Stream CiphersWith symmetric key, we use the same key to encrypt and to decrypt. The most popular symmetric key methods are AES and ChaCha20. In its pursest form, AES is a block cipher, with 128-bit block sizes. Unfortunately block ciphers can be slow, as they require the processing of a block of data. In a stream cipher, we basically create a key stream which is then EX-ORed with the plaintext stream. To decrypt, we basically just do the same, and EX-OR the cipher stream with the key stream. With a block cipher we need padding, and there is no padding required for a stream cipher. Overall, stream ciphers are generally faster in their operation, and often require less processing.
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