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How to Generate Signing Keys using OpenSSL Command Line Utilities

These instructions generate a new self-signed X.509 Certificate Chain for signing UEFI Capsules, using OpenSSL command line utilities as an example.

NOTE: These instructions only cover how to generate a new X.509 Certificate Chain. It is up to the product owner to properly handle and protect a the cryptographic pair of private keys and public X.509 certificates used to sign and authenticate capsule-based system firmware update images.

The OpenSSL configuration and OpenSSL commands on this page were verified using the pre-built 32-bit OpenSSL for Windows binaries, Version 1.0.2j Light. Other versions of OpenSSL may require different command flags or configuration settings.

Setup OpenSSL Command Line Environment

NOTE: The steps below are based on Microsoft Windows. Linux packages for OpenSSL will typically setup the environment correctly.

set OPENSSL_HOME=c:\OpenSSL-Win32\bin
set OPENSSL_CONF=%OPENSSL_HOME%\openssl.cfg

The openssl.cfg file must be reviewed to find the current CA path setting.

[ CA_default ]
    dir = ./demoCA              # Where everything is kept

The demoCA directory may need to be initialized before our command sequence will work properly:

rmdir /s/q .\demoCA
mkdir .\demoCA
mkdir .\demoCA\newcerts
type NUL > .\demoCA\index.txt
echo 01 > .\demoCA\serial

Generate a new Self-signed X.509 Certificate Chain

The following steps demonstrate how to generate a three layer certificate chain (RootCA -> IntermediateCA -> SigningCert) using OpenSSL. A prefix should be used for all files referenced by OpenSSL commands. The prefix used in this demonstration is New. Many OpenSSL commands prompt the user for input, so the OpenSSL commands below should be run one at a time.

Private key files are password protected using the -aes256 flag. The sequence of commands provided in this demonstration will prompt for a password multiple times.

The openssl req -new command prompts the user for several pieces of information. A unique value for Common Name must be provided for each of the three certificates generated or the process can not be completed.

Generate the Root Pair

Generate a Root Key

openssl genrsa -aes256 -out NewRoot.key 2048

Generate a self-signed Root Certificate

openssl req -new -x509 -days 3650 -key NewRoot.key -out NewRoot.crt

openssl x509 -in NewRoot.crt -out NewRoot.cer -outform DER

openssl x509 -inform DER -in NewRoot.cer -outform PEM -out NewRoot.pub.pem

Generate the Intermediate Pair

Generate the Intermediate Key

openssl genrsa -aes256 -out NewSub.key 2048

Generate the Intermediate Certificate

openssl req -new -days 3650 -key NewSub.key -out NewSub.csr

openssl ca -extensions v3_ca -in NewSub.csr -days 3650 -out NewSub.crt -cert NewRoot.crt -keyfile NewRoot.key

openssl x509 -in NewSub.crt -out NewSub.cer -outform DER

openssl x509 -inform DER -in NewSub.cer -outform PEM -out NewSub.pub.pem

Generate User Key Pair for Data Signing

Generate User Key

openssl genrsa -aes256 -out NewCert.key 2048

Generate User Certificate

openssl req -new -days 3650 -key NewCert.key -out NewCert.csr

openssl ca -in NewCert.csr -days 3650 -out NewCert.crt -cert NewSub.crt -keyfile NewSub.key

openssl x509 -in NewCert.crt -out NewCert.cer -outform DER

openssl x509 -inform DER -in NewCert.cer -outform PEM -out NewCert.pub.pem

Convert the Key and Certificate for signing. The password is removed with -nodes flag for convenience in this demonstration. If the -nodes flag is removed, the EDK II build will prompt for a password every time a capsule is signed.

openssl pkcs12 -export -out NewCert.pfx -inkey NewCert.key -in NewCert.crt

openssl pkcs12 -in NewCert.pfx -nodes -out NewCert.pem

Verify Data Signing & Verification with the New X.509 Certificate Chain

Create a Test File

echo Hello World > test.bin

Generate Detached PKCS7 Signature from Signed Test File

openssl smime -sign -binary -signer NewCert.pem -outform DER -md sha256 -certfile NewSub.pub.pem -out test.bin.p7 -in test.bin

Verify PKCS7 Signature of Signed Test File

openssl smime -verify -inform DER -in test.bin.p7 -content test.bin -CAfile NewRoot.pub.pem -out test.org.bin

X.509 Certificate Chain Files

Once all the steps above have been completed successfully, the following generated files are used to sign and authenticate capsule based system firmware update images.

• NewRoot.cer: Public key that is used to configure the gEfiSecurityPkgTokenSpaceGuid.PcdPkcs7CertBuffer PCD value. This PCD is used by EDK II firmware to authenticate a signed system firmware update image.
• NewRoot.pub.pem: Trusted public certificate that is passed in the --trusted-public-cert flag of the EDK II Pkcs7Sign utility.
• NewSub.pub.pem: Other public certificate that is passed in the --other-public-cert flag of the EDK II Pkcs7Sign utility.
• NewCert.pem: Signer private certificate that is passed in the --signer-private-cert flag of the EDK II Pkcs7Sign utility.

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