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Does authenticated encryption add any protection to a signed digital envelope? |
I want to build an app that uses client-side encryption for storing encrypted data on the server. A user-specific master key would be used, so to easily share it between devices a encrypted version of it would be stored on the server.
The user's passphrase would be used for both 1) encrypting the master key and 2) a... |
Is this client-side password hash scheme secure? |
My question is fairly simple. I have more than two nodes which needs to communicate very efficiently from computational point of view. One of the nodes can become a coordinator between the nodes. Nodes do have certificate and private keys. To let the nodes communicate with each other efficiently I plan to use a symmetr... |
We are working with a third party vendor who is very tight lipped about their security protocols, and one of our customers who used this vendor's products is claiming that approximately one in every 250 times they initialize the system, it generates a key file that is 127 bits instead of 128, and gets rejected. They be... |
How often does RSA-OAEP have a leading zero? |
> What is meant by vectors here?
Just the inputs and outputs of the function. The function $f$ takes, as input, a sequence of bits (for example, 1010), and returns a sequence of bits (for example, 1100); the text refers to such a sequence of bits as a *vector*
> Can someone explain this?
Well, the idea is tha... |
I actually was wondering if anyone could help me out with the following problem:
Let's assume we are attacking the first SubBytes() operation on AES with the help of a differential power analysis attack, for a DPA attack we need to know the plaintext in order to create the hypothesis and to apply the used power mode... |
Why should the input value on a DPA attack be non-constant? |
I need some suggestions about the use of the CRC in my application. I need to be sure about the BIOS run by the CPU. I have a FPGA between the BIOS flash and the CPU that sniff every read performed by the CPU on the BIOS memory. The initial idea was to compute the SHA1 of the data stream to authenticate and to be sure ... |
I actually was wondering if anyone could help me out with the following problem:
Let's assume we are attacking the first `SubBytes()` operation on AES with the help of a differential power analysis attack, for a DPA attack we need to know the plaintext in order to create the hypothesis and to apply the used power mo... |
I actually was wondering if anyone could help me out with the following problem:
Let's assume we are attacking the first `SubBytes()` operation on AES with the help of a differential power analysis attack, for a DPA attack we need to know the plaintext in order to create the hypothesis and to apply the used power mo... |
Regarding your comment "Would the database need to be compromised for a dictionary attack to be useful?"
The answer is no.
A dictionary attack would require a username/email (which might either be known or could come from a small dictionary) and then trying words from the dictionary. This is attempting to get in ... |
The definition of pseudo randomness that leads to pseudo random function talks about indistingishability of a key-ed function and a random function.
i.e. The key-ed function family $\{F_k\}$ is PRF if $|Pr[D^{F_k}(1^n)=1] - Pr[D^{f}(1^n)=1]|$ is negligible for $k\leftarrow\mathcal{K}$ and $f\leftarrow\mathcal{F}$.
... |
(By items I mean hashable objects.) As an example (with obviously way too short hashes for readability), say I [packed my bag](https://en.wikipedia.org/wiki/I_packed_my_bag) and in it I put
* a shovel (hashed to `S`)
* a bucket (hashed to `B`)
* a towel (hashed to `T`)
* a random number (hashed to `R`)
Now fr... |
I hashed my bag and in it I put... "Is there a hash for unordered items?" |
(By items I mean hashable objects.) As an example (with obviously way too short hashes for readability), say I [packed my bag](https://en.wikipedia.org/wiki/I_packed_my_bag) and in it I put
* a shovel (hashed to `S`)
* a bucket (hashed to `B`)
* a towel (hashed to `T`)
* a random number (hashed to `R`)
Now fr... |
We are working with a third party vendor who is very tight lipped about their security protocols, and one of our customers who used this vendor's products is claiming that approximately one in every 250 times they initialize the system, it generates a key file that is 127 bits instead of 128, and gets rejected. They be... |
We are working with a third party vendor who is very tight lipped about their security protocols, and one of our customers who used this vendor's products is claiming that approximately one in every 250 times they initialize the system, it generates a key file that is 127 bits instead of 128, and gets rejected. They be... |
The general scenario of hybrid encryption is to use public key cryptography for the exchange of a one time *session key* that can be used for the encryption of the plaintext with a symmetric encryption algorithm. A digital signature attached to that structure is what I know as a *digital envelope*. Furthermore, some re... |
> What is meant by vectors here?
Just the inputs and outputs of the function. The function $f$ takes, as input, a sequence of bits (for example, 1010), and returns a sequence of bits (for example, 1100); the text refers to such a sequence of bits as a *vector*
> Can someone explain this?
Well, the idea is tha... |
i'm new in cryptography and i just started reading diffie-hellman algorithm . now i want to know what is `mitm` (Man In The Middle ) ?
thank you . |
what is mitm attack in diffie-hellmen key exchange algorithm? |
"Recently" the Ukraine standardized a new blockcipher *Kalyna*, which according to the abstract of [this paper][1] (warning: the paper contains *a lot* of test-vectors) is basically a modified version of AES.
The high-level changes (to Rijndael) were described as "four new S-boxes, new pre- and post-whitening, a new... |
Is standardizing a modified AES a good idea? |
I'm new to cryptography and I just started reading diffie-hellman key exchange.<br>
Now I want to know what is `mitm` (Man In The Middle ) ? |
What is a mitm (attack) in diffie-hellman key exchange? |
I'm new to cryptography and I just started learning about the Diffie-Hellman key agreement. I read that this system is vulnerable to a **man-in-the-middle attack** when used alone. What kind of attack is this?
|
What is a man-in-the-middle attack (for instance in Diffie-Hellman)? |
"Recently" the Ukraine standardized a new block cipher *Kalyna*, which according to the abstract of [this paper][1] (warning: the paper contains *a lot* of test-vectors) is basically a modified version of AES.
The high-level changes (to Rijndael) were described as "four new S-boxes, new pre- and post-whitening, a ne... |
I want to do a very simple thing:
Given two vectors, i want to encrypt them and do some calculation,
then decrypt the result and get the inner product between both vectors.
Can you recommend me for some lib that can do this thing?
Any other material will help me as well.
I found HELIB, but i still dont k... |
I want to do a very simple thing:
Given two vectors, I want to encrypt them and do some calculation,
then decrypt the result and get the inner product between both vectors.
Can you recommend me some library that can do this thing?
Any other material will help me as well.
I found HELIB, but I still dont know... |
I know that 3DES is NOT vulnerable to DC , LC .
But is it because the attacks requires too many input\output pairs ?
Or because it's impossible ? (i.e requires more than 2^64 pair ) |
What is the complexity for attacking 3DES in linear or differential cryptanalysis? |
This one time pad encryption scheme is secure? |
The encryption scheme is secure? |
The most likely rationale to change the AES design is political. It's a NIST standard, designed in Western Europe.
It's a bad idea! How much scrutiny has it received? Almost none. How much will it receive? Almost none. Bad idea. |
**Classic scheme:**
1. Given `password` and `hashing` algorithm
2. Generate `salt`
3. Calculate `hash=hashing(password, salt)`
4. Separately storing `hash` & `salt`
Checking password validity: comparing stored `hash` with calculated `test_hash=hashing(test_password, salt)`. If `hash=test_hash` - password i... |
**Classic scheme:**
1. Given `password` and `hashing` algorithm
2. Generate `salt`
3. Calculate `hash=hashing(password, salt)`
4. Separately storing `hash` & `salt`
Checking password validity: comparing stored `hash` with calculated `test_hash=hashing(test_password, salt)`. If `hash=test_hash` - password i... |
I'm trying to find a sufficient encryption mode that supports random read _and_ write access. It seems like XTS is a perfect fit, since in my use case authentication and integrity insurance are handled elsewhere, and from my current understanding, these are the only two drawbacks of XTS.
The only thing I don't get (... |
Does XTS provide random write access? |
Easy explanation of IND-XXXX security niveaus? |
Easy explanation of "IND-" security niveaus? |
Easy explanation of "IND-" security notions? |
I would like to create two raw ASCII text messages with the same MD5. Is it possible? If not, what similar-but-less-strict attack could work?
Or to rephrase my last question: what are the minimum prerequisites for the messages alphabet?
Bonus question: does the Flame and Hashclash attacks have different prerequisit... |
It is said that, given a group $\mathbb{Z}^*_p$ we can alway have a subgroup whose order is prime. To this end, for a prime value $q$, set $p=2q+1$ then $\forall x_i \in \mathbb{Z}^*_p$ compute $x_i^2 \bmod p$.
**Questions**:
1- Do we need to only work on the values exist in this subgroup (whose order is prime)... |
It is said that, given a group $\mathbb{Z}^*_p$, we can always have a subgroup whose order is prime. To this end, for a prime value $q$, set $p=2q+1$ then $\forall x_i \in \mathbb{Z}^*_p$ compute $x_i^2 \bmod p$.
**Questions**:
1. Do we need to only work on the values that exist in this subgroup (whose order is... |
I started reading "Cryptography: theory and practice" by Stinson, and I am trying to understand the reason behind the choices for the different components of AES since they seem quite arbitrary.
1) In the begging ADDROUNDKEY is performed, why does this not allow for perfect secrecy: the key and plaintext are same key ... |
It is said that, given a group $\mathbb{Z}^*_p$, we can always have a subgroup whose order is prime. To this end, for a safe prime $p=2q+1$, compute $x_i^2 \bmod p$ for all $x_i \in \mathbb{Z}^*_p$.
**Questions**:
1. Do we need to only work on the values that exist in this subgroup (whose order is prime)?
2. Wh... |
I would like to create two ASCII text messages with the same MD5. Is this possible? If not, is there a similar but less strict attack that could work?
Or to rephrase my last question: what are the minimum prerequisites for the message's alphabet?
Bonus question: Do the Flame and Hashclash attacks have different pre... |
Is there any practical attack to create a printable chosen prefix MD5 collision? |
I want to implement a simple protocol, and I'd like to verify it through BAN or GNY logic. I would assume that if these logics are still used that there would be some programs available that would automate this. In fact I found one paper on how to automate GNY logic, and another mentioning a tool called SPEAR that au... |
Does anyone still use BAN or GNY logic in practice? |
I've seen many pseudocodes of this form in the Montgomery Multiplication related theses: (C, S) := a[j]*b[0]+C. What's the meaning of "(C, S):=", or how is the real code that converted from this pseudocode like? |
I ("SEJPM" as of now) have contacted the authors asked them the same questions as in my question. I'm posting this as community wiki, as it's not *my* answer to this question but rather theirs. Now the responses follow:
----------
First off, the authors are working on a design rationale in english for their new... |
I will specifically address your question 3; that is, quite a lot of block ciphers (and hash functions) consist of a regular round structure (where you repeatedly do the same thing over and over); why is this?
Well, one incentive for doing that is that it makes the cipher easier to analyze; we can study the round fu... |
"Not vulnerable" is not how I would describe it, but my understanding is that the existing attacks on DES cannot directly not work with 3DES.
At the moment, the best attack against single DES is a linear attack which requires $2^{43}$ plaintext-ciphertext pairs, and has a time complexity of at between $2^{39}$ and $... |
I've got a system with a slow data transfer channel. Transferring a message through several channels does increase the transfer speed significatnly.
AES-CBC+HMAC is good except that verifying the MAC cannot be done in parallel. Encryption can be parallel by using CTR, but MAC calculation still needs to be sequential... |
Parallel authentication of encrypted data. What AE type to choose? |
I've got a system with a slow data transfer channel. Transferring a message through several channels does increase the transfer speed significatnly.
AES-CBC+HMAC is good except that verifying the MAC cannot be done in parallel. Encryption can be parallel by using CTR, but MAC calculation still needs to be sequential... |
I started reading "Cryptography: theory and practice" by Stinson, and I am trying to understand the reason behind the choices for the different components of AES since they seem quite arbitrary.
1. In the beginning ADDROUNDKEY is performed, why does this not allow for perfect secrecy: the key and plaintext are same ... |
I've seen pseudocode of this form in the Montgomery Multiplication related theses: $(C, S) := a[j]*b[0]+C$. What's the meaning of "$(C, S):=$", or what is the real code that converted from this pseudocode like? |
Maybe the answer to my question is obvious, but I have doubt.
I have noticed that hash functions are studied in two forms, keyed hash functions or unkeyed... In general, lecture notes present hash function without key.
Is there a key generation algorithm for a keyed hash function ?
Thanks |
Maybe the answer to my question is obvious, but I have doubt...
I have noticed that hash functions are studied in two forms, keyed hash functions or unkeyed. In general, lecture notes present hash function without key.
Is there a key generation algorithm for a keyed hash function? |
What are the advantahe of using OFB (output feedback mode)? |
(By items I mean hashable objects.) As an example (with obviously way too short hashes for readability), say I [packed my bag](https://en.wikipedia.org/wiki/I_packed_my_bag) and in it I put
* a shovel (hashed to `S`)
* a bucket (hashed to `B`)
* a towel (hashed to `T`)
* a random number (hashed to `R`)
Now fr... |
Examining his claims about "Thundercloud":
* You can use it with "any existing software, operating system, or device" (a massive amount of effort---by whom?)
* Has its "own cryptographic language that is completely independent of any existing security technology" (this is a **negative** thing: abandoning the entire... |
What are the advantages of using OFB (Output Feedback Mode)? |
> I have a problem with OFB mode, because I have heard that it is stronger than CFB.
On the contrary I would say that CFB is stronger.
OFB means encrypting the IV again and again to produce the keystream. If you end up in a cycle, the keystream [will start repeating itself][1]. (This should not be a practical wea... |
> I have a problem with OFB mode, because I have heard that it is stronger than CFB.
On the contrary I would say that CFB is stronger.
OFB means encrypting the IV again and again to produce the keystream. If you end up in a cycle, the keystream [will start repeating itself][1]. (This should not be a practical wea... |
Making sure this oracle you're talking about is not available to an attacker is a bit harder than just saying so.
When we first heard of the Vaudenay attack on CBC (https://www.iacr.org/archive/eurocrypt2002/23320530/cbc02_e02d.pdf) we thought that we had done enough to "get rid of the oracle" and we found out with... |
The Stanford [license for SRP][1] says:
> Broader use of the SRP authentication technology, such as variants
> incorporating the use of an explicit server secret (SRP-Z), may
> require a license;
yet I cannot find a succinct description of the SRP-Z protocol and why it might be useful. As a follow up question ... |
What is SRP-Z from? |
**Classic scheme:**
1. Given `password` and `hashing` algorithm
2. Generate `salt`
3. Calculate `hash=hashing(password, salt)`
4. Separately storing `hash` & `salt`
Checking password validity: comparing stored `hash` with calculated `test_hash=hashing(test_password, salt)`. If `hash=test_hash` - password i... |
At the time of this writing, there are 3 sources for parameters for the McEliece public-key cryptosystem out there.
The first paper is the [original McEliece paper][1], which only specifies $(n,k,t)=(1024,524,50)$, which is known to be broken as of today with an effort of around $2^{60}$ by [Bernstein, Lange and Pet... |
How to choose McEliece's parameters? |
At the time of this writing, there are 3 sources for parameters for the McEliece public-key cryptosystem out there.
The first paper is the [original McEliece paper][1], which only specifies $(n,k,t)=(1024,524,50)$, which is known to be broken as of today with an effort of around $2^{60}$ by [Bernstein, Lange and Pet... |
In what cases will RSA not work? |
I'm working on an implementation of Krawczyk and Eronen [HDKF from RFC 5869](https://tools.ietf.org/html/rfc5869). From Krawczyk's original paper, he identifies four inputs to a KDF in [Cryptographic Extraction and Key Derivation: The HKDF Scheme](https://eprint.iacr.org/2010/264). The four inputs are:
1. base key... |
Software interface for KDF and PBKDF? |
The MAC size is reduced into 80 bits in [truncated_hmac extension][1] , which says "forging of MAC values cannot be done off-line: in TLS, a single failed MAC guess will cause the immediate termination of the TLS session."
So can I reduce MAC size smaller again, say 32 bits? The attacker has only 1/2^32 chance to fo... |
can I recude the MAC size in TLS? |
The MAC size is reduced to 80 bits in [truncated_hmac extension][1] , which says "forging of MAC values cannot be done off-line: in TLS, a single failed MAC guess will cause the immediate termination of the TLS session."
So can I reduce MAC size to something even smaller, say 32 bits? The attacker has only $1/2^{32}... |
Can I reduce the MAC size in TLS? |
In differential privacy solutions and more specifically for queries that they do entail counting the proposed solutions define the Laplace distribution that is best calibrated for low error. Other solutions for non-numerical queries propose exponential distribution. However, it is not clear why noise from a Laplace dis... |
I'm working on an implementation of Krawczyk and Eronen [HDKF from RFC 5869](https://tools.ietf.org/html/rfc5869). From Krawczyk's original paper, he identifies four inputs to a KDF in [Cryptographic Extraction and Key Derivation: The HKDF Scheme](https://eprint.iacr.org/2010/264). The four inputs are:
1. base key... |
The MAC size is reduced to 80 bits in [truncated_hmac extension][1] , which says "forging of MAC values cannot be done off-line: in TLS, a single failed MAC guess will cause the immediate termination of the TLS session."
Question 1:
So can I reduce MAC size to something even smaller, say 32 bits? The attacker has o... |
The MAC size is reduced to 80 bits in [truncated_hmac extension][1] , which says "forging of MAC values cannot be done off-line: in TLS, a single failed MAC guess will cause the immediate termination of the TLS session."
Question 1:
So can I reduce MAC size to something even smaller, say 32 bits?
Question 2:
Th... |
Just like we have AES in crypotography, which is the most secure technique in Steganography? |
Which is the most secure steganography technique? |
Just like we have AES in crypotography, which is the most secure technique in Steganography?
I am looking for a technique in which the standard image characteristic modifications it does go undetected(as yet). |
The MAC size is reduced to 80 bits in [truncated_hmac extension][1] , which says "forging of MAC values cannot be done off-line: in TLS, a single failed MAC guess will cause the immediate termination of the TLS session."
Question 1 (main question):
So can I reduce MAC size to something even smaller, say 32 bits?
... |
I'm working on an implementation of Krawczyk and Eronen [HKDF from RFC 5869](https://tools.ietf.org/html/rfc5869). From Krawczyk's original paper, he identifies four inputs to a KDF in [Cryptographic Extraction and Key Derivation: The HKDF Scheme](https://eprint.iacr.org/2010/264). The four inputs are:
1. base key... |
> 1. Is it fair to say a PBKDF is a specialization of KDF?
Sure. A PBKDF is a KDF, just one that uses a password/passphrase as the entropy source.
OTOH, a KBKDF (key-based KDF, if you want to call it that) is *also* a specialization of a KDF. A different specialization, which is why it may not be a good idea to t... |
I am wondering how much hashing a password used as key for a symmetric key algorhytm helps preventing brute force attack on crypted text.
let's assume i want to crypt text A using key B using AES-256. I expect user to input not secure keys, such as: ['apple', '22march', 'newyork'].
So i hash these keys with PBKDF... |
How much pre-hashing a password increase security against brute force attack? |
I am currently learning, and I'm stuck on something that I thought is very simple. On many academic sources they suggest using Extended Euclidean Algorithm to calculate the multiplicative inverse for calculation of the S-Box, but I could not find a proper explanation how to do that. Every practical approach calculates ... |
I am currently learning, and I'm stuck on something that I thought is very simple. On many academic sources they suggest using Extended Euclidean Algorithm to calculate the multiplicative inverse for calculation of the S-Box, but I could not find a proper explanation how to do that. Every practical approach calculates ... |
The PKCS#11 standard has transitioned from RSA to the OASIS group:
https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=pkcs11
I am not sure why RSA/EMC's site doesn't mention this.
I believe that v2.30 was close to finalization, but was never formally released. I am not sure what happened but v2.40 is n... |
Just like we have AES in crypotography, which is the most secure technique in Steganography?
I am looking for a technique in which the standard image characteristic modifications it does go undetected(as yet).
This question is regarding image steganography and I want to store few bytes of information. |
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