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Originally Posted by swaghauler
The initial systems used 4-bit, 6-bit, and 8-bit (the most common in the Cold War era) representations for each LETTER in the LINK system. This meant that a 100-letter phrase would need 800 characters to be decrypted and placed in a proper order to read that phrase. Modern systems now use 128-bit encryption PER LETTER!
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This is not quite accurate. A bit means "binary digit". Each bit can represent two states, on or off (1 or 0). A 100 letter phrases encoded as bytes (8 bits per byte) will weigh in at 800 bits, not characters.
Encryption like SAVILLE used is what's called a stream cipher. With a stream cipher a key fed into an algorithm to generate what's called a "key stream". Every bit of input data is combined with a bit of the key stream, usually with an exclusive-OR operation, to get an enciphered bit. A key stream essentially looks like random noise, least it should look like noise, and so long as you feed the same key into that algorithm if you feed in the enciphered bit you'll get the plaintext bit back out.
The size of the key is really describing the periodicity of the key stream. If the key was small, say only 8 bits, you could easily generate all the key streams from every possible key since there's only 256. Assuming your encryption algorithm doesn't have some other mathematical, process, or equipment weakness your key size increases the difficulty of someone trying every possible key. At 128 bits there's more possible keys that atoms in the universe IIRC. So it's not every letter being encoded with 128 bits but some pseudorandom extremely long pattern generated by the 128 bit key.
Quote:
Originally Posted by swaghauler
Thus you will need a computer and special software that can do MILLIONS of operations per second to decrypt Digital Encryption. Therefore this is an IMPOSSIBLE Task to perform.
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If a message is digitally encrypted I would put the difficulty as literally impossible. Unless there's some sort of key a character can get ahold of there's no practical way to crack the encryption. For military gear that means having the encrypted signals and having an intact key loading device and the appropriate encryption equipment. Without all that you'd need a billion years to find the encryption key.