PKCS stands for Public Key Cryptography Standards. They were developed by RSA Data Security. These standards act as a means of interoperability between the vendors out there. There are 15 parts, but numbers 2 and 4 have been rolled into PKCS #1.

PKCS #1 is encryption using the RSA algorithm. PKCS #3 uses the Diffie-Hellman algorithms. It is how you exchange a key between two people. PKCS #5 covers passwords.

PKCS #6 is the extended certificate syntax. It describes the extra information like e-mail addresses within certificates. PKCS #7 covers the use of envelopes. An example is S/MIME.

PKCS #8 is for private key encryption. I will cover PKCS 9 through 15 next time around. Be ready for things such as Cryptoki.