5
votes
2answers
251 views

Anonymous Gravatar Problem

Gravatar is a service that serves avatars for users based on md5(email_address). The hash is embedded on websites, so it's public. One of the problems with this ...
21
votes
2answers
8k views

What is entropy?

We discuss a lot of topics and use measures of entropy to determine how difficult it is for an attacker to be successful. What does entropy mean in the context of cryptography? How is entropy ...
0
votes
1answer
75 views

Crack RSA with additional information [duplicate]

Suppose $N=3953$, Alice encryption key is $e_A = 337$ and bobs is $e_B=23$. Eve happens to know the corresponding decryption keys, $d_A=3385$ and $d_B=2663$. Can I use this information to find the ...
0
votes
1answer
155 views

ECIES with AES-GCM

The Elliptic Curve Integrated Encryption Scheme (ECIES) describes how to derive a "temporal" key, encrypt a message (eg. using AES) and creating a MAC. However, from my understanding using AES in GCM ...
1
vote
1answer
84 views

How to store and use a Cryptographic Seed in a database [closed]

Companies such as Barclays use cryptographic seeds (for their PINsentry system), RSA do the same for RSA SecurID, but how do they safely secure the seeds in the database. With passwords you just hash ...
1
vote
2answers
164 views

Equivalent key size between HMAC and AES?

I have seem comparison between AES and RSA, e.g., AES 128 bit key is equivalent to RSA modulus 3072 bits. Is there such comparison between AES key size and HMAC?
0
votes
1answer
154 views

Is it necessary to encrypt nonce in cryptographic communication?

Server and client have a pre-shared key K. Assuming that that pre-shared key is safe, so nobody other than server/client can encrypt/decrypt. Client sends a nonce N to server, server then sends back ...
1
vote
0answers
77 views

Pseudorandom number generators based on hard problems in mathematics

I know that Dual_EC_DRBG's security is based on the ellitpic curve discrete logarithm problem, Micali-Schnorr is based on the difficulty of factorization, and MQ_DRBG is based on multivariate ...
1
vote
1answer
91 views

Questions about updating the secret key of RSA?

I want to update the secret key of RSA. I understand there exists a common modular attack on RSA. Precisely, if adversary knows $(e_1, m^{e_1})$ and $(e_2, m^{e_2})$, where $e_1$ and $e_2$ are the ...
4
votes
2answers
198 views

Alternative sources of random numbers

Considering that algorithmic methods for generating unpredictable streams are hard to come by, I've wondered if any of these potential sources are good for making keys, seeds, and the like: stocks, ...
1
vote
1answer
56 views

How does the attacker include input before compression and encryption in CRIME?

I have read this article about the CRIME attack against TLS and SPDY. The article says that: What is not yet clear is how the attacker is including their input in the source material before it ...
0
votes
1answer
75 views

Requirement for the exponent generation during DH protocol [duplicate]

The setting is classic DH protocol. Alice computes $A = g^a \bmod p$. Alice then sends $A$ to Bob. Then Bob will send $B = g^b \bmod p$ to Alice. Are there any requirements for the values $a$ and ...
2
votes
1answer
179 views

Crypto++: How to re-generate pseurandom integers in Crypto++

I'm using Crypto++ to implement my protocol to mask a value $y_i$ by a seudorandom value $r_i$ such that $m_i=y_i \cdot r_i$. Since there are many $r_i$'s I want to generate them using PRG and then ...
1
vote
1answer
232 views

Counter Mode (CTR) and mult-CPA

I am not sure if Counter Mode (CTR) encryption is mult-CPA (chosen-plaintext attack) secure or not.
1
vote
5answers
2k views

How easily could this be cracked?

I'm looking into encrypting files like this: First, I SHA-1 hash the password. Let's say the password is something normal like "hello123", and then hashed. Then I encrypt a file using this: ...
2
votes
2answers
355 views

Explanation of each of the parameters used in ECC

I'm having a very difficult time finding a clear explanation of the parameters used elliptic curve cryptography. I know for certain that $p$ is the number or order or whatever of the given field that ...
1
vote
1answer
104 views

Hashing - Digital Signing and Trivial Stretching

Two very basic questions: 1. Digital Signing Why is it not possible to just simply replace the hash value from the request? Examples: ...
4
votes
2answers
335 views

Can we say that if $P=NP$ there is no CPA secure public key encryption?

I've learned that public key encryption is based on the problem of Discrete Log (as regard to group theory) which believed to be hard. But, can we say that it doesn't matter on which problem our ...
4
votes
1answer
242 views

McEliece information set decoding attack vulnerability

Wikipedia states that McEliece is open to "information set decoding attack". What is an "information set decoding attack" and how serious is the vulnerability? (is it just a matter of choosing proper ...
2
votes
2answers
143 views

Does key derivation with known parameters add any security?

First up: this is a question about a concept that I try to wrap my head around; it is not about the specific implementation. Anyway… I have the following scenario (simplified to show the problem I ...
7
votes
1answer
179 views

Malicious DH groups

Can an attacker construct a DH group, large enough to be considered secure (say, a modulus of 2048-bits), such that the group appears safe, but the attacker is able to solve the DLP in the group ...
1
vote
1answer
463 views

What is the forward cipher function of AES-XTS?

We're using OpenSSLs EVP_aes_265_xts encryption on data (with unique, random, IVs for every new message encrypted) - which is working well. But, I've been asked; what is the forward cipher function ...
0
votes
1answer
80 views

Text in random image encoder: is it flawed?

I have created a small cryptographic programme: You input your text A random image is generated Random coordinate pairs in number equal to the chars of the message are generated. The red component ...
2
votes
1answer
76 views

How to construct the blind factors in practice?

I'm Implementing a protocol that uses masking techniques (or blinding factors), so we can mask a value $y_0$ as $m_0=y_0 \cdot r_0$ where $y_0 \in \mathbb{Z}_p$ and $r_0 \stackrel {R}\leftarrow ...
1
vote
2answers
84 views

If Blum Blum Shub is modified to use a prime modulus, is it still secure?

The definition of the Blum Blum Shub cryptographically secure pseudorandom number generator is $x=x^2 \mod N$ where $N=p \times q$, $p \in \mathbb P$, and $q \in \mathbb P$. Supposedly, the security ...
-1
votes
2answers
257 views

Is the complexity of Caesar (shift) ciphers “n * n!”?

Can we say that any shift cipher to be decrypted needs an algorithm of complexity “n * n!”? (where n is number of possible ...
1
vote
1answer
320 views

What is the importance of adding round key in AES

I know this may not be the place to ask this but I have found it difficult to find an answer to this question. I know the steps of the AES encryption algorithm but I am finding it difficult to ...
2
votes
1answer
426 views

Is this key management scheme secure?

I'm designing a scheme for management of a small number of cryptographic keys (< 100 at any given time) and I had an idea: rather than storing all the keys, could I just store one master key and ...
4
votes
1answer
455 views

How does partial key escrow work?

It is being speculated that one of the ways that NSA leaker Edward Snowden may have created his "insurance policy" – distributing sensitive documents to various individuals with instructions to ...
-2
votes
5answers
244 views

Is symmetric encryption no longer necessary?

Here is it: Symmetric encryption is no longer necessary, because all security services can be implemented with public-key cryptography. Moreover, in public key cryptography the operations for ...
-3
votes
1answer
126 views

Attacking multi block MAC constructions

For variable-length messages, there are three different ways to generate the tags. $Tag = MAC_k(\Sigma_i m_i)$. $t_i = MAC_k(m_i)$ and $Tag = (t_1, ..., t_l)$. $t_i = MAC_k(i||m_i)$ ...
6
votes
3answers
4k views

Analogue encryption algorithms

I have a basic understanding of how strong encryption works on digital data. Bits can be changed so that they appear completely random and map one-to-one back to the original set, given the correct ...
1
vote
1answer
94 views

Pseudorandom function library [closed]

I'm wondering if there is any library supporting pseudo-random function, so I can specify the key length and output domain. Is it correct that I need to use a block cipher for this purpose? Any ...
0
votes
2answers
132 views

Why not just encrypt the message and the hash of the message to achieve cryptographic integrity? [duplicate]

I've always seen MACs as a way to provide integrity and authentication. You would just append it to some message in clear. But this is clearly not the case when you're doing Encrypt Then Mac. When ...
1
vote
1answer
211 views

Diffie-Hellman Application

Alice and Bob want to perform a Diffie-Hellman key exchange using the group $G$, a primitive root $g$, Alice’s secret key $k_A$ and Bob’s secret key $k_B$. In each case below compute the element of ...
1
vote
1answer
631 views

CBC-MAC: is it secure to authenticate a fixed length ciphertext?

Suppose I have a fixed-length arbitrary ciphertext. To authenticate such ciphertext: I generate a random AES Key $K_{auth}$. Then I compute the CBC-MAC Tag of the ciphertext with $K_{auth}$. ...
1
vote
1answer
399 views

Security of SecRandomCopyBytes on OSX and iOS

How secure is SecRandomCopyBytes() (Apple's RNG)? Has anyone ever reviewed it?
0
votes
1answer
97 views

Is the key deducible with AES CTR when we know about the plaintext, IV and the ciphertext? [duplicate]

Simply as stated, with AES running in CTR mode, can somebody work out the key (without brute-forcing) given we know about the plaintext, IV and also the ciphertext. Assuming we also know about the ...
0
votes
1answer
63 views

Check if this cryptosystem is safe

Let $G$ be any group where group operations, as well as finding the inverse of an element, can be performed quickly, but the discrete log problem is difficult. Consider the following cryptosystem: ...
1
vote
1answer
177 views

3DES Modes EED orEDE?

Can we use EED with 2 keys (K1 K1 K3) rather than EDE (k1,k2,k1) ? We measure the strength of DES by the effort (in term of number of tries) in finding some K1 & K2 to match a known plaintext and ...
1
vote
2answers
123 views

what is PFS game?

when i reading about this paper, in the Setup of SIM section 5.2, it says that "According to the definition of PFS game", i wonder what the definition of PFS game ...
2
votes
2answers
343 views

Why does NaCL have different keys for signing and encryption?

I want to start using NaCL to sign messages that will go into a message queue, and I noticed that it generates different keys for each operation. Is there a reason for this? Can I not use the same PK ...
0
votes
1answer
69 views

Self changeable key [closed]

If key changes itself when it send/receive message what would be could breaking method? So: $E: m×k$ in which $k$ is last generated key $D: c×k$ in which $k$ is last generated key $k{_n} = ...
0
votes
0answers
147 views

Strategies for securing public key storage on software

I´m kind of new in this so I apologize in advance for any noob mistakes (feel free to point it out) We are developing a licensing mechanism on our software, and I would like some advice. The ...
3
votes
1answer
161 views

Save the last cycle in GCM GHASH calculation

I need to implement GCM GHASH in hardware, using FPGA. The data bus is 640 bits, so I will use 5 adder/multiplier blocks in parallel. The message size is fixed and AAD is 0. A little example: ...
1
vote
1answer
119 views

Is the idea of a known plaintext attack really that new?

As you can probably guess, I just watched The Imitation Game, which hasn't really gotten points for historical accuracy... During World War II, Turing and his team fret that they can't know the ...
0
votes
1answer
135 views

FIPS-Compliant SHA2

I want to use SHA-512 for hashing in a system that must be FIPS-compliant. When I look at the FIPS 140 list of approved providers, I don't see SHA from any provider as being an approved algorithm, I ...
0
votes
0answers
164 views

Deriving a decryption equation

Consider a very simple symmetric block encryption algorithm, in which 32-bits blocks of plaintext are encrypted using a 64-bit key. Encryption is defined as C = (P⊕KL)⊗KR where C = ciphertext; K = ...
7
votes
3answers
509 views

Testing the Fortuna random number generator?

I have implemented the Fortuna random number generator as described in chapter 10 of "Practical Cryptography" (Ferguson and Schneier, Wiley, 2003), the result can be found at ...

15 30 50 per page