.csr- This is a Certificate Signing Request. Some applications can generate these for submission to certificate-authorities. It includes some/all of the key details of the requested certificate such as subject, organization, state, whatnot. These get signed by the CA and a certificate is returned. The returned certificate is the public certificate, which itself can be in a couple of formats.
.pem- This is the public-key of a specific certificate. In apache installs, this frequently resides in /etc/ssl/servercerts. This is also the format used for Certificate Authority certificates (/etc/ssl/certs)
.key- This is the private-key of a specific certificate. In apache installs, this frequently resides in /etc/ssl/private. The rights on this directory and the certificates is very important, and some programs will refuse to load these certificates if they are set wrong.
.p12- A passworded container format that contains both public and private certificate pairs. Every time I get one I have to google to remember the openssl-fu required to break it into
.der- Fills the same function as a
.pemfile, but a different format. OpenSSL can convert these to
.pem. I've only ever run into them in the wild with Novell's eDirectory certificate authority.
.pemfile with a different extension. This extension is recognized by Windows Explorer as a certificate, which
.crl- A certificate revocation list. Certificate Authorities produce these as a way to de-authorize certificates before expiration.
#创建一个名为mykey.pem的private key文件 $ openssl genrsa -out mykey.pem 1024 #通过mykey.pem这个内容为private key的文件，计算出public key后，进行保存到mykey.pub这个文件中 $ openssl rsa -in mykey.pem -pubout > mykey.pub