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Dec
6
comment Why Merkle Tree doesn't suffer Birthday attack?
Birthday attack against what? Collision resistance? All hashes suffer from that one, including merkle-trees, that's why we need 256 bit hashes for 128 bits of collision resistance.
Dec
5
comment Probability approximation of no collisions
@user822719 Yes. The factor 2 in the denominator comes from $1+2+3+ ... +(t-1)=\frac{t\cdot(t-1)}{2}$.
Dec
4
comment How can I factorize a 350 bit (106 decimal digits) number in two prime factors?
What kind of machine is that?
Dec
3
comment Does including the size of the hashed data improve security over just the hash
When you have an incorrectly implemented Merkle tree hash (pretty common, e.g. Bitcoin and Amazon fell for that), you need to compare the size as well.
Dec
3
comment Is every output of a hash function possible?
Duplicate on stackoverflow: Do cryptographic hash functions reach each possible value, e.g. are they surjective?
Dec
2
comment Few questions about CBC MAC
Fixed length messages is a sufficient but not a necessary condition for CBC-MAC's security. It's enough if no message is the prefix of another message. A length prefix is one way of achieving that.
Dec
1
comment Big block cipher as memory-hard function
Should be vulnerable to a variant of the attack where you store sqrt(n) values and recompute the rest on demand.
Nov
30
comment Are there comprehensive alternatives to RSA?
Group based crypto (elliptic curves and finite fields) supports both signing (DSA, Schnorr, etc.) and encryption (ECIES/DLIES). But using a single key for both may not be the best idea (just like it may not be the best idea with RSA).
Nov
30
comment Why does the time complexity of RSA encryption and decryption depend on the size of the modulus?
The cost of multiplying numbers depends on the size of those numbers.
Nov
29
comment Implementation specific differences between RDRAND and RDSEED
Are you sure that there is a statistically significant difference between RDSEED and RDRAND in those randomness tests? That seems very unlikely to me.
Nov
27
comment Edwards / Montgomery ECC over binary extension fields
Related: Binary Edwards curves - Explicit-Formulas Database
Nov
27
comment How can I use the whole potential of DES?
DES, like all modern crypto algorithms, works on a sequence of bytes. How you encode the message as bytes is out of scope for crypto. For text UTF-8 is the standard choice, if your data is different, you need to choose a different encoding.
Nov
26
comment ECC keys vulnerable to brute force attack?
Related: How strong is the ECDSA algorithm? and Why can ECC key sizes be smaller than RSA keys for similar security?
Nov
26
comment Does the RSA algorithm use repeated squaring?
See Exponentiation by squaring is the basic algorithm. Most implementations use the CRT method for a 4x speedup compared to computing $m = c^d \pmod n$.
Nov
24
comment Which blind signature schemes exist, and how do they compare?
Related: A note on blind signature schemes - Matthew Green's blog
Nov
24
comment Taking half of a X bits hash key as secure as using a X/2 bit hash function?
For the hashes we use in practice, truncation is safe. But it might be possible to construct pathological hashes where this is not the case.
Nov
23
comment Elliptic Curve Blind Signature Implementation
Related: A note on blind signature schemes - Matthew Green's blog
Nov
23
comment Elliptic Curve Blind Signature Implementation
If you look at anoncvs.aldigital.co.uk/lucre/theory2.pdf , it's clearly group based crypto, not RSA based crypto. AFAIK the main point of lucre was avoiding Chaum's (now expired) patents on RSA based blind signatures.
Nov
23
comment Encryption and HMAC key derivation
You might want to replace the last step by HKDF-Expand.
Nov
23
comment Elliptic Curve Blind Signature Implementation
You first need to find a secure scheme. I've seen ECC blind signature papers describing schemes that are clearly not secure. The lucre paper is relatively well known, so it have seen some analysis.