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Apr
16
comment What is a Key Derivation Function?
Hugo Krawczyk has defined HKDF, which is intended to be a practical KDF based on HMAC. He wrote paper on subject: Cryptographic Extraction and Key Derivation: The HKDF Scheme. Because goals of KDF are not often well pronounced, this paper formalizes model for Key Derivation Functions (page 6). The formalized model from this paper could be suitable definition sufficient for your purposes.
Apr
15
comment Asymmetric encryption that is secure for (almost) any foreseeable future
@HadrienG: These proofs of 128-bit security being strong enough assume that brute force is only possible approach. Unfortunately, given long enough time, it is not sure if brute force remains the only possibility, one hundred years is such time.
Apr
15
awarded  Nice Answer
Apr
5
comment Removing “security by obscurity” from port knocking
en.wikipedia.org/wiki/Password-authenticated_key_agreement
Apr
5
comment Removing “security by obscurity” from port knocking
Why use 2048-bit shared key? The protocol could use 2048-bit public keys instead. With those you could implement a PAKE scheme. It is kind of possible to use PAKE scheme to "fix" "security by obscurity" aspect of port knocking, but the communication will become less efficient than in some other means. (In the end protocol likely becomes e.g. non-interactive zero knowledge proof.)
Mar
18
revised Creating a small number from a random octet string
fixed accidental double inverse
Mar
18
answered Creating a small number from a random octet string
Mar
5
answered Will SHA1 or Other Hash Functions Ever Contain Quotes
Mar
2
comment 128 bit 3DES Key and AES Key: what's the difference?
I feel it is partially misleading to claim NIST has deprecated Triple DES. According to NIST Special Publication 800-131A: Transitions: Recommendation for Transitioning the Use of Cryptographic Algorithms and Key Lengths Two-key Triple DES Encryption (i.e., Triple-DES with 128-bit key) has been deprecated (i.e. restricted use), and will be disallowed after the end of 2015. However, the Triple-DES variant with 192-bit key, is acceptable.
Feb
12
revised Text in random image encoder: is it flawed?
Added note on Mersenne twister.
Feb
12
answered Text in random image encoder: is it flawed?
Feb
7
awarded  Yearling
Feb
5
comment How much can we compress RSA public keys?
One approach to reduce persistent storage requirements is storing $HASH(pk)$ (on e.g. EEPROM) instead of $pk$. This of course means that there needs to be some alternative location, which is able to provide full $pk$ for operating. Also total storage required grows.
Feb
3
comment Computing p and q from private key
This step is fast to calculate because the other value ($2^t$) is multiple of 2. In fact, t is the number of zero bits on the least significant bits of k. An easy way to calculate r in many big number packages is to shift k right t steps. Either calculate the zeroes or shift one bit a time as long as the value is even.
Jan
18
comment open source whitebox-crypto implementation
From perspective of having a secure implementation, using lookup tables is not always as good as a black-box implementation, because of subchannels information (e.g., timing). Table lookups tend to be take variable time due to cache effects.
Oct
31
comment Simplest code for 64-bit block RSA-like encryption/decryption and key generation
For something like RSA you need larger block than 64 bits. The parameter size currently is around 2048 bits. Furthermore, crypto.stackexchange.com is for questions on cryptography, not for requests to provide implementation. Please, reconsider what you need (for instance study RSA bit more so you know what you need) and then ask again on a more appropriate forum, possibly, stackoverflow.com.
Oct
24
comment AES-GCM Disadvantage
One factor reasonable for consideration could be size of implementation: AES-GCM consists of two significantly different cryptographic functions, AES and GHASH. Compared to some other authenticated encryption algorithms, this means it potentially takes more code or gates to implement AES-GCM than e.g. AES-CCM.
Oct
8
comment How exactly does AES-NI work?
Actually, ciphers (such as AES) tend to be more power efficient in hardware implementation than software implementation. This often also means faster, but not necessarily (the clocks for main cpu and crypto HW can be different).
Oct
2
awarded  Nice Answer
Sep
29
comment Is there any area where AES-CBC cannot be used ? If so, why ?
Error Oracle Attacks on CBC Mode: Is There a Future for CBC Mode Encryption? and Evaluation of Some Blockcipher Modes of Operation also seem to conclude that CBC mode is legacy with little future, and point out many of these shortcomings. For some areas the resources mentioned may provide useful additional information.