instruction stringlengths 15 30k |
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When I want to encrypt chat messages (in ASCII) before sending, whether it brings some bit of security if I add some extra bytes to the message or shuffle it in some way? I can even try to make data to look like uniform distribution.
Because chat messages consist only of letters and even words, but don't contain bin... |
I [read](http://zucalg.forumotion.net/t8-on-the-construct-of-good-sboxes) that we do not know if there exists an 8x8 sbox with differential uniformity = 2.
I suppose we cannot compute every possible sbox because there are $64!$ possible s-boxes. Am I right? |
Given that:
> You should always use *proven* secure hashing and encryption algorithms,
> rather than attempting to write your own.
What's the process for criteria for an algorithm being *proven*?
Is it necessarily a peer review process? Does an algorithm need to withstand exploit attempts for N amount of time... |
How are secure hashing and encryption algorithms proven? |
> Is it necessarily a peer review process? Does an algorithm need to withstand exploit attempts for N amount of time by M many experts?
> Or, is there a mathematical proving process that security experts can apply on their own to evaluate an algorithm?
Yes, yes, and sometimes.
Some algorithms can be proved sec... |
I often heard about private key storage, but rarely about key life cycle in memory.
For example, when SSL is used from one peer, the private key is used to sign messages or decrypt other peers' messages, so it has to be in memory as long as the http process goes on.
It may raise some security issues that clear p... |
Carter-Wegman MAC variants (VMAC, UMAC etc) are known to be very fast and efficient when compared to MAC algorithms that are based on block ciphers and compression functions (like HMAC, CMAC etc).
However, Carter-Wegman MAC variants are not very popular on the internet like HMAC. Why is this so? Do Carter-Wegman MAC... |
I have been reading up on IND-CCA2 security and was wondering: Are there IND-CCA2 secure schemes that do not require plaintext awareness? I'm guessing yes - could someone point me to these schemes?
I was looking at Cramer-Shoup, and it seems like the general idea is that we make the message complex so that it's hard... |
IND-CCA2 secure schemes without Plaintext Awareness? |
I have been reading up on IND-CCA2 security and was wondering: Are there efficient IND-CCA2 secure schemes that do not require plaintext awareness? I'm guessing yes - could someone point me to these schemes?
I was looking at Cramer-Shoup, and it seems like the general idea is that we make the message complex so that... |
This may sound a little bit of basic but here it goes…
Which of the following is correct?
1. *“Cryptography is under the security field”*, or
2. *“Security is under the cryptography field?”*
Cryptography is all about encryption and decryption. Encryption/Decryption requires a key. Isn't security the same?... |
This may sound a little bit of basic but here it goes…
Which of the following is correct?
1. *“Cryptography is under the security field”*, or
2. *“Security is under the cryptography field?”*
Cryptography is all about encryption and decryption. Encryption/Decryption requires a key. Isn't security the same?... |
This may sound a little bit of basic but here it goes…
Which of the following is correct?
1. *“Cryptography is under the security field”*, or
2. *“Security is under the cryptography field?”*
Cryptography is all about encryption and decryption. Encryption/Decryption requires a key. Isn't security the same?... |
> Is it necessarily a peer review process? Does an algorithm need to withstand exploit attempts for N amount of time by M many experts?
> Or, is there a mathematical proving process that security experts can apply on their own to evaluate an algorithm?
Yes, yes, and sometimes.
Some algorithms can be proved sec... |
In [SRP-6](http://srp.stanford.edu/design.html) $B$ is calculated as $B=kv+ g^b, k=3$. What is the purpose of $k$, and why was it fixed as $3$?
(In SRP-6a, this value $3$ is [replaced by][1] $k = H(N,g)$, but this question is about SRP-6.)
[1]: http://crypto.stackexchange.com/questions/3509/why-does-srp-6a-us... |
Why does the SRP-6 calculation of B include a multiplier k = 3? |
I think this question has no real answer as it stands and is even hard to answer if we would clearly define what we mean by "cryptography" and what we mean by "security" (Below I assume that you mean "information security" by security, because security is even harder to define).
Moreover, your definition of cryptog... |
I have been reading up on IND-CCA2 security and was wondering: Are there efficient IND-CCA2 secure schemes that do not require plaintext awareness? I'm guessing yes - could someone point me to these schemes?
I was looking at Cramer-Shoup, and it seems like the general idea is that we make the message complex so that... |
In HOTP authentication, is there a way for a system to detect that the token has been desynchronized? If so how does it know that the OTP was generated from a desynchronized (but valid) token and is not just a fake/random OTP? |
> When I want to encrypt chat messages (in ascii) before sending,
> whether it brings some bit of security if I add some extra bytes to
> the message or shuffle it in some way? I can even try to make data to
> look like uniform distribution.
I recommend to encode your chat messages with base64 before encrypting a... |
In the [ElGamal signature scheme][1] we calculate a signature for a (hashed) message $m$ as
$r \equiv_p g^k$,
$s \equiv_{p-1} (m - xr) k^{-1}$
and verify it by checking
$g^m \equiv_p y^r r^s$.
Here $r$ is a *group element* which is in some cases used as an *exponent*. This is not a problem, as long as th... |
Below is a short excerpt of available DH cipher suites available on a machine.
I understand EDH is ephemeral DH, and that ECDH is for Elliptic-Curve DH which is computationally faster. ECDHE is both of those aspects together. The confusing bit how there are EDH cipher suites and DHE suites. The [wikipedia article... |
Agreeing with @otus but adding more background and context than I think belongs in comments:
This is an OpenSSL question though you don't say so; all other SSL/TLS software I've looked at uses the RFC spellings DHE ECDHE DH_anon ECDH_anon, but OpenSSL was written yonks ago with EDH in some places (mostly the ones da... |
Background:
Hello, I'm working on a hobby project in which I might want to implement a key derivation function within a somewhat resource limited embedded system. For standard crypto functions, I only have access to SHA and AES (no KDFs). So I was thinking of rewriting one of the standard ones (like bcrypt or scry... |
Is this a plausible KDF? |
Is this a plausible password based KDF? |
Is Using variant of AES will give the same level of security as AES gives, say by just repacing S box with another one,MDS matrix of Mixcolumn,...?. |
what are the variants of AES? |
I am new here and fairly new to cryptography, so if I say something wrong, let me know. I am trying to set up a system where a user can receive a temporary license key over the phone, put it into the system, and get the privileges and expiration date which was encoded into the license key. The limitation for this key i... |
I am new here and fairly new to cryptography, so if I say something wrong, let me know.
I am trying to set up a system where a user can receive a temporary license key over the phone, put it into the system, and get the privileges and expiration date which was encoded into the license key.
The limitation for th... |
ECC cryptography with shorter signature when not needing high security? |
Would variants of AES provide the same level of security as AES, say by just replacing the S-box with another one, MDS matrix of Mixcolumn, etc.? |
Variants of AES? |
What are the practical differences between 256-bit, 192-bit, and 128-bit AES encryption? |
I use AES both CBC and CBC-MAC to encrypt some stuff.
I openssl generate one key for CBC and one different key for CBC-MAC.
1) Does the second key (for CBC-MAC) need to be secret ?
2) How to join such key with the ciphertext ? by contatenate it at the end ?
Thanks. |
CBC-MAC key can be added to ciphertext? |
**Background:**
Hello, I'm working on a hobby project in which I might want to implement a key derivation function within a somewhat resource limited embedded system. For standard crypto functions, I only have access to SHA and AES (no KDFs). So, I was thinking of rewriting one of the standard ones (like bcrypt or s... |
Is this a plausible KBKDF? |
I use AES both CBC and CBC-MAC to encrypt some stuff. Using OpenSSL I generate one key for CBC and one different key for CBC-MAC.
1. Does the second key (for CBC-MAC) need to be secret?
2. How to join such key with the ciphertext? By contatenating it at the end? |
I use AES both CBC and CBC-MAC to encrypt some stuff. I generate one key for CBC and one different key for CBC-MAC.
1. Does the second key (for CBC-MAC) need to be secret?
2. How to join such key with the ciphertext? By contatenating it at the end? |
From the sound of your questions, it almost appears that you have some confusion between the CBC-MAC key and the CBC-MAC tag.
The CBC-MAC algorithm takes the message (in this case, most likely the ciphertext) and a secret key; it outputs a tag (which can be public). The security property of CBC-MAC is that someone ... |
From the sound of your questions, it almost appears that you have some confusion between the CBC-MAC key and the CBC-MAC tag.
The CBC-MAC algorithm takes the message (in this case, most likely the ciphertext) and a secret key; it outputs a tag (which can be public). The security property of CBC-MAC is that someone ... |
Is this a plausible PBKDF? |
A “Password Based Key Derivation Function” is a key derivation function ([tag:kdf]) that uses a key in the computation.
Prominent examples are:
- **PBKDF1** (Password-Based Key Derivation Function 1), which could only produce derived keys up to 160 bits long.
- **PBKDF2** (Password-Based Key Derivation Functio... |
Haven't found any clear cut answer in Google so its up to you guys:
DK = PBKDF2(PRF, Password, Salt, c, dkLen)
here, what is the upper limit of password length? I tried up to 16 characters and it works. How far can I go?
And I read somewhere that salt has no upper limit! is it really true? |
Haven't found any clear cut answer in Google so its up to you guys:
DK = PBKDF2(PRF, Password, Salt, c, dkLen)
Here, what is the upper limit of password length? I tried up to 16 characters and it works. How far can I go? I read somewhere that salt has no upper limit! Is it really true? |
I have one question about convergent encryption.
Suppose I use AES-256 in CBC mode. I need a 256 bits key and a 128 bits IV. If I use SHA-256 to hash one file, then I can use directly that hash as the key.
When decryption occurs, is integrity and authenticity given by checking the hash of the decrypted plaintext,... |
In general (if possible to determine) which would make an output harder to turn into plain text with a computer?
* Extreme Length (minor complexity change)
* Extreme algorithmic complexity (minor length change)
(Assuming these are hidden patterns of course)
Possible simple example for length might be a se... |
Which causes longer "break" time (in general)? |
In general (if possible to determine) which would make an output harder to turn into plain text with a computer?
* Extreme Length (minor complexity change)
* Extreme algorithmic complexity (minor length change)
(Assuming these are hidden patterns of course)
Possible simple example for length might be a sent... |
Is it secure to derive an AES key from a MAC? |
My personal opinion: "proven secure" is more of an advertising slogan than anything else. The one-time pad and certain multiparty protocols can be shown to have some kind of information-theoretic security; these are exceptions to the rule. "Don't roll your own crypto" is still sensible advice however.
For the rest o... |
Why does DES use exactly 16 rounds and not more or less than 16? What is the significance of using 16 rounds? |
Why does DES use exactly 16 rounds? |
I've read lots about null length IVs being bad for most modes. In a scenario where passing a 128-bit IV along with each message isn't feasible, how would generating the IV from a smaller passed-along value impact the strength of the security?
Each user will have their own symmetric key that does get re-generated pe... |
What's the consequence of having a short initialization vector (IV)? Is one mode better in that case? |
I've read lots about null-length IVs being bad for most modes. In a scenario where passing a 128-bit IV along with each message isn't feasible, how would generating the IV from a smaller passed-along value impact the strength of security?
Each user will have their own symmetric key that does get re-generated periodi... |
What's the consequence of having a short IV? Is one mode better in that case? |
Is there an efficient way to map `2^n` `64bit` vectors to `2^n` `n bit` vectors ? `n < 64`
|
Is there an efficient way to map $2^n$ 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$?
|
Efficiently map $2^n$ 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$? |
Cipher modes typically assume data is streamed or read from a reliable channel with guaranteed ordering. However, many communication transports, such as UDP, are not reliable and don't guarantee order of delivery. What are some cipher modes which are packet-oriented and can deal with unreliable, unordered datagrams? |
What's the best packet cipher mode for use with UDP for example? Advantages or disadvantages of any alternatives? |
Is there an efficient way to map $2^n$ unique 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$?
|
Efficiently map $2^n$ unique 64-bit vectors to $2^n$ $n$-bit vectors where $n < 64$? |
Is there a table (or a whitepaper from official sources) that compares the size of X509 certificates generated with **RSA** (starting from 1024 bits) and **ECDSA** (starting from 160 bits) ? Thanks for the support. |
Is possible keep the "one wayness property" of certain one way function in Merkle-Damgard construction? I'm doing this question because according [Collision-Resistant hashing: Towards making UOWHFs practical][1] the target collision resistant property fail in Merkle-Damgard construction.
[1]: http://link.springe... |
I am learning Groth-Sahai NIZK proof system for Bilinear groups. While going through the literature, I am getting confused on how the proof system is related to Subspace Decision, SXDH or DLIN assumptions. In the proof system, what I understood is to prove the ownership of solution of a set of equations, e.g. Quadratic... |
After reading about public/private key cryptography, there are still a few points I don't really understand.
Based on the way (I understand) challenges work, the public key is used to encrypt a sequence which the private key can be used to decrypt:
1. When a key pair is freshly generated, does it matter which ke... |
Can all asymmetric key pairs be reversed? |
Suppose:
- The "counter field" is about: NONCE || CTR-VALUE.
- I have multiples messages Ma, Mb, Mc, ...
- Each message can be divided into x-bits blocks (Ma1, Ma2, Ma3, ...).
1) Each message M (for instance Ma) is encrypted following a randomly and uniquely generated key. In this case, does I really need th... |
Counter Mode: how to choose the nonce part of the counter? |
Suppose:
- The "counter field" is about: NONCE || CTR-VALUE.
- I have multiples messages Ma, Mb, Mc, ...
- Each message can be divided into x-bits blocks (Ma1, Ma2, Ma3, ...).
1) Each message M (for instance Ma) is encrypted following a randomly and uniquely generated key. In this case, does I really need th... |
Suppose:
- The "counter field" is about: NONCE || CTR-VALUE.
- I have multiples messages $M_a, M_b, M_c, \dots$
- Each message can be divided into x-bits blocks ($M_{a1}, M_{a2}, M_{a3}, \dots$).
1. Each message $M$ (for instance $M_a$) is encrypted following a randomly and uniquely generated key. In this ca... |
I have to hold a workshop for teenagers at our university about Cryptography. They will be about 16 years old. I'm planning to do a competition with prizes - there will be different tasks and each one will yield points, and the winners will get sweets. However, for the amount of time I'm planning to kill with this game... |
In symmetric cryptography, a scheme is not considered secure if the data transmitted is only encrypted. The adversary will be able to modify messages to generate forged encrypted messages without having the key.
Is this applicable to asymmetric crypto such as RSA? |
In symmetric cryptography, a scheme is not considered secure if the data transmitted is only encrypted. The adversary will be able to modify messages to generate encrypted messages of his choice without having the key.
Is this applicable to asymmetric crypto such as RSA? |
Is it possible keep the "one wayness property" of certain one way function in Merkle-Damgård construction? I'm asking this question because according to [Collision-Resistant hashing: Towards making UOWHFs practical][1] the target collision resistant property fail in Merkle-Damgård construction.
[1]: http://link.... |
I have just found a way to crack AES-128 in a reasonable time (1-2 days), how do I publish this and how do I prove this? I remember reading about lots of people who cracked DES and other ciphers but how did they publish their work? |
found a way to crack AES-128 what now? |
Yes, a Merkle–Damgård hash can be one-way. Even MD5 hasn't been broken in that way.
Target collision resistance (TCR) is a notion [similar to][1] second preimage resistance (but for keyed functions). Preimage resistance, i.e. one-wayness, [does not imply][2] second preimage resistance, so a hash function can be one-... |
In this [Intel blog posting][1], the author claims:
> The amount of work required to brute-force predict a random value that has n bits of entropy is $O(2^n)$. If you concatenate two values together, the entropy required to brute force the result becomes only $2^n + 2^n = 2^{n+1}$. By combining two n-bit random valu... |
In complete honesty: if you have to ask this question, it's overwhelmingly unlikely that you have actually succeeded in breaking the security of AES. At *best*, you *may* have discovered a well-known attack against misuse of particular block cipher modes; for instance, plaintext recovery with a chosen-ciphertext attack... |
In complete honesty: if you have to ask this question, it's overwhelmingly unlikely that you have actually succeeded in breaking the security of AES. At *best*, you *may* have discovered a well-known attack against misuse of particular block cipher modes; for instance, plaintext recovery with a chosen-ciphertext attack... |
Caveat: as very rightly pointed in that [other answer][1], using a fixed/no IV does make some attacks less difficult. I wish the following answer would have been less affirmative. I have accordingly made adjustments in *italic*.
**There's no *imperious* need for an IV when unique keys are used.**
When each key is... |
I have just found a way to crack AES-128 in a reasonable time (1-2 days). How do I publish and prove this? I remember reading about lots of people who cracked DES and other ciphers but how did they publish their work? |
Found a way to crack AES-128, what now? |
With RSA (or any asymmetric cryptography, for that matter), the key question is "how do you know you can trust the other peer's public key?". Without authentication, you could be sending your message using the attacker's public key.
**Example 1:** the first time you SSH to a host, you are prompted to confirm that yo... |
I've got an academic curiosity regarding some of the old Japanese naval codes used during World War II specifically… but I was just wondering if any of the codebooks from this era had been made available, or if they are still protected materials? |
You could challenge them to devise low-tech, *physical* zero-knowledge proofs (of knowledge) for games like "Where's Waldo?" and Sudoku, then show them some methods that really work and why. I've done this before with high school CS students and they seemed to really like it.
For "Where's Waldo?" one can prepare a ... |
Give every kid a deck of cards (2 decks of cards?) and a short (unique) text message on paper.
Each kid encodes the message -- by arranging the cards in some order; writing on the cards is cheating.
Then every kid decodes a deck of cards (arranged by some *other* kid) and write the message on paper.
Challenge th... |
In light of the NIST Dual EC DRBG scandal, I was intrigued by a [NIST slide][1] (slide 9) that said the two points P and Q can be chosen so that the chooser can *prove* they don't have a backdoor. This seems rather magical to me, so I'm looking for some more information. I'm assuming they're referring to something mor... |
Perhaps you could do something with Visual Cryptography.
Maybe something like:
* Gather a few low-resolution images (symbols or short text phrases), perhaps a few more images than you have kids
* Use visual cryptography to split each image into 2 random-looking images, and print each random-looking image on its ... |
Is OCB as secure as GCM or CCM ?
Since OCB design is quite different from GCM and CCM, I was wondering if the security properties of these latters are satisfied by OCB, as well.
Thank you. |
Assumes that we have 3 signature algorithms, $S^A$ with key pair $(sk^A,pk^A)$, $S^B$ with key pair $(sk^B,pk^B)$,$S^C$ with key pair $(sk^C,pk^C)$. We denote by $\epsilon$, $\epsilon'$ and $\epsilon''$ the advantages for breaking $S^A$, $S^B$ and $S^C$ respectively.
I have a composed signature algorithm which works... |
OMAC is specified as the underlying algorithm to provide authentication within the EAX authenticated encryption (with associated data). Would that be OMAC1 or OMAC2?
If it is OMAC1, does that mean it is identical to AES-CMAC if EAX mode uses the AES block cipher as primitive?
|
I've read the following two sentences within a beta protocol specification.
> The off-card entity is responsible of computing the intermediate hash over the first part of the data to be signed. The intermediate hash-code is transferred to the token by the PSO:HASH command together with the remaining part of the data... |
How to distribute symmetric key between n entities? |
If there are $n$ servers for broadcasting symmetric key in such a manner that following holds:
1. No server alone can find the key $K$ alone.
2. Any two servers can pass $k_i$ and $k_j$ such that $K=f(k_i, k_j)$ where $i\neq j$
How can a symmetric key be distribute between $n$ entities? |
How to distribute symmetric key between $n$ entities? |
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