mTLS with TPM bound private key

Simple http client/server in golang where the private key used in the connection is generated and embedded within a Trusted Platform Module.

This repo mostly uses the crypto.Signer implementation from my own library implementing that interface for TPM ("github.com/salrashid123/signer/tpm") and not the one from from go-tpm-tools.

The steps here will create two GCP VMs with TPMs create TPM based RSA keys, generate a CSR using those keys, then an external CA will issue an x509 cert using that csr.

Finally, the client will establish an mTLS https connection to the server

---

• update 7/17/23: This sample use RSA keys involves several steps and a custom crypto.signer. If you want to see one-way TLS where the server's private key is embedded in a TPM and the private key is cryptographically verified (tpm remote attestation), please instead see https://github.com/salrashid123/tls_ak

---

NOTE: this repo is not supported by Google

NOTE:

• The TPM is a device so concurrent access (eg via goroutines) will result in exceptions: Unable to Open TPM: open /dev/tpm0: device or resource busy

---

Server

First create a server and install golang go version go1.16.5 linux/amd64

gcloud compute  instances create   ts-server     \
   --zone=us-central1-a --machine-type=e2-medium \
   --tags tpm       --no-service-account  --no-scopes  \
   --shielded-secure-boot --shielded-vtpm --shielded-integrity-monitoring  \
   --image-family=debian-11        --image-project=debian-cloud

gcloud compute firewall-rules create allow-https-tpm --action=ALLOW --rules=tcp:8081 --source-ranges=0.0.0.0/0 --target-tags=tpm

gcloud compute ssh ts-server

# in vm:
sudo su -
apt-get update

## we need to install the latest tpm2_tools that support rsapss imports
apt -y install   autoconf-archive   libcmocka0   libcmocka-dev   procps  \
   iproute2   build-essential   git   pkg-config   gcc   libtool   automake \
     libssl-dev   uthash-dev   autoconf   doxygen  libcurl4-openssl-dev dbus-x11 libglib2.0-dev libjson-c-dev acl

cd
git clone https://github.com/tpm2-software/tpm2-tss.git
  cd tpm2-tss
  ./bootstrap
  ./configure --with-udevrulesdir=/etc/udev/rules.d
  make -j$(nproc)
  make install
  udevadm control --reload-rules && sudo udevadm trigger
  ldconfig

cd
git clone https://github.com/tpm2-software/tpm2-tools.git
  cd tpm2-tools
  ./bootstrap
  ./configure
  make check
  make install


wget https://go.dev/dl/go1.21.1.linux-amd64.tar.gz
rm -rf /usr/local/go && tar -C /usr/local -xzf go1.21.1.linux-amd64.tar.gz
export PATH=$PATH:/usr/local/go/bin

# get the source repo
git clone https://github.com/salrashid123/signer.git
cd signer/util

# tpm2_flushcontext -t -s -l
# tpm2_evictcontrol -C o -c 0x81008001
tpm2_createprimary -C o -c rprimary.ctx
tpm2_create -G rsa2048:rsapss:null -g sha256 -u rkey.pub -r rkey.priv -C rprimary.ctx
tpm2_load -C rprimary.ctx -u rkey.pub -r rkey.priv -c rkey.ctx
tpm2_evictcontrol -C o -c rkey.ctx 0x81008001

## IMPORTANT edit csrgen/csrgen.go 
### set SignatureAlgorithm: x509.SHA256WithRSAPSS,  since TLS 1.3 uses PSS 
	# var csrtemplate = x509.CertificateRequest{
	# 	Subject: pkix.Name{
	# 		Organization:       []string{"Acme Co"},
	# 		OrganizationalUnit: []string{"Enterprise"},
	# 		Locality:           []string{"Mountain View"},
	# 		Province:           []string{"California"},
	# 		Country:            []string{"US"},
	# 		CommonName:         *san,
	# 	},
	# 	DNSNames:           []string{*san},
	# 	SignatureAlgorithm: x509.SHA256WithRSAPSS,
	# }

go run csrgen/csrgen.go --filename /tmp/server.csr --sni server.domain.com  --persistentHandle=0x81008001
openssl req -in /tmp/server.csr -noout -text

# switch to this repo: generate the server certificate 
# 
cd go_tpm_https_embed/certs/
export SAN=DNS:server.domain.com
openssl ca  -config single-root-ca.conf -in /tmp/server.csr -out server.crt  -subj "/C=US/ST=California/L=Mountain View/O=Google/OU=Enterprise/CN=server.domain.com"  -extensions server_ext

# run the server
go run src/server/server.go -cacert certs/ca/root-ca.crt -servercert certs/server.crt  --persistentHandle=0x81008001 -port :8081

curl mTLS

You can test the config locally using the pre-generated client certificates provided in this repo

export SERVER_IP=`gcloud compute instances describe ts-server --format="value(networkInterfaces.accessConfigs[0].natIP)"`

curl -v -H "Host: server.domain.com"  --resolve  server.domain.com:8081:$SERVER_IP \
   --cert certs/certs/user10.crt --key certs/certs/user10.key \
    --cacert certs/ca/root-ca.crt https://server.domain.com:8081/

Client

gcloud compute  instances create   ts-client     \
   --zone=us-central1-a --machine-type=e2-medium \
   --tags tpm       --no-service-account  --no-scopes  \
   --shielded-secure-boot --shielded-vtpm --shielded-integrity-monitoring  \
   --image-family=debian-11 --image-project=debian-cloud

gcloud compute ssh ts-client

sudo su -
apt-get update

apt -y install   autoconf-archive   libcmocka0   libcmocka-dev   procps  \
   iproute2   build-essential   git   pkg-config   gcc   libtool   automake \
     libssl-dev   uthash-dev   autoconf   doxygen  libcurl4-openssl-dev dbus-x11 libglib2.0-dev libjson-c-dev acl

cd
git clone https://github.com/tpm2-software/tpm2-tss.git
  cd tpm2-tss
  ./bootstrap
  ./configure --with-udevrulesdir=/etc/udev/rules.d
  make -j$(nproc)
  make install
  udevadm control --reload-rules && sudo udevadm trigger
  ldconfig

cd
git clone https://github.com/tpm2-software/tpm2-tools.git
  cd tpm2-tools
  ./bootstrap
  ./configure
  make check
  make install


wget https://go.dev/dl/go1.21.1.linux-amd64.tar.gz
rm -rf /usr/local/go && tar -C /usr/local -xzf go1.21.1.linux-amd64.tar.gz
export PATH=$PATH:/usr/local/go/bin


# tpm2_flushcontext -t -s -l
# tpm2_evictcontrol -C o -c 0x81008000
tpm2_createprimary -C o -c rprimary.ctx
tpm2_create -G rsa2048:rsapss:null  -g sha256 -u rkey.pub -r rkey.priv -C rprimary.ctx
tpm2_load -C rprimary.ctx -u rkey.pub -r rkey.priv -c rkey.ctx
tpm2_evictcontrol -C o -c rkey.ctx 0x81008000

# get the source repo
git clone https://github.com/salrashid123/signer.git
cd signer/util

## IMPORTANT edit util/csrgen/csrgen.go 
### set SignatureAlgorithm: x509.SHA256WithRSAPSS,  since TLS 1.3 uses PSS 

go run csrgen/csrgen.go --filename /tmp/kclient.csr --sni server.domain.com  --persistentHandle=0x81008000

## switch back to the root of this repo
cd go_tpm_https_embed/certs/
export SAN=DNS:client.domain.com
openssl ca  -config single-root-ca.conf -in /tmp/kclient.csr -out kclient.crt  \
   -subj "/C=US/ST=California/L=Mountain View/O=Google/OU=Enterprise/CN=client.domain.com"  -extensions client_reqext

# run the client using the server's IPaddress or just connect to the internal dns alias
# echo $SERVER_IP
go run src/client/client.go -cacert certs/ca/root-ca.crt --persistentHandle=0x81008000 --address ts-server

At this point, you should see a simple 'ok' from the sever

References

Other references:

• Trusted Platform Module (TPM) and Google Cloud KMS based mTLS auth to HashiCorp Vault
• Docker daemon mTLS with Trusted Platform Module
• TPM TLS with nginx, openssl: https://github.com/salrashid123/go_tpm_https#nginx]

RSA-PSS padding:

• Synthesized PSS support
• PSS advertising during TLS handshake for TPM signing
• TLS salt length auto detection, switch from DIGEST to AUTO