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Let $\mathbb{G}_1,\mathbb{G}_2,\mathbb{G}_T$ be yclic group of the same order and $ e: \mathbb{G}_1 \times \mathbb{G}_2\rightarrow \mathbb{G}_T$, such that $u\in \mathbb{G}_1, g \in \mathbb{G}_2, a,b,r \in \mathbb{Z}$.
Question 1: is the following equation correct? Is there any situation under which it might be cor... |
Let $\mathbb{G}_1,\mathbb{G}_2,\mathbb{G}_T$ be yclic group of the same order and $ e: \mathbb{G}_1 \times \mathbb{G}_2\rightarrow \mathbb{G}_T$, such that $u\in \mathbb{G}_1, g \in \mathbb{G}_2, a,b,r \in \mathbb{Z}$.
Question 1: is the following equation correct? Is there any situation under which it might be cor... |
Let $\mathbb{G}_1,\mathbb{G}_2,\mathbb{G}_T$ be yclic group of the same order and $ e: \mathbb{G}_1 \times \mathbb{G}_2\rightarrow \mathbb{G}_T$, such that $u\in \mathbb{G}_1, g \in \mathbb{G}_2, a,b,r \in \mathbb{Z}$.
Question 1: is the following equation correct? Is there any situation under which it might be cor... |
I'm interested in using a modified form of SRP as a peer-to-peer authentication method. Since neither side is acting as a host, one of the primary design goals for SRP (that the client doesn't need to know anything but an identity and password, so no key management is required) isn't really necessary.
There's a var... |
I have a question about decryption.
Let's say I have a bunch of files that are encrypted. Someone gains access to those files, and finds out that he already has one of them, unencrypted.
My question is, can he use that file to make a comparison with the encrypted version of the file to find the key, therefor be a... |
If you define $u$ as element of $G_1$, then you can't just use it in $G_2$ (in the first equation), like you did in your equation. Besides, you missed to state, if $u$ and $g$ are generators of those groups. The following holds:
$$e(u^a,g^{\frac{b}{a}}) = e(u,g)^b = e(u^b,g)$$
Anyway, you didn't do that in the ac... |
I'm interested in using a modified form of SRP as a peer-to-peer authentication method. Since neither side is acting as a host, one of the primary design goals for SRP (that the client doesn't need to know anything but an identity and password, so no key management is required) isn't really necessary.
There's a var... |
Find a key and decrypt all the files? Definitely not, if it's proper encryption.
Still, if the encryption does not properly seed itself, or take at least some sort of steps to make it non-deterministic, then the attacker may be able to glean *some* information from the other files.
For example the encryption mig... |
I read something about the [padding oracle attack][1] when analysing the use of an AES-encryption of data in a database and was "scared" it could be a serious issue.
But after investigating a bit further, I now came to the conclusion that in our specific scenario it should be no matter at all. I would like to validate... |
Is a padding oracle attack possible if data is only encrypted internally on a server (e.g. for storage)? |
I am reading the Pinocchio paper (verifiable computation): http://research.microsoft.com/pubs/180286/pinocchio.pdf
The paper is rather hard for me. I am considering this calculation problem: $(c_1*c_2+c_3*c_4)*c_5$
Similar to the Figure 2 in the paper. I denote $c_1*c_2=c_6$, $c_3*c_4=c_7$, and $(c_6+c_7)*c_5=c_8$.... |
I am reading the Pinocchio paper (verifiable computation): http://research.microsoft.com/pubs/180286/pinocchio.pdf
The paper is rather hard for me. I am considering this calculation problem: $(c_1*c_2+c_3*c_4)*c_5$
Similar to the Figure 2 in the paper. I denote $c_1*c_2=c_6$, $c_3*c_4=c_7$, and $(c_6+c_7)*c_5=c_8$.... |
I am reading the Pinocchio paper (verifiable computation): http://research.microsoft.com/pubs/180286/pinocchio.pdf
The paper is rather hard for me. I am considering this calculation problem: $(c_1*c_2+c_3*c_4)*c_5$
Similar to the Figure 2 in the paper. I denote $c_1*c_2=c_6$, $c_3*c_4=c_7$, and $(c_6+c_7)*c_5=c_8$.... |
I've already read how to build and upload them, but I'm wondering how revocation certificates work, what informations they hold and so on.
Suppose my private key is compromised, but I have a revocation certificate hidden somewhere.
How the keyserver matches the revocation certificate to the compromised key? Is it... |
How do revocation certificates work in PGP? |
I encrypt 2 random keys with the same 'one' time pad. You can get both encrypted keys. You don't know anything besides the size.
Is there a way to attack the two time pad in this scenario?
And what if I would encrypt 1000 random keys. is there a way to attack the 'one' time pad?
PS. I have read a lot of posts ... |
How to attack the Two Time Pad? |
Let's just consider keys of bitlength 1, it works like that for any length.
- We have $k_1$ and $k_2$, the 2 random keys.
- And we have $k_3$, the OTP key.
- And then we give $x_1 = k_1 \oplus k_3$ and $x_2 = k_2 \oplus k_3$ to the attacker
How can you attack the OTP? You can't. However, you don't need it. Bec... |
I've encountered an interesting problem where we can basically say the following:
* We need to encrypt messages, but we have no room to store IVs. We can synthesize IVs; however an attacker would be able to observe different blocks encrypted with the same IV.
* We can detect message tampering directly. That is, we ... |
I'm trying to understand Matsui's linear attack on DES and I have something I don't understand in his paper. In his paper he say that:
$NS_{5}(16,15)=12$ (which is OK)
and from that he say that:
$X[15]\bigoplus F_5(X,K)[7,18,24,29]=K[22]$
My problem here are the indices 7,18,24,29 - where did they come from... |
Why Might XOR's Lead to Hash Functions Lacking 2nd Pre-image Resistance? |
First, don't roll your own crypto.
Second, why would you want to use CBC-MAC, if you have GMAC (GCM-mode) and CMAC and even better HMAC? (all of which are better than CBC-MAC)
Third, don't try to fix problems that have been fixed. (see second)
Fourth, I'm not aware of this construction being standardized and I... |
I've encountered an interesting problem where we can basically say the following:
* We need to encrypt messages, but we have no room to store IVs. We can synthesize IVs; however an attacker would be able to observe different blocks encrypted with the same IV.
* We can detect message tampering directly. That is, we ... |
Given have two public keys $k1$ and $k2$, $E_{k1}(E_{k2}(m_1))$ and $m_2$.
Is it possible to calculate $E_{k1}(E_{k2}(m_1 + m2))$? (or with multiplication instead of addition)
At a first glance, I thought that it is possible:
1. Calculate $E_{k2}(m_2)$.
2. Calculate $E_{k1}(E_{k2}(m_1))^{E_{k2}(m_2)}$.
3. Fr... |
I would like to know, if the following process would harm the security of a fictional system if the persisted data would be stolen: in this system a user has a **single password**. The password will be used in order to **derivate two different keys** using the **same key derivation function** (PBKDF2/bcrypt/scrypt) wit... |
Is it safe to derivate two different keys with the same password and the same key derivation function using two different salts? |
I would like to know, if the following process would harm the security of a fictional system if the persisted data would be stolen: in this system a user has a **single password**. The password will be used in order to **derivate two different keys** using the **same key derivation function** (PBKDF2/bcrypt/scrypt) wit... |
I would like to know why the sender and receiver must be synchronized in Synchronous stream cipher as said in [Synchronous stream cipher][1].Why there is no synchronization between the sender and receiver in Asynchronous stream cipher?
I'm thinking that a plain text is first encrypted and then decrypted.I can't get ... |
Why the sender and reciever must be synchronised in Synchronous stream cipher? |
I would like to know why the sender and receiver must be synchronized in
<br>
synchronous stream ciphers as said in [Synchronous stream cipher][1]. Why is there no synchronization between the sender and receiver in asynchronous stream ciphers?
I'm thinking that a plain text is first encrypted and then decrypted. I... |
Why must the sender and receiver be synchronised in synchronous stream ciphers? |
I recently started a coursera course "cryptography 1" provided by Stanford university. In one point when explaining zero proof knowledge the instructor mentions the following:
> Almost any puzzle that you want to prove you have an answer to, you
> can prove it is your knowledge. For example let's say that you have ... |
I recently started a coursera course "cryptography 1" provided by Stanford university. In one point when explaining zero proof knowledge the instructor mentions the following:
> Almost any puzzle that you want to prove you have an answer to, you
> can prove it is your knowledge. For example let's say that you have ... |
I have read too many different options for encryption that I now feel quite lost. I need a simple, secure (don't we all) scheme for encrypting integers (32-bit) with the following requirements:
- Ciphertext is also an integer (32-bit) or a long (64-bit)
- For integers x1=x2 then ciphertexts E(x1)=E(x2)
- For integ... |
I would like to know if the following process would harm the security of a fictional system if the persisted data would be stolen: in this system a user has a **single password**. The password will be used in order to **derive two different keys** using the **same key derivation function** (PBKDF2/bcrypt/scrypt) with t... |
Is it safe to derive two different keys with the same password and key derivation function using two different salts? |
I would like to know if the following process would harm the security of a fictional system if the persisted data would be stolen: in this system a user has a **single password**. The password will be used in order to **derive two different keys** using the **same key derivation function** (PBKDF2/bcrypt/scrypt) with t... |
In the original paper, ElGamal(1985) starts his discussion of signatures by saying:
"The signature ..... is chosen such that the equation:
$\alpha^m = y^r r^s \text{mod p}$ (equation 3 from the paper)
is satisfied."
(In this paper:
$m$ is the message, $s$ is the signature, $y=\alpha^x$ mod $p$ is the publi... |
Why does the ElGamal signature have the specific form that it does? |
I've been reading up on [Yubico's implementation of U2F][1]. What I understand so far is that two things are calculated. So upon registration first you calculate a private key by
$PrivateKey = HMAC(AppID+nonce,DeviceKey)$
This is then used to simulate the encrypted private key which is sent to the server in the ... |
I've been reading up on [Yubico's implementation of U2F][1]. What I understand so far is that two things are calculated. So upon registration first you calculate a private key by
$PrivateKey = HMAC(AppID+nonce,DeviceKey)$
This is then used to simulate the encrypted private key which is sent to the server in the ... |
I read about zero knowledge proofs and had an idea.
Let's say you want to create an account at a website. You choose a password $p$ and from $p$ you derive deterministically a public & private key pair $(e,d)$ and send $e$ to the server. Every time you want to log in, you and the server play a game: The server sends... |
I read about zero knowledge proofs and had an idea.
Let's say you want to create an account at a website. You choose a password $p$ and from $p$ you derive deterministically a public & private key pair $(e,d)$ and send $e$ to the server. Every time you want to log in, you and the server play a game: The server sends... |
Registration and log in through public key cryptography? |
I read about zero knowledge proofs.
Let's say you want to create an account at a website. You choose a password $p$ and from $p$ you derive deterministically a public & private key pair $(e,d)$ and send $e$ to the server. Every time you want to log in, you and the server play a game: The server sends you an encrypte... |
I read on Wikipedia that zero-knowledge proofs are not used for authentication in practice. Instead (I think) the server is entrusted with seeing a password in plaintext form, which it should then add a salt to and hash. But for a split moment, the server knows the secret. Why should I implicitly trust the server like ... |
Why aren't zero-knowledge proofs used for authentication in practice? |
I read on Wikipedia that zero-knowledge proofs are not used for authentication in practice. Instead (I think) the server is entrusted with seeing a password in plaintext form, which it should then add a salt to and hash. But for a split moment, the server knows the secret. Why should I implicitly trust the server like ... |
Having a client (ex. your web browser) use zero-knowledge proofs to authenticate itself to a server only makes sense if the server knows about the client's public key in advance, and if the client keeps the same private key forever. So you could have the client-side generate a keypair when you register your account, an... |
Having a client (ex. your web browser) use zero-knowledge proofs to authenticate itself to a server only makes sense if the server knows about the client's public key in advance, and if the client keeps the same private key forever. So you could have the client-side generate a keypair when you register your account, an... |
Having a client (ex. your web browser) use zero-knowledge proofs to authenticate itself to a server only makes sense if the server knows about the client's public key in advance, and if the client keeps the same private key forever. So you could have the client-side generate a keypair when you register your account, an... |
Having a client (ex. your web browser) use zero-knowledge proofs to authenticate itself to a server only makes sense if the server knows about the client's public key in advance, and if the client keeps the same private key forever. So you could have the client-side generate a keypair when you register your account, an... |
I've been reading up on [Yubico's implementation of U2F][1]. What I understand so far is that two things are calculated. So upon registration first you calculate a private key by
$PrivateKey = HMAC(AppID+nonce,DeviceKey)$
This is then used to simulate the encrypted private key which is sent to the server in the ... |
From [wikipedia:][1] "They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words."
In this context what do they mean with words? is it the same as a 32 bit (or 64 bit) block in a block cipher? just simply the size in which it divides up it's input?
[1]: http://en.wikipedia.org/wiki/... |
*[Codes][1] are not to be confused with [ciphers][2]. It is known that all known ciphers are theoretically breakable except the [one-time pad][3] and this isn't what the question is about.*
Some cryptographic [codes][4] are akin to inventing one's own secret language, along with new words, new expressions, and new g... |
Are well designed crypographic codes unbreakable? (NOT ciphers) |
From [wikipedia:][1] "They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words."
In this context what do they mean with words? is it the same as a 32 bit (or 64 bit) block in a block cipher? just simply the size in which it divides up it's input?
[1]: http://en.wikipedia.org/wiki/... |
*[Codes][1] are not to be confused with [ciphers][2]. It is known that all known ciphers are theoretically breakable except the [one-time pad][3] and this isn't what the question is about.*
Some cryptographic [codes][4] are akin to inventing one's own secret language, along with new words, new expressions, and new g... |
on the [NIST website for Message authentication][1] There is a mention of 2 approved algorithms, i am curious about the first one. the link to FIPS 113, Computer Data Authentication appears to be dead since it redirects me to the homepage of NIST.gov
On a dutch Wikipedia article (the only wiki article i could find ... |
I have a list DES encrypted keys, they come in two lengths, 32 chars hex (16 bytes) or - I believe - 64 chars. I know the key, which is 8 ascii chars (I might add that I am the rightful owner of the key and all data). Is is possible to decrypt the keys, given this information, or is is impossible without additional inf... |
We all know the OTP is unbreakable and we all love the OTP (judging by the amount of question on this site).
The strength of the OTP is not that it is unable to find a word without the key but you can find any word. Now obviously if we could create a cipher which output would be only letters and several keys would o... |
Why are there no OTP ciphers? |
I read on Wikipedia that zero-knowledge proofs are not used for authentication in practice. Instead (I think) the server is entrusted with seeing a password in plaintext form, which it should then add a salt to and hash. But for a split moment, the server knows the secret. Why should I implicitly trust the server like ... |
@gammatester gave most of the answer, but he didn't address the last question:
> would this make HMAC the only NIST approved MAC?
No, as of right now, the block cipher-based Message Authentication Codes CMAC and GMAC are also approved. In addition, if you use the approved mode CCM with a empty message, that's ef... |
I have a list of DES encrypted strings/data, they come in two lengths, 32 chars hex (16 bytes) or - I believe - 64 chars. I know the key, which is 8 ascii chars (I might add that I am the rightful owner of the key and all data). Is is possible to decrypt the strings, given this information, or is is impossible without ... |
I read on Wikipedia that zero-knowledge proofs are not used for authentication in practice. Instead (I think) the server is entrusted with seeing a password in plaintext form, which it should then add a salt to and hash. But for a split moment, the server knows the secret. Why should I implicitly trust the server like ... |
We all know the OTP is unbreakable and we all love the OTP (judging by the amount of question on this site).
The strength of the OTP is not that it is unable to find a word without the key but you can find any word. Now obviously if we could create a cipher which output would be only letters and several keys would o... |
We all know the OTP is unbreakable and we all love the OTP (judging by the amount of question on this site).
The strength of the OTP is not that it is unable to find a word without the key but you can find any word. Now obviously if we could create a cipher which output would be only letters and several keys would o... |
I am working on implementing info security into custom m2m radiolink communication system, which has some restrictions: MCU based endpoint can transmit to gateway with packets max 16 bytes long, and the cyphertext **should not exceed that**, gateway can also downlink to endpoint with packets up to 64 bytes. Minimizatio... |
What crypto scheme should I use on embedded m2m system with assymetric uplink/downlink bandwidth? |
I am considering using modular exponentiation as a one-way hash function. More specifically, here is the scenario.
1) Input ($m$): the input messages are small (16-bit)
2) Exponent ($e$): the exponent is a 160-bit integer, chosen only once, and randomly; the exponent is not public
3) Prime ($p$): a 2048 bit sa... |
> Let $f$ = $\{f_k\}$ be a pseudorandom function family.
> Let $G(x)$ be a pseudo-random generator such that:
> $G(x) = f_x(0^k)f_x(1^k)$ where $k=|x|$.
I don't understand the meaning of $1^n$ and $0^n$, and the differences between them, in that context.
What do they represent?
What is the special role / ef... |
I have a block of data which I know is encrypted using a chained 64-bit xor (sorry if that makes no sense, I'm not familiar with crypto lingo). I know a little bit about what the plaintext should look like, and I also know the algorithm used to decrypt the data.
What I know about the data:
- 6 x 0x20 sized 'chun... |
Suppose Alice and Bob both want to determine whether the other has a crush on him/her, but they only wish to share the information if the crush is mutual. Is there a cryptographic protocol that makes this possible without using trusted third parties? It is safe to assume that they will not lie during their "encrypted a... |
Suppose an adversary gets a message-ciphertext pair $(M,C)$, where $C=DES_K(M)$. They do an exhaustive key reach to locate the lexicographically first key $T$ for which $C=DES_T(M)$. What's the probability that $T=K$? |
If a DES key correctly decrypts one message, what's the probability it's the real key? |
I've looked in many places (NIST, text books, online resources) and I cannot find an answer to the definition of the term "key" from a semantic point of view.
Is it the "key" to the cipher-text (i.e. like a door key to lock/unlock), or is the the "key" to the algorithm (i.e. a crucial factor to make it work, like a... |
I am writing a peering server - the server assigns randomly generated public IDs to users, and I want users to be able to reclaim their ids in the future, but only to be able to claim ids that they have been assigned, not arbitrary ids or ids belonging to other users.
I also want to avoid storing any information on... |
Is it safe to use a secret salted hash of a public id for client to prove ownership of id to a server that knows salt but does not store ids? |
I'm looking for an information-theoretic upper bound on leakage by timing measurement. I'm assuming that an attacker
- wants to leak out of a black box a secret key of $k$ bits that is secretly injected into the black box;
- has written the black box's code (which can read the key and act accordingly), and can craf... |
I was looking how SHA 512 works, and I have a question. Imagine I want a hash from input N of 512 bits, to get a Hash in hexadecimal where the first eight numbers are 12345678. How could I determine the input N, to get that output hash? |
I was looking at how SHA-512 works, and I have a question. Imagine I want an input $N$ of 512 bits whose hash in hexadecimal starts with the digits `12345678`. How could I determine an input $N$ to get that hash output? |
What is this statement all about? When I look at a block cipher it seems pretty hard to break it and the mathematics behind insure a good complexity. It may refer to key generation, initialization vector (IV), padding scheme ? |
The Winternitz scheme is typically cited as being an OTS scheme. Can it also be used as a one-time encryption scheme?
If it can be used as a one-time encryption scheme, then is it possible to easily convert it into a many-time encryption scheme? |
Can Winternitz be easily converted to a many-time encryption scheme? |
The Winternitz scheme is typically cited as being an OTS scheme. Can it also be used as a one-time encryption scheme?
If it can be used as a one-time encryption scheme, then is it possible to easily convert it into a many-time encryption scheme that uses either a single key or different keys that may be generated in... |
> Can it also be used as a one-time encryption scheme?
You cannot build asymmetric encryption from just hash functions. There is an impossibility proof for that. So for asymmetric encryption the answer is **no**.
For symmetric encryption, you can simply use the hash function directly to build encryption, no need ... |
NIST has 3 validated "Recommendation for Random Number Generation Using Deterministic Random Bit Generators" (DRBG's) that are based on NIST SP 800-90A:
1. **Hash_DRBG (based on hash functions)**
2. **HMAC_DRBG (Based on Hash-based message authentication code)**
3. **CTR_DRBG (based on block ciphers)**
If ... |
Can I use the output from a DRBG directly as K for AES, or do I need to use a key generator algorithm? |
I'm experimenting with this library [Botan][1]
which includes a module for format preserving encryption based on FE1 mode.
The parameters for the Encrypt method are as follows
/// <summary>
/// Generic Z_n FPE encryption, FE1 scheme
/// </summary>
/// <param name="modulus">... |
How to select a 'tweak' used in FE1 mode format preserving encryption? |
The tweak is a service that the encryption method provides for you. What it allows you to do is provide context separation for various encryptions using the same key.
Here's the problem that it is trying to help with: suppose you use the same key to encrypt a number of items; for example, suppose you're encrypting ... |
First let me admit that I am not a mathematician or a cryptographer. I am responsible for assisting in making a recommendation on a project that is consolidating payment processes within a company’s internal network. We have payment files which are being created by various applications; Several legacy applications ar... |
First let me admit that I am not a mathematician or a cryptographer.
I am responsible for assisting in making a recommendation on a project that is consolidating payment processes within a company's internal network.
We have payment files which are being created by various applications; Several legacy applications ... |
I've looked in many places (NIST, text books, online resources) and I cannot find an answer to the definition of the term "key" from a semantic point of view.
Is it the "key" to cipher-texts (i.e. like a door key to lock/unlock), or is the the "key" to the algorithm (i.e. a crucial factor to make it work, like a ke... |
Questions like these are hard to answer because who can predict what the future holds, right?
That said, there are some things I wanted to share.
>Prefer symmetric cryptography over public-key cryptography. Prefer conventional discrete-log-based systems over elliptic-curve systems; the latter have constants that ... |
It seems that quite a few currently available encryption schemes will possibly be broken by quantum computing. Are there any symmetric encryption schemes that will remain unbroken (either because of their design or by increasing the key size)? In particular are there any such schemes that may be used with a single key ... |
Are there any quantum-resistant symmetric encryption schemes? |
I'm working on an app and need to encrypt some structured data. The data will be turned into a string form (JSON) before getting encrypted.
The data format I'm using will always start with a `{` character and end with a `}` character. Does this make encryption less secure? Are there any methods for more securely enc... |
Is it a bad idea to use PGP encryption for structured/predictable data? |
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