[Review] 3 Main Types of Encryption: Hash, Symmetric, Asymmetric

http://computer-trickster.blogspot.tw/2015/11/encryption.html

Symmetric cryptography

• encrypter, and decrypter — need access to the same key.
• The tricky part is how to store the key and make it available only to the software that needs it.
• Best use:
  1)In services that store encrypted data on behalf of a user (like cloud backup services)
  2)To encrypt computer or device storage(Computer password)
  3)To create a secure channel between two network endpoints, provided there’s a separate scheme for securely exchanging the key

Asymmetric cryptography (public key cryptography)

• known as public key cryptography, uses public and private keys to encrypt and decrypt data.
• Either of the keys can be used to encrypt a message; the opposite key from the one used to encrypt the message is used for decryption.

Hash

• Hashing is used only to verify data
• the same input will always produce the same output
• it’s impossible to reverse it back to the original data
• given knowledge of only the hash, it’s infeasible to create another string of data that will create the same hash (called a “collision” in crypto parlance)
• Three resistance:
  Pre-Image Resistance:
  when: h(x) = z
  hard to find: h(z)-1 = x
• Second Pre-Image Resistance: if a hash function h for an input x produces hash value h(x), then it should be difficult to find any other input value y such that h(y) = h(x).

Reference:

http://computer-trickster.blogspot.tw/2015/11/encryption.html

https://spin.atomicobject.com/2014/11/20/encryption-symmetric-asymmetric-hashing/

http://packetlife.net/blog/2010/nov/23/symmetric-asymmetric-encryption-hashing/