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I don't understand what you're saying. Brute force is always possible. Succeding is only a matter of time. Suppose you find the password for one of those files,

by dewiz 13y ago

I don't understand what you're saying. Brute force is always possible. Succeding is only a matter of time. Suppose you find the password for one of those files, then you would be able to decrypt all your ransom data. When it comes to recovering your data, you might be ready to have a brute force running for long long long time 😊

spiffytech 13y ago
Technically, if the universe went on forever, yes, you could brute force AES. However, with a well-chosen key (i.e., 256 random bits, and not merely a weaker password that was expanded into a 256-bit key), the odds are pretty decent that all life in the universe will end before you guess the key. A listener to Security Now wrote in to episode 340 with this for perspective: I took 256-bit encryption and assumed that the only way to crack it was, as we currently believe, a brute-force attack against the 256-bit key. ... So let's say the tricksy government has a secret algorithm that somehow allows them to weaken the strength to one trillionth of the original. That's a good number, one trillionth. And let's say they had a computer that can try 100 trillion guesses per second. And let's say this computer was one cubic millimeter in size, and let's say they build a cracking complex the size of the entire Earth made out of these one cubic millimeter crypto cracking computers. If I did my math right, it would still take 34 trillion years to crack. I've double-checked the math, that's how long it takes to exhaust the 256-bit keyspace, even in an unreasonably-generous scenario. You could halve that time to get the average time it takes to find any given 256-bit key, since you won't, on average, have to search the entire key space. We trust AES 256 because, as long as the algorithm is sound, it is actually impossible to brute-force in any useful time frame, for even insane definitions of "useful". Even in some scenarios where the algorithm isn't sound, as above, it's still impossible. The author of BitCrypt didn't use AES 256, however. They used AES 192, which is drastically weaker. According to the same calculations, it would take 0.00067 days to brute-force an AES 192 key. With a planet-sized cracking machine, impossibly fast computers, and a substantially weakened algorithm. However, it gets better - the author of BitKeeper didn't actually choose a 256-bit key, they chose a 16-character password that was expanded into a key, and that's what we can crack to decrypt an individual BitCrypt file. In our hypothetical (yet unrealistic) scenario, this can be done in under a second. So: brute-forcing well-implemented AES (good key, good key length) is impossible, no matter how you slice it. Brute forcing AES with a questionable key length is still impossible with anything remotely resembling the technology we'll see in our lifetimes. Brute-forcing a file encrypted by low-quality malware is absolutely possible, as the article shows :)

by dewiz 13y ago

spiffytech 13y ago

Technically, if the universe went on forever, yes, you could brute force AES. However, with a well-chosen key (i.e., 256 random bits, and not merely a weaker password that was expanded into a 256-bit key), the odds are pretty decent that all life in the universe will end before you guess the key. A listener to Security Now wrote in to episode 340 with this for perspective: I took 256-bit encryption and assumed that the only way to crack it was, as we currently believe, a brute-force attack against the 256-bit key. ... So let's say the tricksy government has a secret algorithm that somehow allows them to weaken the strength to one trillionth of the original. That's a good number, one trillionth. And let's say they had a computer that can try 100 trillion guesses per second. And let's say this computer was one cubic millimeter in size, and let's say they build a cracking complex the size of the entire Earth made out of these one cubic millimeter crypto cracking computers. If I did my math right, it would still take 34 trillion years to crack. I've double-checked the math, that's how long it takes to exhaust the 256-bit keyspace, even in an unreasonably-generous scenario. You could halve that time to get the average time it takes to find any given 256-bit key, since you won't, on average, have to search the entire key space. We trust AES 256 because, as long as the algorithm is sound, it is actually impossible to brute-force in any useful time frame, for even insane definitions of "useful". Even in some scenarios where the algorithm isn't sound, as above, it's still impossible. The author of BitCrypt didn't use AES 256, however. They used AES 192, which is drastically weaker. According to the same calculations, it would take 0.00067 days to brute-force an AES 192 key. With a planet-sized cracking machine, impossibly fast computers, and a substantially weakened algorithm. However, it gets better - the author of BitKeeper didn't actually choose a 256-bit key, they chose a 16-character password that was expanded into a key, and that's what we can crack to decrypt an individual BitCrypt file. In our hypothetical (yet unrealistic) scenario, this can be done in under a second. So: brute-forcing well-implemented AES (good key, good key length) is impossible, no matter how you slice it. Brute forcing AES with a questionable key length is still impossible with anything remotely resembling the technology we'll see in our lifetimes. Brute-forcing a file encrypted by low-quality malware is absolutely possible, as the article shows :)