All Questions

95 views

Is substitution with random prefix codes secure? [closed]

The following paper interests me very much: D. W. Gillman, M. Mohtashemi, R. I. Rivest, On breaking a Huffman code. IEEE Trans. Inf. Th. Vol.42 (1996), pp 972-976. However, unfortunately due to my ...
1k views

Cycle attack on RSA

I originally posted this question in the mathematics section, you can see it here. Let $p$ and $q$ be large primes, $n=pq$ and $e : 0<e<\phi(n), \space gcd(e, \phi(n))=1$ the public encyption ...
147 views

Does changing the random number selected for each message increase security in Schnorr's scheme?

I was reading about Schnorr's scheme and in that for signing the signer generates a random number and continues with his operation. I am trying to implement this in a scenario where the signature ...
537 views

Decrypt AES-128 with key file but missing IV? [duplicate]

I want to decrypt a file that has been encrypted using AES-128 in CBC mode using OpenSSL. I got the “.key” file – which is 32 digits – but when I try to decrypt with OpenSSL, the program asks me for ...
589 views

Why should I use Authenticated Encryption instead of just encryption?

There are various different modes of operation for block cipher use, some of which provide "encryption" and some of which provide authenticated encryption. Why should I use an authenticated ...
392 views

Generating a number using SHA512 that users can later verify (once I publish secret seed)

I've wrote following C# method that basically takes 3 seeds and gives you number in 0-100 range. I then use that number for variety of purposes but for this question the most important one is the ...
171 views

Demonstrating Diffie-Hellman key exchange using only p, A, B;

I'm trying to figure out how to demonstrate DH key exchange using what is given to me. I'm unsure of how to tackle the problem. Question: Demonstrate Diffie-Hellman key exchange. Given p=104933, ...
121 views

57 views

Operation sequence authentication shared storage

Let's say there is a shared storage: USB flash drive, external HDD, or whatever you like. I'll refer to it as disk. Also, there are multiple parties, let's say Alice and Bob (may be thousands of them) ...
58 views

Expand 1-n Oblivious Transfer to retreave only an item I, for which permissions exist

To my understanding in a 1-n Oblivious Transfer the Sender has some Values $X_1...X_N$ and the receiver wants to retreave some $X_I$, with $1 \le I \le N$. Can one now somehow guarantee, that the ...
517 views

TLS/SSL's usage of Non-Ephemeral DH vs DHE

These questions revolve around DH and ECDH vs DHE and ECDHE. Specifically within the context of TLS/SSL. There are three ...
53 views

Re-encryption mixnet

Can an Elgamal-based re-encryption mechanism be used in a free route mixnet topology? Until 2006 it was not possible, but I couldn't find the later research results or achievements. Can anyone suggest ...
73 views

Testing hardware random number generators? [closed]

I would like to know how to test hardware random number generators. What techniques, tools or tricks to solve the problem ? Any practical difficulties, implementation complexities etc.
171 views

Security Consideration on The Use of Random Number in Digital Signature

key-exchange protocol allows two parties to establish a shared key over public network. Lacking of authentication the original Diffie–Hellman key exchange is insecure under man-in- -the-middle ...
470 views

Authenticated DH, what protocols are secure?

I read about STS + variants being insecure in the SIGMA paper, which then proposes SIGMA as a replacement. Are the SIGMA variants still considered secure or are there some other protocol that's ...
224 views

Why the need to hash before signing small data?

I’ve got two questions: I’m doing the following: Data : uuid + int + nonce Signature: ECDSA(sha256(Data) ) To verify the signature: ...
152 views

HKDF vs TLS PRF. Which of the one is better? [closed]

Which of the one (HKDF or TLS1.1+ PRF) is more secure and why?
145 views

Using the same private key for two ECC key pairs

Let $(d_1,Q_1)$ and $(d_2,Q_2)$ be ECC key pairs over two different elliptic curves (say NIST P-224 and NIST P-256). According to the Elliptic Curve Discrete Logarithm Problem (ECDLP), if the private ...
213 views

Is it possible to weaken a bitcoin private key by “using” it elsewhere?

What are the increased possibilities (if any) of being able to crack a private key given the following: The associated bitcoin (ECDSA Secp256k1-based) public key is known. The private key has been ...
1k views

Is Porticor's “homomorphic” key encryption something that can really be done or is it just marketing hype?

Porticor has an interesting file encryption offering for encrypting and decrypting files in an MySQL database quickly. They are an Amazon AWS (Amazon Web Service) Partner Network technology partner ...
34 views

Is it possible to weaken a bitcoin private key by 'using' it elsewhere? [duplicate]

What are the increased possibilities (if any) of being able to crack a private key given the following: The associated bitcoin (ECDSA Secp256k1-based) public key is known. The private key has been ...
710 views

If PGP and GPG both follow the OpenPGP standard, are they 100% compatible in all use cases?

If someone gives me their PGP key, can I use it with GPG, and vice versa, all the time (100% interchangeable)? Or are there times when they are not compatible, when only PGP can be used with a PGP ...
84 views

Any field in a PKI certificate where some text info can be stored?

I want to store 5-10 lines of Text Info in a PKI Certificate. All I want is that when using common tools like openssl command line or certutil from Microsoft, this text info should be displayed as is. ...
170 views

Proof of storage scheme

I'm familiar with client puzzles, where the client performs some work and there is a way to prove to the server that the client has done so. Is there a way to do this, but where the client's resource ...
40 views

Assuming the alert protocol is encrypted AFTER a session has been established and the structure below, how does the client know whether to expect encrypted data or not? ...
141 views

Defending hybrid encryption schemes against padding oracle attacks

I intend to use a generic integrated/hybrid encryption scheme for transmitting information between a client and a server. Key encapsulation: a 128-bit symmetric key is generated and asymmetrically ...
343 views

Discrete log problem, when we have many examples

Suppose I have many instances of the discrete log problem, all using the same unknown exponent. Is this problem easier than the standard discrete log problem? Oh, heck, I should be more precise. ...
85 views

What might be assumed about a PRF if the key has been chosen?

The defining feature of a PRF $f:\{0,1\}^k\times\{0,1\}^s\mapsto\{0,1\}^*$ is that, if the first parameter is selected at random, it should be indistinguishable from a function ...
83 views

Generating shared secret random permutation

There are three blind card game players. Each player does not trust any other, even prejudicing other two players may not be blind, or there may be others in the room, peeking at their cards. In ...
70 views

Is Encryption without knowing the input directly possible at all?

I know the question is rather unusual, but let me clarify what I'm searching for: There is one person, lets call her $Alice$. $Alice$ has $n$ plaintexts $t_1..t_n$ and $n$ public keys $pk_1..pk_n$ of ...
231 views

Cryptographically strong pseudo-random seq. generators

If a pseudo-random sequence generator is built so that it uses an n-bit seed and outputs a string that is of length x. Let's say one wants to generate a bit string of length y and uses the previous ...
251 views

Is symmetric key encrypted with server's public key secure

I'm trying to implement lightweight yet secure protocol for communicating two trusted parties with each other. Consider following scheme: Alice wants to establish secure two-sided channel with ...
145 views

Why does Fortuna RNG use double SHA-256?

In the paper for Fortuna the authors say that you can use any good digest algorithm (obviously as long as its output is 256 bit) and then they recommend double SHA-256. Why? What's the benefit? What ...
80 views

Implementing AugPAKE over ECC

The AugPAKE spec says it can be implemented over elliptic curves. This sounds very promising, but they don't actually back that claim. Can this really be achieved? If so, how would one go about ...
751 views

At what stage is DHE and RSA used during the SSL/TLS handshake?

At what stage of the SSL/TLS handshake is the DHE and RSA used and what is the purpose of using a pre-master secret when you could just use RSA to exchange the symmetric key (i.e. AES) for further ...
82 views

Perl DES PCBC as protection against decryption/crypt analysis

Is error propagation in DES PCBC a good method to prevent decryption/crypt analysis by third parties? If I had a very large file encrypted with Perl's DES with the PCBC option, and then removed the ...
63 views

Near preimages, applicable to Bitcoin?

Bitcoin mining relies on generating a smaller hash than the so-called target (a function of the so-called difficultly), thus is vulnerable to a truncated preimage attack (you just need to obtain a ...
51 views

ECDSA signature verifiable 1-way transformations

Alice signs a message $m$ with her private key, yielding a signature ($r$,$s$). I want to prove to someone else that I have this signature, but I don't want them to have the knowledge of what ...
78 views

Is it possible to encrypt data in such a way that it cannot be decrypted with the key used to encrypt it but can be decrypted with another key

I'm very new to cryptography and encryption so I apologize if the answer to this is well known, but I can't find anything in my research. The crux of the problem is the need to store data on an ...
50 views

Can CBC encryption have separate keys for separate blocks of plain text?

Can we have separate key for separate blocks which we get while operating a plain text message using CBC encryption model? If yes, what are it's advantage? Please enlighten me.
67 views

How to make a crypto-currency robust to 51% attacks?

For Example: In Bitcoin it is theoretically possible to double spend if you control > 50% of the computational power in the network. Also it is possible to apply "selfish mining" with far less than ...
70 views

Is it secure to choose d in a RSA key pair?

An RSA key pair consists of the private key $(n,d)$ and a public key $(n,e)$ such that $de \equiv 1 \bmod{\lambda(n)}$. Usually one chooses a small $e$ and computes $d$ by inverting it modulo ...
468 views

Besides key and ciphertext sizes what are other advantages of elliptic curve versions of various protocols?

There are elliptic curve variants of Diffie-Hellman, ElGamal, DSA and possibly other protocols/algorithms. I know that these elliptic curve variants have smaller key and ciphertext sizes which will ...
402 views

Verify Signature Failed [closed]

I am writing a small module which will verify signed message. Message will be signed using private key in Smart Card. The inputs are: Signed Message Original Message Public Key / Certificate with ...
125 views

Code-breaking software [closed]

Is there any (free) software available to check for standard encryption algorithms such as the Caesar cipher? Advanced encryption algorithms such as RSA, DES, AES, etc. are not necessary.
426 views

Encrypting with private key in Public Key InfraStructure [closed]

In Public key infrastructure, the MD5 of a piece of data is encrypted with the private key of a sender and this encrypted MD5 – along with the data – is again encrypted using an algorithm like AES or ...
177 views

Difference between lightweight, online and low memory Authenticated Encryption schemes

What is the basic difference between the following types of Authenticated Encryption (AE) schemes? Lightweight Authenticated encryption Online Authenticated Encryption Authenticated Encryption for ...
For all $c_0\leftarrow m_0 \oplus k$ there exists a $k'$ such that $c_1 \leftarrow m_1 \oplus k'$, where $m_0 \neq m_1$ and $c_0 = c_1$. Assuming a truly random $k$, the first assignment is a ...