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visits member for 2 years, 11 months
seen Aug 25 at 15:29

Apr
25
comment ECC Complexity order of point addition, scalar point multiplication and selecting random point
@poncho you're right, I've edited the answer.
Apr
24
comment Do I need two keys for AES CBC and HMAC or can I use the same key for both operations?
In a higher level API is easier to avoid mistakes, since they take care of the low-level stuff. The reason for not using SHA-256 is in the link provided in the answer, but in short: it's too fast, which makes brute force attacks faster. Furthermore its output is limited to 256 bits and you may need more for generating both keys.
Jan
18
comment /dev/random only needed for key generation / CPU pattern encryption
You shouldn't be able to break it, the CPU doesn't "leave a pattern".
Aug
23
comment Create a field in PBC
RELIC is alpha in the sense that you shouldn't use it for production. But it's fine for research.
Jul
5
comment DSA, RSA, ECDSA etc - which one is cheapest for signing?
ECDSA should be faster than BLS, since it can use a special prime for the finite field arithmetic. And if you need short sigatures, Zhang/Safavi-Naini/Susilo should be faster than BLS since it uses a fixed point multiplication.
Jul
3
comment How much stronger is RSA-2048 compared to RSA-1024?
@user27296 it's implicit in Reid's answer. It's not $2^{1024}$ times harder because GNFS can attack it faster than simple brute force. It's $2^{32}$ times harder, as mentioned.
Mar
6
comment How are Elliptic Curve Cryptography and Pairing Based Cryptography related?
Yes, but the only alternative I know is PBC using elliptic nets, which are related but different to ECC.
Feb
1
comment Decryption a chunk of file with AES
That's completely up to you. In your example, you have 10 chunks; you can decrypt the first five in one thread and the last five in another. The only restriction is that the size of each chunk must be a multiple of the block size of the cipher, e.g. 16 bytes in the case of AES.
Feb
1
comment Decryption a chunk of file with AES
Sorry, I'm not sure what is you question. Read the initial counter value. Determine the number of blocks, divide by the number of (e.g.) cores, and decrypt each chunk of blocks in each core.
Jan
25
comment Modulus for elliptic curve point multiplication
I strongly suggest you to refer to a stardard reference like Hankerson et. al's "Guide to Elliptic Curve Cryptography" or Menezes et. al's "Handbook of Applied Cryptography". Anyway, if the result of the subtraction is negative, simply add $p$ to the result (since you're working modulo $p$, this will not "change" the value).
Jan
22
comment Modulus for elliptic curve point multiplication
You can use any irreducible polynomial. Usually it's $x^2 + 1$, which is irreducible if $-1$ does not have a square root modulo $p$. The same for other degrees: use a $n$-degree irreducible polynomial. Note that for efficiency a "tower of extensions" is often used (e.g. quartic extension can be built as an quadratic over another quadratic). Ask another question if you need details. I also suggest reading this: everything2.com/user/Swap/writeups/finite+field
Sep
27
comment why $e(g,g)^N=1$ in bilinear pairings holds?
Yes, since $e(g^{a_1},g^{a_2})^N = e(g,g)^{N a_1 a_2} = (e(g,g)^N)^{a_1 a_2} = 1^{a_1 a_2} = 1$.
Sep
27
comment why $e(g,g)^N=1$ in bilinear pairings holds?
No, if the order of $g$ is the composite $N$, then $g^q$ and $g^p$ will be different than $1$. The reason that $e(g,g)^N = 1$ holds is that $e(g,g)$ is the generator of $\mathbb{G}_T$ and has order $N$.
May
4
comment Elliptic curves for ECDSA
You can find $n$ by factoring the order of the curve, which you have found with e.g. Schoof's algorithm. Then $n$ will be the largest factor, and $h$ is the order divided by $n$.
Feb
10
comment Best choice of finite field for AES on a 4-bit microcontroller?
@IlmariKaronen: I guess you're right. Thinking back, you can compute inverses in $GF(2^4)$ by simply trying all 15 possibilities. It seems that this issue warrants some research :)
Feb
9
comment Best choice of finite field for AES on a 4-bit microcontroller?
Using composite field arithmetic allows you to compute an inverse by computing a single inverse in $GF(2^4)$. It seems to me that the code required to compute this would itself be greater than 256 bytes, killing any advantage over using a precomputed S-box. But it's hard to say without actually implementing it.
Jan
26
comment Helper data authentication in PUFs
I guess my question wasn't clear enough, sorry for that! Suppose that the PUF is used by some device to derive a key that is used to encrypt and authenticate its hard drive, for example. There is no user interaction. If the device generates and stores a key to sign $P$, then an attacker can change both the key and $P$ (that is, assume that there is no secure storage) and the security would be compromised. If you assume there is a safe place to store the second key and $P$, then why use a PUF in the first place if you can generate a key and store it there?
Jan
24
comment Helper data authentication in PUFs
Thanks for the clarification, but I still don't understand something: how can I protect it against modification? For that I would need a key, but I'm using the PUF to get a key in the first place. Is there any kind of guarantee that an attacker can't change $P$ in such a way to force the system to derive a key $R'$ of his choice?
Jan
24
comment Helper data authentication in PUFs
I see, it makes sense if the PUF is used for authentication. But what if the PUF is used to generate a key for a device?
Jan
10
comment Would it be secure to use random numbers from random.org in a cryptographic solution?
One application I can come up with is for validating randomness tests. But for the usual applications (e.g. generating keys), I don't see how random.org could be useful.