Write a C program Implement counter mode using perm384bc. The user will supply a nonce that is a buffer of 12 bytes, a key that is a buffer of 32 bytes, and both a source and destination buffer that are nbytes long. Here are some implementation suggestions.
- Auto-allocate on the stack two 48-byte arrays, one to hold your counter block and one to hold your perm384bc output.
- Initialize your counter block to begin with your 12-byte nonce followed by 36 bytes of zero.
You can then loop doing the following each iteration until nbytes becomes zero.
- increment your block
- use perm384bc with your block as input and your buffer as output
- xor min(48, nbytes) bytes of the buffer with your source and write the result to your destination
- move your source and destination pointers forward by the number of bytes you just wrote
- decrement nbytes by the number of bytes you just wrote