instruction stringlengths 15 30k |
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So, I have to encrypt plaintext data to get ciphertext data and append authentication tag lets say at the end of the ciphertext data?
That is correct, the auth tag is generally appended to the ciphertext. The Nonce component of the counter is also required.
> I would like to know now, what is the Auth Data an... |
Say you have a plain text: "How are you today?" and you encrypt it so it becomes: "LKD03Loel03skj1Q03"
Now you have multiple people that need to know the plain text of this cipher text but you do not want them to have the same key. It might be they each come up with their own password or they all have a key which id... |
I would like to know how secure is [ccrypt](http://ccrypt.sourceforge.net/) to encrypt files (like images, videos and other non-plain text data) using single password of 20+ chars length.
It uses Rijndael with 256-bit block size and 256-bit key size.
Is there any better alternative to encrypt files of this kind o... |
As far as I know these are the well known protocols that offer PFS
* TLS/SSL (with DHE-RSA, DHE-DSS, ECDHE-RSA or ECDHE-ECDSA)
* SSH ([RFC4253](http://tools.ietf.org/html/rfc4253))
* OTR ([Protocol Version 3 Spec](https://otr.cypherpunks.ca/Protocol-v3-4.0.0.html))
* IPsec ([RFC 2412](http://tools.ietf.org... |
What are the well known protocols that offer perfect forward secrecy? |
I am currently working in security in mobile ad-hoc networks.
I have several clusters, and I want to send some data encrypted with its public key, from the cluster head to the cluster members. I assume that each member has its own private key so it can decrypt the data.
I ask about how to get a single public key ... |
Digesting doesn't require any key and can be performed on the client side. Why does the PKCS#11 token interface standard have a C_digest method? For example, why should I send my data to a PKCS11 HSM whereas I can do this in my client? |
Why is C_digest defined in PKCS#11? |
Pretty much what the title says. DES was suspected of having one, but I couldn't imagine what it could possibly look like if only the NSA knew how to use it. Dual_EC_DRBG's backdoor is asymmetric, but it's not a cipher. Could one have a kletographic symmetric key cipher? |
What would a backdoor in symmetric key cipher look like? |
Dingo13, the answer is that P and S boxes are effectively two halves of the same thing. This is the reason people confuse the two.
Despite the Wikipedia plagiarism, e-sushi's S-P network diagram is an excellent example of the reason for needing both. The object of a cryptographic function is to alter the input in ... |
Let's say both Prover and Verifier would use nth power instead of 2nd when creating public keys and when verifying. I know it would slow it down but would that cause the protocol to be more secure? |
Would the Fiat Shamir identification scheme be more secure if I design it with an exponents higher than 2? |
In Diffie-Hellman protocol for key exchange over an unsecured channel, we choose `g` and `p` which `g` is generator of `Zp*`. However I want to know why this assumption make below equation come true, assuming Alice and Bob choose `a` and `b` as secret keys:<br/>
(g^b mod p)^a mod p = (g^a mod p)^b mod p
In ot... |
Diffie-Helman key equivalence proof? |
In the Diffie-Hellman protocol for key exchange over an unsecured channel, we choose $p$ and $g$, where $g$ is a generator of $\mathbf{Z}_p^*$. However I want to know why this assumption makes the equation below true, assuming Alice and Bob choose $a$ and $b$ as secret keys:
$$(g^b \bmod p)^a \bmod p = (g^a \bmod p)... |
I am trying to write an assay about Non Interactive Zero-Knowledge proofs and would like to take the simple discrete logarithm problem example fallowing the Feige-Fiat-Shamir heuristics.
I understand the interactive steps are:
1. P wants to proof he knows x where y = g^x
2. P picks a random v and compute... |
Whenever possible, Security Stack Exchange is going to recommend "don't roll your own" crypto. Is there a library which implements ElGamal that you can use instead where it has been tested and vetted? Implementing Crypto is always difficult and unless you are experienced in the area, you should try to avoid doing as mu... |
Are there any known weaknesses with ElGamal algorithm? |
Say you have a plain text:
> How are you today?
and you encrypt it so it becomes:
> LKD03Loel03skj1Q03
Now you have multiple people that need to know the plain text of this cipher text but you do not want them to have the same key. It might be they each come up with their own password or they all have a k... |
For instance say you encrypt text using the one time pad and you end up with some scrambled text that appears illegible. If you reused the key for multiple times for enough text, someone could potentially crack the message using something like crib-dragging.
However say you use the one time pad technique to encrypt... |
Does encrypting numerics with a reused one time pad, have the same weakness as encrypting plain text? |
For instance say you encrypt text using the one time pad and you end up with some scrambled text that appears illegible. If you reused the key for multiple times for enough text, someone could potentially crack the message using something like crib-dragging.
However say you use the one time pad technique to encrypt... |
How obvious is it to decrypt numerics encrypted with a reused one time pad? |
For instance say you encrypt text using the one time pad and you end up with some scrambled text that appears illegible. If you reused the key for multiple times for enough text, someone could potentially crack the message using something like crib-dragging. The hacker tries and tries until eventually comes up with a ... |
In the Diffie-Hellman protocol for key exchange over an unsecured channel, we choose $p$ and $g$, where $g$ is a generator of $\mathbf{Z}_p^*$. However I want to know why this assumption makes the equation below true, assuming Alice and Bob choose $a$ and $b$ as secret keys:
$$(g^b \bmod p)^a \bmod p = (g^a \bmod p)... |
How does $g$ being a generator imply Diffie-Hellman's correctness? |
As far as I know these are the well known protocols that offer PFS
* TLS/SSL (with DHE-RSA, DHE-DSS, ECDHE-RSA or ECDHE-ECDSA)
* SSH ([RFC4253](http://tools.ietf.org/html/rfc4253))
* OTR ([Protocol Version 3 Spec](https://otr.cypherpunks.ca/Protocol-v3-4.0.0.html))
* IPsec (with IKEv1 and IKEv2) ([RFC 2412... |
I've seen some posts and info online, but they are from 2009, 2010, 2011 or 2012, which is 3-6 years ago, which is a very long time. So I'm looking for an up-to-date answer about which of these is the safest encryption to be used, or rather most unbreakable? Particularly interested in encryption programs, so performanc... |
I've seen some posts and info online, but they are from 2009, 2010, 2011 or 2012, which is 3-6 years ago, which is a very long time. So I'm looking for an up-to-date answer about which of these is the safest encryption to be used, or rather most unbreakable? Particularly interested in encryption programs, so performanc... |
Assuming $x=a^2 \pmod n$ and knowing $x$, $p$, $q$ how is it possible to obtain $a$?
|
On many Linux/GNU distributions CCrypt (`ccrypt`) by Peter Selinger is available as a method to encrypt files. How does the protocol work and is it secure?
Note: this should not be confused with the CCCrypt API by Apple. |
How does the ccrypt protocol work and is it secure? |
On many Linux/GNU distributions CCrypt (`ccrypt`) by Peter Selinger is available as a command line utility to encrypt files. How does the protocol work and is it secure?
Note: this should not be confused with the CCCrypt API by Apple. |
On many Linux/GNU distributions [CCrypt (`ccrypt`) by Peter Selinger](http://ccrypt.sourceforge.net/) is available as a command line utility to encrypt files. How does the protocol work and is it secure?
Note: this should not be confused with the CCCrypt API by Apple. |
Could someone even recognize that the values are encrypted? Well, maybe, maybe not.
You're correct that the values would all appear to be valid dates (this is known as [format-preserving encryption](//en.wikipedia.org/wiki/Format-preserving_encryption), by the way), so they would not look *obviously* encrypted, the... |
I vaguely know that prime numbers are very important in cryptography, but I assume for most encryption methods, they tend to stay rather 'small'. Are we really using massive prime numbers for encryption? Why would modern encryption start to fail if the set of prime numbers was finite? |
Why would cryptography fall apart if there were a finite number of primes? |
I've been learning about Vigenere ciphers and then thought of another method to Encrypt and decrypt that.
This's my method to encrypt :
I have a msg : "messages from father to his son"
I have a key : "home"
And the cipher text : "tsewmkwk fxse krhtjr mv lzl gvv"
I've created the Mathematics algor... |
Are there cryptographic schemes that make encrypted traffic look like unencrypted traffic? |
Are there cryptographic schemes that mask as unencrypted traffic? |
While studying the design and the desirable properties of an AES S-box , I came to know that Algebraic Complexity is also an important property of an S-box which is usually considered while evaluating the properties of an S-box. After reading several papers (such as <a href="http://citeseerx.ist.psu.edu/viewdoc/downloa... |
Apologies if this is really basic but i couldnt find the answer to this.
I have heard some info sec colleagues talking about creating an AES key in preference to a DES or 3DES key but i dont know the difference; i thought a key was just a random string of bits?? Is there a difference? Can you use the same key with ... |
128 bit 3DES Key and AES Key: whats the difference? |
The key itself is really just a bitstring for (nearly?) all block ciphers. You can use the same key for different algorithms, but the cipher may need keys of different lengths. For example, AES can use keys with 128, 192 and 256 bit. 3DES is slightly more complex. It can use 2 keys or 3 keys with each 56 bit. 1 key wou... |
How does ccrypt work? |
I am trying to find out some disadvantages of ElGamal cryptography but I'm not able to figure out what's wrong with the algorithm. The only one I found is that a known-plain text attack is possible in ElGamal if the same $r$ is used twice during encryption.
Are there any other disadvantages of ElGamal encryption?
|
Apologies if this is really basic but I couldn't find the answer to this.
I have heard some Info Sec colleagues talking about creating an AES key in preference to a DES or 3DES key but I don't know the difference; I thought a key was just a random string of bits? Is there a difference? Can you use the same key with ... |
128 bit 3DES Key and AES Key: what's the difference? |
My question is related to [another question in Cryptography about TLS 1.1 and 1.2][1]. I have read both RFC 2246 The TLS Protocol Version 1.0 and RFC 4346 The TLS Protocol Version 1.1. What I know is that one of their differences is TLS 1.0 uses implicit initialization IV (from the key_block) and TLS 1.1 uses explicit ... |
What are the steps to decrypt a TLS 1.1 record? |
> Why is it common practice to create a hash of the message and sign that instead of signing the message directly?
Well, the RSA operation can't handle messages longer than the modulus size. That means that if you have a 2048 bit RSA key, you would be unable to directly sign any messages longer than 256 bytes long ... |
> Why is it common practice to create a hash of the message and sign that instead of signing the message directly?
Well, the RSA operation can't handle messages longer than the modulus size. That means that if you have a 2048 bit RSA key, you would be unable to directly sign any messages longer than 256 bytes long ... |
Both an AES-128 key (as defined by [FIPS 197][1]), and a TDES Keying Option 2 key (as defined by [FIPS SP-800-67][2]) are 128-bit bitstrings. Similarly, both an AES-192 key and a TDES Keying Option 1 key are 192-bit bitstrings. The differences are:
- In AES, all bits of a key matter to the result; in TDES,... |
Is it possible to use FPE to encrypt names and language words like 'Bob' 'the' 'tree', in order to preserve both length and format (like keeping characters within a certain range like A-Z a-z)
The only way I can think of at the moment is to reduce each character to it's decimal value between 0 - 26 and encrypt that.... |
Is format preserving encryption suitable for use with words or names? |
Is it possible to use FPE to encrypt names and language words like 'Bob' 'the' 'tree', in order to preserve both length and format (like keeping characters within a certain range like A-Z a-z)
The only way I can think of at the moment is to reduce each character to it's decimal value and encrypt that. But that doe... |
Given an integer you want to factor $N$, GNFS starts by selecting a monic irreducible polynomial $f \in \mathbb{Z}[X]$ and an integer $m$ such that $f(m) \equiv 0 \text{ mod } N$. In practice, if $m$ is chosen first then $f$ can just be chosen to be the $m$-base expansion of $n$, which is simple to compute. But how is ... |
How to choose the integer in the general number field sieve (GNFS)? |
How to choose the integer m in the general number field sieve (GNFS)? |
I am reading the [paper][1] by John B. Kam and Georges I. Davida (1979) titled `Structured Design of Substitution-Permutation Encryption Networks`.
On page 749 it reads the following:
**Definition: Given a one-one corespondence: f:{0,1}<sup>n</sup> --> f:{0,1}<sup>n</sup>, f is said to be complete if, for every ... |
What are the security pitfalls that may occur by signing a list of file hashes, versus signing individual files?
In short, the security trade-offs between:
for file in $FILES; do
gpg --clearsign $file
done
And:
sha256sum $FILES > signatures
gpg --clearsign signatures
|
Shamir's secret sharing can be considered multiplicatively homomorphic, if one is aware of the fact that multiplying two shares of a (n,t)-threshold shared secret yields a share of the same secret, but over a (n, 2t)-threshold sharing.
To overcome this, there is a secure degree reduction protocol, which is already e... |
Shamir's secret sharing can be considered multiplicatively homomorphic, if one is aware of the fact that multiplying two shares of a (n,t)-threshold shared secret yields a share of the same secret, but over a (n, 2t)-threshold sharing.
To overcome this, there is a secure degree reduction protocol, which is already e... |
Say Alice and Bob have a shared secret $s$.
Alice and Bob establish an encrypted channel and verify that it hasn't been MitM'ed by exchanging $r_1$ and $r_2$ where $r_1$ and $r_2$ are randomly generated by Bob and Alice respectively and sent over the channel. Alice computes $HMAC(C,r_1,s)$ and Bob computes $HMAC(C,r... |
What is the advantage of using the social millionaire protocol to authenticate vs HMACing some random number? |
> 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?
Consider a function f... |
Say I have a 64-bit message/key:
P1: 1011.......
K1: 0101.......
I run this message/key pair through DES in ECB mode and obtain some cipher that looks like the following:
C1: 1001.......
Now I take a new message/key pair that is the bitwise complement of the first and put it through the same al... |
Will the complement of a 64-bit key and message produce the complement ciphertext if ECB is used in DES? |
How to compare between the result(hashed Value) of two cryptography algorithms in term of security? To proof that x algorithm is more secure than y algorithm. |
How to compare between the result of two cryptography algorithms in term of security? |
As far as i know , performing [Differential][1] or [linear][2] cryptanalysis always requires a knowledge of the S_boxes content and order .Yet In Bruce Schneier's [applied cryptography][3] , it is stated that randomly key dependent s_boxes and\or randomly reordered s_boxes for DES , can make the algorithm weaker .
So... |
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 eachother effieciently I plan to use a symmetr... |
I am looking at the kolblitz method for encoding, first step is "Choose an elliptic curve and its associated auxiliary base parameter, k". I have not heard the term associated auxiliary base parameter before, does it mean the order? |
Koblitz encoding a message to a point, what is the curveassociated auxiliary base parameter? |
I read that AES can be broken by solving a Linear Integer Programm (IP).
1. From a given encrypted text, how can one construct this IP?
2. How big is the system?
|
I read that AES can be broken by solving a Linear Integer Program (IP).
1. From a given encrypted text, how can one construct this IP?
2. How big is the system?
|
How to compare the results (e.g. hashed values) of two cryptographic algorithms (e.g. SHA-1 and SipHash) in terms of security? Or is there some other way to do this?
That is, how could one prove that algorithm *X* is more secure than algorithm *Y*? |
How to compare the results of two cryptographic algorithms in terms of security? |
Say Alice and Bob have a shared secret $s$.
Alice and Bob establish an encrypted channel and verify that it hasn't been MitM'ed by exchanging $r_1$ and $r_2$ where $r_1$ and $r_2$ are randomly generated by Bob and Alice respectively and sent over the channel. Alice computes $HMAC(C || r_1,s)$ and Bob computes $HMAC(... |
Say Alice and Bob have a shared secret $s$.
Alice and Bob establish an encrypted channel and verify that it hasn't been MitM'ed by exchanging $r_1$ and $r_2$ where $r_1$ and $r_2$ are randomly generated by Bob and Alice respectively and sent over the channel. Alice computes $HMAC(C \mathbin\| r_1,s)$ and Bob compute... |
Say Alice and Bob have a shared secret $s$.
Alice and Bob establish an encrypted channel and verify that it hasn't been MitM'ed by exchanging $r_1$ and $r_2$, where $r_1$ and $r_2$ are randomly generated by Bob and Alice respectively and sent over the channel. Alice computes $\operatorname{HMAC}(C \mathbin\| r_1, s)... |
What is the advantage of using the socialist millionaire protocol to authenticate vs HMACing some random number? |
As far as I know, performing [differential][1] or [linear][2] cryptanalysis always requires a knowledge of the S-boxes' content and order. Yet in Bruce Schneier's [_Applied Cryptography_][3], it is stated that random key dependent S-boxes and/or randomly reordered S-boxes for DES can make the algorithm weaker.
So my... |
Based on a quick Google search, I assume you're reading the paper "Modified Koblitz Encoding Method for ECC" by Kodali and Sarma (_Int.J.Rec.Tr.Eng.Tech._, vol. 8, no. 1, Jan 2013).
The fact that the paper doesn't actually cite any source for the encoding scheme, or even cite *anything* by Koblitz, makes me a bit sk... |
I am looking at the Koblitz method for encoding a message as an elliptic curve point. The first step given in the paper I'm reading is:
> "Choose an elliptic curve and its associated auxiliary base parameter, k."
I have not heard the term "associated auxiliary base parameter" before. Does it mean the order of t... |
Koblitz encoding a message to a point, what is the "associated auxiliary base parameter"? |
> 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?
Consider a function f... |
Theoretically is CBC mode harder to bruteforce when compared with ECB?
>Assumptions
>
> 1. We ignore the XOR operations
>
> 2. IV is made public |
Is CBC theoretically harder to brute force when compared with ECB? |
A modern trend in cryptography consists of defining security as rigorously as possible, and then designing schemes which are secure according to those definitions. Proving security comes in the form of reducing one scheme to a more basic problem or scheme. Furthermore, there are many different ways of formalizing secur... |
Is the reduction from left-or-right IND-CPA to real-or-random IND-CPA tight? |
Based on a quick Google search, I assume you're reading the paper "Modified Koblitz Encoding Method for ECC" by Kodali and Sarma (_Int.J.Rec.Tr.Eng.Tech._, vol. 8, no. 1, Jan 2013).
The fact that the paper doesn't actually cite any source for the encoding scheme, or even cite *anything* by Koblitz, makes me a bit sk... |
Theoretically is CBC mode harder to bruteforce when compared with ECB?
>Assumptions
>
> 1. We ignore computational cost for the XOR operations
>
> 2. IV is made public |
I don't get the modulo 10001 operation in mixColumns so much.
If I have to take the byte computations mod 100011011 anyway what leads me to a result of 4byte length, why do I need the mod 10001 operation?
Where is my mistake in thinking?
Can you maybe give me an example where I'd need it?
Thank you =) |
Suppose we have $g^x \equiv h \pmod N$ Where $N = pq$ and $p$, $q$ are distinct primes. Also $(p-1)/2$ and $(q-1)/2$ are primes.
If we know what $x$, $g$ and $h$ are, is it possible for us to know what $p$ and $q$ are?
I'm trying to find out but I'm running into closed doors.
<br/>I tried the following:
<br/> $g... |
As a hint, suppose we pick a random $h$, and compute $g = h^3 \bmod N$. We then find the minimal value $x$ where $g^x \equiv h \pmod{N}$ (and, yes, such an $x$ will exist, assuming $p, q > 7$).
What can we deduce from such a value of $x$? |
Recently someone gave me algorithim as follows:
XOR = Key XOR Random1 XOR Random2.
They think that in order for someone to extract "Key" from XOR they would need Random1 and Random2.. but looking at the above algorithm, i think it should be fairly easy for someone to guess or extract the Key w/o Random1 and Ran... |
How to compare between two cryptographic algorithms (e.g. SHA-1 and SipHash) in terms of security?
That is, how could one prove that algorithm *X* is more secure than algorithm *Y*? |
How to compare the of two cryptographic algorithms in terms of security? |
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