Detecting and preventing tampering

We can use steganography to assure that our message isn't tampered with. If we can't find our digital watermark properly encoded, we know that our picture was touched. This is one way to detect tampering. A more robust technique to detect tampering is to use hash totals. There are a number of hash algorithms used to produce a summary or signature of a sequence of bytes. We send both the message and the hash code separately. If the received message doesn't match the hash code, we know something went wrong. One common use case for hashes is to confirm a proper download of a file. After downloading a file, we should compare the hash of the file we got with a separately published hash value; if the hash values don't match, something's wrong with the file. We can delete it before opening it.

While it seems like encryption would prevent tampering, it requires careful management of the encryption keys. Encryption is no panacea. It&apos...