Converting SSL certicates

Often when we you buy / get a new certificate you need to have another certificate depending on your needs.

PEM Format

The PEM format is the most common format that CA’s issue certificates in. PEM certificates usually have extentions such as .pem, .crt, .cer, and .key. They are Base64 encoded ASCII files and contain “—–BEGIN CERTIFICATE—–” and “—–END CERTIFICATE—–” statements. Server certificates, intermediate certificates, and private keys can all be put into the PEM format.

Apache and other similar servers like Citrix NetScaler use PEM format certificates. Several PEM certificates, and even the private key, can be included in one file, one below the other, but most platforms, such as Apache, expect the certificates and private key to be in separate files.

DER Format

The DER format is simply a binary form of a certificate instead of the ASCII PEM format. It sometimes has a file extension of .der but it often has a file extension of .cer so the only way to tell the difference between a DER .cer file and a PEM .cer file is to open it in a text editor and look for the BEGIN/END statements. All types of certificates and private keys can be encoded in DER format. DER is typically used with JAVA related platforms.

PKCS#7/P7B Format

The PKCS#7 or P7B format is usually stored in Base64 ASCII format and has a file extention of .p7b or .p7c. P7B certificates contain “—–BEGIN PKCS7—–” and “—–END PKCS7—–” statements. A P7B file only contains certificates and chain certificates, not the private key. Several platforms support P7B files including Microsoft Windows and Java Tomcat.

PKCS#12/PFX Format

The PKCS#12 or PFX format is a binary format for storing the server certificate, any 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.

When converting a PFX file to PEM format, OpenSSL will put all the certificates and the private key into a single file. You will need to open the file in a text editor and copy each certificate and private key (including the BEGIN/END statments) to its own individual text file and save them as certificate.cer, CACert.cer, and privateKey.key respectively.

OpenSSL Commands to Convert SSL Certificates

There are several online convertors for SSL certificates but I urge you to use convert the certificate locally via OpenSSL. You don’t wont to store your PRIVATE key on someone else it’s machine. If you do it locally you have the private key on your machine. I good point here is that you should have some form of disk encryption on your laptop in event that your PC/laptop is stolen that the keys remain safe. Use the following OpenSSL commands to convert SSL certificate to different formats:

OpenSSL Convert PEM

Convert PEM to DER

openssl x509 -outform der -in certificate.pem -out certificate.der

Convert PEM to P7B

openssl crl2pkcs7 -nocrl -certfile certificate.cer -out certificate.p7b -certfile CACert.cer

Convert PEM to PFX

openssl pkcs12 -export -out certificate.pfx -inkey privateKey.key -in certificate.crt -certfile CACert.crt

OpenSSL Convert DER

Convert DER to PEM

openssl x509 -inform der -in certificate.cer -out certificate.pem

OpenSSL Convert P7B

Convert P7B to PEM

openssl pkcs7 -print_certs -in certificate.p7b -out certificate.cer

Convert P7B to PFX

openssl pkcs7 -print_certs -in certificate.p7b -out certificate.cer

openssl pkcs12 -export -in certificate.cer -inkey privateKey.key -out certificate.pfx -certfile CACert.cer

openssl pkcs12 -export -in certificate.cer -inkey privateKey.key -out certificate.pfx

OpenSSL Convert PFX

Convert PFX to PEM

openssl pkcs12 -in certificate.pfx -out certificate.cer -nodes