instruction stringlengths 15 30k |
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In the algorithm for [BPS Format Preserving Encryption][1]
I am trying to write a C# implementation of this algorithm but so far I'm stuck on the tweak. Is this tweak always the same length (64bit)?
Why did they choose the length 64bit for the tweak?
[1]: http://csrc.nist.gov/groups/ST/toolkit/BCM/docume... |
Why is the tweak length 64bit in BPS FPE algorithm? |
Note that the security notion targeted by MAC's is not IND-CCA, but *EUF-CMA (Existentially Unforgability against Chosen Message Attacks)*.
You can read the formal definition on page 156 here: https://cseweb.ucsd.edu/~mihir/papers/gb.pdf.
Suppose we have a MAC scheme $M =(\mathcal{K}, \mathsf{MAC}, \mathsf{VF})$ wh... |
In the algorithm for [BPS Format Preserving Encryption][1]
Is this tweak always the same length (64bit)?
Why did they choose the length 64bit for the tweak?
[1]: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/bps/bps-spec.pdf |
Yes, the exponent can be any odd value greater than 1.
We usually insist on prime values of $e$; why is this? Well, it does make generating key pairs a bit easier.
When we generate an RSA key pair, standard practice is to pick a public exponent $e$, and then select primes $p$ and $q$ that work with that $e$. An... |
I am trying to make an enigma machine simulating software. I know how the machine works but am having trouble trying to understand what my code's logic should be BEFORE the alphabets get to the reflectors.
Suppose 1, 2 and 3 represent each rotor's settings in an enigma machine (they're what I got from wikipedia):
... |
How exactly is an enigma simulation software supposed to encrypt alphabets? |
I read the question [Symmetric mutual authentication with client using a derived secret](https://crypto.stackexchange.com/q/22931/27977) and its [answer](https://crypto.stackexchange.com/a/24010/27977) which, if I'm not mistaken, assert that it should be safe to use the proposed protocol for mutual authentication betwe... |
Is it safe to use single-block AES for mutual authentication? |
I read the question [Symmetric mutual authentication with client using a derived secret](https://crypto.stackexchange.com/q/22931/27977) and its [answer](https://crypto.stackexchange.com/a/24010/27977) which, if I'm not mistaken, assert that it should be safe to use the proposed protocol for mutual authentication betwe... |
EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The site wont allow me too add more links but google "enigma rotor details" and see the wikipedia page
There is a similarly worded question here but i... |
EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The rotor wiring and other details from https://en.wikipedia.org/wiki/Enigma_rotor_details
I am trying to make an enigma machine simulating software. ... |
> Now I would like to use a single-block AES128 for the HMAC calculation in this scheme [...]
HMAC requires a hash function with a variable input size, so you cannot just use AES in it. If you want to use some other MAC instead of HMAC, you can use AES. AES ECB is a secure MAC for single block messages, so that woul... |
Note that the security notion targeted by MAC's is not IND-CCA, but *EUF-CMA (Existentially Unforgability against Chosen Message Attacks)*.
You can read the formal definition on page 156 here: https://cseweb.ucsd.edu/~mihir/papers/gb.pdf.
Suppose we have a MAC scheme $M =(\mathcal{K}, \mathsf{MAC}, \mathsf{VF})$ wh... |
Note that the security notion targeted by MACs is not IND-CCA, but *EUF-CMA (Existentially Unforgability against Chosen Message Attacks)*.
You can read the formal definition on page 156 here: https://cseweb.ucsd.edu/~mihir/papers/gb.pdf.
Suppose we have a MAC scheme $M =(\mathcal{K}, \mathsf{MAC}, \mathsf{VF})$ whi... |
I'm new to cryptography and please clarify if my below assumption is wrong.
Lets assume, that two different banks creating CSR and they get identical public and private key pairs of RSA. In such scenario, how does the conflict be managed. Will the administrator be notified about the conflict ?
will the CA check... |
Is it possbile to get same set of public and private keys twice while creating CSR ? If so where does the conflict happens !? |
Are the products like DocuSign and SignEasy valid? |
I read [this](https://www.bentasker.co.uk/documentation/security/282-infiltrating-a-network-via-powerline-homeplugav-adapters) post from Ben Tasker describing how to take control of a powerline network. Since I am interested in security, I tried to do the same thing, to see if it was possible. I used Devolo devices, si... |
i want to generate an RSA public public key file using openssl (or other tools) having public modulus and exponent, so i can use it later to encrypt files
i have this:
the modulus:
"BEB90F8AF5D8A7C7DA8CA74AC43E1EE8A48E6860C0D46A5D690BEA082E3A74E1"
+"571F2C58E94EE339862A49A811A31BB4A48F41B3BC... |
Which ECB ciphertext stealing scheme is this? |
I have several questions on using AES 128bit in the [BPS format preserving encryption][1]
Which modes are acceptable? (Should the block cipher used at each round be deterministic (ECB) or probabilistic (CBC, CTR etc)
What IV to set? Can I set it to the constant zero?
[1]: http://csrc.nist.gov/groups/ST/to... |
Rather straightforward question in the title. I'd refrain from adding more, but I need add content to this question.
All block cipher modes of operation that I understand are generic schemes. They are not restricted by key size or block size. So why is GCM restricted to 128-bit block sizes?
Oh, and how does it wo... |
What is GCM and why is it only usuable for ciphers with a 128-bit block size? |
All block cipher modes of operation that I understand are generic schemes. They are not restricted by key size or block size. So why is GCM restricted to 128-bit block sizes?
|
Why is it only GCM usable for ciphers with a 128-bit block size? |
A few days ago, I was asked to sign an online document over [DocuSign][1] as well as on SignEasy, any the signature were accepted just by a physical signature sent over email or on the app. They did not even ask me to generate a private key whose public key I should upload to their website. So, I felt that the process ... |
How can cryptographic signatures be somehow linked to a physical signature? |
I would like to encrypt some files using AES, Ill derive key from password using some standard PBKD function and use that as AES encryption key.
My question is, if user forgets the main password, then he has no input into PBKD function thus no way of getting the AES encryption key.
What algorithm/technique should... |
How to generate backup key for PBKD functions? |
I would like to encrypt some files using AES, Ill derive key from password using some standard PBKD function and use that as AES encryption key.
My question is, if user forgets the main password, then he has no input into PBKD function thus no way of getting the AES encryption key.
What algorithm/technique should... |
I'm trying to understand why the secret keys used by Alice and Bob in Diffie-Hellman are $a,b ∈ ℤ∗p$.
Say $a$ is $p - 1$, wouldn't the transmitted $g^a$ be 1 mod $p$ by $FLT$? Now anytime a passive listener sees a 1 being transmitted would know one of the secret keys and could easily compute the message. Im sure ... |
Why is GCM only usable for ciphers with a 128-bit block size? |
The "obvious" (it really isn't *that* obvious) thing you are missing is: **The same reasoning could be applied to literally *any* other private key!** There is nothing special about $a=\lvert(\mathbb Z/p\mathbb Z)^\times\rvert=p-1$ (which would, by the way, more commonly be represented as $0$ modulo itself), except tha... |
The short answer is that there's no link between your physical signature and any cryptographic signature. Indeed, from the [high-level description of how DocuSign works](https://www.docusign.com/how-it-works/electronic-signature) and [their security manifesto](https://www.docusign.com/how-it-works/security) there's no ... |
In looking at GPG's `gen_prime()` function, found within the `cyphers/primegen.c` file of `libgcrypt`, I noticed that the functions saves a list of the remainders from dividing the initial, randomly generated large number by the first 669 or so small prime numbers. What is the purpose of doing that? I don't see any rea... |
Why does GnuPG save an array of remainders when generating prime numbers? |
I'm trying to understand why the secret keys used by Alice and Bob in Diffie-Hellman are $a,b ∈ ℤ∗p$.
Say $a$ is $p - 1$, wouldn't the transmitted $g^a$ be 1 mod $p$ by $FLT$? Now anytime a passive listener sees a 1 being transmitted would know one of the secret keys and could easily compute the message. I'm sure... |
> Now I would like to use a single-block AES128 for the HMAC calculation in this scheme [...]
HMAC requires a hash function with a variable input size, so you cannot just use AES in it. If you want to use some other MAC instead of HMAC, you can use AES. AES ECB is a secure MAC for single block messages, so that woul... |
All block cipher modes of operation that I understand are generic schemes. They are not restricted by key size or block size. So why is GCM restricted to 128-bit block size?
|
What would be the recipe to add error propagation to a one time pad?
I.e. if I change a single letter in the clear text message, I want
the encrypted message to change starting from that letter and up to the
end of the encrypted message.
|
Is it possible to add error propagation to OTP? |
I am maintaining an application that uses PKCS#11 to talk to a smartcard. Somehow a session gets generated, but i cant figure out where in the code.
I am using c# and the [PKCS11Interop][1] wrapper. The funny thing is that if in my main application i do a `slot.GetTokenInfo()` i can see that there is one session ope... |
Bitlocker as example uses AES 128 Bit encryption as default - if it was brute forced how it can be done , I mean where's the file that will be brute forced to generate the password (If I'm right that file is suppose to be the 128 keys generated from the encryption right?)
I'm not asking about software to do this ( I'... |
If I'm understanding your question right, you're asking *"How to brute-force the Bitlocker encryption without being able to install stuff and without using "backdoors" and without having the key-file (if used)?"*
**You can't brute-force AES-128 without the said key-file.**<br>
The reason for this is that the key fi... |
Given X1 and X2 such that md5(X1) = md5(X2) and Y1 and Y2 such that md5(Y1) = md5(Y2), and knowing the following property of md5:
> if md5(a) = md5(b), md5(a|s) = md5(b|s)
is there a way to find Z1, Z2, Z3, and Z4 such that md5(Z1) = md5(Z2) = md5(Z3) = md5(Z4)? |
Has there been any research on entropy efficient information-theoretically secure PRNGs? |
Can someone please check my work and correct me if I am wrong, I am just starting to learn about DES. I am trying to solve the following problem:
> Show that `S1(x1) XOR S1 (x2) != S1(x1 XOR x2)`.
`x1 = 000000`, `x2 = 000001`
So, we get `S1(x1)` first: `00` is our row, and `0000` is our column which is `(0,... |
One of the necessary components to the Schnorr Digital Signature scheme is a pair of prime numbers $p$ and $q$ such that $q$ divides $p-1.$ However, there is never a modular inverse taken of q so why is there an extra constraint on $q$? Couldn't $q$ be a number that divides $p-1$ but not prime? |
Is this distributed OTP scheme secure? |
For example, let's say I want two cryptographically strong RNGs (R1 and R2).
And I want them to have the following property:
R1 (resp. R2) will never generate the same random number twice.
R1 (resp. R2) will never generate a random number that R2 (resp. R1) can generate.
Is it possible for three RNGs, 4, N ?
|
Is it possible to create "non overlapping" RNGs? |
For example, let's say I want two cryptographically strong RNGs (R1 and R2).
And I want them to have the following property:
R1 (resp. R2) will never generate the same random number twice.
R1 (resp. R2) will never generate a random number that R2 (resp. R1) can generate.
Is it possible for three RNGs, 4, N ?
U... |
I'm trying to get into pairing-based cryptography and I don't see why the group order of the group G in the pairing function
e:G*G-> G_t
has to be a prime number.
I don't find an argument why groups of order p^k for a prime number p and some entire number k cannot be used? |
Perhaps this has been answered before. Grovers algorithm should result in a 256 bit hash being complexity 128 bits to crack.
I was wondering, what if you had a 512 bit hash , and xor'd the lower 256 with the upper 256 bits to result in a final 256 bit hash number.
Does this increase the complexity (ie decrea... |
Perhaps this has been answered before. Grovers algorithm should result in a 256 bit hash being complexity 128 bits to crack.
I was wondering, what if you had a 512 bit hash , and xor'd the lower 256 with the upper 256 bits to result in a final 256 bit hash number.
Does this increase the complexity (ie decreasi... |
Why we need bilinear groups of composite order? What's the special security property of the composite order group in comparison with one of prime order? To put it in another way when do we need composite order groups for bilinear maps and when prime order? |
When do we need composite order groups for bilinear maps and when prime order? |
Good evening, I am writing a paper and I got comments from the reviewer that i dont quiet understand. please would you help me know if there is a difference between CPA(chosen plaintext attack) and IND-CPA( indistinguishability under chosen plaintext attack) in evaluating the security of an encryption scheme?
|
Perhaps this has been answered before. Grover's algorithm should result in a 256 bit hash being complexity 128 bits to crack.
I was wondering, what if you had a 512 bit hash , and xor'd the lower 256 with the upper 256 bits to result in a final 256 bit hash number.
Does this increase the complexity (ie: decreas... |
I am writing a paper and I got comments from the reviewer that I don’t really understand.
Is there any difference between a CPA (Chosen Plaintext Attack) and IND-CPA (Indistinguishability under Chosen Plaintext Attack) when evaluating the security of an encryption scheme?
|
What is the difference between CPA and IND-CPA? |
As I understand, there are a few requirements for a good hash function.
1. Hard to find any message from a given hash
2. Hard to find any 2 messages which give the same hash
3. A single bit change in the input message should lead to change of each bit of the output with a probability of 0.5 (as close as possibl... |
As I understand, there are a few requirements for a good hash function.
1. Hard to find any message from a given hash
2. Hard to find any 2 messages which give the same hash
3. A single bit change in the input message should lead to change of each bit of the output with a probability of 0.5 (as close as possibl... |
- For all PRNGs (including CSPRNGs) lets say there is a sequence x, y, z, then when the PRNG cycles back to x, then the sequence following it will be exactly the same as before. Is this true for all PRNGs?
- Are there any rules about minimum cycle length for CSPRNGs used for Stream Cipher? Because if a cycle happen... |
[Provably secure cryptographic hash functions](https://en.wikipedia.org/wiki/Security_of_cryptographic_hash_functions#Provably_secure_hash_functions) are often built using the same sort of operations as what are used in asymmetric crypto. The major problem with these constructions are that they are very inefficient. Al... |
Can an encryption method be used as a hash function? |
As I understand, there are a few requirements for a good hash function.
1. Hard to find any message from a given hash
2. Hard to find any 2 messages which give the same hash
3. A single bit change in the input message should lead to change of each bit of the output with a probability of 0.5 (as close as possibl... |
[Nimbus][1] or [Thinbus][2] two popular SRP implementations in Java and Javascript compute the proof of password as you describe `H(A|B|S)` where you can supply different hash functions such as SHA1 or SHA256 or better.
The actual [protocol design document][3] states `H(H(N) xor H(g), H(I), s, A, B, K)` where `K=H(... |
1. I'm using ECDH for generating ECDH public parameters (p,a,b,G,n), I try to get this values using `openssl ecparam -in cert.pem -text -noout`
For `Generator` $G=(x,y)$ I get :
Generator (uncompressed):
04:aa:87:ca:22:be:8b:05:37:8e:b1:c7:1e:f3:20:
ad:74:6e:1d:3b:62:8b:a7:9b:98:59:... |
How to exctract ECDH parameters from an OpenSSL-generated $G$? |
I have the trusted root certificate which I am validating using the self signed key. I also have the intermediate certificate, which i am validating using the root certificate.
Now when i am validating the certificate do i need to trace back the whole chain to validate the certificate?
Or can i say i have done TPC, i... |
This is problem 10 of Chapter 4 "Symmetric Encryption" from Lecture notes by Bellare and Rogaway.
> An IND-CPA secure encryption scheme might not conceal identities, in
> the following sense: given a pair of ciphertexts C, C′ for
> equal-length messages, it might be “obvious” if the ciphertexts were
> encrypted u... |
[Nimbus][1] or [Thinbus][2] two popular SRP implementations in Java and Javascript compute the proof of password as you describe `H(A|B|S)` where you can supply your own hash functions such as SHA1 or SHA256 or stronger.
The actual [protocol design document][3] states `H(H(N) xor H(g), H(I), s, A, B, K)` where `K=H... |
[Nimbus][1] or [Thinbus][2] are two popular SRP implementations in Java and Javascript compute the proof of password as you describe `H(A|B|S)` where you can supply your own hash functions such as SHA1 or SHA256 or stronger.
The actual [protocol design document][3] states `H(H(N) xor H(g), H(I), s, A, B, K)` where ... |
This is problem 10 of Chapter 4 "Symmetric Encryption" from Lecture notes by Bellare and Rogaway.
> An IND-CPA secure encryption scheme might not conceal identities, in
> the following sense: given a pair of ciphertexts C, C′ for
> equal-length messages, it might be “obvious” if the ciphertexts were
> encrypted u... |
If I use TOTP to generate codes with different "expiration", using the same Key for HMAC, will I create some kind of weakness? |
Is it secure to use TOTP with same key and differect time-counters? |
- 1. Bob calculates a private and public key.
- 2. Bob sends his public key to John.
- 3. Jeff is a third party unwanted member and manages to snatch the public key mid-transfer.
- 4. John encrypts his message and sends it to Bob.
- 5. Jeff again is able to steal this encrypted message for himself.
- 6. Bob ... |
How is RSA able to prevent brute forcing using the public key? |
Everywhere I read, this is being stated as a requirement. But nobody bothered to explain why this must be so.
Specifically, Yarrow and Fortuna both use a block cipher as the generator, and both limit the amount of output that can be produced by a particular key. The key is changed (aka rekey) once the limit is reach... |
Why must a CSPRNG's output be indistinguishable from true random? |
In textbook RSA, the euler $\phi$ function is used to define the private exponent d. On the other hand, real world cryptographic specifications require the carmichael lcm function to define d'.
It is clear that the d' divides d, and therefore using d' may be more efficient then using d.
My question is: Are there an... |
In textbook RSA, the Euler $\varphi$ function
$$\varphi(pq) := (p-1)(q-1)$$
is used to define the private exponent $d$. On the other hand, real-world cryptographic specifications require the Carmichael lcm function
$$\lambda(pq) := \operatorname{lcm}(p-1,q-1)$$
to define $d'$.
It is clear that the $d'$ divides $d$... |
If I use TOTP to generate codes with different "expiration" time, using the same key for HMAC, will I create some kind of weakness? |
Is it secure to use TOTP with same key and different time-counters? |
Is there any easy threshold signature scheme? |
WHy does AES file Encryption not ensure perfect secrecy ?
I understand that Pr[E(K,M1)=C1] = Pr[E(K,M2)=C2] given M1!=M2 holds for perfect secrecy of a scheme.
However, AES seems to offer this for any message. |
A hash function H is secure in terms of pre-image resis-tance. Does this imply that H has second pre-image (aka weak collision) resistance? |
Why does AES file encryption not ensure perfect secrecy?
I understand that $\Pr[E(K,M_1)=C_1] = \Pr[E(K,M_2)=C_2]$ given $M1\neq M2$ holds for perfect secrecy of a scheme.<br>
However, this seems to hold for any message with AES. |
Is a perfect hash function always bijective ?
In Wiki "In mathematical terms, it is a total injective function" but it does not mean, that it is bijective. |
Everywhere I read lists as a requirement that, to qualify as a CSPRNG, the output has to be indistinguishable from true random. But nobody bothered to explain why this cryptographers impose such a strong requirement.
Specifically, Yarrow and Fortuna both use a block cipher as the generator, and both limit the amount... |
Why do we require a CSPRNG's output to be indistinguishable from true random? |
I have a scenario that uses RFC-3526's Diffie-Hellman Group 14 for 2048 bit key exchanges. From the document, it specifies the P (prime) value in hexadecimal value as:
FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1
29024E08 8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD
EF9519B3 CD3A431B 302... |
ephemeral-ephemeral ECDH is it susceptible to MITM attack ? if yes, can you please give me a detailed answer ( Workflow that can be followed by the attacker) and how we can prevent this attack (static-ephemeral or we can keep ephemeral-ephemeral and change some parameters)?
Thank you in advance |
Here is the POW system: you are given a string and you need to compute a suffix so that first few bits of the MD5 value are all 0. I know MD5 is collision vulnerable, but is it safe to use MD5 here, or, state it in another way, is there a non-bruteforce way to compute the suffix? |
Is it safe to use MD5 in a proof of work system? |
So for Playfair, we choose a keyword and put that in the keytable with no duplicates. Then, we fill the rest of the table with alphabets in order that are not in the keyword without 'J'.
Does the length of the keyword matter? I am wondering because I wanted to know whether having just a random 25 characters long wor... |
Does the length of the keyword used for keytable for Playfair matter? |
How can I prove I have some certain facebook account online by signature ? |
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