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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 3 months
seen 6 hours ago

Nov
21
revised Applying differential cryptanalysis to ciphers with addition mod $2^{32}$
edited title
Nov
21
comment Authentication of machine before installation (to stop piracy)
This isn't about crypto. At best it's about security, but even there it's security-through-obscurity.
Nov
21
comment Authentication of machine before installation (to stop piracy)
An attacker can always rewrite the client and remove the the check.
Nov
21
comment When using Curve25519, why does the private key always have a fixed bit at 2^254?
Sorry but I still don't get it. 1) The actual code starts with $P$ and $\infty = (x=1,z=0)$ 2) Why does the code not work if it always starts the ladder at bit 254, but that bit happens to be 0? 3) Your Montgomery ladder link is dead
Nov
21
reviewed Approve suggested edit on hill cipher encryption way 1x3 plaintext matrix
Nov
20
comment When using Curve25519, why does the private key always have a fixed bit at 2^254?
That this answer is tautological. I read the paper including those paragraphs and still Why does having a fixed position for the leading 1 improve performance? I didn't notice an algorithm in the code that relies on this bit being set. Does the code produce incorrect results if this bit is wrong?
Nov
20
reviewed Approve suggested edit on How to prove this LFSR equation?
Nov
20
reviewed Approve suggested edit on hybrid PKE scheme CCA2 insecurity
Nov
20
revised How can I implement the elliptic curve MOV attack myself?
added 20 characters in body
Nov
18
comment Why not just generate random strings for one-time password (OTP)?
Your idea has been used for online banking. My bank used to send me a list with 100 single-use TANs. Then for each transaction ask for one of them.
Nov
18
comment Efficient parameters for group Diffie-Hellman
@poncho Could you describe how to use that oracle to break CDH?
Nov
18
answered Efficient parameters for group Diffie-Hellman
Nov
18
comment Efficient parameters for group Diffie-Hellman
@daniel How would you do that? multiplying public keys translates to addition in the exponent.
Nov
18
comment Efficient parameters for group Diffie-Hellman
@RickyDemer It's large enough to make group DH annoying since you need one round of communication for every member in the group.
Nov
18
comment Efficient parameters for group Diffie-Hellman
You'd need to compute $K^{(a^{-1})}$. Only those who hold the private key $a$ can do this. Multiplying with $(g^a)^{-1} = g^{-a}$ would subtract $a$ from the exponent, not divide the exponent by $a$.
Nov
14
comment Elliptic Curve Encryption Ciphertext Size
Depends on the details of the ECIES implementation. The overhead is one ECC point. For example with an 256 bit curve (offering 128 bits of security) and compressed points the overhead would be 32 bytes. With uncompressed points you need 64 bytes. Often you'll lose a bit more for headers. The symmetric encryption might cost a bit as well for padding or MACs.
Nov
14
comment Are there any bijective one-way functions not based on number-theoretic hardness assumptions?
I don't understand the details of your suggestion, but it seems very unlikely that you can obtain a function that's both hard to invert and bijective like that.
Nov
14
comment Any real world implementation using message recovery?
@DrLecter Even when using a hash as part of the signature one could put the (beginning of the) message into the remaining space.
Nov
14
comment Could MITM securely identify identity?
You could simply run a key-exchange between alice's long term key and the FW's key and use it to authenticate the ciphertext with a MAC based on the shared key. No need for MitM, decryption, etc. Essentially as a wrapper around these protocols.
Nov
14
reviewed Approve suggested edit on Why have 4th and 5th steps in Needham-Schroeder Protocol?