/certificate_chain_demo

Basic example of chaining certificates

Certificate Chaining PoC for Root, Intermediate and end device

Create ROOT CA

Generate Private key
openssl genrsa -aes256 -out ROOT_CA.key 2048
Generate CSR with above key
openssl req -key ROOT_CA.key -new -x509 -days 7300 -sha256 -out ROOT_CA.pem

Create Intermediate CA Key

openssl genrsa -aes256 -out Intermediate.key.pem 2048
Generate CSR with above key
openssl req -addext basicConstraints=critical,CA:TRUE -new -sha256 -key Intermediate.key.pem -out Intermediate.csr.pem

Verify Intermediate's CSR

openssl req -verify -in Intermediate.csr.pem -text -noout

Sign this Intermediate CSR by Root CA

mkdir demoCA
touch demoCA/index.txt
echo 1122334455667788 > demoCA/serial
openssl ca -policy policy_anything -extensions v3_ca -days 3650 -outdir . -cert ROOT_CA.pem -keyfile ROOT_CA.key -in Intermediate.csr.pem -out Intermediate.crt

Dump certificate information

openssl x509 -in Intermediate.crt -noout -text

Verify if root CA signed Intermediate

openssl verify -CAfile ROOT_CA.pem Intermediate.crt

Create DEVICE_XXX certificate key

openssl genrsa -aes256 -out DEVICE_XXX.key.pem 2048

For Elliptical Curve Key use.

This is ideal for IoT devices because it gives the security of 2048 in 256 bit of randomness with low compute power

openssl ecparam -name secp384r1 -genkey -noout -out secp384r1.pem

Generate DEVICE_XXX CSR

openssl req -new -sha256 -key DEVICE_XXX.key.pem -out DEVICE_XXX.csr.pem

Sign CSR by Intermediate Key

openssl ca -days 3650 -outdir . -cert Intermediate.crt -keyfile Intermediate.key.pem -in DEVICE_XXX.csr.pem -out DEVICE_XXX.crt

Verify the complete chain

openssl verify -CAfile ROOT_CA.pem -untrusted Intermediate.crt DEVICE_XXX.crt

Convert certificate to pem format

openssl x509 -outform pem -in DEVICE_XXX.crt -out DEVICE_XXX.pem