convert certificate to different formats

Convert CER to PFX in OpenSSL

OpenSSL runs from the command line, so you have to open a terminal window. In Linux, you do that with the keyboard shortcut Ctrl+Alt+F1 or Ctrl+Alt+T. Windows 10 users should open the Run box in their menu, type CMD into the box, and then click Ctrl+Shift+Enter to run the command prompt as an administrator.
After you have the command prompt, type the command to turn yours.CER file and it’s associated.KEY file into a PFX. The syntax looks like this:
openssl pkcs12 -export -in yourcertificate.cer -inkey yourkey.key -out yourcertificate.pfx
You replace “yourcertificate” and “yourkey” with the correct filenames for your actual certificate, and when you click OpenSSL, it creates the PFX file. You can also go the other way from .PFX to .CER by reversing the filenames. The same technique works for changing a certificate’s filename extension. You can convert .PEM to .CRT or .CRT to .CER, as needed.
You should have the following files (Filenames are just for reference)

  • Your generated CSR (cert.csr)
  • Your Private Key File (key.pem)
  • Your SSL certificate provided by the CA (cert.cer)
  • The Intermediate Certificate provided by the CA (CA.cer)

Using OpenSSL run the following command

openssl pkcs12 -export -in cert.cer -inkey key.pem -out certificate.pfx -certfile CA.cer
Note: OpenSSL is an open source tool that is not provided or supported by Thawte

Some common conversion commands are listed below:
Note: The PEM format is the most common format used for certificates. Extensions used for PEM certificates are cer, crt, and pem. They are Base64 encoded ASCII files. The DER format is the binary form of the certificate. DER formatted certificates do not contain the “BEGIN CERTIFICATE/END CERTIFICATE” statements. DER formatted certificates most often use the ‘.der’ extension.

Convert x509 to PEM
openssl x509 -in certificatename.cer -outform PEM -out certificatename.pem

Convert PEM to DER
openssl x509 -outform der -in certificatename.pem -out certificatename.der

Convert DER to PEM
openssl x509 -inform der -in certificatename.der -out certificatename.pem

Convert PEM to P7B
Note: The PKCS#7 or P7B format is stored in Base64 ASCII format and has a file extension of .p7b or .p7c.
A P7B file only contains certificates and chain certificates (Intermediate CAs), not the private key. The most common platforms that support P7B files are Microsoft Windows and Java Tomcat.
openssl crl2pkcs7 -nocrl -certfile certificatename.pem -out certificatename.p7b -certfile CACert.cer

Convert PKCS7 to PEM
openssl pkcs7 -print_certs -in certificatename.p7b -out certificatename.pem

Convert pfx to PEM
Note: The PKCS#12 or PFX format is a binary format for storing the server certificate, intermediate certificates, and the private key in one encryptable file. PFX files usually have extensions such as .pfx and .p12. PFX files are typically used on Windows machines to import and export certificates and private keys.
openssl pkcs12 -in certificatename.pfx -out certificatename.pem

Convert PFX to PKCS#8
Note: This requires 2 commands

STEP 1: Convert PFX to PEM
openssl pkcs12 -in certificatename.pfx -nocerts -nodes -out certificatename.pem

STEP 2: Convert PEM to PKCS8
openSSL pkcs8 -in certificatename.pem -topk8 -nocrypt -out certificatename.pk8

Convert P7B to PFX
Note: This requires 2 commands

STEP 1: Convert P7B to CER
openssl pkcs7 -print_certs -in certificatename.p7b -out certificatename.cer

STEP 2: Convert CER and Private Key to PFX
openssl pkcs12 -export -in certificatename.cer -inkey privateKey.key -out certificatename.pfx -certfile  cacert.cer

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