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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 5 months
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Dec
11
comment Do test vectors ensure a cipher is free of backdoors?
I'd rather define it as if m=CONST return k. Attacker controlled plaintexts or ciphertexts are more common and leaking the key is more useful. (or as DrLecter suggests a bijection of k to reduce the detection risk)
Dec
11
comment Could someone reuse client certificates?
A leak of the server side key only compromises past traffic if the RSA key exchange was used, not if (EC)DHE_RSA was used.
Dec
11
comment Diffie-Hellman Secret Exponent Size and Shared Secret Usage
A weird choice. 2048 bit modulus has about 112 bits of security, a 512 bit exponent 256 bits of security. A 3000 bit modulus with a 256 bit exponent would have a higher security level and similar performance. Or use ECC which is about 10x as fast.
Dec
11
comment In RSA, why is it important choosing e so that it is coprime to φ(n)?
Your last paragraph only works for prime $e$.
Dec
11
comment In RSA, why is it important choosing e so that it is coprime to φ(n)?
The Rabin cryptosystem is similar to RSA but uses e=2, which trivially divides $\phi(n)$. It needs to do extra work since this makes decryption ambiguous.
Dec
11
comment Is it possible to modify SSL handshakes to enable PFS while still using RSA during the handshake?
Creating a new DH key is cheap: One modular exponentiation with fixed base (or the even cheaper elliptic curve equivalent). With RSA you need to create two large primes. Creating an RSA key costs only a fraction of a second, but you don't want to create a new one for each and every connection.
Dec
11
comment Is it possible to modify SSL handshakes to enable PFS while still using RSA during the handshake?
To achieve forward secrecy you need to throw away the keys you used in the handshake so your future self won't be able to decrypt the handshake anymore. Both sides need to use an ephemeral key (With RSA key-exchange the client's ephemeral key is a symmetric secret). As long as the server keeps its RSA key used in a plain RSA key-exchange, you haven't achieved forward secrecy.
Dec
10
comment Encryption Key derivation from numeric PIN?
if n>20 it should be fine
Dec
10
comment Is it possible to modify SSL handshakes to enable PFS while still using RSA during the handshake?
1) If you invent your own ciphersuite, you could use ephemeral RSA. But creating a new RSA key is much more expensive than generating a DH key. So you might want to reuse it across connections and only rotate every minute. 2) You could use the plain RSA suite to achieve a limited form of forward secrecy if you frequently obtain a new certificate. Might be expensive depending on the CA.
Dec
9
comment Would this prevent FNV1a 32 bit hash collision?
What goal do you want to achieve? Your character wise hashing is no better than ROT13 encryption.
Dec
8
comment Assuming that we had a way of finding primes, could RSA be used without computers?
Why RSA? Using DH over a pregenerated elliptic curve or a pregenerated finite field should be faster and doesn't require per-key primes.
Dec
8
comment Assuming that we had a way of finding primes, could RSA be used without computers?
Exponentiation without computers is still pretty annoying
Dec
7
comment why RSA uses Semiprime numbers?
Factoring a big number which has less than two big factors is much easier.
Dec
6
comment Why are these techniques not feasible to crack RSA?
Your last sentence isn't just misleading, it's plain wrong. Calculating $\phi(n)$ and factoring $n$ are equivalent. The RSA problem is about solving $c=m^e \pmod n$ for $m$. While best known way is to factor $n$ and compute $\phi(n)$, it might be possible to solve this equation without learning $\phi(n)$
Dec
6
comment Can insecure algorithms be combined to form a secure algorithm?
But they aim at pseudo-randomness, not collision resistance and they xor the hashes instead of concatenating them.
Dec
6
comment Why are these techniques not feasible to crack RSA?
@AliGajani If you know $\phi(n)$,your technique works. In fact it's how $d$ is computed during RSA key generation. But an attacker does not know $\phi(n)$, so they can't use this technique.
Dec
6
revised Why are these techniques not feasible to crack RSA?
deleted 8 characters in body
Dec
6
reviewed Approve Why are these techniques not feasible to crack RSA?
Dec
5
comment counting points not on elliptic curve
Your notation is confusing since you use $a,b$ as curve parameters and as the coordinates of a point.
Dec
5
comment Can cryptocurrency mining devices be used for cryptanalysis?
@HenrickHellström Password hashing with different password guesses is parallel as well. If you had fixed SHA-256 cores and flexible logic between the calls, that could be used for both hashing and mining. But I doubt miners contains those flexible parts required to repurpose them to crack PBKDF2.