Notice: I'm doing this to learn. I know not to use a homemade cipher for anything that requires security. I also have heard before I'm not supposed to be trying this, but I learn best through trying to make things from scratch, even if I fail.
Ciphers are incredibly complex, to the point most people probably don't appreciate them, myself included. Trying to make one from scratch might help with this, so I'm looking for a list of qualities/achievables that can be worked towards for years to come.
This is the list so far, for a good block cipher at different learning levels:
- Encrypted output can not be broken by hand. The level of encryption during WW1 or so.
Changing a single bit in the input should have a 50% average chance of changing each bit of output.
Each byte should have a 1/256 chance of not changing (basically #1 ^ 8)
The number of bytes found in similar by search should be very few (I need to write down the math, but my estimate is around 5%)
- Not sure yet?
- Immune to Differential cryptanalysis?
This list is very incomplete, but gives an example of what I'm looking for.
What is your list of achievable qualities for block cipher at different skill levels?