Proof of Concept: Zepher TPM2 Software Stack

Overview

This repo demonstrates the use of a TPM 2.0 for server authentication on Zephyr. The PoC is implemented on top of the Enhanced System API (ESAPI), since the Feature API (FAPI) adds additional dependencies to JSON-C and OpenSSL. Moreover, the tpm2-tools are also implemented on top of ESAPI, therefore the ESAPI is sufficient.

The main has 2 code path. This first will generate an CSR on every boot. The second will launch an TLS 1.2 echo server on port 4433 (IPv6).

Hardware Requirements

The driver works with MCUs that have SPI drivers that honor SPI_HOLD_ON_CS and SPI_LOCK_ON only. If the hardware IP block does not support SPI_HOLD_ON_CS it is recommendet to use gpio-cs control.

The PoC is tested using an Infineon SLB 9670 TPM2.0 Arduino HAT on:

• NXP FRDM-K64F
• nRF52 DK (has no ethernet interface)

Software Requirements

• Zephyr
• TPM TIS
• TPM2 TSS
• TPM2 TSS Zephyr

Checkout using WEST

west init -m https://github.com/drandreas/zephyr-tpm2-poc.git zephyr-tpm2-poc
cd zephyr-tpm2-poc
west update

Build and flash

~ $ west build -p -b frdm_k64f zephyr-tpm2-poc
# or
~ $ west build -p -b frdm_k64f zephyr-tpm2-poc -- -DCONF_FILE=prj.min.conf
# or
~ $ west build -p -b nrf52dk_nrf52832 zephyr-tpm2-poc/
# followed by
~ $ west flash

Aproximate memory and flash size

Stripped down image (prj.min.conf):

Memory region         Used Size  Region Size  %age Used
           FLASH:      197000 B         1 MB     18.79%
            SRAM:         60 KB       192 KB     31.25%
        IDT_LIST:         152 B         2 KB      7.42%

Full image (default prj.conf)

Memory region         Used Size  Region Size  %age Used
           FLASH:      293132 B         1 MB     27.96%
            SRAM:       74160 B       192 KB     37.72%
        IDT_LIST:         216 B         2 KB     10.55%

Note: The heap size, a couple of kB, is not included in this numbers.

Test Server

Target output during inital boot:

*** Booting Zephyr OS build zephyr-v2.4.0  ***
Server CRT or TPM Blob not compiled in, Creating CSR
Please change the source code and assign the PEM below to "tpm_blob[]"
-----BEGIN TSS2 PRIVATE KEY-----
MIHNBgdngQUKAQMAoAMBAf8CAQEEWABWACMACwAEBHIAAAAQABAAAwAQACA+QUDa
4kSqSBZCOsYowd+lHNqZWxb3waDtd3wICwigcQAgO4u8jri79avPyOXm9fwUnuEo
/ei+UKQ4vXCMDjowCdAEYABeACCA6d13/ZdvCtVOAfqyD73gmYYCuyZI/zJLIRTw
uAWE4QAQMPQPyl7V5MFH7MbTZkV6YrhcQyK473XR6MALh4NcjAQYvV6AQPyXLyon
eQhtw1dV19WP5zxdSax2IQ==
-----END TSS2 PRIVATE KEY-----

Please sign the PEM on your desktop and assign the certificate to "server_certificate[]"
Hint: cd zephyr-tpm2-poc/data
      openssl ca -config openssl.cnf -startdate 200101000000Z -enddate 300101000000Z -in /dev/stdin

-----BEGIN CERTIFICATE REQUEST-----
MIHsMIGRAgEAMBExDzANBgNVBAMMBnplcGh5cjBZMBMGByqGSM49AgEGCCqGSM49
AwEHA0IABD5BQNriRKpIFkI6xijB36Uc2plbFvfBoO13fAgLCKBxO4u8jri79avP
yOXm9fwUnuEo/ei+UKQ4vXCMDjowCdCgHjAcBgkqhkiG9w0BCQ4xDzANMAsGA1Ud
DwQEAwIDyDAMBggqhkjOPQQDAgUAA0gAMEUCIBoxjDl7MsLxkwXzLUV2tmUdxpu8
4owovJfUCCgdwoz9AiEA7oc3AFcvblYO6VSpGNagvymnVqH2gAIAh5yBQDmhzr4=
-----END CERTIFICATE REQUEST-----

Target output after CRT and TPM Blob have been assigned (in source code):

*** Booting Zephyr OS build zephyr-v2.4.0  ***
[00:00:00.060,000] <inf> tpm_tis_spi: TPM 2.0 (device-id 0x1b, rev-id 22)
[00:00:00.060,000] <inf> tpm2: Preparing TPM Blob for echo_server...
[00:00:03.001,000] <inf> eth_mcux: ETH_0 enabled 100M full-duplex mode.
[00:00:05.061,000] <inf> tpm2: My IPv6 Address: [fe80::1234:5678]
[00:00:05.061,000] <inf> tpm2: Waiting for TCP connection on port 4433

Connect from a Linux/Mac/Windows using openssl (you need to adjust the scope ID to match your outgoing interface):

openssl s_client -showcerts -CAfile zephyr-tpm2-poc/data/ca.pem -servername zephyr -connect "[fe80::1234:5678%eth0]"