1. Message is not encrypted and just obfuscated by random string which is seeded by known public key. Quite low confidentiality.

2. This is symmetric encryption approach. K1 and K2 need to be privy as preshared key with R to make sure no leak of information. So the key exchange need to be strong to ensure the encryption is not compromise revealing "x". The encryption can be fast and for bulk encryption.

3. This is similar to (2) but asymmetric approach is used for digital signature. It would be stronger than (2) but can be slow so normally for shorter "x".

4. Normally for mass user mailing list to send encrypted message. Each user's asymmetric keyset allows more users to be appended using the same symmetric key for encrypting "x". However the end result cryptogram can be huge. Like SMIME.

Overall as long as there is encryption and signature of message, the CI and NR is maintained. It is just a matter of cipher algorithm strength and its keysize used to determine strength level. The A does not really play a big part in the example so far as I see it.. Hope this help.

2. This is symmetric encryption approach. K1 and K2 need to be privy as preshared key with R to make sure no leak of information. So the key exchange need to be strong to ensure the encryption is not compromise revealing "x". The encryption can be fast and for bulk encryption.

3. This is similar to (2) but asymmetric approach is used for digital signature. It would be stronger than (2) but can be slow so normally for shorter "x".

4. Normally for mass user mailing list to send encrypted message. Each user's asymmetric keyset allows more users to be appended using the same symmetric key for encrypting "x". However the end result cryptogram can be huge. Like SMIME.

Overall as long as there is encryption and signature of message, the CI and NR is maintained. It is just a matter of cipher algorithm strength and its keysize used to determine strength level. The A does not really play a big part in the example so far as I see it.. Hope this help.