L01. Basic Cryptography Concept - ZyXEL Communications ZyWALL 5 Support Notes

ZyWALL 5 Support Notes
L. PKI FAQ

L01. Basic Cryptography concept

Encryption and decryption are two major operations involved in cryptography. Whenever we would
like to send some secret over an insecure media, such as Internet, we may encrypt the secret before
sending it out. The receiver thus needs the corresponding decryption key to recover the encrypted
secrete. We need to have keys for both encryption and decryption. The key used to encrypt data is
called the encryption key, and the key for decryption is called the decryption key.
Cryptography can be categorized into two types, symmetric and asymmetric cryptography. For
symmetric cryptography, the encryption key is the same with the decryption. Otherwise, we the
cryptography as asymmetric.
Symmetric cryptography, such as DES, 3DES, AES, is normally used for data transmission, since it
requires less computation power than asymmetric cryptography. The task of privately choosing a key
before communicating, however, can be problematic. Applications in real case may use asymmetric
cryptography for to protect distribution of keys (symmetric), and uses symmetric cryptography for
data transmission.
Asymmetric cryptography solves the key exchange problem by defining an algorithm which uses two
keys, each of which can be used to encrypt a message. If one key is used to encrypt a message, then
the other must be used to decrypt it. This makes it possible to receive secure messages by simply
publishing one key (the public key) and keeping the other secret (the private key).
L02. What is PKI?
PKI is acronym of Public Key Infrastructure. A PKI is a comprehensive system of policies, processes,
and technologies working together to enable users of the Internet to exchange information securely
and confidentially. Public Key Infrastructures are based on the use of cryptography – the scrambling
of information by a mathematical formula and a virtual key so that it can only be decoded by an
authorized party using a related key.
A PKI uses pairs of cryptographic keys provided by a trusted third party known as a Certification
Authority (CA). Central to the workings of a PKI, a CA issues digital certificates that positively
identify the holder's identity. A Certification Authority maintains accessible directories of valid
certificates, and a list of certificates it has revoked.
L03. What are the security services PKI provides?
PKI brings to the electronic world the security and confidentiality features provided by the physical
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