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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 1 month
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2d
comment Asymmetric algorithm for one time signing of small cleartext
What do you mean by "suited"? Standard reusable signatures like ECDSA work well for any message size and cost about 64 bytes. What improvements do you expect?
Aug
28
comment Repeatable crypto
1) AES-SIV 2) convergent encryption AKA message locked encryption AKA content-hash-key (CHK). Be sure to include a convergence secret, to avoid the confirmation and learning the remaining information attacks
Aug
27
comment Is hashing a list of hashes safe?
There is one common pitfall: In hashtrees you often need to tag leaves and inner notes differently, to ensure an unambiguous tree structure. You didn't include enough context to know if this applies to your scheme as well, but I suspect that you need to use different prefixes when hashing a list of hashes and when hashing a plain file.
Aug
27
comment Is using EAX mode with a 64-bit block cipher a bad idea?
@owlstead 1) I don't get your question. In my comment I worry about birthday attacks, and D.W.'s answer confirms that the proof of security breaks down as you approach the birthday bound. So we're saying pretty much the same thing, except that D.W. wasn't too lazy to look at the details. 2) As a software guy, a cipher not being available doesn't enter my considerations. There are so many good ciphers that I certainly wouldn't bother with a 64 bit cipher, unless I specifically want one. For my taste even 128 bit blocks are a bit on the low side, I prefer 256 bit blocks.
Aug
26
comment Are variable-length crypto hash functions still susceptible to collisions?
You don't gain any collision resistance by increasing the output size beyond the capacity. A chain is only as strong as its weakest link, and the link between each consumed block is the capacity.
Aug
26
comment Partial hash code protocol for security tokens providing signatures
One link I found: community.oracle.com/thread/1751753 which mentions an APDU format.
Aug
25
comment Found a way to crack AES-128, what now?
1) Consider implementing it. That way you can be sure you made no mistake and you have evidence that you're not crank. Extraordinary claims require extraordinary evidence. 2) Write a paper using LaTeX typesetting and following proper cryptographic notation and submit it to a conference or journal.
Aug
23
comment Efficiently map $2^n$ unique 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$?
@Jean You can always use a standard hash function, if the number of collisions is acceptable is for you to decide.
Aug
22
comment ECC cryptography with shorter signature when not needing high security?
@owlstead Considering that the academic ECDL record is 113 bits, a 128 curve should be acceptable for license keys. It's generally easier to crack the application, removing the key check than it is to compute that DL.
Aug
21
comment Is this a plausible PBKDF?
@esushi? Why KBKDF? This is clearly password based, not key based.
Aug
21
comment ECC cryptography with shorter signature when not needing high security?
The shortest usable signatures I know are BLS at twice the security level in size. You can truncate a few bits, raising the verification cost exponentially. Even if you'd use a 112 bit curve (which matches the largest academic ECDL break) this only goes down to about 90 bits.
Aug
21
comment Is this a plausible PBKDF?
Please include a compact description using mathematical notation or pseudo code instead of long c code full of unnecessary details.
Aug
20
comment Recover plaintext from truncated ciphertext using AES for FPE
Ending up with the ciphertext equaling the plaintext is not a problem. The probability for that is 1 in 10^19.
Aug
20
comment Recover plaintext from truncated ciphertext using AES for FPE
Read the Feistel network article I linked.
Aug
20
comment Recover plaintext from truncated ciphertext using AES for FPE
You might want to take a look at FFX mode which uses a pretty similar principl.
Aug
20
comment Recover plaintext from truncated ciphertext using AES for FPE
Truncation is not reversible. These truncated values are only used in the Feistel network. The feistel network ensures reversibility even when using a non reversible function.
Aug
20
comment Regular MACs vs Carter-Wegman MAC
WC style MACs need a nonce and leak the key if you ever reuse one.
Aug
20
comment Regular MACs vs Carter-Wegman MAC
AES-GCM is becoming pretty common. Salsa20/ChaChaPoly1305 are are used occasionally as well.
Aug
20
comment A patched SHA1 attempt for password verification
Unsalted SHA-1 is just as crappy a password hash as MD5.
Aug
20
comment A patched SHA1 attempt for password verification
Just send the password in plaintext (over HTTPS/SSL/TLS) to the server and use a proper password hash on the server. It's the job of TLS to protect data in transit, don't try to invent your own crappy hashing scheme instead.