Trusted Platform Module 2.0
Private keys and X.509 certificates stored in a TPM 2.0 device can be accessed
and used by the pki tool (using the --keyid and
--cakeyid options), the pt-tls-client (using
the --keyid and --certid options), and of course the
strongSwan IKE daemon.
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.
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 4.1.3: https://github.com/tpm2-software/tpm2-tss/releases/tag/4.1.3
-
tpm2-tools version 5.7: https://github.com/tpm2-software/tpm2-tools/releases/tag/5.7
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
New TPM 2.0 Devices with stronger RSA and ECC Keys
Starting with version 5.3 of the tpm2-tools, RSA keys with lengths > 2048
bits and ECC keys with lengths > 256 bits are supported. Also signatures can be
based on sha384 or sha512 hashes if the TPM 2.0 firmware supports them.
E.g. the following TPM 2.0 device manufactured by STMicroelectronics has support
for NIST_P384 ECC keys and signatures based on `"SHA384" hashes:
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
Endorsement Keys
An EK with an RSA 3072 bit key is derived with the following command
$ tpm2_createek -G rsa3072 -c 0x81010001
and an EK with an ECC 384 bit key with the command
$ tpm2_createek -G ecc384 -c 0x81010002
Attestation Keys
An AK with an RSA 3072 bit key is derived with the following command
$ tpm2_createak -C 0x81010001 -G rsa3072 -g sha256 -s rsassa -c ak_rsa.ctx -u ak_rsa.pub -n ak_rsa.name
and an AK with an ECC 384 bit key with the command
$ tpm2_createak -C 0x81010002 -G ecc384 -g sha384 -s ecdsa -c ak_ecc.ctx -u ak_ecc.pub -n ak_ecc.name
IBM TPM 2.0 Simulator
A tpm-server Docker container with a readily installed
IBM TPM 2.0 Simulator plus the tpm2-tools and
the strongSwan pki tool allows you to freely experiment
with the larger RSA and ECC keys.
Publications
-
TCG Developer Blog April 2018: Easy TPM 2.0 Access with the strongSwan VPN Solution.