3 ms·

A one time pad must be truly random to be secure. A music stream is far from that.

by chopin 7y ago

oarsinsync 7y ago
'The Nth 4096 bits from this week's mod(N,100) top video on YouTube' Can you tell me what's wrong with that approach? In my head, it seems reasonable.
- backdoorsgalore 7y ago
  You are making two choices here: one out of say 10K and the other out of 100. You'd be lucky to end up with 20 bits of entropy. That can be cracked in a microsecond (exaggerating a bit and/or assuming a distributed data parallel cracking algo on a massive botnet), assuming the data source (youtube) is accessible, and this recipe is known, which it is now since you described it in public.
- chopin 7y ago
  There are recurring patterns in a video or audio stream. More often than not these coincide with recurring patterns in the message, revealing information. For the sake of an example, take some pages of a novel as the one time pad. There will be statistical variations (not all ciphers in the ciphertext come with equal frequency) in the ciphertext, where the combination ocuring most will correspond to an "e" in the plain text and an "e" in the one time pad because both occur most often in English language. You can calculate the probabilities for each combination and thus deduce the plain text provided it is long enough. For a one time pad to be secure it must be truly random or pseudo-random. As a way out you can agree to a seed to a secure pseudo random algorithm but that's commonly called a password or pre-shared secret. In fact it's more secure to use just the string 'The Nth 4096 bits from this week's mod(N,100) top video on YouTube' as pre-shared secret.
  - backdoorsgalore 7y ago
    Right, but "truly random" or "pseudo random" won't matter for decoding if the 4096 can be guessed by brute force. A video file has at most tens of thousands of 4096 blocks, and he'd be picking from 100 of top videos on youtube at a known approximate date range. That's nothing as far as entropy goes.... 20-something bits.
Taniwha 7y ago
The LSB are pretty close to this (unless it's Cage's 4'33)
- chopin 7y ago
  Maybe, but I wouldn't want to rely on it. I don't know anything about real world music encodings but for the analog signal you have zero-crossings at fairly regular intervals.

A one time pad must be truly random to be secure. A music stream is far from that.

by chopin 7y ago

A one time pad must be truly random to be secure. A music stream is far from that.

'The Nth 4096 bits from this week's mod(N,100) top video on YouTube' Can you tell me what's wrong with that approach? In my head, it seems reasonable.

backdoorsgalore 7y ago
You are making two choices here: one out of say 10K and the other out of 100. You'd be lucky to end up with 20 bits of entropy. That can be cracked in a microsecond (exaggerating a bit and/or assuming a distributed data parallel cracking algo on a massive botnet), assuming the data source (youtube) is accessible, and this recipe is known, which it is now since you described it in public.
chopin 7y ago
There are recurring patterns in a video or audio stream. More often than not these coincide with recurring patterns in the message, revealing information. For the sake of an example, take some pages of a novel as the one time pad. There will be statistical variations (not all ciphers in the ciphertext come with equal frequency) in the ciphertext, where the combination ocuring most will correspond to an "e" in the plain text and an "e" in the one time pad because both occur most often in English language. You can calculate the probabilities for each combination and thus deduce the plain text provided it is long enough. For a one time pad to be secure it must be truly random or pseudo-random. As a way out you can agree to a seed to a secure pseudo random algorithm but that's commonly called a password or pre-shared secret. In fact it's more secure to use just the string 'The Nth 4096 bits from this week's mod(N,100) top video on YouTube' as pre-shared secret.
- backdoorsgalore 7y ago
  Right, but "truly random" or "pseudo random" won't matter for decoding if the 4096 can be guessed by brute force. A video file has at most tens of thousands of 4096 blocks, and he'd be picking from 100 of top videos on youtube at a known approximate date range. That's nothing as far as entropy goes.... 20-something bits.

Taniwha 7y ago

The LSB are pretty close to this (unless it's Cage's 4'33)

chopin 7y ago
Maybe, but I wouldn't want to rely on it. I don't know anything about real world music encodings but for the analog signal you have zero-crossings at fairly regular intervals.