在ANSI C中加密，在Java中解密

Question

I have to send a short string from ANSI C application to Java application through a socket - already done. Because its important data I have to encrypt it using password like "abc123". How should I do it in the simpliest way?

Answer 1

As mentioned it depends very much on how secure you want this to be, the sensible answer is to find a Java and C implementation of the same cryptosystem and use those.

If you are willing to accept the lower security that usually comes with home brewing these things which I assume you are by the "simplest way" in your question and assuming both the source and runtime for both ends are secure. IE you only need to worry about the data in transit being intercepted. You could just use whatever password you desire as a seed for a pseudo random number generator (remainder of dividing a large prime by the byte index or similar) and XOR the bytes of data with the random numbers generated. Not the most secure but would be very quick to implement.

uint8_t encrypt(uint8_t iData, size_t iPos) {
  // Super large prime, our 'password', best kept super secret
  const uint64_t iSeed = 32416190071; 
  // Mostly to stop divide by zero
  // Also starting in the obvious place gives more info on the prime
  const size_t iOffset = 10;

  uint8_t iPad = iSeed % (iPos + iOffset);

  return iPad^iData;
}

Answer 2

By "socket" I assume you mean a TCP/IP connection. In that case you should consider using Secure Sockets Layer (SSL). SSL pretty much solves most of the security problems associated with sending data across the wire. The only thing you need to work out is how to distribute keys to each end of the pipe.

I strongly recommend that you don't roll your own system. Crypto is hard to get right so use an existing, well tested implementation.

If you're talking about a Unix domain socket then you probably don't need to bother with encryption since domain sockets are just inter-process pipes.

Answer 3

Char encrypt(char ch) {
 Return (ch ^0x55);
}