instruction stringlengths 15 30k |
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If we only know the period of a Stream Cipher, let's say 150-200 bit in length, how can we use this information to attack a stream cipher?
Taking a look at this link, http://crypto.stackexchange.com/questions/24004/what-is-the-period-of-a-cipher I see that the period of the stream cipher is simply the amount of dat... |
For an assignment question, I am trying to prove formally that double encryption with two keys by the shift-cipher encryption function results in a shift cipher as well.
If the Shift-cipher encryption function is defined as:
$E_K(M)= (M + K) mod 26$
and suppose that we let $M = (x_1, ... , x_{m-1}, x_m)$ = an a... |
DES keys are traditionally stored as 8-byte blobs, with only the high 7 bits of each byte being meaningful to the algorithm; the low bit of each byte is set so that the population count of the byte is odd. This makes DES have a key size of 56 bits, rather than 64 bits.
Is there a standard format for storing a 56-bi... |
Is there a standard format for compact 56-bit DES keys? |
I'm thinking to sign a message using a key that is made up of a publicly shared key and a privately shared key. The operation for mixing the two keys could be concatenation, if it suffices.
To formalise it a bit, the signature is essentially `MD5(msg, concat(pub, priv))`.
Since the entire key isn't (completely) kno... |
I'm thinking to sign a message using a key that is made up of a publicly shared key and a privately shared key. The operation for mixing the two keys could be concatenation, if it suffices.
To formalise it a bit, the signature is essentially `MD5(msg, concat(pub, priv))`.
Since the entire key isn't (completely) kno... |
I'm thinking to sign a message using a key that is made up of a publicly shared key and a privately shared key. The operation for mixing the two keys could be concatenation, if it suffices.
To formalise it a bit, the signature is essentially `MD5(msg, concat(pub, priv))`.
Since the entire key isn't (completely) kno... |
I'm thinking to sign a message using a key that is made up of a publicly shared key and a privately shared key. The operation for mixing the two keys could be concatenation, if it suffices.
To formalise it a bit, the signature is essentially $$MD5(msg, concat(pub, priv))$$
Since the entire key isn't (completely... |
As the other answers already state here, game-based definitions are easier to write proofs for, but simulation-based definitions are often clearer in terms of the security guarantee that you get. The best example of this is IND-CPA (game-based definition) versus semantic security (simulation-based definition). Note tha... |
My question relates to the station-to-station protocol as described in https://en.wikipedia.org/wiki/Station-to-Station_protocol [1] and http://cacr.uwaterloo.ca/hac/ [2] p 519.
(1) Alice → Bob : gx
(2) Alice ← Bob : gy, EK(SB(gy, gx))
(3) Alice → Bob : EK(SA(gx, gy))
I fail to understand the reason... |
Why is (gy, gx) signed in STS (station-to-station)? |
I need a cryptographic scheme to generate a deterministic chain of private keys that look random to outside observer but can always be reconstructed from a single root key, also:
- Neither private keys nor their corresponding public keys should contain any information about each other.
- In case of some private... |
Is this key generation scheme secure? |
Is this scheme to derive multiple keys secure? |
I'm tring to choose one way to Encryption for my research?
,I want to choose one algorithm for multilayer algorithm ,that is the best one & applicable and what about homomorphic
|
Wikipedia says sha1 produces a 160-bit (20-byte) hash value. So if i compute the sha1 of all possible sha1 values, which as far as i understand is at current time impossible both to calculate and store, will i get all possible sha1 values? Would i be able to collide anything? |
If i compute the sha1 of all possible 40 digits hexadecimal strings, will i get al possible sha1 hashes? |
I'm tring to choose an way for an Encryption mothod for my research?
So,I want to choose one-layer encryption or multilayer encryption,and I want it to be easy to applicable.
when I search about it, I found Homomorphic and linear programing that used for encryption. But still I could not find an way that never used... |
I'm currently prototyping something with the NTRU encryption scheme but I wish to use it in "reverse" -- distribute private keys so anyone can decrypt, but keep the public keys secret and thus only allow certain entities to create new messages. Is NTRU still secure under such a scheme? It seems from the literature that... |
Is reverse NTRU still secure? |
I often encounter the phrase "I am not a cryptographer". Is there a generally accepted definition for who *is* a cryptographer? What qualifications would be expected?
For instance, should that person be expected to hold a relevant degree, or to have published $N$ papers?
Alternatively, would someone performing ... |
> [let] the last 8 bytes be the HMAC(key, msg)
64 bits is a pretty small tag size, and not considered "cryptographically strong". I would suggest using the full HMAC output if possible, or [see here](https://crypto.stackexchange.com/questions/20553/requirement-for-the-length-of-a-hmac-tag) for some discussion of re... |
I need to convert elements of the finite field $GF(p^k)$, p an odd prime, to an octet strings.
In the document IEEE P1363 there is a FE2OSP funtion which is probably not usable for that case.
Do you know of any well accepted standard which describes that encoding? |
I need to convert elements of the finite field $GF(p^k)$, p an odd prime, to an octet strings.
To be more precice, I want to include elliptic curve points over $GF(p^2)$ in a subjectPublickeyinfo of an X.509 certificate.
In the document IEEE P1363 there is a FE2OSP funtion which is probably not usable for that case. ... |
I know about ElGamal scheme and its key generation, encryption, and decryption methods. I'm not sure about what is meant by batch ElGamal.
Can someone please clarify it. How it differs from ElGamal and what are the attacks possible on that scheme. How do we prevent them?
|
It's been said that [CRC-64 is bijective for a 64-bit block][1].
It the corresponding statement true for typical cryptographic hashes, like MD5, SHA-1, SHA-2 or SHA-3?
For example, would SHA-512 be bijective when hashing a single 512 bit block?
[1]: http://crypto.stackexchange.com/questions/282/what-alphan... |
Are common cryptographic hashes bijective when hashing a single block of the same size as the output? |
I need to convert elements of the finite field $GF(p^k)$, where $p$ is an odd prime, to octet strings.
To be more precise, I want to include elliptic curve points over $GF(p^2)$ in a *Subject Public Key Info* of an X.509 certificate.
In the document IEEE P1363 there is a FE2OSP function which is probably not usable... |
Wikipedia says sha1 produces a 160-bit (20-byte) hash value. So if I compute the SHA-1 of all possible SHA-1 values, which as far as I understand is at current time impossible both to calculate and store, will I get all possible SHA-1 values? Would I be able to collide anything? |
If I compute the SHA-1 of all possible 40 digits hexadecimal strings, will I get all possible sha1 hashes? |
Ok,
if there is no standard, then "I do it my way":
Let $i$ be a root of a fixed minimum polynomial of $GF(p^2)$ and $x$ be an element in $GF(p^2)$. Then $x:= x_1+x_2*i$ can be represented as a vector $(x_1,x_2) \in GF(p)^2$.
Now convert $x_1$ and $x_2$ with the FE2OSP function form IEEE P1363 and concatenate the... |
Ok,
if there is no standard, then "I do it my way":
Let $i$ be a root of a fixed minimum polynomial of $GF(p^2)$ and $x$ be an element in $GF(p^2)$. Then $x:= x_1+x_2*i$ can be represented as a vector $(x_1,x_2) \in GF(p)^2$.
Now convert $x_1$ and $x_2$ with the FE2OSP function form IEEE P1363 and concatenate the... |
I would like to implement a protocol using elliptic curves. I'm thinking of using [MIRACL][1] so using curves in their Weierstrass form is preferable as it doesn't support them. I don't want to start picking random curves, however, looking at the available [safe cuves][2], none of the curves is in Weierstrass form. Do ... |
Consider a scenario in which group of people use common modulus 'n' in RSA crypto system.
where n=pq, p and q are large prime numbers.
Is there any chance for an attacker outside the group can view the original message? |
Consider a scenario in which group of people use common modulus 'n' in RSA crypto system.
where n=pq, p and q are large prime numbers.
Is there any chance for an attacker outside the group can view the original message?
Let me explain my solution. Assume group members receive the same messages. So, c1= m^e1 mod... |
Anonymity and authentication look to be seemingly contradictory but are both possible together ? I tried reading couple of papers but could not get the big picture. So what are the major approaches tried in solving anonymity preserving authentication ? (Am not really looking for references or recommendations but the so... |
Are Anonymity and Authentication possible together? |
Consider a scenario in which a group of people use a common modulus $n$ in the RSA crypto system,<br>
where $n=pq$, $p$ and $q$ are large distinct prime numbers.
Is there any chance for an attacker outside the group to view the original message?
Let me explain my solution. Assume the group members receive the s... |
Several years ago a group of malware authors began using code like this:
for (j = 0; j < length; j++)
ptr = (ptr ^ VALUEA) - VALUEB;
for encoding, and this to decode
for (j = 0; j < length; j++)
ptr = (ptr + VALUEB) ^ VALUEA;
I've recently seen this pop up in seemingly legitimate softwa... |
Is there specific name for simple XOR with ADD/SUB encoding? |
I am interesting to learn the low level implementation of (the Efficient Fully Homomorphic Encryption from (Standard) LWE) Click [here](http://people.csail.mit.edu/vinodv/6892-Fall2013/lwehom.pdf) and I am wondering if anyone can answer the following questions:
1-Does BV scheme work on binary numbers (0,1) or not?
... |
How does the Efficient Fully Homomorphic Encryption from (Standard) LWE work? |
Let's look at a version where the responder does NOT sign message 2.
(1) Tom → Frans : gx
(2) Tom ← Frans : gy, EK(gx, gy)
(3) Tom → Frans : EK(SA(gx, gy))
What if there is someone in the middle?
(1) Tom → gx → DIRNSA → gd → Frans
(2) Tom ← gd, EK(gx, gd) ← DIRNSA ← gy, EK(gd, gy) ← Fran... |
I am interesting to learn the low level implementation of
<br>
[Efficient Fully Homomorphic Encryption from (Standard) LWE](http://people.csail.mit.edu/vinodv/6892-Fall2013/lwehom.pdf)
<br>
and I am wondering if anyone can answer the following questions:
1 - Does the BV scheme work on binary numbers (0,1) or not... |
Several years ago a group of malware authors began using code like this:
for (j = 0; j < length; j++)
ptr[j] = (ptr[j] ^ VALUEA) - VALUEB;
for encoding, and this to decode
for (j = 0; j < length; j++)
ptr[j] = (ptr[j] + VALUEB) ^ VALUEA;
I've recently seen this pop up in seemingly legit... |
Consider a scenario in which a group of people use a common modulus $n$ in the textbook RSA crypto system,<br>
where $n=pq$, $p$ and $q$ are large distinct prime numbers.
Is there any chance for an attacker outside the group to view the original message?
Let me explain my solution. Assume the group members rece... |
Root cerificates are normally self-signed.
What is the reason behind that convention?
I mean, one must trust the root certificate in a non cryptographic way anyhow. |
must root certificates be self signed? |
Among the reason why root public keys are often expressed as a self-signed certificate are:
1. It cryptographically protects against a deliberate alteration of an attribute of the public key (e.g. extension of validity period, or of what the key can be used for).
2. It strongly protects against accidental alteratio... |
Take a Elliptical curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point?
Example
Private key 1 -> (x, y)
x = 0x79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798L
y = 0x483ada7726a3c4655da4fbfc0e11... |
Elliptical curve cryptography Determine if a public key point y is negative or positive, odd or even? |
I know various applications of RSA signatures. I wonder, is there any real-world applications of ElGamal signatures and encryption?
Give me an insight of this. |
Take a Elliptical curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point?
Example
Private key 1 -> (x, y)
x = 0x79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798L
y = 0x483ada7726a3c4655da4fbfc0e11... |
Take a Elliptical curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point?
Example
Private key 1 -> (x, y)
x = 0x79be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798L
y = 0x483ada7726a3c4655da4fbfc0e11... |
Treyfer for example has slower diffusion in decryption. It has full diffusion between words in 2 rounds for encryption and 7 rounds for decryption.
Can we ignore decryption and consider 2 rounds, if we don't use decryption? For example we are using Treyfer in CTR mode. |
Does diffusion of decryption matter when your not using it? |
Root certificates are normally self-signed.
What is the reason behind that convention?
I mean, one must trust the root certificate in a non cryptographic way anyhow. |
Must root certificates be self signed? |
Does decryption matter when it is not being used? |
I am thinking about this problem:
The server has a two-column table $T=\{c_1,c_2\}$. A user has a query $q$ that is sent to server. The server find an item $x$ in the first column satisfying $x=q$ and return the item $y$ in the second column to the user ($x$ and $y$ are in the same row).
The requirements are that... |
[Treyfer](https://en.wikipedia.org/wiki/Treyfer) for example has slower diffusion in decryption. It has full diffusion between words in 2 rounds for encryption and 7 rounds for decryption.
Can we ignore decryption and consider 2 rounds, if we don't use decryption? For example we are using Treyfer in CTR mode. |
[Treyfer](https://en.wikipedia.org/wiki/Treyfer) for example has slower diffusion in decryption. It has full diffusion between words in 2 rounds for encryption and 7 rounds for decryption.
Can we ignore decryption and consider 2 rounds, if we don't use decryption? For example we are using Treyfer in CTR mode.
Can... |
## No Signature
Let's look at a version where the responder does NOT sign message 2.
(1) Tom → Frans : gx
(2) Tom ← Frans : gy, EK(gx, gy)
(3) Tom → Frans : EK(SA(gx, gy))
What if there is someone in the middle?
(1) Tom → gx → DIRNSA → gd → Frans
(2) Tom ← gd, EK(gx, gd) ← DIRNSA ← gy... |
[Treyfer](https://en.wikipedia.org/wiki/Treyfer) for example has slower diffusion in decryption. It has full diffusion between words in 2 rounds for encryption and 7 rounds for decryption.
Do we have to consider the (bad) cryptographic properties of the decryption algorithm, if we're only using the encryption algori... |
Do we have to consider the cryptographic properties of the decryption, if we're only using the encryption? |
## No Signature
Let's look at a version where the responder does NOT sign message 2.
(1) Tom → Frans : gx
(2) Tom ← Frans : gy, EK(gx, gy)
(3) Tom → Frans : EK(SA(gx, gy))
What if there is someone in the middle?
(1) Tom → gx → DIRNSA → gd → Frans
(2) Tom ← gd, EK(gx, gd) ← DIRNSA ← gy... |
[Treyfer](https://en.wikipedia.org/wiki/Treyfer) for example has slower diffusion in decryption. It has full diffusion between words in 2 rounds for encryption and 7 rounds for decryption.
Do we have to consider the (bad) cryptographic properties of the decryption algorithm, if we're only using the encryption algori... |
**TL;DR**
No, the approach is not secure. Use a standard like [CMAC](https://en.wikipedia.org/wiki/CMAC) instead. Or even better, check your AES accelerator module to see if it supports any [AEAD](https://en.wikipedia.org/wiki/Authenticated_encryption) modes of encryption like [GCM](https://en.wikipedia.org/wiki/Gal... |
How does the small n attack work? |
I know various applications of RSA signatures. I wonder, is there any real-world applications of ElGamal signatures and encryption? |
It took more than a decade from when MD5 looked like it was going to break to the point when it was actually broken. That's more than a decade of warning.
How can we be sure that when our cryptosystems are flawed, we'll have enough warning-time to change them?
How can we be sure that, say, ECC won't get broken ov... |
> I know PBKDF2 is essentially "useless" against anyone with a GPU rig and I have read that bcrypt is "useless" to anyone with an FPGA setup.
Neither is useless. Newer alternatives like scrypt and the eventual PHC winner make better use of the defenders' resources, but even a thousand iterations of PBKDF2 is useful,... |
Can we implement Encryption Algorithms like RC4,AES and DES in Verilog? if no what are the limitations? |
I'm working on a project in MCU environment with GPRS connection to exchange data securely with the cloud. The encryption algorithm has been selected to use AES. I did some search on internet and figured out that ECDH key agreement protocol quite fits into the requirements. And the good news is that there're some secur... |
Do ECDH and ECDSA combined solution provide an authenticated protocol exchange solution in MCU environment? |
I'm working on a project in MCU environment with GPRS connection to exchange data securely with the cloud. The encryption algorithm has been selected to use AES. I did some search on internet and figured out that ECDH key agreement protocol quite fits into the requirements. And the good news is that there're some secur... |
I would like to implement a protocol using elliptic curves. I'm thinking of using [MIRACL][1] so using curves in their Weierstrass form is preferable as it doesn't support them. I don't want to start picking random curves, however, looking at the available [safe curves][2], none of the curves is in Weierstrass form. Do... |
I am interesting to learn the low level implementation of [Efficient Fully Homomorphic Encryption from (Standard) LWE](http://people.csail.mit.edu/vinodv/6892-Fall2013/lwehom.pdf) and I am wondering if anyone can answer the following questions:
1. Does the BV scheme work on binary numbers (0,1) or not?
2. Does t... |
Safe curves in Weistrass form? |
My question is about how difficult is for someone having compromised the PSK and sniff all (DT)LS handshake, (so getting the NONCE), to get the encryption keys ?
I understand :
getting the pre-master secret is straight forward
but then, what about the master secret MS ?
because MS is calculated with PRF_HM... |
My question is about how difficult is for someone having compromised the PSK and sniff all (DT)LS handshake, (so getting the NONCE), to get the encryption keys?
I understand :
getting the pre-master secret is straight forward
but then, what about the master secret MS?
because MS is calculated with PRF_HMAC... |
In the BPS specification [document][1] it says
> We denote by f the number of output bits of the internal function F
What is this if the internal function is AES? Would it be the block size (e.g. 128)?
[1]: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/bps/bps-spec.pdf |
What are the number of output bits of the internal function F used in BPS algorithm? |
I'm working on a project in MCU (micro controller) environment with GPRS connection to exchange data securely with the cloud. The encryption algorithm has been selected to use AES.
I did some search on internet and figured out that ECDH key agreement protocol quite fits the requirements. The good news is that there ... |
I would like to implement a protocol using elliptic curves. I'm thinking of using [MIRACL][1] so using curves in their Weierstrass form is preferable as it they are supported by this framework.
I don't want to start picking random curves, so I am looking at the available [safe curves][2]. None of the curves is in We... |
Safe curves in Weierstrass form? |
I was presented with this seemingly paradoxical information, and am hoping someone can explain what I'm missing here.
I have an encrypt-and-mac scheme here.If I want to transmit message **m** to Bob, I'd first **Enc_k1(m) = c**, **MAC_k2(m) = t**, and then send **c||t** over to Bob. So far, I understand that this sc... |
How can a Encrypt-And-MAC scheme be insecure if the encryption is CCA secure? |
I was presented with this seemingly paradoxical information, and am hoping someone can explain what I'm missing here.
I have an encrypt-and-mac scheme here.If I want to transmit message **m** to Bob, I'd first **Enc_k1(m) = c**, **MAC_k2(m) = t**, and then send **c||t** over to Bob. So far, I understand that this sc... |
Why is public key cryptography (RSA) used in sites like Google or Facebook? |
I am new in cryptography domain and try to build some understanding on RSA key pair generation.
My doubt is on RSA public key exponent value . Can exponent be any value (prime or non prime numbers)? i am not getting proper answer for this.
if someone has useful link for this please help to share.
Regards
Nikh... |
I need an algorithm that can take an integer, an arbitrary range, a key of 16/24/32 bytes, and an initialization vector of 16 bytes(ideally), and return an integer in the same range.
My latest attempt at this repeatedly encrypts an integer with AES_OFB until it is in the requested range. I'm using a stream cipher so... |
Is there a way to encrypt an integer within an arbitrary range? |
I am using a vendor library that signs a text producing a PKCS#7 message. I'm not sure of the content of this message. Does a pkcs#7 message must contain the signed message, the certificate, the payload? Does it have to start with ----BEGIN PKCS7---- ----END PKCS7----? |
First, this a different take on my previous question: http://crypto.stackexchange.com/questions/25535/pailler-encryption-of-small-integers-to-32-bit-integers
I have to encode small integers (range 0-50) using the Paillier cryptosystem. Those values will be encountered many times (100,000) in my dataset.
**Versio... |
I am using a vendor library that signs a text producing a PKCS#7 message. I'm not sure of the content of this message.
Does a pkcs#7 message have to contain the signed message, the certificate, the payload? Does it have to start with `----BEGIN PKCS7----` and end with `----END PKCS7----`? |
In the algorithm for [BPS Format Preserving Encryption][1]
what is the tweak value? 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)? What possible input values can the user provide for the tweak?
[1]: http://csrc.nist... |
What is the tweak in BPS FPE algorithm? |
>Does the limited range of the values, makes cracking the Paillier cryptosystem easier?
That depends. I'm assuming that you are generating good, large random $r$ values, just reusing them for the same plaintexts. The main problem with this is that you loose semantic security. It however does not lead to a key leakag... |
First, this a different take on my previous question: http://crypto.stackexchange.com/questions/25535/pailler-encryption-of-small-integers-to-32-bit-integers
I have to encode small integers (range 0-50) using the Paillier cryptosystem. Those values will be encountered many times (100,000) in my dataset.
**Versio... |
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