"the threat model was looking at observing text, not changing it." Encryption aims to provide not just confidentiality but also integrity and authenticity. Thr

"the threat model was looking at observing text, not changing it." Encryption aims to provide not just confidentiality but also integrity and authenticity. Three guesses what the integrity means. "I haven't heard about anybody making things tamper-proof from a government that has got your keys." Ok seriously reconsider taking a course or two on cryptography before venturing any further. The malleability of Vernam ciphers like stream ciphers and OTP -- even when the attacker is not in possession of the key -- is a well known thing. "if you have 3, 4, 5, horcruxes, then they would still all need to cooperate to get the messages in order to do this perfect XOR" Nope. It's enough they change one of the ciphertext parts if they can guess the plaintext for whatever reason. This is known as a known plaintext attack or KPA. You should address it as part of your scheme, look into one-time MACs and Carter-Wegman MACs.