# All Questions

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### Calculation of time needed to crack DES with my CPU

I have a laptop that has the CPU and the RAMs shown below in the images. My question is that, using this CPU and the RAMs, how much time would it take for me to crack an old school DES algorithm ...
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### BLAKE2 input parameters

Being a newbie, I was reading papers on the recent crop of hash functions and BLAKE2 intrigued me. Then I wanted to play around with the "blake2s" code in the code package. If I were to implement a ...
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### Twofish vs. Serpent vs. AES (or a combo)

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 ...
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### 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 ...
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### How does $g$ being a generator imply Diffie-Hellman's correctness?

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 ...
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### Differences between Work Factor and Time Complexity

I am interested to know if work factor means the same thing as time complexity. Quoting Work Factor : Uncovering keys in cryptosystems The Work Factor of a cryptosystem is related to its ...
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### Would the Fiat Shamir identification scheme be more secure if I design it with an exponents higher than 2?

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?
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### Working a problem that uses RSA encryption:

To overcome weaknesses of the textbook version of RSA encryption, commonly some form of padding is applied.Consider the following suggestion for an asymmetric RSA-based encryption scheme: Key ...
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I am currently working on my diploma project, a high security NFC door lock and need to exchange very sensible data. That's why I thought of PGP encryption, which is as far as I know one of the ...
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### What would a backdoor in symmetric key cipher look like? [duplicate]

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 ...
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### What are the well known protocols that offer perfect forward secrecy?

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) OTR (Protocol Version 3 Spec) IPsec (with IKEv1 and IKEv2) ...
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### Runtime of a particular step of karatsuba algorithm [on hold]

I am new to algorithms and was trying to calculate the runtime cost of each step of the karatsuba algorithm. Assuming you know what the karatsuba algorithm is, So I was not sure of the calculation ...
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### Drawback of elgamal encryption

I am trying to find out some disadvantages of ElGamal cryptography but not able to finger out except one known-plain text attack is possible in ElGamal if same $r$ is used twice during encryption.
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### Multiple keys for the same ciphertext

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 ...
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### ccrypt and its security

I would like to know how secure is ccrypt 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 ...
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### GCM implementation

I want to write GCM implementation myself (only for research purposes). So far, I have successfully written CTR implementation (for AES), but now I ran into few problems with GCM. If I'm not wrong, ...
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### How does knowing the factorization of N can help to obtain the secret?

Assuming x=a^2 mod n and knowing x,p,q how is it possible to obtain a?
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### Is this JS library using openssl genrsa -rand improperly?

pem, a JS wrapper around openssl, has the following code in it: var params = ['genrsa', '-rand', '/var/log/mail:/var/log/messages', keyBitsize ]; Am ...
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### Exponentiation with fully homomorphic encryption [duplicate]

I have often heard that because a fully homomorphic encryption scheme allows for both additions and multiplications on encrypted data, most other operations can be simulated. I don't understand how ...
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### Standard serialization format for libsodium-based messages

Does anyone know of a standardized serialization format which can be (or already is) widely used for encrypted messages? For a variety of reasons (mostly complexity, age and poor support across a lot ...
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### Explanation of multivariate cryptography [on hold]

How do the key generation, encryption, decryption, signing, and verification processes in multivariate cryptography work? How about an example or at least a simplified general one? Also, what is the ...
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### Are there any known weaknesses with ElGamal algorithm?

I am working on a messaging system and plan to use ElGamal asymmetric encryption to protect the message contents during storage and transmission. (This would be in addition to TLS used during ...
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### PHP: How to show supported client ciphers [on hold]

How to print a list of ciphers offered in ClientHello? How does e.g. mikestoolbox.org or hotaru.thinkindifferent.net show which cipher is used / offered by client? Thanks for helping.
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### Send an encrypted question and return answer without decryption

Oke bear with me for a minute. Once upon a time someone mentioned a hypothetical way where you would send an encrypted question to Google and Google would return an answer without decrypting it. As ...
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### Are there any asymmetric composite order group bilinear pairings?

Are there any asymmetric composite order group bilinear pairings? Is there a drawback of asymmetric over symmetric bilinear pairings of composite order either in efficiency or in security ?
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### Acceptably secure solution for users to log in with a short unique code only (no username) [migrated]

I am creating a website whereby users are given an account by invitation only, and are sent a unique code by post. Users can then log in (at least the first time) by entering the code only. The goal ...
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### Hashes and Ciphers

So I'm brand new to cryptography, I'm confused on a few fundamental issues, and my normal avenues of research aren't bearing any fruit. I'm hoping someone can describe the relationship between ...
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### Vigenere ciphers : Need help for math analysis [on hold]

I've been learning about Vigenere ciphers and then thought of another method to Encrypt and decrypt that. This's my method to encrypt : ...
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### decrypt numbers multiplied by a certain floating point number

A friend has about 10K numbers in a an excel sheet. He wanted to encrypt these numbers in order to share the file with a 3rd party that will help him reorganize the tables. What he did, to hide the ...
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### websites to have people break encryptions [on hold]

I have built an encrypted text editor and was wondering if there were sites out there that you could post encrypted text and have some actual smart people try and break it. I would like to test this ...
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### Why can the last block contain a full block of padding in CBC Encryption?

I'm trying to understand the SSL Poodle Attack and I'm wondering why the last block of a CBC Record can be full of padding? Wouldn't that mean that the useful data was already a multiple of the key ...
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### Why are the outputs of the md5sum tool and Crypto++'s MD5 different?

Could you please tell me what is the difference of coreutils' md5sum and sha*sum tools (...
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### Multiple private keys for single public key

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 ...
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### PBKDF2 for login key, scrypt for encryption key

I need to derive two keys from a single password client side. One for in-browser login, the other for encryption. Is the following secure ? ...
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### Using the chinese remainder theorem as a part of the proof, show that 2^700 = 1 mod 3625 [on hold]

Using the chinese remainder theorem as a part of the proof, show that 2^700 = 1 mod 3625 Using the chinese remainder theorem as a part of the proof, show that 2^700 = 1 mod 3625
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### Why is C_digest defined in PKCS#11?

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 ...
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### What aspect of elliptic curve encryption paradigms makes them especially susceptible to quantum based attack algorithms?

This was a statement made during a talk at today's DFN-CERT conference but unfortunately it wasn't explained further. Can anyone shed light on why elliptic curves are susceptible to quantum based ...
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### How to choose an algorithm

I have some understanding of Cryptography and I would like to know if there is a tool or website to help me choose an algorithm based on my own needs (I'm being vague in purpose). I'm looking for a ...
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### Reduction of a modular exponentiation's base does not change the result

Can anyone help me to prove this property used in the RSA correctness theorem? $a^b\bmod{n}\equiv (a\bmod{n})^b\bmod{n}$ Specifically, here is what I have done: this is what i mean. i can't ...
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### Getting Certificate KeyContainerName to initialize CspParameters [migrated]

How can I get the name of a Key Container that's in a smart card required for initialization of CspParameters? CspParameters^ cspa = gcnew CspParameters(ProviderType, ProviderName, keyContainerName, ...
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### RSA Key composition

I'm trying to figure out how it is composed the RSA key. Follow what I know : For a RSA 2048, 2048 is the bit length of the module. The public key is composed by $(e,M)$ when $e$ is the public ...
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### ECDSA Public key randomness

If I have a 256bit ECDSA public key how likely is it that the same public key will be generated by another person. Will it take on average 2^256 tries to generate same public key? If I xor the first ...
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### AES GCM vs other encryption modes in embedded environment for network traffic

I'm doing a lot of research since I'm doing an internship for a company where I need to upgrade their security level. Their own protocol needs a cryptographic upgrade and I'm leaning towards AES since ...
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### Solve the congruence using Pohlig-Hellman algorithm

Use the Pohlig-Hellman algorithm to compute a solution to: $3^x\equiv 2 \pmod {65537}$ My attempt: $p-1 = 65537-1 = 65536= 2^{16}$ $x= 2^0x_0+2^1x_1+2^2x_2+...+2^{15}x_{15}$ For $x_0$: ...
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### RSA key pair generator in “C” - HELP [on hold]

So, here's my problem. Every single library i try to compile (OpenSSL, WolfSSl, PolarSSL) an other not very know gives me error on compiling to. Everthing gives the compiler a reason to just don't ...
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### Are RSA keys stronger than McEliece keys?

What the title asks. I'm currently of the opinion that differences in key size don't make either stronger or weaker than the other in this case.
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### encryption of message “DATACONFANTIALITY” with key playfair using playfair cipher

actually i have solved the above mentioned problem but i want to check weather it is correct or not. my question is that how to encrypt the message DATACONFANTIALITY using the playfair cipher where ...
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### Calculating hash of hash in C [closed]

I've been working with Openssl libcrypto for a long time and I'm quite familiar with it but now I've got a problem I cannot solve in my own, so I need your help. I'm creating a hash of a short string ...
### In a additive group is it hard to calculate $bg$ given $ag, g, abg$
The ECDH problem defined that given $g,ag,bg$ it is difficult to calculate $abg$. But it is also difficult to calculate $bg$ given $ag,g,abg$. where $g$ is generator and a,b are elements of group.