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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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Mar
13
comment Which eliptic curves in OpenSSL 1.0.1f meet all / most of the SafeCurves requirements?
Apart from rigidness those "weaknesses" are features of montgomery/edwards curves. Those features don't gain you anything if you use weierstrass form in your implementation.
Mar
13
comment Are there use cases where a signature itself needs to be signed?
@JohannesErnst I'd rather encapsulate it, like {data={...}, sigs=[{sig1}, {sig2}]}. If one signature needs to be signed, the outer signature can encapsulate the previous one, else add them to the array.
Mar
13
comment Are there use cases where a signature itself needs to be signed?
You should take a look at JSON Web Signature (JWS). I didn't read it myself, so I can't vouch for its quality.
Mar
13
revised Why does SHA-1 have 80 rounds?
added 149 characters in body
Mar
13
comment counter to indicate hotp count
@RichieFrame Shouldn't matter.
Mar
13
comment How do I convert the definition of E-521 into a curve definition a la Bouncy Castle?
I'd rather start with a Curve25519/Ed25519 and replace the field arithmetic operations. Converting to weierstrass misses the point of edwards/montgomery curves. Montgomery addition is differential, so you can't simply reuse the BC code for weierstrass scalar multiplication. Finding a $F_{521}$ implementation shouldn't be too hard, considering it's also used in NIST-P521.
Mar
13
revised Why does SHA-1 have 80 rounds?
added 11 characters in body; edited tags; edited title
Mar
13
answered Why does SHA-1 have 80 rounds?
Mar
13
comment How does the key size per data bit influence the security?
@Marste 1) TLS in its typical use doesn't bother changing the key during the lifetime of a connection 2) Changing the key within a connection strengthens forward secrecy 3) More samples don't help brute-force, but might aid cryptoanalysis. There is also a block size dependent limit, which is only a couple of GB for 64 bit blocks. Older protocols worry about these issues since we didn't have AES yet. Nowadays it's less of a concern.
Mar
12
comment How do I convert the definition of E-521 into a curve definition a la Bouncy Castle?
I suspect this library only supports weierstrass form, so you'd need to either convert (bad idea IMO) or implement a custom EccPoint class with edwards arithmetic. But last time I checked BC C# had quite bas ECC implementations. Not resistant to side channel attacks and slow as hell (using affine coordinates).
Mar
12
comment How do I convert the definition of E-521 into a curve definition a la Bouncy Castle?
FpCurve is for prime fields, F2mCurve for binary fields. This field is prime, so you need to choose FpCurve.
Mar
12
revised Where did Martin Hellman acknowledge Ralph Merkle's contribution to public-key cryptography?
added 62 characters in body; edited tags
Mar
12
awarded  Nice Question
Mar
11
comment Is there a flaw in whole disk encryption vs volume or folder encryption?
Yes, you're wrong. Modern cryptography doesn't allow an attacker to learn the key given (plaintext, ciphertext) pairs. This is a "known plaintext" attack.
Mar
10
comment I need a 64-bit cryptographic hash for 96 bits of data
But you can't really get "very high" collision resistance with a 64 bit hash. For example if you have 4 billion entries, collisions become likely, but you can't neglect them with only a few million entries.
Mar
10
comment I need a 64-bit cryptographic hash for 96 bits of data
Just take the first 64 bits of SHA-256 output. It's as good as 64 bit hashes get.
Mar
10
comment Sane implementations of Bitcoin cryptography routines w.r.t. side-channel attacks
Most operations don't need side channel resistance - they operate on public data. ECDSA signing is the major one, but even it is relatively hard to attack since you can't easily get high precision timing information.
Mar
10
comment Where can I download a database of RSA keys?
You probably could extract a bunch from the public SSL Observatory data dump.
Mar
10
comment Non-standard signature security definition conforming ed25519 malleability
@Gracchus There hasn't been a new version of SUPERCOP and most people wouldn't consider malleability a vulnerability of the signature scheme in the first place.
Mar
7
comment How to calculate the maximum output size for data encrypted with a RSA Private Key?
I've seen RSA/ECB/PKCS1Padding used in java contexts pretty often. But I'm not sure what it actually does. It might be equivalent to none, or perhaps it splits the message if it's too long.