# Has anyone invented this type of crytography? Is it even possible? **URL:** \ **Category:** Factual Questions\ **Created:** [May 16, 2012, 11:53am UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079 "2012-05-16T11:53:05Z")\ **Posts on this page:** 8\ **Page:** 2
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [May 16, 2012, 8:43pm UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079/21 "2012-05-16T20:43:39Z")
A simpler implementation would be a decryption program that with a secondary password simply returned gibberish from the encrypted data with the error “Unrecoverable error: Encryption failed, restore from backup.” ---
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [May 17, 2012, 1:37am UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079/22 "2012-05-17T01:37:22Z")
> [@Mangetout](#): > > I think that’s the crunch. You want an encrypted file that unpacks into two different, specific, coherent results depending on the key. > > I think this means something has to get bigger - either the encrypted file (in its simplest form, the data could just be interleaved somehow). Otherwise, the key has to do ‘work’ on the encrypted file, and thus would need to be longer (and in fact would just be part of the encrypted load). > > Compression theory applies here too - you just can’t guarantee to be able to fit twice the normal amount of information in the same container. I could be wrong (this is just a gut feel), but it seems that the resulting file doesn’t necessarily have to be larger but the trade-off is compute time to determine the two transformations with minimal keys that arrive at the desired outcomes. ---
**Author:** ![crypto](https://avatars.discourse-cdn.com/v4/letter/c/b3f665/32.png) [@crypto](https://boards.straightdope.com/u/crypto)\ **Post date:** [May 17, 2012, 3:10am UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079/23 "2012-05-17T03:10:23Z")
This is the **Zodiac** speaking, Maybe I’m not reading this correctly, but isn’t this what PGP essentially did? It made each user have a public key and a private key, so the public key could be compromised without losing the encrypted data. Or are we talking about a way to encrypt data that, if the key is compromised and the data is decrypted, it will in actuality still be hiding the REAL secret message? Sorry if I’ve confused the issue more. I am not sure I’ve understood the OPs requirements. ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [May 17, 2012, 4:48am UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079/24 "2012-05-17T04:48:16Z")
What if you used some kind of palimpsest encryption? Take a file of apparently random noise, a simple image, a musical sample, etc, and apply a password to get a message hidden in the data. Apply another password to THAT and get an even more deeply buried message…ad infinitum. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [May 17, 2012, 7:05am UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079/25 "2012-05-17T07:05:39Z")
> [@Dewey\_Finn](#): > > I think you’re thinking of [steganography](http://en.wikipedia.org/wiki/Steganography), but an expert will notice that the file size is too large to be just a picture and will then attempt to find the hidden data. Not really. Here’s a _very_ simple steganography method for Jpeg that will _reduce_ an image’s size (slightly) and actually improve the image’s SNR! The count of odd coefficients in a Jpeg block will be either even or odd. Concatenate those count parity bits to form the secret message. This might mean the secret is less than 1% the size of the Jpeg file (say, 1 bit per 64 pixels), a problem with all steganography techniques. Starting from the unaltered Jpeg (and having its higher-precision form available for the algorithm), half the blocks will need their odd/even sense flipped to yield the desired secret message. Flip, when needed, whichever coefficient is closest to threshold, so its change will have minimal effect on image quality. In many cases the best flip will be to change a +1 or -1 to zero – a change which will actually improve SNR, though only the best (non-steganographic!) Jpeg compressors take advantage of the idea. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [May 17, 2012, 8:05am UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079/26 "2012-05-17T08:05:38Z")
> [@iamthewalrus\_3](#): > > You’ve invented a threat (loss of data) that cryptography is not intended to solve, and pointed out that it doesn’t solve it. And, in fact, it’s a problem that’s mostly obviated by the fact that encryption doesn’t exist. The solution to losing the only copy of your data is to have backups that the bad guys can’t get to. _Before_ good encryption, it made sense to have only a few copies of sensitive data, and to guard them carefully, since any copy could be leaked and reveal you. If you have strong encryption, then there’s little cost to having a _bunch_ of copies of your secure data. The thing you have to keep secret is the key. > > The problem cryptography is intended to solve is keeping an adversary from finding out the contents of the data. Only a particularly foolish criminal would be dismayed that his data was being deleted in front of him. Once the adversary has your storage medium, you can’t ever trust it again. Furthermore, it would take a particularly foolish adversary to actually delete the only copy they have. You may have backups. If they delete their copy, then all they’ve done is limit their chance to later decode it. I never said that the interrogator destroyed their only copy - they may have destroyed the suspects only copy. People tend to equate _hidden_ with _safe_ - in the case of a hidden partition, this is **not true**. It is also not true of a bunch of other things, like money in a mattress, but people do it all the time. People also do not maintain backups, and are less likely to do so when it takes considerable work, like maintaining encrypted copies. The corollary is also true, multiple copies of encrypted data make it more likely that the data is important. Some people get emotionally invested in their data. Particularly if the data in question is personal and specific and not able to be recovered or represents a great deal of effort. I have heard that in the case of something like child pornography, this attachment to the material can be extremely strong, and can override self-preservation. Encryption is intended to raise the cost of accessing data without the specific key - no encryption is immune from a brute-force attack, but the cost/time of that attack is expected to be higher than the value of the encrypted data. But knowing that there is possible data to be found is often as important as the data itself. And sometimes people reveal more than they intend. Si ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 17, 2012, 8:37am UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079/27 "2012-05-17T08:37:15Z")
> [@RaftPeople](#): > > I could be wrong (this is just a gut feel), but it seems that the resulting file doesn’t necessarily have to be larger but the trade-off is compute time to determine the two transformations with minimal keys that arrive at the desired outcomes. Yes, but only for some cases - in others, the result of the computation will be that _no minimal key is possible_. If it were otherwise, we’d be able to encode any amount of data into a finite space. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 17, 2012, 8:38am UTC](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079/28 "2012-05-17T08:38:46Z")
> [@Enola\_Straight](#): > > What if you used some kind of palimpsest encryption? > > Take a file of apparently random noise, a simple image, a musical sample, etc, and apply a password to get a message hidden in the data. > > Apply another password to THAT and get an even more deeply buried message…ad infinitum. That’s exactly what the OP is asking, but it’s not possible. [Previous page](https://boards.straightdope.com/t/has-anyone-invented-this-type-of-crytography-is-it-even-possible/622079.md?page=1)