Encryption is the process of encoding data into a form that cannot be understood by unauthorized users. Sensitive data stored in the device should be encrypted to preserve its security. You can encode data to save it as shared preferences, as files in the internal storage, in databases, or even in external storage. But you should remember that sensitive data must not be stored on external storage. There are two types of encryption methods:
Symmetric: In symmetric encryption, the keys for encoding and decoding are the same. Some examples of well-known symmetric algorithms are DES, Triple DES, AES, Serpent, Twofish, and Blowfish.
Asymmetric or public-key: In asymmetric or public-key encryption, the key for encoding is different from the key for decoding. The encryption key can be public and hence, anyone can encode data using the public key. But only the owner of the private key is able to decode it. Some examples of well-known asymmetric algorithms are RSA, Diffie-Hellman, ElGamal...
