[benwilber0]

Not exactly "innovative", since it's one of the oldest encryption methods, but the One-Time Pad[0] is considered "perfect encryption" and proven to be unbreakable. The mere possibility of unbreakable encryption could fill up a thesis by itself.

[0] http://www.cs.utsa.edu/~wagner/laws/pad.html

<strike>edit to clarify: "unbreakable" is the wrong word, since it could be brute-forced with enough time and energy, like any encryption method.</strike>

yes it is completely unbreakable.

[kabdib]

No, one-time pads are really unbreakable. You can't tell if the key you generated, which yielded "ATTACK AT DAWN", decrypted to the real message. It might have been "HN != SLASHDOT" -- all decrypts are equally likely.

[benwilber0]

edited thanks. he even explicitly said that it was unbreakable in the article I linked :-).

[mseebach]

The problem, of course, is that you're just flipping the problem around. For every bit you need to send A->B, you need to first securely send a bit B->A (the pad). That's practical for a number of applications, and obviously not for many others.

[sounds]

Combined with envelope keys it can be effective for many applications.

An envelope key is a securely, randomly generated key used to encrypt the large payload. Then the envelope key (much smaller than the payload) can be encrypted using a one time pad.

The result is that the precious bits of encryption provided by the one time pad are used up at a predictable rate.

Guessing the envelope key is more probable than guessing the one time pad key, but that only breaks a single message's encryption.

[Someone]

If you use good encryption and a reasonable key size, that’s good in practice, but theoretically, that’s a lot less secure than a one time pad.

An attacker can ‘simply’ try all possible keys and use statistics to filter out those that look like natural language.

If the encrypted text is large enough, chances are you will be left with only one plausible plaintext.

Also, AFAIK, we don’t know whether good encryption using a key much shorter than the plaintext, in the sense that an attacker can’t use statistics on the encrypted text to learn something about the key, exists at all.

[sounds]

Your final aside, "good encryption using a key much shorter than the plaintext," is something I hadn't really thought much about and seems like a reasonable way to go directly from a one time pad to the ciphertext.

As you say, there doesn't seem to be a way to guess the key length from the ciphertext. Ignoring side channel attacks for the moment, it does seem like the one time pad could encrypt the entire message simply by using some clever way of "extending" the key.

[mseebach]

> it does seem like the one time pad could encrypt the entire message simply by using some clever way of "extending" the key

Any way of meaningfully extending the key will be vulnerable to a kind of analysis well understood 70 years ago.

This is basically what almost the entire field of cryptography is about: Figure out how you can effectively and securely encrypt things with a key that's a lot shorter than your cleartext.

[Someone]

Indeed. The two simplest examples are the Caesar cipher (https://learncryptography.com/classical-encryption/caesar-ci..., key length of 1 character) and the Vigenère Cipher (https://learncryptography.com/classical-encryption/vigenere-..., key length as long as you want it to be)

Both extend the key by repeating it. That is not a good idea.

[ISL]

I don't believe that it can be brute forced, as brute-forcing may yield multiple reasonable decryptions with conflicting interpretations.

[hawski]

I was wondering if using randomly generated shared 1GB or so file as a kind of one-time pad would be useful. Xor data with it using it as circular buffer, do messages must be of the same length or it will go out of sync.

[mseebach]

If you reuse your pad, you're vulnerable to frequency analysis, which is literally the oldest trick in the book. You might as well send in plaintext.

[hawski]

How easy would it be if you would go through the entire 1GB and only then from the beginning? I guess it is a question of how big messages are.

[mseebach]

If you're only reusing it once, then I guess frequency analysis gets tricky, but the problem you have instead is that you have provided a validation function: Where, using a one-time-pad, any key that yields plausible cleartext is a possible candidate, if you have two cyphertexts encoded with the same (piece of) the one-time-pad, only keys that result in plausible decrypted cleartext for both cyphertexts are possible candidates.

This was how an early break-through in breaking the Enigma was achieved (tangentially, as the Enigma isn't a one-time-pad, but the analysis is similar): Codes were rotated daily, but the first message sent out every morning with the new codes was a weather-report. Thus, the team could immediately cull the search-space to keys that would decrypt to "Weather on [date]" for the first n characters.

[vectorEQ]

this is the only fully 100% proven crypto method. rest is 'weak' , only saved by lack of computing power, not actual difficulty of algorithm. problem with otp is dat if you can send the pad... you mightswell not use it. as the pad needs to be sent over secure channel. So it's unbreakable, but also impractical.