Adequate encryption?

[robbiegregg]

Hi

I would like to be able to encrypt a double precision number and then save it to a binary file. Does anyone know whether or not it is secure to encrypt individual numbers? I'm guessing it is far more safer to encrypt a larger block of data.

Cheers
Robbie

[cilu]

Of course. It doesn't make sense to encrypt a single number. If you want to do something at "number" level, mingle the bits. For instance switch bit 34 with 6, 8 with 9, 9 with 10, 10 with 1, XOR bits 45, 21 and 51, etc.

[Marc G]

That's also why most encryption algorithms use blocks of data. When a block is not filled they often require you to pad the data with some padding byte to ensure 1 block.

[hoxsiew]

It all depends on what you are trying to accomplish. A stream cypher like RC4 would work but might be overkill. A simple XOR with a static password might be sufficient. 8 chars is 64 bits. memcpy or cast your double to char and XOR character-wise:

  double d=3.14159265;
  unsigned char *p,pw[]="abcdefgh";

  p=(unsigned char *)&d;

  for(int i=0;i<8;i++){
    p[i]^=pw[i];
  }

To decrypt, just run it through again.