I'm trying to create a "Information Theoretically Secure" cryptosystem, inspired on the One-Time Pad.
Now I'm facing the obstacle of authentication...
How good is this solution (that uses the "Encrypt than MAC" method)? And can this benefit of the "Information Theoretic Security" provided by the OTP?
|| = concatenation OTPKey = (OTPKeyPartForThePlaintext || OTPKeyPartForTheDigest) ciphertext = (plaintext XOR OTPKeyPartForThePlaintext) digest = sha256(OTPKey || ciphertext) encryptedDigest = (digest XOR OTPKeyPartForTheDigest) message = (ciphertext || encryptedDigest)
Thank you :)