1
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1answer
95 views

Adversary to Any Collision Resistance Hash Function

I'm reading a notion Any Collision Resistance for Hash Functions. In the lecture define a collision finder CF. CF is said to $(t,\epsilon)$-break the family of hash functions $F_K$ if the ...
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1answer
140 views

Is encrypting a public key with a symmetric key safe?

Assume the sender wants to share their ephemeral/long-term public key with intended receiver only and both share symmetric key. Is it secure to encrypt the (full/partial) public key (of RSA, ECC) ...
1
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1answer
226 views

What is a Trapdoor in Merkle Signature?

Merkle signature (pag. 40) use than public key (verification key) the root of the Merkle Tree and than private key (to sign) the set of pre-images of the $g(Y_i)$ where $Y_i$ is the verification key ...
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1answer
101 views

How does the length of the plaintext affect the cipher strength?

Let the block length 64-bit, 256-bit key, cipher text accordingly - 64 bits. What is the strength of the block cipher, if any unknown attacks, which could reduce its strength. We can only brute force. ...
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1answer
152 views

Secure function evaluation

Consider 3 parties, Alice, Bob and Charlie. Suppose each party has a bit as input, i.e. Alice, Bob and Charlie hold $a, b, c \in \{0, 1\}$ respectively. Show how construct a scheme with which ...
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1answer
296 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 ...
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1answer
129 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
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1answer
675 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. ...
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1answer
287 views

randomly generated key reused with XOR

If I have a long randomly generated key (k), XORed with a message (m), but since the message is longer than the key, there is a chance of reusing the keystream with the same message, but the key is ...
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1answer
65 views

Why do authors say conflicting things regarding leak-free stages in their paper?

In this paper the last sentence of the first paragraph in the abstract states: We assume a (necessary) “leak-free” preprocessing stage. But then later on in section 1.4 they say Another ...
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1answer
632 views

What's the difference between the long term key and the session keys?

I'm currently studying secret key cryptography, and I've come across the terms "long-term key" and "session key". What's the difference between these two kinds of keys?
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1answer
119 views

How do you use the Tiger hash function with GPG?

I've searched Google and the GnuPG documentation and I haven't been able to find an answer. Some pointers in the right direction would be greatly appreciated.
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1answer
3k views

Can AES use PKCS#5 padding

From What is the difference between PKCS#5 padding and PKCS#7 padding, I understand that PKCS#5 is defined for 8 byte block sizes. Does this rule it out as a padding option for AES since AES has a ...
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2answers
185 views

Can you get two unpredictable hashes from the same message with, e.g. SHA1?

I'd like to create a database of questions and answers so that an attacker with access to the database can't obtain either the questions or the answers. If H0 and ...
1
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1answer
210 views

Is there proof to the relation between the gap Diffie-Hellman problem and the the Cha-Cheon signature scheme?

I am trying to prove that: "If the gap Diffie-Hellman problem is easy, then the Cha-Cheon signature scheme will be broken." Can you help me to prove it? Is there any proof to the relation between ...
1
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1answer
119 views

Efficiency of computing $e(P,Q)$ Vs $g^a \pmod{p}$?

The definition of $e$ can be seen here. I want to know the accurate comparison of efficiency between $e(\cdot,\cdot)$ and $g^a \pmod{p}$. If computing $e(P,Q)$ is less efficient than computing $g^a ...
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1answer
255 views

Can Secp 256 K1 curves “map” to a value on FIPS 186-3 or P-256?

I'm looking at Secp 256K1 vs UProve's FIPS 186-3 or P-256 implementation. Is there any relationship between the curves such that I can consistently "map" or "project" values from one curve to ...
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1answer
69 views

RSA Proof - di-mgt - modulo properties

I´m trying to follow one of the very detailed RSA Proofs given by di-mgt: "RSA theory", but unfortunately I stuck at the beginning of solution (chapter 3). I don´t understand where the second part ...
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3answers
317 views

Encoding numbers that can be decoded mentally?

I have a lot of objects, all of which need a particular number tagged on them so I can quickly tell the customer accordingly. But the problem is that the customer should not know what these numbers ...
1
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1answer
218 views

Encryption algorithms and the “One-Time pad” [duplicate]

I am not well versed in the field but I believe I know the basics. All encryption algorithms that I know of utilize direct data manipulation to encrypt a message (string of bits) such as shifting, ...
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2answers
405 views

How do we prove that AES, DES etc. are secure?

How do we prove that AES, DES etc. are secure? I've read about them and know the basics on how they work, but I still don't quite understand how we can be sure they are secure? What are the proofs?
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2answers
258 views

Re-using parts of a one time pad to encrypt a new one?

The main problem with OTP's is the fact that they can only be used once. Would it be possible to use a random number that's, say, 512 digits, then use 256 of those for the (non-random) message, the ...
1
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1answer
236 views

how to mathematically prove a key exchange algorithm [closed]

I want to know the basic methodology that can be used to prove that a key exchange algorithm is secure. I am not asking about any specific algorithm. I want to know what should be proven and how to ...
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2answers
289 views

Shamir's Secret Share [duplicate]

I'm not quite sure the benefits of working over a prime modulus in Shamir's secret share- but doesn't limiting the numbers you pull from make the secret easier to guess? Instead of being over the real ...
1
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1answer
342 views

Dual_EC_DRBG and OpenSSL on a Mac

Since there is not much info anywhere on the Internet related to this: Does anyone know if OpenSSL's default CSPRNG is Dual_EC_DRBG or not? Their wiki is not very clear… Related to the first ...
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1answer
1k views

Reusing keys with AES-CBC

I heard that key/IV pairs must not be reused in AES-CTR, or when using any stream cipher for that matter. Yet the attacks described do not seem to apply to AES-CBC. Is reusing the same key several ...
1
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1answer
341 views

Is my understanding of CPA indistinguishability experiment correct?

Following are steps to conduct Chosen Plaintext Attack (CPA) indistinguishibility experiment $PrivK_\mathcal{A,E}^{eav}(n)$. $\mathcal{A}$ is the adversary $\mathcal{E}$ is the encryption scheme ...
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1answer
159 views

Security of (cryptographic) padding compared to other methods for blockcompletion for block ciphers

As said in the heading, I want to know how the security of different padding methods, e.g. ANSI X.923, ISO 10126 and PKCS7, is compared to other methods to reach the needed block size, like ciphertext ...
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1answer
673 views

Break a simple compression function of a cryptographic hash function

I have a very simple compression function, which looks like this in C++: ...
1
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1answer
207 views

Relationship between Elliptic Curve Discrete Log, Integer Discrete Log, and Integer Factorization

I am trying to look into a relation between the following three problems which are widely used to build public crypto systems: Integer Discrete log Elliptic Curve Discrete log Integer Factorization ...
1
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1answer
187 views

What are the security effects of reusing a public RSA key to encrypt large data by blocks? [duplicate]

I'm trying to figure out a way to do public key encryption on a very large piece of data. For this, I of course want one side to do the encrypting but is unable to decrypt the data, and the other ...
1
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1answer
632 views

How to supply the GCM authentication tag to the OpenSSL command line tools?

I'm using AES-256-GCM for authenticated encryption. In order to decrypt, the ruby OpenSSL library requires an auth_tag parameter (in addition to the key and iv). ...
1
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1answer
128 views

Does it necessarily mean that an RSA moduli generated with poor randomness is not random?

In 2012 a group of researchers collected a large amount of RSA moduli and calculated their greatest common divisor in order to find common factors between them. By finding a common factor they could ...
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1answer
869 views

Reduction of Integer factorization to Discrete logarithm problem

I was reading Eric Bach paper entitles "Discrete logarithms and factoring", in which he states the following reductions: solving the integer factorization problem suffices to solve the discrete ...
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2answers
350 views

How can Alice prove that a message has not been tampered with?

In terms of the usual suspects. The problem I have is that Alice wants to send Bob a message M, which gives Bob permission to perform some actions. However Alice wants to verify, from time to ...
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1answer
298 views

What operations are used in symmetric cryptography and why?

In continuation to Why are bitwise rotations used in cryptography?: what other operations are commonly used in symmetric cryptography? Are there particular operations on numbers that are good for ...
1
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1answer
123 views

How to build a secure AE scheme with generic composition?

I am actually looking for using a secure Encrypt-Then-MAC AE scheme , and consider using either an existing "ready-to-use" dedicated AEAD mode (GCM, OCB, CCM, EAX, etc ..) or an alternate composed ...
1
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1answer
2k views

How long to bruteforce a RSA key [duplicate]

Suppose I have a 2048 bit RSA public key, and want to brute force the corresponding private key. I guess there are 2048^16 possible combinations? How long would this take me to brute force with an ...
1
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2answers
103 views

Prepend information about encryption implementation to the stored data

I want to preface this by saying i will not be using any of this code/information in a live project, this is only for learning/fun (so I welcome some speculation) I was looking at how the PHP crypt() ...
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1answer
558 views

How is text converted to a number for RSA? [duplicate]

According to http://en.wikipedia.org/wiki/RSA_%28algorithm%29#Key_generation the key length is the number of bits in n. So how can a message of many megabytes (millions of bits) be modded by a 1024 ...
1
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1answer
267 views

ECC Point Multiplication of Product

I can calculate $Q = a\,b\,G$ in several ways: $Q = a \, (b \, G)$ or $Q = b \, (a \, G)$. These give the same result, as expected. But if I do $c = (a \, b) \bmod n$ where $a \, b$ is much greater ...
1
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1answer
162 views

Which keys are necessary to decrypt Application data in a SSL connection?

I'm debugging an application which communicates between client and server using a SSL/TLS connection, and want to capture and analyze the sent data. Are the client write keys and server write keys ...
1
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2answers
351 views

Are there any hand ciphers not obsoleted by computer cryptanalysis? [duplicate]

Computerized cryptanalysis has obviously made formerly "secure" hand ciphers like Playfair, Four Square, and the Hill Cipher obsolete because they can be defeated in seconds. But is there a hand ...
1
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1answer
155 views

Is this a sensible cryptographic protocol intending to reduce the impact of compromised security?

I'm in the process of designing a cryptographic protocol which will reduce the impact an attacker will have if they gained root access to a server storing data. The basic crux of it is that keys ...
1
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1answer
315 views

Designing a security system from scratch with a custom protocol, suggestions needed

For the reasons I cannot go into details, I need to design my own protocol and overall security system which will be used to establish secure data exchange between various devices (most notably ...
1
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1answer
355 views

What does $(\mathbb{Z}_n^*)^2$ mean?

In a paper they write once, $(\mathbb{Z}_n^*)^2$. Is this the group of quadratic residues or is it something else? Here the theorem: Under the strong RSA assumption, given a modulus $n$, along with ...
1
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4answers
349 views

Using the output of a stream cipher, how to guarantee the integrity of 4 bytes of data?

I am designing a simple and secure stream communication protocol. My idea was to build each message sent to the wire as: (message size || clear text || UHASH(message size || clear text)) $\oplus$ ...
1
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1answer
141 views

Connections between Instance Hiding and Fully Homomorphic Encryption

Another approach taken by researchers for carrying out computations over encrypted data is Instance Hiding. In brief, If a user wants to outsource the computation of a function for a particular input ...
1
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1answer
110 views

How to learn the first bit of m in padded RSA

Consider the following version of padded RSA encryption, where encryption of $m$ is done by setting $m′ = (0^k~||~r~||~00000000~||~m)$ for a random $r$ (of length 8 btyes = 64 bits) and then computing ...
1
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2answers
243 views

How secure is passing a MAC to Python's random.seed before using random.choice to generate a MAC?

I'd like to use Python's random.choice seeded with a HMAC-SHA1 tag to generate a MAC encoded in a variable set of chars. ...

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