Stream Ciphers

Stream ciphers provide only confidentiality. Data integrity and authenticity is not guaranteed. Users should use AEAD ciphers whenever possible.

The following stream ciphers provide reasonable confidentiality.

Name	Key Size	IV Length
aes-128-ctr	16	16
aes-192-ctr	24	16
aes-256-ctr	32	16
aes-128-cfb	16	16
aes-192-cfb	24	16
aes-256-cfb	32	16
camellia-128-cfb	16	16
camellia-192-cfb	24	16
camellia-256-cfb	32	16
chacha20-ietf	32	12

The following stream ciphers have inherent weaknesses (see discussion at #36). DO NOT USE. Implementors are advised to remove them as soon as possible.

Name	Key Size	IV Length
bf-cfb	16	8
chacha20	32	8
salsa20	32	8
rc4-md5	16	16

Stream Encryption/Decryption

Stream_encrypt is a function that takes a secret key, an initialization vector, a message, and produces a ciphertext with the same length as the message.

Stream_encrypt(key, IV, message) => ciphertext

Stream_decrypt is a function that takes a secret key, an initializaiton vector, a ciphertext, and produces the original message.

Stream_decrypt(key, IV, ciphertext) => message

The key can be input directly from user or generated from a password. The key derivation is following EVP_BytesToKey(3) in OpenSSL. The detailed spec can be found here: https://wiki.openssl.org/index.php/Manual:EVP_BytesToKey(3)

TCP

A stream cipher encrypted TCP stream starts with a randomly generated initializaiton vector, followed by encrypted payload data.

[IV][encrypted payload]

UDP

A stream cipher encrypted UDP packet has the following structure

[IV][encrypted payload]

Each UDP packet is encrypted/decrypted independently with a randomly generated initialization vector.