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

### 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.
can be used to encrypt a message; the*Either of the keys*from the one used to encrypt the message is used for decryption.*opposite key*

### 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 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).*Second Pre-Image Resistance:*

### 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/