instruction stringlengths 15 30k |
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I have been reading about SHA-2 family and I found a lot of In depth details, but I am Confused about how Secure hash is related to TLS and AES, TLS which is present SSL, encrypts data between server and client but, does it make use of SHA and for what, like what kind of data?
Also, AES is used for passwords as far as... |
I would like to know if there exists a protocol which performs the following operation in a privacy-preserving fashion:
- User $U$ wants to know whether a record is stored in the database. The primary key of the record is an id which is known by the user.
- User $U$ sends a "private" query containing the record i... |
I have been reading about SHA-2 family and I found a lot of in depth details, but I am confused about how it is related to TLS and AES. TLS encrypts data between server and client, but does it make use of SHA and for what, like what kind of data? |
As one of the authors of the paper, let me give you an answer. The operation $F$ is indeed applied to both $x$ and $x'$. By stating that $\oplus$ is invariant under rotation, we mean that if you first rotate $x$ and $x'$ and take the difference with $\oplus$, you get the same result as if you first take the difference ... |
I would like to know if there exists a protocol which performs the following operation in a privacy-preserving fashion:
- User $U$ wants to know whether a record is stored in the database. The primary key of the record is an id which is known by the user.
- User $U$ sends a "private" query containing the record i... |
anyone knows any reference that proof it ? Please Help . |
How Proof all Subgroup point of prime order elliptic curve have prime order [#G=#E]? |
I'm reading [FSB cryptographic hash function][1] and the authors say that security of this function depends on NP-Complete Problem: "Decoding Linear Code Unlike most other cryptographic hash functions in use today" and I'm agree with the first part of claim. But I have a doubt respect to conventional hash functions for... |
From Lagrange you know that the orders of elements in a finite group are divisors of the group order. Now you have a prime order group of order $p$ and thus the possible orders are $1$ and $p$. Now, the identity has order $1$ and are there any other elements different from the identtiy that can have order $1$? (no) Wha... |
From Lagrange you know that the orders of elements in a finite group are divisors of the group order. Now you have a prime order group of order $p$ and thus the possible orders are $1$ and $p$. Now, the identity has order $1$ and are there any other elements different from the identtiy that can have order $1$? (no) Wha... |
How is it possibile to cryptographically make a document truly read only? As in read only I imply that the user can obviously view it which can be achieved by coding which pixels have which colors. But how is it done in the industry? and what's more important is it possibile to password-protect it too?
I have consider... |
Some cryptographers feel that the ultimate goal for an encryption scheme is [semantic security][1] or, even better, [perfect security][2].
An encryption scheme that supports de-duplication also allows the backup server -- and the attacker, who we assume steals every backup tape that the server sysadmins send to the ... |
Some cryptographers feel that the ultimate goal for an encryption scheme is [semantic security][1] or, even better, [perfect security][2].
An encryption scheme that supports de-duplication also allows the backup server -- and the attacker, who we assume steals every backup tape that the server sysadmins send to the ... |
In the NSA's document, "[The Case for Elliptic Curve Cryptography][1]", we have
> +---------------+-------------------------+-----------------+
| Symmetric Key | RSA and Diffie-Hellman | Elliptic Curve |
| Size (bits) | Key Size (bits) | Key Size (bits) |
+---------------+-------------... |
Why is the P-521 elliptic curve not in Suite B if AES-256 is? |
The MAC algortihm which is used along with a secret key to generate a MAC tag on the sender end ,is it same at the receiver end also who again uses a MAC algorithm to generate a tag?
If yes, then how is the MAC algorithm generated. Is it just a function(a mathematical function to compute)??
If no, then how does t... |
If the goal is to demonstrate that you are who you say you are, I think the following will work: Bob wants to know that you are Amy. Bob encrypts a number using Amy's public key and then asks her what that number is. If Bob gets back the number, "Amy" at least had Amy's private key.
From what I have read, this is no... |
While going through [this][1] paper, I came across the idea of Set Membership proofs. The proof allows a prover to prove that a value is contained in some set. The point where I am confused is, all the elements of the set are known to the prover. All three steps of the proof generation can be run by anyone including th... |
What does Set Membership actually prove? |
While going through [this][1] paper, I came across the idea of Set Membership proofs. The proof allows a prover to prove that a value is contained in some set. The point where I am confused is, all the elements of the set are known to the prover. All three steps of the proof generation can be run by anyone including th... |
We know that MAC algorithm and key are used in both sender and receiver side to get the matching MAC tages to prove that the data is authentic.
Now in HMAC we know that, it makes use of crytographic hash function which is irreversible, so when we use HMAC from the sender side to encypt a message using the HMAC formu... |
In SSL/TLS we use symmetric and asymmetric keys to encrypt the data, this means that the keys are used to encrypt the data (preserve the integrity) or provide a secure channel for the data to be sent??
Hashing algortihtms **inside of the SSL handshake protocol**,as far as i know are used to provide data integrity. S... |
Are SSL/TLS used for maintaining data confidentiality? |
In SSL/TLS, we use symmetric and asymmetric keys to encrypt the data. Does that mean that the keys are used to encrypt the data (preserve the integrity) or provide a secure channel for the data to be sent?
And as far as I know, hashing algorithms – inside of the SSL handshake protocol – are used to provide data inte... |
Suppose a $1000$-bit key used in the one-time pad is not randomly and uniformly generated.
$1)$ Suppose that the values of the first $5$ bits are $0$, and the other $995$ bits are randomly generated and uniformly distributed (each bit with value $0$ and $1$ with probability $0.5$), what is the entropy of the key?
... |
The question whether SSL/TLS is used for maintaining data confidentiality, is actually not as straight-forward as one might think. It depends.
We might disregard the deprecated SSL cipher suites that provided authenticity and integrity with a NULL bulk encryption algorithm. Even if you only take the cipher suites th... |
Suppose a $1000$-bit key used in the one-time pad is not randomly and uniformly generated.
$1)$ Suppose that the values of the first $5$ bits are $0$, and the other $995$ bits are randomly generated and uniformly distributed (each bit with value $0$ and $1$ with probability $0.5$), what is the entropy of the key?
... |
Description of partial hashes
---
Partial hashes are canonical forms of digest state that can be transferred from one hash implementation to another, so that the other, limited device (e.g. a smart card chip) can finish the hash calculation with the remaining data. This scheme is used to create a signature generati... |
Is a length padding technique in a hash function used to avoid length extension attacks ? |
What is the exact purpose of length padding in hash functions? |
Why does the padding in Merkle–Damgård hash functions like MD5 contain the message length? |
What is the exact purpose of length padding in Merkle–Damgård hash functions? |
What is the minimum number of unique pairs of `digests` and `inputs` to a [one-time pass](https://github.com/nathforge/pyotp/blob/master/src/pyotp/otp.py) needed to verify that a secret is equal to a given `s` where the output is an integer with of at most `digits` digits.
My back-of-a-napkin calculation is simply:
... |
Suppose a $1000$-bit key used in the one-time pad is not randomly and uniformly generated.
1. Suppose that the values of the first $5$ bits are $0$, and the other $995$ bits are randomly generated and uniformly distributed (each bit with value $0$ and $1$ with probability $0.5$), what is the entropy of the key?
2... |
Say I'm connecting to a web server secured with TLS but with a self-signed certificate. Accordingly, I call the owners of the server and ask them what SHA1 fingerprint they have.
They start reading out the hex digits to me and I follow along, but before reaching the end, I just say "That's fine thanks, no need to re... |
What is the minimum number of unique pairs of `digests` and `inputs` to a [one-time pass](https://github.com/nathforge/pyotp/blob/master/src/pyotp/otp.py) needed to verify that a secret is equal to a given `s` where the output is an integer with of at most `digits` base-10 digits.
My back-of-a-napkin calculation is ... |
What is the minimum number of unique pairs of `digests` and `inputs` to a [one-time pass](https://github.com/nathforge/pyotp/blob/master/src/pyotp/otp.py) needed to verify that a secret is equal to a given `s` where the output is an integer with of at most `digits` base-10 digits.
My back-of-a-napkin calculation is:... |
What is the minimum number of unique pairs of `digests` and `inputs` to a [one-time pass](https://github.com/nathforge/pyotp/blob/master/src/pyotp/otp.py) needed to verify that a secret is equal to a given `s` where the output is an integer with of at most `digits` base-10 digits.
My back-of-a-napkin calculation is:... |
What is the minimum number of unique pairs of `digests` and `inputs` to a [one-time pass](https://github.com/nathforge/pyotp/blob/master/src/pyotp/otp.py) needed to verify that a secret is equal to a given `s` where the output is an integer with of at most `digits` base-10 digits.
My back-of-a-napkin calculation is:... |
Description of intermediate hashes
---
Intermediate (or partial) hashes are canonical forms of digest state that can be transferred from one hash implementation to another, so that the other, limited device (e.g. a smart card chip) can finish the hash calculation with the remaining data. This scheme is used to crea... |
ECB is considered to be insecure when used for confidentiality because identical plaintext result with identical ciphertext. But what if we use ECB for authentication?
Assume A wants to transmit an authenticated message X to B. A and B have a shared key. What if A encrypts X using AES-ECB and outputs Y as an authent... |
ECB is considered to be insecure when used for confidentiality because identical plaintext result with identical ciphertext. But what if we use ECB for authentication?
Assume A wants to transmit an authenticated message X to B. A and B have a shared key. What if A encrypts the plaintext X using AES-ECB and outputs Y... |
What is the minimum number of unique pairs of `digests` and `inputs` to a [one-time pass](https://github.com/nathforge/pyotp/blob/master/src/pyotp/otp.py) needed to verify that a secret is equal to a given `s` where the output is an integer with of at most `digits` base-10 digits.
My back-of-a-napkin calculation is ... |
We know that MAC algorithm and key are used in both sender and receiver side to get the matching MAC tages to prove that the data is authentic.
Now in HMAC we know that, it makes use of crytographic hash function which is irreversible, so when we use HMAC from the sender side to encypt a message using the HMAC formu... |
1. Which public key encryption scheme is re-randomizable?
2. Is there any library for re-randomizable encryption scheme?
3. If not, how can I re-randomize a given public key encryption scheme?
I cannot find any papers about re-randomizable encryption. |
Which public key encryption scheme is re-randomizable? How can I re-randomize an encryption scheme? |
I have learned from Applied Cryptography that triple encryption with three independent keys in encryption-decryption-encryption (EDE) process gives security not higher then $2^{2n}$ when it comes to meet-in-the-middle attack, where n is keysize. If the triple encryption is done in encryption-encryption-encryption (EEE)... |
The DES retail MAC, also known as ISO 9797-1 mode 3 with DES, computes the MAC of a block of data using a 16-byte (112 bit) key. It can be seen as CBC-MAC using simple DES with the first half of the key for all the blocks, except the last where 3DES where the full key is used. I've left padding and truncation out of th... |
What are options to compute DES retail MAC (aka ISO 9797-1 mode 3) under PKCS#11? |
I'm implementing a format-preserving encryption scheme similar to those described in the [literature][1]. I want to sanity test my PRP using some statistical tests like [TestU01][2]. However, I'm not sure how applicable these kinds of tests are to PRPs since they are designed to test PRNGs. Are there statistical tests ... |
Recently, I was given three ciphers to crack for my cryptography class. At this point, I have guessed that one of them is likely a Hill cipher (probably 3x3, as that is the most complex we have done so far).
I have made a fairly good guess of two options for the first seven characters in the cipher, but I found mys... |
Suppose a $1000$-bit key used in the one-time pad is not randomly and uniformly generated.
1. Suppose that the values of the first $5$ bits are $0$, and the other $995$ bits are randomly generated and uniformly distributed (each bit with value $0$ and $1$ with probability $0.5$), what is the entropy of the key?
2... |
Prove that if only one character is encrypted using a shift cipher, then the shift cipher is perfectly secure.
I want to show that $P(P=p | C=c)=P(P=p)$. But I don't know how to relate. Can anyone guide me?
|
[This paper](http://www.google.co.in/url?q=http://coitweb.uncc.edu/~yzheng/publications/files/ieiceE71-8b.pdf&sa=U&ei=kOcHVO7NJ8fluQTrx4KwBA&ved=0CC8QFjAE&sig2=HllGFI2a1i927bofmOAhjg&usg=AFQjCNE9rJTsTRTIaBBD1E3ux54gRJXjAw) considers the exponent to be an odd integer.
When k = 2, it is called the quadratic residuosit... |
The DES retail MAC, also known as ISO 9797-1 mode 3 with DES, computes the MAC of a block of data using a 16-byte (112 bit) key. It can be seen as CBC-MAC using simple DES with the first half of the key for all the blocks, except the last where 3DES with the full key is used. I've left padding and truncation out of the... |
Assume a password storage scheme using a computationally-expensive hash algorithm and a CSPRNG salt. User ID, salt, and hash value are stored in a table; if the table is compromised, all three values are available to an adversary.
Is there any value in computing a new salt when a user changes his password? (I thi... |
Change Salt when Changing Password? |
secp256r1 and secp256k1 are both examples of two [eliptic curves](http://en.wikipedia.org/wiki/Elliptic_curve) used in various asymmetric cryptography.
Googling for these shows most of the top results are Bitcoin related.
I've heard the claim that
> Satoshi picked non-standard crypto which conventional wisdo... |
Is secp256r1 more secure than secp256k1? |
I have learned from Applied Cryptography that triple encryption with three independent keys in encryption-decryption-encryption (EDE) process gives security not higher then $2^{2n}$ when it comes to meet-in-the-middle attack, where $n$ is keysize. If the triple encryption is done in encryption-encryption-encryption (EE... |
We are implementing searchable encryption techniques proposed by Song et al in Java for a paper[1]. The schemes need a Stream Cipher for achieving search over encrypted data.
The stream of random bits should be reproducible later while decryption given the same "Seed".
Now we plan to generate the stream of random ... |
Is this correct way to generate stream cipher using AES CTR mode? |
**Assumptions:**
- $A$ wants to communicate with $B$
- $A$ knows a public key $P_B$ which is trusted by a third party and belongs to $B$
- $A$ knows the address of someone who pretends to be $B$
**$A$ wants to send a message to $B$ using *ECIES*:**
1. $A$ calculates a random private key $K$ and the related p... |
ECIES: Purpose of MAC? |
**Assumptions:**
- $A$ wants to communicate with $B$
- $A$ knows a public key $P_B$ which is trusted by a third party and belongs to $B$
- $A$ knows the address of someone who *pretends* to be $B$
**$A$ wants to send a message to $B$ using *ECIES*:**
1. $A$ calculates a random private key $K$ and the related... |
> Can $A$ assume that only $B$ can read the message?
Only someone with the private key corresponding to $B_B$ can read the message. If $A$ can assume that only $B$ has it, that works.
> As $B$ does not know anything about $A$ what is the cryptographic purpose of the MAC?
So that someone else cannot modify the... |
We are implementing searchable encryption techniques proposed by Song et al in Java for a [paper](http://www.cs.berkeley.edu/~dawnsong/papers/se.pdf)[1]. The schemes need a Stream Cipher for achieving search over encrypted data.
The stream of random bits should be reproducible later while decryption given the same "Se... |
So if I did this: AES_k(C) ⊕ AES_k(C), where C is a 128 bit incrementing counter, and keys for both transforms are random and unique and the xor occurs on every 16 byte block, would the xored output be less secure than the size of state used to seed the generator? Does this method reduce security or introduce vulnerabi... |
Would xoring 2 independant AES CTRs to produce p-rand introduce vulnerabilities? |
So if I did this: AES_k(C) ⊕ AES_k(C), where C is a 128 bit incrementing counter, and keys and counters for both transforms are random and unique and the xor occurs on every 16 byte block, would the xored output be less secure than the size of state used to seed the generator? Does this method reduce security or introd... |
> Can $A$ assume that only $B$ can read the message?
Only someone with the private key corresponding to $P_B$ can read the message. If $A$ can assume that only $B$ has it, that works.
> As $B$ does not know anything about $A$ what is the cryptographic purpose of the MAC?
So that someone else cannot modify the... |
So if I did this: AES_k1(C1) ⊕ AES_k2(C2), where C is a 128 bit incrementing counter, and keys and counters for both transforms are random and unique and the xor occurs on every 16 byte block, would the xored output be less secure than the size of state used to seed the generator? Does this method reduce security or in... |
According to [Wikipedia][1] the *ECIES* algorithm has two optional shared information $S_1$ and $S_2$. They are used as follows:
1. Generate a random shared secret $Z$ according to *ECIES*, which will never be reused
2. Derive symmetric keys $k_1|k_2=KDF(Z_x|S_1)$
3. Encrypt the message $c=\text{ENCRYPT}_{k_1}(m)$... |
ECIES: Purpose of optional shared information? |
Assuming
$$AES_{k_1}(C_1) \oplus AES_{k_2}(C_2)$$
where AES is used in CTR mode, $C$ is a 128 bit incrementing counter, keys and counters for both transforms are random as well as unique, and the XOR occurs on every 16 byte block.
If I did this, would the XORed output be less secure than the size of state used... |
The main difference is that secp256r1 is a prime field curve, while secp256k1 is a Koblitz curve. Koblitz curves are known to be a few bits weaker than prime field curves, but since we are talking about 256-bit curves, neither is broken in "5-10 years" unless there's a breakthrough.
The other difference is how the p... |
Using: SHA256(N), where N is 64 bytes of output from the Windows CryptGenRandom function. Are there any known vulnerabilities with using this method to create key material? Should N be more than the SHA256 block size of 64 bytes? Aligning to block size means 2 passes through the hashing function, (block and finalize), ... |
Is using SHA256 to extract entropy from a random nonce a good way to create keying material? |
Is using SHA256 to extract entropy from a p-rand nonce a good way to create keying material? |
Using: SHA256(N), where N is 64 bytes of output from the Windows CryptGenRandom function. Are there any known vulnerabilities with using this method to create key material? Should N be more than the SHA256 block size of 64 bytes? Aligning to block size means 2 passes through the (internal) hashing function, (block and ... |
Using $SHA256(N)$, where $N$ is 64 bytes of output from the Microsoft Windows `CryptGenRandom` function. Are there any known vulnerabilities with using this method to create key material? Should $N$ be more than the SHA256 block size of 64 bytes? Aligning to block size means 2 passes through the (internal) hashing func... |
Please help me pick right design of software…
I have to design client-server software, where the server should verify that the client runs software from specific source code. It has to be verifiable that the software doesn't simulate actions (results of algorithms). So, we accept that client could be compromised. ... |
Curves secp256r1 and secp256k1 are both examples of two [eliptic curves](http://en.wikipedia.org/wiki/Elliptic_curve) used in various asymmetric cryptography.
Googling for these shows most of the top results are Bitcoin related. I've heard the claim that…
> Satoshi picked non-standard crypto which conventional w... |
Prevent double-spending with decentralized digital currencies without all transactions being public? |
FIPS 180-3 defines the initial hash value for SHA-256 as the first 32 bits of the fractional parts of the square roots of the first 8 primes 2..19. What would be the risks of using a different value (for example: a random salt)? Conceptually, this would be the same as prepending the message with a block which hashed ... |
I'm currently interested in the problem of generating random-looking URLs from sequential database IDs, like how they do it in link shorteners. One way to do this is to encrypt the sequential database ids using a 32 bit block cypher and [base62 encode](https://en.wikipedia.org/wiki/Base64) the result so it can be writt... |
Is it possible to generate a secure permutation F over 32-bit integers even if F(0) ... F(n) is public knowledge? |
I'm currently interested in the problem of generating random-looking URLs from sequential database IDs, like how they do it in link shorteners. One way to do this is to encrypt the sequential database ids using a 32 bit block cypher and [base62 encode](https://en.wikipedia.org/wiki/Base64) the result so it can be writt... |
I'm currently interested in the problem of generating random-looking URLs from sequential database IDs, like how they do it in link shorteners. One way to do this is to encrypt the sequential database ids using a 32 bit block cypher and [base62 encode](https://en.wikipedia.org/wiki/Base64) the result so it can be writt... |
Why is Rijndael restricted to key length in {128, 160, 192, 224, 256} bits (and not larger)? The algorithm looks to me like it would support an arbitrary-sized key (multiple of 32).
The rounds operate without the key. Between rounds, the state is XORed with as many key bytes as are needed according to the block size... |
Why is Rijndael (AES) key length restricted? |
Why is Rijndael restricted to key length in {128, 160, 192, 224, 256} bits (and not larger)? The algorithm looks to me like it would support an arbitrary-sized key (multiple of 32).
The rounds operate without the key. Between rounds, the state is XORed with as many key bytes as are needed according to the block size... |
Why is Rijndael key length restricted? |
The [key schedule][1] uses constants that differ between the key sizes. For arbitrary sized keys you would have to define an algorithm for deriving them. Each key size also uses a different number of rounds, for which you would have to do the same.
Also, what's the point? 256-bit keys are [enough for all eternity][2... |
Can you use threshold encryption and a mixnet? It might not be the fastest thing in the world but it uses well-understood components.
# Setup
1. Every player generates an ElGamal keypair and proves knowledge of their secret key. The joint public key is the product of all public keys. (If you're worried about res... |
> - Is this (cryptographically) secure?
That is hard to say without knowing the exact details of the bitcoin protocol (which I would like to understand better, but don't have the time at the moment). Looking at the document you linked to, the public child key is created as $\text{HMAC-SHA512}(Key = c_{par}, Data = s... |
> - Is this (cryptographically) secure?
That is hard to say without knowing the exact details of the bitcoin protocol (which I would like to understand better, but don't have the time at the moment). Looking at the document you linked to, the public child key is created as $\text{HMAC-SHA512}(Key = c_{par}, Data = s... |
I'm trying to crack my thermostat's network protocol.
I've captured several rounds of network traffic and here is what I've got to work with.
* Communicating via HTTP POST
* The POST data is JSON followed by ciphertext.
* The JSON contains:
* A device unique id: 48 bits
* An eiv (initialization vector?): ... |
I am looking at G now, but is there a better, (in terms of security and speed), means by which a byte array can be expanded that doesn't involve another cipher, just a method? I need to expand 1024 bytes to 4096, and speed is less important than overall entropy. I am also trying to find something that doesn't use a ran... |
What is the most secure key expansion routine amoung block ciphers? |
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