Cryptography
is the practice and study of techniques for secure communication in the
presence of third parties. We could see a lot of coding and decoding in the
movies; people-spies, military leaders, and criminals always use it to send
messages. However, in recent decades, the field has expanded and more about techniques
for message integrity checking, sender/receiver identity authentications,
digital signatures, interactive proofs and secure computation.
The three types
of Cryptography Algorithms:
Secret Key
Cryptography (SKC): Uses a single key for both encryption and decryption. With SKC,
the key must be known by both the sender and the receiver; that, in practical,
is the secret. The biggest difficulty with this approach, of course, is the
distribution of the key.
Public Key
Cryptography (PKC): Uses one key for encryption and another for decryption. PKC
depends upon the existence of so-called one-way functions, or mathematical
functions that are easy to compute whereas their inverse function is relatively
difficult to compute. [1] A simple example: if I tell you four times nine, you
will easily get 36; but if I tell you 36, you may think about which two numbers
could be for a while.
Hash
Functions: it is also called message digests and one-way encryption, in some
sense, use no key. Instead, a fixed-length hash value is computed based on the
plaintext that makes it impossible for either the contents or length of the
plaintext to be recovered. [2]
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