Types of Cryptography
Symmetric Key Cryptography
Symmetric, or secret key, cryptography is where you use the SAME
"key" (think of this as a mathematical formula) to both encrypt and
decrypt data. This is the kind of cryptography used in WW-II, where
code was "cracked" by the enemy so confidential information about
troop movements could be gathered
To summarize Symmetric Key Cryptography
Assuming to users Bob and Alice, if Bob wants to send
Alice
an encrypted
messages · Bob has one secret key · If Alice wants to send Bob a
secret message · Bob Sends Alice a copy of his secret key ·
Alice
encrypts message
with Bob's secret key · Bob decrypts message with his secret key
Problems:
1.How does Bob get secret key to Alice?
2.What if Alice is a
double agent?
3.What if Alice, Bob, Charley, & Dan need to
exchange messages? Need n! Keys
With single-key cryptography you have the problems of how to
share the secret key -- how does Bob get the secret key to
Alice
safely, and of
managing a large number of secret keys. Moreover if too many people
share the same secret key, then if even one of them is bad, a mole,
all messages are compromised. So A Better method: Public Key
Cryptography
Asymmetric Key (Public Key) Cryptography
In public key cryptography, a public and private key are created
simultaneously using the same algorithm (a popular one is known as
RSA) by a certificate authority (CA). The private key is given only
to the requesting party and the public key is made publicly
available (as part of a digital certificate) in a directory that all
parties can access. The private key is never shared with anyone or
sent across the Internet. You use the private key to decrypt text
that has been encrypted with your public key by someone else (who
can find out what your public key is from a public directory). Thus,
if I send you a message, I can find out your public key (but not
your private key) from a central administrator and encrypt a message
to you using your public key. When you receive it, you decrypt it
with your private key. In addition to encrypting messages (which
ensures privacy), you can authenticate yourself to me (so I know
that it is really you who sent the message) by using your private
key to encrypt a digital certificates. When I receive it, I can use
your public key to decrypt it
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