Reputation
13,641
Next tag badge:
99/100 score
17/20 answers
Badges
1 34 70
Impact
~260k people reached

Apr
27
comment Are more S boxes more secure in a SP-Network?
1) The increased pressure on the CPU cache might be more expensive than what you gain from being able to reduce the number of rounds. 2) You can't add special s-box instructions to the CPU if there are many sboxes (see AES-NI)
Apr
27
comment Can cycle finding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?
Working on a prototype implementation, I noticed that my assumptions about how iterated hashes cycle were wrong. I didn't know that a few cycles and their tails dominate.
Apr
26
comment Can cycle finding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?
You can't just equate the number of operations with time, you also need to take parallelism into account. (And DJB argues that you can't neglect the cost of memory access circuitry for many attacks either.) With cycle-finding I'd expect the cost of memory to be cheap compared to the cost of all those parallel DES computation circuits. For example such a computer might have ~4 GB of memory and $2^{20}$+ DES circuits, running for ~$2^{36}$ timesteps (where each timestep is one DES invocation).
Apr
26
reviewed Approve Can cycle finding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?
Apr
26
reviewed No Action Needed If you hashed a hash an infinite number of times would you end up with a unique hash?
Apr
26
reviewed No Action Needed Password length versus hash length?
Apr
26
reviewed No Action Needed Key iteration count while using random keyfile larger than master key
Apr
26
comment Can cycle finding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?
1) In the simplest case we could truncate. If we need a tweak to repeat the whole experiment with a different hash function (not sure if that's required) we can use any kind of tweakable hash (preferably a cheap one) 2) I don't think the block-size matters at all with most modes of operation (including ECB, CBC and CTR). We simply need a long enough known plaintext/ciphertext pair.
Apr
26
comment Why does applying 56-bit DES twice only give 57 bits of security?
@fgrieu I originally planned to verify the technique experimentally with small keys before posting about it, but since I don't have the time for that at the moment, I've asked it as a question: Can cycle findinding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?
Apr
26
asked Can cycle finding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?
Apr
25
revised SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)
added 185 characters in body
Apr
25
comment SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)
@EvgeniVaknin Depends on the hardware. AES will probably be faster than SHACAL-2 on most processors. But on processors without AES-NI the difference will be smaller than the ratio of the number of rounds. You also need to keep in mind that a hash gives an attacker much more control over the inputs, so the same block cipher might need more rounds when used as hash compared to being used as encryption.
Apr
25
revised SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)
added 121 characters in body
Apr
25
comment SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)
You can use AES to build a secure MAC (CBC MAC and its derivatives). Unlike your suggestion, these constructions use AES with a random key, which the attacker doesn't know.
Apr
25
answered SHACAL-2 vs. AES as underlying block cipher for Secure Hash (aka SHA-256)
Apr
25
comment Why can't I use ECB with some obfuscation for transient RAM?
Why not do it properly? XTS mode is similar to your idea (it combines the address with the data), but actually secure.
Apr
25
reviewed Reviewed Encryption of plain text using stream cipher algorithm
Apr
25
reviewed No Action Needed Does SRP reduce to DH key exchange when shared password is not secret?
Apr
24
comment Prime factorization
@tylo GNFS depends on the size of the number. But some other algorithms like ECM depend on the size of the smallest factor. If your factors are small enough so that ECM is faster, then the cost will depend on the size of the factors. If all the factors are big enough so that GNFS is faster, the size of the factors doesn't matter.
Apr
24
comment Prime factorization
Since factoring a 512 bit semiprime costs about $100, it's clearly more than a standard computer can do in a few hours. Your number has 392 bits, so factoring would be relatively cheap, but I don't know if it'd fall below your limit. If the number has small factors, ECM should be faster than GNFS.