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1

Vigenere matches the description, though its security problems when the key is shorter than the message are well known.


-1

I call an algorithm meeting this spec "rolling xor". It's only strong at the one-time-pad level though.


9

Examining his claims about "Thundercloud": You can use it with "any existing software, operating system, or device" (a massive amount of effort---by whom?) Has its "own cryptographic language that is completely independent of any existing security technology" (this is a negative thing: abandoning the entire knowledge base of cryptography is incredibly ...


1

Yes, he is full of crap. If you go to KeyLength, you can compare key lengths for different cryptosystems and see how long they're expected to be secure for. It's just a performance vs security tradeoff that implementers make. Most people don't see the point in schlepping around megabytes of key material for cryptosystems that are expected to be secure ...


0

Use Keylength.com There are several metrics that try to estimate for how many years a given keylength may last you. The length calculator at Keylength.com (http://www.keylength.com/en/compare/ ) uses eight such heuristics to give you a general idea which size you should choose. You can go both directions. You can either enter a year and receive a ...


0

No, that's not possible because of the reasons given in the other answer. Unless the block size is linked with the key size, or if the cipher is not cryptographically secure, you should not be able to find out the key size by just looking at the ciphertext. This is true even if you know the algorithm. Note that this does not take side channel attacks into ...


1

First, note that $192=3\cdot64$, so the real key length of 3DES is $192$ bits. However, since $8$ bits in each subkey are parity bits, this reduces to $3\cdot56=168$ bits of non-redundant key material. Now, the reason that 3DES' effective key length is usually classified as $2\cdot56=112$ bits is that 3DES is susceptible to a meet-in-the-middle attack: When ...


1

DES has been specified to take a 64 bit key, but only 56 of them are used. The remainder are parity bits. The key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits For 3DES the nominal key ...


0

Something that might bite is that the ASN encoding requires the numbers to be positive. So when a 2048-bit random prime happens to have a '1' as the first bit, it is prefixed with a byte of 0 to make it positive. This means half of your 2048-bit primes are 256 byte and the others are 257 bytes.



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