Cryptographic hash function is an algorithm that takes block of data of arbitrary length as an input and output a short fixed length sequence of bit (usually 128 ~ 256 bits) and which ideally should have following four properties.
- It is very easy to compute the hash value for any message.
- It is infeasible to generate a message that has given hash data
- It is infeasible to modify a message without changing the hash
- It is infeasible to generate two different messages with the same hash
Cryptographic hash function is one-way functions to compute its value easily but it is technically impossible to get the original message back that has given hash value.
Java supports the most popular cryptographic hash functions as below:
- MD5
- SHA-1
- SHA-256
- SHA-384
- SHA-512
Symmetric key algorithms are algorithm for cryptographic that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext.
Block cipher mode
- DES (64 bits)
- Triple DES (64 bits)
- AES (128 bits)