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bio website github.com/CodesInChaos
location Frankfurt, Germany
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visits member for 3 years, 8 months
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Feb
15
comment Alternative sources of random numbers
1) You need something secret to seed a CSPRNG. 2) How would you obtain that data? If you download it, and you even trust the source to keep the data secret, you still need enough random data beforehand to initiate a TLS connection. But if you already have a good random seed, why bother with that stuff?
Feb
14
comment Factoring two RSA modulus with known $|p_1 - p_2| < \ell $
if $p_1=p_2$ you can simply compute the greatest-common-divisor of $N_1$ and $N_2$ to factor them.
Feb
13
comment Which characters to take into account when calculating unicity distance?
You can get much lower if you use dictionaries containing English words.
Feb
13
comment Malicious DH groups
AFAIK Miller-Rabin rejects non primes with probability of at least 3/4, so after 40 passes even maliciously constructed prime candidates should only pass with probabiility <$2^{-80}$.
Feb
12
comment Java RSA Padding: no libraries used
For signatures you could use full-domain-hash (FDH). For encryption you could use hybrid encryption based on RSA-KEM.
Feb
12
comment General questions about cryptography for password security
See How to securely hash passwords? on security.se.
Feb
12
comment Analogue encryption algorithms
From the wikipedia article you linked, it sounds like the signal is digital, not analog.
Feb
12
comment Analogue encryption algorithms
Frequency hopping isn't really encryption. It's main purpose is not even confidentiality of the message content, but avoiding jamming (DoS attack) and might make it harder to find the position of the sender.
Feb
11
comment AES encryption takes more time to decrypt than encrypt
Can you include a link to the library you're using?
Feb
11
comment Pseudorandom function library
I'd first use HMAC-SHA-2 to reduce the input to a fixed size key and then use that key in a stream cipher to obtain arbitrary length output.
Feb
11
comment Attacking multi block MAC constructions
@xxx I have deleted my comment mentioning your original name. But please refrain from vandalizing the question or my answer. You asked the question and can't take it back.
Feb
11
comment AES encryption takes more time to decrypt than encrypt
You could use a mode that only requires encryption, such as CTR mode.
Feb
10
comment Why does NaCL have different keys for signing and encryption?
NaCl uses authenticated encryption (crypto_box). You can use crypto_box for authentication (typically with long term keys) and confidentiality (typically with ephemeral keys). Sharing long term keys between signatures and crypto_box based authentication is useful.
Feb
10
comment Strategies for securing public key storage on software
Obfuscation isn't enough, but that doesn't mean there is something better either. Software DRM inherently relies on security through obscurity.
Feb
9
comment Remove padding (CBC) from decrypted text
The IV generation code makes no sense. 32 Base64 characters would correspond to a cipher with 192 bit blocks, which is highly unusual.
Feb
8
comment Hash function as secure as one-time pad?
The identity function is collision resistant. Preimage resistance is obviously impossible against a computationally unbounded attacker if the cost of each hash xomputation is bounded.
Feb
3
comment Python implementation of a blind signature scheme which doesn't involve RSA
RSA based blind signatures are relatively easy to understand and IMO have less room for mistakes than group based blind signatures. If you want simpler padding, use FDH instead of PSS. I trust them significantly more, the only major downside is performance. One pitfall is that you should make sure that GCD(m, N) = 1, not only GCD(r, N) = 1.
Feb
2
comment Multiple encryption of part of block
1) This technique is known as Ciphertext stealing. It's secure in principle, but as @mikeazo already pointed out using ECB and using 64 bit block ciphers is generally a bad idea. 2) There are fancier length preserving encryption schemes. 3) I strongly recommend adding a nonce/IV and a MAC. While these increase the size of the message, the security implications of not having them can be severe.
Jan
30
comment How secure is it to use password as AES key?
At minimum it's bad style, since AES expects a uniformly random key. It also means that the password needs to be much stronger than what you'd need if you used a proper password based KDF.
Jan
30
comment Merkle hash tree updates
The basic variant of merkle trees is only efficient for leaf replacements and appending to the end of the dat, but not efficient insertions/deletions in the middle. But there are other hash tree constructions that allow efficient insertions.