I am new to cryptography, I have used OpenSSL and its
aes-256-cfb cipher before to do stream encryption, which works great. Now I am going to try
libsodium, since it's light and its APIs look concise, but I can't get it working.
I tried its
XChaCha20 stream cipher, but it only has the
crypto_stream_xchacha20_xor_ic functions, I can easily encrypt and decrypt messages when the message lengths appear in pairs, like encrypting 20 bytes, then decrypting 20 bytes, this works fine. but it will fail if encrypting 20 bytes, then decrypting 10 bytes and decrypting 10 more bytes. The latter case is what I want, I am implementing a proxy, I would like to read random length (i.e. not in blocks and no boundaries) of data from one TCP connection, encrypt and stream the data through another TCP connection, the other end of the connection reads random length of the encrypted data and decrypts it.
For what I want,
xoring my data wouldn't work, since there's no
context object like OpenSSL's
EVP_CIPHER_CTX and no information like how many bytes have been encrypted/decrypted is kept, this looks weird to me, if it doesn't support this kind of stream mode, why is it called a stream cipher?
My question: Is it possible to do what I want using libsodium, if so, how?