SHA, MD5, AES and DES - Usage in brief

We are confused about SHA, MD5, AES, and DES. If we understand these in brief then we can go for depth knowledge.

So I keep it simple....

SHA(Secure Hash Algorithms)/MD5(Message Digest) isn't encryption, it's a one-way hash function.

AES (Advanced Encryption Standard)/DES (Data Encryption Standard)  is a symmetric encryption standard.

One-way hash function -> Document/Data convert to compact digital fingerprint. but you can do the reverse.

Symmetric encryption standard -> Document/Data encrypt and recover as it as by decryption using key.

SHA and AES serve different purposes. SHA is used to generate a hash of data and AES is used to encrypt data

eg.
You are downloading any software binaries, if something goes wrong while downloading then software binaries gets corrupt.
You can now generated the comparable SHA hash (using any number of open tools) for your downloaded data. You can now compare the two hashs to make sure they match - which would validate that the image you downloaded is correct. 

refer below link --
https://en.wikipedia.org/wiki/Md5sum


SHA is used to validate data that was not corrupted. You have every right to see the data in the ISO/exe.

AES, on the other hand, is used to encrypt data, or prevent people from viewing that data with knowing some secret.

Generally we use both SHA/MD5 + AES/DES, to transfer the data. SHA/MD5 is used to validate/authenticate the data, AES/DES to decrypt the data. So data is more secured. 


SNMPv3 is good example for SHA/MD5 and AES/DES.
We will discuss later how to use security in java...