When authenticating with a vendor using a custom webservice, the vendor requested that we use an x509 certificate with a 2048 byte key and an SHA256 hash (sometimes referred to as SHA2, though SHA2 actually refers to the group of hashes containing SHA256, 384, and 512). Since I’d used IIS to generate our certificate (IIS will only generate a certificate using an SHA1 hash), and it involved quite a bit of research to get a certificate with an SHA256 signature hash on it, I wanted to detail the steps here:
- First, download and install OpenSSL from Shining Light. The “Light” version of the package will do, since you’re only using basic functionality.
- Generate your Certificate request (CSR), specifying an SHA256 signature hash
openssl req -nodes -sha256 -newkey rsa:2048 -keyout C:\SomeFolder\PrivateKey.key -out C:\SomeFolder\CertificateRequest.csr
- You’ll be prompted for a few certificate fields, including your state, company name, computer name on your certificate, etc. Enter these as they come up.
- This will generate two files – PrivateKey.key (which contains the un-encrypted version of your private key – protect this file, as somebody who obtains it along with your signed public key can impersonate you), and CertificateRequest.csr (your certificate signing request, which is not sensative).
- Though this isn’t required, if you want to confirm what you’re entered in the CSR, you can view the details using another OpenSSL command line
openssl req -in C:\SomeFolder\CertificateRequest.csr -text -noout
- Now that you have your CSR, submit it to whatever signing authority you use – for us, it was Verisign, but there are any number of different CAs out there that can sign it.
- Once your CA has signed the CSR, you’ll get back either a binary p7b file (which we’ll called SignedKeyFromCA.p7b) containing your certificate signed public key (and, possibly, the certificate chain your CA used as well), or either a binary or base64 CER file containing just your certificate. Whatever you receive back, you’ll need to convert it to a Base64 CER (called SignedKeyFromCA.cer here), since that’s what OpenSSL expects.
- To combine your private key with the signed public key to create a certificate:
openssl pkcs12 -export -in c:\Temp\SignedKeyFromCA.cer -inkey c:\temp\openssl.key -out SignedKeyPair.p12
- Since you’re exporting your private key in this file, you’ll be required to encrypt it with a password, which OpenSSL will prompt you for (twice).
- You’ve now got your signed key pair – SignedKeyPair.p12. You can either use this pkcs12 file in your code, or you can import in into your web server (assuming it supports SHA256 hashes). IIS7, for example, supports importing this certificate and using it for SSL, but just doesn’t support generating a SHA2 CSR in the first place.
Enjoy! If you have any issues, please feel free to post a comment and I’ll do my best to answer it!