3
votes
1answer
195 views

Is there a cryptographic hash function that can be performed with pencil and paper?

Imagine I'm signing up for the 99th new web site this month. I somehow take my secret key (which I have written down on a card in my wallet) and the domain name of the site and feed them both into ...
2
votes
2answers
93 views

MD5 theoretical question

Ok, so this is a very possible stupid question, but one of those things that has sat at the back of my mind for a while. We all know that MD5 has issues, and these have been known for about a decade. ...
1
vote
1answer
97 views

SHA-1 Keyed Hash Function

I know that SHA-1 is an unkeyed cryptographic hash function when used in practice. But, in the theory, all hash function are defined with keys. My question is: How I will be able to formalize the ...
0
votes
1answer
113 views

How to store keys for a cascading encryption?

What is the best way to implement a cascade encryption? I'm trying to figure out how to cipher a string (or message) using Serpent-Twofish-AES and then store the keys. I'll provide an explanation, ...
2
votes
2answers
117 views

How does secret sharing solve the partial exposure problem?

I have been trying to understand how secret sharing methods like Shamir's secret sharing solve the problem of a share revealing information about the secret. I guess there are some random numbers ...
0
votes
1answer
101 views

Explicit Key SHA-1

I'm reading “Collision-Resistant Hashing? Towards Making UOWHFs Practical” and in the Section 2 it says: Hash functions like MD5 or SHA-1 have no explicit key. But no notion of ...
0
votes
1answer
116 views

Why is appending the key to a mesage and then hashing that insecure if the hash isn't weakly collision resistant? [duplicate]

Suppose I have H(M|K) and that H is not weakly collision resistant. If I have a message mac pair (M,MAC), how is it possible to find another message mac pair (M2,MAC2)? My thinking for this problem is ...
1
vote
1answer
255 views

Can you explain partial private key extract algorithm in certificateless Public key cryptography?

Related to the algorithms of certificate-less Signature approach of Al-Riyami and Paterson… Why is there a need for a "partial private key extract algorithm"? Why should it be needed when ...
4
votes
2answers
232 views

Can anyone give an example where (asymmetric) crypto can go wrong due to selection of wrong groups?

Basically the title says it all. It would be great if someone could tell give an example using provable security. More information about groups can be found at: ...
2
votes
0answers
74 views

Are there public $p$ and $q$ numbers for use in DSA?

There are many RFC documents giving large primes to use in Diffie-Hellman. However, I couldn't find standards on the $p$ and $q$ large primes used in the DSA signature scheme. This is proving to be a ...
-1
votes
1answer
135 views

How do I cryptanalyze a password field?

In a PostgreSQL database, I can see the following fields in a table (for a specific record): User = administrator Password = "ceMv9Me6go" Now the following are true: The password length is not ...
0
votes
1answer
402 views

Diffie-Hellman Secret Exponent Size and Shared Secret Usage [closed]

I'm developing my own protocol and I'll use Diffie-Hellman to achieve PFS. It will work in this way: The symmetric encryption algorithm will be AES_256_CBC. The DH parameters will be: P: a 2048-bit ...
4
votes
1answer
204 views

Can two people with different one time pads securely exchange a message like this?

Alice has a message, generates a one time pad, encrypts her message and sends it to Bob. Bob generates his own one time pad, encrypts the message again, and sends it back to Alice. Alice then decrypts ...
3
votes
1answer
125 views

How can two (or more) parties share and agree upon a common random seed?

I really don't know how to call this simple problem: Two (or more) parties need to establish a common (non-secret) value to be used as a seed for a deterministic RNG. The only requirement is that each ...
6
votes
2answers
177 views

Why don't we use MACs to store passwords?

These days, the best practice for storing passwords is to use a scheme like scrypt or bcrypt. The goal of these schemes is to make dictionary attack inefficient for an attacker but it also slows down ...
2
votes
1answer
917 views

Is it true for Java that the transformation mode and padding is ignored when using RSA?

Consider GregS's comment to this question (more specific to bouncycastle's provider implementation): http://stackoverflow.com/questions/11717646/bouncycastle-rsa-key-size-and-padding The mode, ...
0
votes
1answer
111 views

No Birthday Attack to TCR

I'm reading the paper “Collision-Resistant Hashing? Towards Making UOWHFs Practical” , which compared TCR (Target Collision Resistant) and ACR (Any collision Resistant). It says we wish to stress ...
2
votes
1answer
57 views

Weaker Notion of Target Collision Resistance

I'm reading the paper “Collision-Resistant Hashing? Towards Making UOWHFs Practical” which states: While it might be easy to find a collision $M,M'$ in $F_K$ by making both $M,M'$ depend on $K$ ...
2
votes
1answer
71 views

Dependence on Keyed Hash Function

I'm reading the paper “Collision-Resistant Hashing? Towards Making UOWHFs Practical” which states: With an ACR hash function $F$ the key $K$ is announced and the adversary wins if she manages to ...
3
votes
1answer
216 views

Public-key cryptosystems without poly-time quantum attacks

It's well-known that Shor's algorithm can solve integer factorization, discrete logarithm and discrete log over elliptic curves in cubic time. This implies that cryptosystems like RSA, ElGamal, and ...
1
vote
1answer
2k views

What does AES256-CTS-HMAC-SHA1-96 mean in relation to Kerberos?

I'm not completely clueless as to what it means, but I'd like to understand it at a higher level. The highest encryption type used by Active Directory domain controllers for Kerberos authentication ...
2
votes
1answer
124 views

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 ...
-1
votes
1answer
99 views

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 ...
1
vote
0answers
81 views

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 ...
1
vote
2answers
120 views

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? ...
1
vote
1answer
108 views

Security based on PRF

I've seen that there is several kinds of PRF, and 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, are they ...
1
vote
1answer
75 views

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 ...
1
vote
1answer
176 views

Why is an IV used in Merkle–Damgård transform?

In Merkle–Damgård 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 ...
2
votes
3answers
555 views

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 ...
1
vote
1answer
229 views

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?
5
votes
1answer
305 views

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 ...
3
votes
1answer
157 views

What does this Authentication protocol achieve and what information is shared?

I'm having trouble with the following question from my class: "What is the purpose of the protocol, and how does it achieve this purpose and what shared information does A and B end up after ...
0
votes
1answer
146 views

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 ?
1
vote
1answer
182 views

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 ...
2
votes
1answer
69 views

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 ...
1
vote
1answer
175 views

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 ...
2
votes
1answer
240 views

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 ...
6
votes
2answers
344 views

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: ...
2
votes
2answers
467 views

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 ...
3
votes
1answer
475 views

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 ...
1
vote
1answer
230 views

Verification of identity by certification authority

I have question about how a user's identity is verified by a Certification Authority. As I understand it, the process works as follows: User generates his private key and (with the help of private ...
1
vote
0answers
143 views

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)? ...
2
votes
2answers
297 views

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 ...
5
votes
3answers
314 views

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?
1
vote
2answers
162 views

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, ...
1
vote
1answer
486 views

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. ...
5
votes
1answer
259 views

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 ...
2
votes
0answers
133 views

How can I construct a distinguisher given an inverter?

Let $ PRG: \{ 0, 1\}^n \rightarrow \{ 0, 1\}^{n+s}$ be a pseudo random generator and let $A$ be an inverter that runs in polynomial time, specifically: $\large \mathbb P_{d \leftarrow PRG(U_n)}[ A(d) ...
1
vote
2answers
137 views

Splitting a password for dual roles [duplicate]

I would like to prompt users for a single passphrase to establish trust with separate, normally (but not always) complementary systems from one password input. I'm essentially looking for a box where ...
2
votes
1answer
335 views

Forge CBC-MAC given the MAC of two messages and of their concatenation

I found this question about CBC-MAC forging and want to make sure I understand it: Let a and be be two strings of block length one. Suppose the sender sends $(a, \text{CBC-MAC}(a)), (b, ...

15 30 50 per page