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Jun
17
comment What are good combinations of public key algorithms or primitives for long term security?
Combining public key encryption schemes is easy: just do independent key exchanges and then hash the shared secret to produce a combined shared secret. Encrypt the actual message with symmetric crypto as usual.
Jun
17
comment Is HMAC needed for a SHA-3 based MAC?
This question is pretty similar to Can Skein be used as a secure MAC in format H(k || m)?
Jun
17
comment Is HMAC needed for a SHA-3 based MAC?
Use the key as prefix not as suffix. Key as suffix is secure as well as long as SHA-3 remains unbroken, but falls once a collision attack is found. If you don't care about the performance cost, still using HMAC is a good choice as well.
Jun
16
comment Functions that are only second-preimage resistant?
@fgrieu I don't see how proving that helps.
Jun
13
comment RSA decrypting of a huge file by parts
With the edit things get even more confused since RSA private keys aren't used for encryption.
Jun
11
comment Given $n$ bits, how many “truly random” sequences/numbers can be constructed?
@RickyDemer Kolmogorov is cute, but unfortunately very theoretical. Only useful for long messages and cannot be computed. Even simplifications are exponentially expensive.
Jun
11
comment Given $n$ bits, how many “truly random” sequences/numbers can be constructed?
Shannon entropy is only defined for a generation process, not for an individual sequence. If a good generator produces an all zero sequence, that's still perfectly random even if it doesn't look like it.
Jun
7
comment What differences between Menezes–Vanstone ECC and ElGamal ECC?
If you want practical ECC encryption, use ECIES. It's simple and offers strong security.
Jun
6
comment Pick faster private exponent
You could consider multi-prime RSA if your implementation supports it.
Jun
4
comment Padding to increase entropy and size of (otherwise) small JSON objects
If you're using proper encryption (with a per-message IV) you don't need to pad the message.
Jun
4
comment Comparing two values without revealing them
This may be usable as fallback solution, but generally order preserving encryption leaks a bit much. If there is an efficient ZKP, it will be much stronger than OPE.
Jun
4
comment Comparing two values without revealing them
This seems to be a combination of a commitment and a zero knowledge proof. Your hashes solve the commitment part, but make the ZKP part impossible. There is a similar problem called Yao's Millionaires' Problem but there alice knowns one value and bob the other. You should search for "Zero knowledge proof" or perhaps "secure multi party computation".
Jun
3
comment Montgomery Ladder vs Double-and-Add
On montgomery curves montgomery ladders enable cheap addition via differential addition in x/z form. In most other situations I'd rather create a lookup table with 32 or so entries and then double 5 times followed by one lookup and one addition.
Jun
2
comment Measure ECC key size
When talking about the size in ECC we generally refer to the field size.
Jun
1
comment Parallel hash construction
Related question: Counter mode secure hash algorithm
May
28
comment RSA and ECDSA performances
Concerning optimized implementations, ECC has one big advantage: A fixed modulus which usually has been chosen to allow efficient reductions. Certain academics like publishing papers about their world record speed ECC implementations, so ECC has seen quite a bit of optimization work targeting modern CPUs. ECC is more complex mathematically, but I think it's actually easier to write a fast ECC implementation compared to a fast RSA implementation.
May
28
comment Is TEA considered secure?
@user54609 8 byte blocks are annoying to use since it makes encrypting more than a GB using a fixed key problematic. In a quick test TEA was rather slow at 45 cycles per byte. Why do you claim it's "super fast"?
May
25
comment Efficiency of chaining AES “groups” of blocks
This technique is responsible for the famous BEAST attack against TLS.
May
21
comment Which tamper-protection algorithm provides the shortest output?
@Vilx- With HMAC the chance of accepting a forgery is $2^{-n}$ for an $n$ bit MAC. With GCM every successful forgery reveals a big part of the key whereas for HMAC the only effect is that you accept a forgery. So if you really need to go below 128 bit MACs, I recommend against GCM. Another issue with GCM is that it needs a nonce and reuse is fatal, whereas HMAC doesn't need a nonce.
May
21
comment Which tamper-protection algorithm provides the shortest output?
I'd go with truncated HMAC-SHA-2 with a length somewhere between 64 and 128 bits. Truncation is fine with HMAC, but do not truncate a GCM / GHash MAC.