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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 2 years, 9 months
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Oct
31
reviewed Approve suggested edit on monotone-access-structure tag wiki excerpt
Oct
31
answered How to calculate entropy of a combined key
Oct
31
reviewed Approve suggested edit on How to calculate entropy of a combined key
Oct
31
reviewed Approve suggested edit on How are IVs used in association with RSA Encryption?
Oct
31
comment How are IVs used in association with RSA Encryption?
What's funny about using random padding is that we usually encrypt random symmetric keys (as part of hybrid encryption), a scenario where randomness isn't actually required.
Oct
31
reviewed Approve suggested edit on If I have the unencrypted text and the encrypted text, can I calculate the key?
Oct
31
comment If I have the unencrypted text and the encrypted text, can I calculate the key?
This is a "known plaintext attack" and if you use a modern algorithm properly you'll be immune to it.
Oct
31
comment How to develop a public key cryptosystem based on a hard problem?
@DrLecter I didn't say that you need that specific property. But that you need a non trivial mathematical property beyond one-way-ness. Commutativity is one example, many other schemes rely on a trapdoor. The chance that an arbitrary hard to invert function has such a property is very small.
Oct
30
reviewed Approve suggested edit on Are there any differences in operation between existing Diffie-Hellman specifications?
Oct
30
comment How to develop a public key cryptosystem based on a hard problem?
We know many many hard to invert functions, but only a handful of fundamentally different asymmetric encryption/key-exchange schemes.
Oct
30
comment How to develop a public key cryptosystem based on a hard problem?
For asymmetric encryption or key-exchange your system needs lots of mathematical structure. Almost all one-way functions are not suitable. For example with diffie-hellman key-exchange you not only need the property that $A=G^a \mod p$ is hard to invert, you also have the property that $A^b=(G^a)^b = G^{ab} = (G^b)^a = B^a$ i.e. you are able to compute the same shared secret using $A$ and $b$ or $B$ and $a$. Where lowercase letters are private keys and upper case letters the corresponding public keys.
Oct
30
comment How to develop a public key cryptosystem based on a hard problem?
You only described a one-way function so far, something similar to a hash function. You didn't say where the asymmetric component comes in.
Oct
30
comment Why is the hashing (SHA256) specification symbol for rotate S and vice versa?
FIPS-180-x is the official specification. No idea who wrote the document you link to. Perhaps it's a draft predating the final specification.
Oct
30
comment Why is the hashing (SHA256) specification symbol for rotate S and vice versa?
What specification are you referring to? Link? I just took a look at FIPS-180-4 which uses ROTL, ROTR for rotations and SHR, << and >> for shifts.
Oct
30
reviewed Approve suggested edit on Why does the new encryption scheme proposed by authors stop an adversary from guessing the subspace of the secret key?
Oct
30
comment How does the IV or initial counter increase internally for each block in AES CTR mode?
There isn't really a one true CTR mode. There are many different variants of CTR mode which differ by how they compute the per-block input from IV and counter.
Oct
29
comment Making ECDSA public keys one bit shorter
For a fixed generator there cannot be a significant subset of weak keypairs since you could use that to break all of them.
Oct
29
comment How good is using AES CTR mode with initial counter as 0?
One problem with constant IV is that it enables multi-target attacks. When using AES-128 an attacker you can break all messages encrypted with this scheme with $2^{128}$ work and break one random message cost only $2^{128}/t$ for $t$ known ciphertext. So I'd avoid constant IVs with 128 bit keys, but 256 bit keys it doesn't really matter.
Oct
29
comment Deterministic nonces in CTR mode
One problem with constant IV is that it enables multi-target attacks. When using AES-128 an attacker you can break all messages encrypted with this scheme with $2^{128}$ work and break one random message cost only $2^{128}/t$ for $t$ known ciphertext. So I'd avoid constant IVs with 128 bit keys, but 256 bit keys it doesn't really matter.
Oct
28
revised Hi Sec National algorithm
deleted 26 characters in body