey:    ECDSA 256 bits
  keyid:     71:49:7c:42:41:e7:c6:81:bc:31:73:f0:0f:7e:4a:e1:2d:53:00:38
  subjkey:   c7:0e:63:f8:7f:6f:f6:55:00:e5:05:7f:5a:3e:6b:6c:e7:d2:d5:13

Generate Another ECC Attestation Key

Multiple AK keys bound to a common EK key can be generated

tpm2_getpubak -E 0x81010003 -g 0x0023 -D 0x000B -s 0x0018 -k 0x81010005 -f ak_ecc5.pub -n ak_ecc5.name

The AK public key can be exported in PKCS#1 format from the TPM using the pki tool

pki --pub --keyid 81010005 > ak_ecc5_pub.der

The fingerprint of the second ECC AK public key can be displayed with the command

pki --print --type pub --in ak_ecc5_pub.der
  pubkey:    ECDSA 256 bits
  keyid:     c4:b4:9c:95:27:9e:ce:81:2f:98:42:c8:1b:f0:54:ff:d4:d1:24:34
  subjkey:   cf:44:f4:f7:9d:97:09:ad:b1:09:3a:8e:6f:23:eb:9f:2c:35:94:c9

Remove a Persistent Key Object

Since the non-volatile memory of the TPM is limited any persistent key object can be removed to free storage space.
The following tpm2-tools command removes the ECC AK key with persistent handle 0x81010005

tpm2_evictcontrol -A o -H 0x81010005 -S 0x81010005

List Persistent Objects

The following tpm2-tools command lists all persistent objects stored by the TPM in non-volatile memory

tpm2_listpersistent
6 persistent objects defined.

0. Persistent handle: 0x81000001
{
        Type: 0x23
        Hash algorithm(nameAlg): 0xb
        Attributes: 0x30072
}
1. Persistent handle: 0x81000002
{
        Type: 0x23
        Hash algorithm(nameAlg): 0xb
        Attributes: 0x60072
}
2. Persistent handle: 0x81010001
{
        Type: 0x1
        Hash algorithm(nameAlg): 0xb
        Attributes: 0x300b2
}
3. Persistent handle: 0x81010002
{
        Type: 0x1
        Hash algorithm(nameAlg): 0xb
        Attributes: 0x50072
}
4. Persistent handle: 0x81010003
{
        Type: 0x23
        Hash algorithm(nameAlg): 0xb
        Attributes: 0x300b2
}
5. Persistent handle: 0x81010004
{
        Type: 0x23
        Hash algorithm(nameAlg): 0xb
        Attributes: 0x50072
}

Access TPM Private Keys via VICI Interface

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

secrets {
    token_ak_rsa {
       handle = 81010002
    }
    token_ak_ecc {
       handle = 81010004
    }
}