Cryptography is the science of keeping data
secure. Cryptography allows you to store information or to communicate
with other parties while preventing non-involved parties from understanding
the stored information or understanding the communication. Encryption
transforms understandable text into an unintelligible piece of data
(ciphertext). Decrypting restores the understandable text from the
unintelligible data. Both processes involve a mathematical formula or
algorithm and a secret sequence of data (the key).
There are two types of cryptography:
- In shared or secret key (symmetric) cryptography, one key is a shared
secret between two communicating parties. Encryption and decryption
both use the same key.
- In public key (asymmetric) cryptography, encryption, and decryption each
use different keys. A party has two keys: A public key and a private
key. The two keys are mathematically related, but it is virtually
impossible to derive the private key from the public key. A message
that is encrypted with someone's public key can be decrypted only with
the associated private key. Alternately, a server or user can use a
private key to "sign" a document and use a public key to decrypt the digital signatures. This verifies the
document's source.