# All Questions

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### Decryption or attacking DES encrypted file

I have a file that has been encrypted using DES and am looking to decrypt and find a secret message encoded. All I have is the file which is full of binary data. There is no key or anything else which ...
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### Can Diffie-Hellman generate values in a specified range?

Is there any way to generate values only between $0$ and $255$ with the Diffie-Hellman method? I need to create keys for communication algorithms with $32$ and $16$ numbers between that range. The ...
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### Perfect Forward Secrecy in MTI/A0

Would the property of perfect forward secrecy still be achieved in MTI/A0 for a session key that was established between C and D when one LL-key aD is revealed so that both LL-keys aC and aD are ...
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### PPT eavesdroper able to output $m_{0}$ and $m_{1}$ of different lengths

I've read the following two questions and their answers: Messages of different lengths and one-time computationally-secret Why is a non fixed-length encryption scheme worse than a fixed-length one? ...
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### Security based on PRF

I've seen that there is several kind of PRFs. Sometimes people speak about strong PRFs. When proofs of a protocol or algorithm are given based on the assumption of the use of a PRF, they speak ...
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### Is there a relation between security of rounds of DES and Luby Rackoff rounds?

DES uses 16 rounds of feistel networks but not considered secure . Where Luby Rackoff constructions which are inspired by DES its proven by Patarin that 7 rounds is secure . Is there a relation ...
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### Why is an IV used in Merkle-Damgard transform?

In Merkle-Damgard transform, a fixed vector IV is chosen at the beginning, and it is hashed together with the first block x1. I wonder why we don't use x1 straightforward, i.e. hash x1 and the next ...
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### How do I test my encryption? (absolute amateur)

I am a hobby programmer with a background in biology and have developed an encryption program based on DNA. I tried to make it hard to crack, but it's essentially a substitution cipher and uses the ...
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### How can an encryption scheme be indistinguishable with multiple messages but vulnerable to an adaptive chosen-plaintext attack?

In order to be indistinguishable with respect to multiple messages, wouldn't the scheme need to be nondeterministic? How would this then possibly be vulnerable to an adaptive CPA?
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### In elliptic curve cryptography, how is “A dot A” computed?

I was just reading Ars Technica's primer on ECC. Somewhere near the middle of the second page, the author introduces the "dot" operation that takes an elliptic curve and two other known points, giving ...
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### What does this Authentication protocol achieve and what information is shared?

I am trying to learn everything I need to know for a Unit on 'Reliable and Secure Systems', but I'm struggling with the basics now. The question that I'm having trouble with is: "What is the ...
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### What is the difference between various modes in FPE?

Format preserving encryption has three modes FE1( FFX) , FE2(VAES) , FE3(BPS) . All of them are based on Feistel Networks .Can somebody explain how they differ from each other ?
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### How do I sign data that's been encrypted using public key? (RSA)

I've received a public key to encrypt my data for the other end to decrypt using their private key. Now, they want us to sign the data as well to ensure non-repudiation. I thought that I should only ...
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### How to pass an arbitrary signature to a certificate

I am trying to sign certificate (X509) using secret sharing. That is shareholders combine their signatures to produce the final signature which will be in this case the signed certificate. However ...
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### Are there any protocols that are truly secure from active and passive MITM attacks?

Are there are any cryptographic protocols or algorithms that can prevent active MITM attacks or interference when initiating a new connection to a server or someone you have not exchange keys with ...
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### Why is it important to generate a pseudorandom permutation from a pseudorandom function?

Most of the papers on block cipher constructions, especially the ones which discuss constructing block ciphers of arbitrary lengths or small domains, the techniques are designed based on building a ...
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### About private keys of certificateless cryptography

While reading Identity Based Cryptography and Certificateless Cryptography , Can any one tell why should private key generator(PKG) or Key generation center (KGC) generate private keys for users..? ...
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### How to Generate rsa keys using specific input numbers in openssl?

I am new to openssl so asking this question here for help. I selected 2 prime numbers p and q. Calculated public pair: (n,e) and private key: d. For ex. ...
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### Is encrypting credit card numbers one by one with rsautl secure?

I wish to encrypt credit card numbers one by one using asymmetric encryption on the command line. My current approach is this… Encrypt: ...
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### Certificateless Signature

Consider the following scenario: There are two users: A and B. Users A and B generate a pair of their own public and private keys PUBa, PRIa and PUBb, PRIb. There is one trusted center(TC) that ...
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### Certificateless cryptography

While reading "Certificateless Public Key Cryptography" by Author Sattam S. Al-Riyami and Kenneth G. Paterson, they have considered generation of private keys by a Key Generation Center (KGC). If the ...
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### OpenPGP/X.509 bridge: how to verify public key?

I'd like to use OpenPGP authentication over TLS, but lack of implementations made me use a temporary solution: an OpenPGP/X.509 bridge certificate. The approach is very similar to the approach used ...
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### Verification of identity by certification authority

I have question "How user's identity by Certification Authority " is verified. While understanding, I am considering the following mathematics.. User generates his private key and with the help of ...
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### About Elliptic Curve ElGamal, 3 simple problems I have trouble with

In Elliptic Curve ElGamal, why are a=b=1 always legal for primes whose lengths are no shorter than 11(2) bits long? Is there any reason why the Point at Infinity can always be encoded as (0,0)? ...
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### Are there any bijective one-way functions not based on number-theoretic hardness assumptions?

I'm trying to find a bijective function $y=F(x)$ which should be easy to compute in one direction but hard to compute in the other, where the one-way property is not based on a number theoretic ...
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### Security proofs for CBC mode

I'm looking for different approaches to proofs for the security of CBC mode encryption. What are the best sources of information about this subject?
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### Would this program be useful in cryptography?

I know nothing of encrypting. I'm not even sure how to tag this. I wrote a program that can calculate this pretty quickly on my macbook pro 2.3GHz IntelCore i7. The two exponents are Mersenne primes, ...
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### Signature algorithm SHA 1-2 with ECDSA

Can someone please explain what key sizes are required for the ECDSA algorithm? I tried a 128 bit EC Key for SHA1withECDSA and it throws an error. However with 256 bit key I could run the algorithm. ...
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### AES-CTR mode and the Biclique Attack

The biclique attacks that break AES (Biclique Cryptanalysis of the full AES) appear to require decryption oracles to work, presumably because the key schedule of AES is weaker in the decryption ...
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### Is honeywords different from k-anonymity? [migrated]

Ari Juels and Ron Rivest propose a technqiue to strengthen password files called honeywords . Basically for each valid password they insert fake passwords (honeywords) and if somebody tries to ...
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### random access stream cipher

Some time ago I was working in a pet project for a type of database engine. And I thought about securing the data in disk with encryption.. and since the main code was already developed.. I had a few ...
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### Appropriate AES key length for short term protection

Currently I'm doing some initial research for a fully connected distributed network communication model. The context here is a peer-to-peer multiplayer protocol, using a majority-voting system. More ...
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### Please explain Pairing based Cryptography with numeric example [closed]

I read concept of Pairing based Cryptography. But while trying understand the concept by doing mathematical calculation, I am facing much problems. So, could you please explain Pairing based ...
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### Elliptic Curve Factorization: Why are elliptic curves suited for this kind of task?

Currently I'm working on a presentation of a paper that talks about the factorization of large numbers. In the paper elliptic curves are presented as a way to factorize large numbers. After hearing a ...