1
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1answer
686 views

Is this fixed length MAC unforgeable?

Consider the following fixed length MAC for messages of length $\ell(n)=2n-2$ using a pseudorandom function $F$: On input of a mesage $m_0||m_1$ ($|m_0| = |m_1| = n-1$) and a key $k \in \{0,1\}^n$, ...
1
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1answer
311 views

Can you help me understand ECC Cryptography and it's algorithm?

I want to know the basic understanding of ECC algorithm for cryptography. But I am not aware of the algorithm. Can anyone provide me with a basic explanation of the algorithm?
1
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1answer
150 views

How is the password sent across for verification?

I am familiar with Challenge-Response Authentication scheme. However I would like to know actual message content sent between client and server for 1 way authentication, over an insecure channel. ...
1
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1answer
869 views

iSeries (AS/400) Database File: password encryption

I am helping with a project in which an old software system on an iSeries is having a brand new .NET UI applied to it. It's going well... except... In order to allow users to login and maintain ...
1
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1answer
19 views

Use $e$ in GGH as shared secret?

I was wondering if we could construct a symmetric encryption scheme by assuming that the secret key itself in GGH is public and the shared "key" is the error vector $e$. To encrypt we would take the ...
1
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2answers
54 views

What does $\langle A, B\rangle$ mean?

I'm reading about CL-PKC and in Al-Riyami's FullIndent, I find some notations I must be sure to understand, to well explain it ...
1
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1answer
45 views

Expire signature

I am looking for a way to have a 'did it expired' key. There's a similar question here, but I have to prevent reusing of the 'did it expired' signature . A possible solution would be a two one-way ...
1
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1answer
40 views

tweakable block cipher and ideal block cipher

Can the set of block ciphers obtained from a tweakable block cipher (using distinct tweaks) be considered as the set of ideal block ciphers ?
1
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1answer
17 views

How do two parties put together the AUTH data in the SKEME protocol?

SKEME is a Key Exchange protocol used in the Internet Key Exchange (IKE). It contains three phases: SHARE, EXCH, and ...
1
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1answer
22 views

Single-scalar multiplication with sign bit

I want to know if there's an "easy" timing-free way to compute the sign of $y$-coordinate of $r G$, for a secret scalar $r$ and $G$ the generator of an elliptic curve. We have several choices for ...
1
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1answer
25 views

How to add passphrase to an RSA key?

If I want to protect a private RSA key, do I just XOR the password into the key, or do I do something else? Is it secure? Edit: I got a good answer from a comment - Hash the password/passphrase with ...
1
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1answer
26 views

Cracking vigenere of non-text cleartext

I've begun a course in crypto on coursera and the first homework was writing a vigenere(xor) cracker. It works, which was a rush :) but it makes one core assumption, one has encrypted a natural ...
1
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1answer
28 views

Is $E′(k,m)=E(0^n,m)$ semantically secure?

$(E,D)$ is a (one-time) semantically secure cipher where the message and ciphertext space is $\{0,1\}^n$. $E'(k,m)$ is defined as $E′(k,m)=E(0^n,m)$ The question is whether $E'(k,m)$ is (one-time) ...
1
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1answer
60 views

How is the block size of a block cipher related to how susceptible the block cipher is to a birthday attack?

For example what can you say about how susceptible Triple-DES is to a birthday attack due to the fact that it has a block size of 64-bits.
1
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1answer
38 views

How to increment the counter value for CTR mode?

I am testing CTR mode on STM32 board. I want to know how the auto increment of counter happens and what is the method to follow if I have to increment the counter manually.
1
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1answer
52 views

Handshake SSLv2, SSLv3, TLS

Can someone confirm that SSLv2, SSLv3, and TLS have the same Handshake process (ClientHello/ServerHello, ..., ClientKeyExchange ...)? If not, can you tell me the main differences between theses three ...
1
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1answer
46 views

Book recommendation about MPC? [closed]

I have hard time finding introductory book talking about details of secure multiple party computation. Is there any recommendations? Thanks for the help. Hope this is not off topic.
1
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1answer
107 views

tls 1.2 finished message stucture

I am implementing TLS 1.2 and using ECDHE_RSA_AES_128_GCM_SHA256 cipher suit. According to RFC 5246 finished messages have {verify_data[verify_data_length]} and verify_data = PRF(master_secret, ...
1
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1answer
39 views

Is it safe to use fast/small hash for key identity?

I have to roll database access keys often, but it's important to know which key each system is using in order to avoid unavailability. I want the systems to report that without exposing the key ...
1
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1answer
44 views

Can we do modulus switching for number theoretic encryption?

Can we do modulus switching for number theoretic encryption such as Paillier or ElGamal?
1
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1answer
24 views

Question about Cipher Block Chaining(CBC)

I'm studying at the moment the CBC Encryption method,and I was asked in an excercise how many bits would be wrong after decryption if during the transmission 2 bits are interchanged. My guess is that ...
1
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1answer
15 views

One time Key Encapsulation Mechanism?

For KEM's, do you only exchange a private key once via the public key encryption and then do all further encryption with this private key, or is a fresh private key sent out with each message? The ...
1
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1answer
50 views

Trying to udnerstand textbook sample solution

I am preparing for the final exam in my Data Security class so I am trying to read and understand the textbook's exercise questions. The sample solution at the end the textbook is more like a hint ...
1
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2answers
44 views

Key management and derivation - Allow changing of the passphrase

I'm working on a program, which allows encrypting files before storing it on a cloud service. Currently I'm trying to figure out how to derive and store the keys. First, I wanted to use a simple ...
1
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1answer
39 views

Attacks on schemes based on elliptic curves when the transmitted points are not on the curve

Some elliptic curve schemes require to send a curve point during the normal execution of the protocol. For example, ElGamal encryption and ElGamal signature require this. On the other hand, ECDSA does ...
1
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2answers
47 views

Using what we already know about the data to decrypt it?

Are there any methods or tools out there that let us use what we know about the data in order to crack the encryption? For example let's say I get access to an encrypted database file but I know ...
1
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2answers
149 views

How to crack unknown 8-bit encryption algorithm?

Can anyone tell me how to crack the encryption of 8 bit algorithm, when you have some clue that CBC mode is used, but the algorithm is secret. You also have some encrypted data (chosen plain text), ...
1
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1answer
25 views

Multiplexed stream cipher

Consider the stream cipher that consists of 3 LFSRs, with the output of one coming being used to determine which of the other 2 is used that clock cycle. Both the IV and the polynomials are secret. ...
1
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1answer
41 views

How to use AES-CBC to password-encrypt a small block of stored data

I have a small block of data (16 bytes) that I am required to encrypt, store (in an unsecure, visible location). Later I have to retrieve and decrypt it. I must use AES-CBC and a user-entered ...
1
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1answer
31 views

SHA-1: number of possible inputs, number of possible outputs, how many inputs have the same output,

From Wikipedia I read SHA-1 function produces an output of 160 bits and expects a max message size of $2^{64}-1$ bits. Is that right? If I order all possible inputs I would produce $\approx ...
1
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1answer
19 views

Determining the degree of freedom for a chi-squared test on a strict avalanche criterion matrix

I have read that the degree of freedom is calculated by subtracting 1 from the number of states a random variable can be in. I am performing a goodness of fit test on a 64*32 strict avalanche ...
1
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1answer
49 views

What would be a typical value for the security parameter of the Fully Homomorphic Encryption over the Integers scheme?

The parameters of the Fully Homomorphic Encryption scheme by Dijk et.al are chosen according to the value of the security parameter ${\lambda}$, section 3 of the aforementioned article. What is the ...
1
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1answer
61 views

UKS attacks. Dangers & Prevention?

I am trying to understand how to prevent a UKS (unknown key-share) attack, but I am having trouble finding many resources out there to help. Let's imagine a hypothetical secure messaging application ...
1
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1answer
73 views

How would an attacker perform an exhaustive key search on a block cipher using ECB mode?

Do you always assume from Kerchoff's principle, that the attacker has access to everything but the decryption key? That is, am I to assume that to perform an exhaustive key search, the attacker has a ...
1
vote
1answer
60 views

Why are there $q^2$ keys for each equivalence class in Pedersen-van Heyst Signature Scheme?

How do you know there are $q^2$ keys for each equivalence class in the Pedersen-van Heyst Signature Scheme? My textbook says this is "easy to see", however, I am not seeing it. Is it because in ...
1
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1answer
38 views

How many bits of plaintext are required to verify a stream cipher key?

If a stream cipher has an $n$-bit internal state, how many bits of known plaintext are required to confirm that particular key is the key? I believe that the answer is at least $n$-bit's of ...
1
vote
1answer
19 views

Will changing the RSA Padding in OpenSSL cause issues?

I'm currently looking at changing the padding type from one of the Oracle Padding attacks to a secure one. Would this break data already encrypted using the old method?
1
vote
1answer
43 views

How would multiple uses of a vigenère cipher be decrypted on paper (classic)?

As far as I can tell (from reading the Wikipedia article about it) decrypting a message encrypted with the vigenère cipher is possible on paper. But what would happen if the message is encrypted ...
1
vote
1answer
38 views

Is there any benefit to using a randomly chosen replacement strategy on a string before or after encrypting it?

This is more of a mental exercise for me than anything else. I've thought about doing something like this before, mostly to make a broken cipher a little more difficult to decrypt to plain text. I've ...
1
vote
2answers
58 views

Using same encryption key in different schemes

Is it safe to encrypt possibly same plaintexts with 2 different algorithms using same secret encryption key? This question is similar to this question except they use 2 keys. More formally: $E_k(m) = ...
1
vote
1answer
77 views

Better security than SHA1 for signature?

An application that I maintain uses Sparkle Update to update itself. I expect attacks from high level attackers (China, USA's NSA, etc.) and have some questions about how secure the cryptography ...
1
vote
1answer
73 views

Are developers expected to implement Diffie-Hellman key exchange themselves?

I noticed that the GO standard library has some really nice functions for performing AES encryption / decryption in various modes. However, I couldn't (yet) find anything for Diffie-Hellman key ...
1
vote
1answer
81 views

Certificateless cryptography Implementation

Hello guys I am trying to implement Certificateless Cryptography algorithm with reference to this base paper. Right now I am trying to implement the code in java. ...
1
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2answers
114 views

Best non-digital cipher?

Is there an undisputed cipher that was considered the best before the computer age? (This is not suppose to be a discussion, it's either a yes or no.) Please give a brief description why it is yes ...
1
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1answer
73 views

Determine whether a given function is a pseudorandom generator/function

I am trying to solve the following three tasks (for exam practice, not as a homework): Define $𝐺 : \{0,1\}^* \rightarrow \{0,1\}^*$ by $G(x_1,...,x_n) = 𝑥_1 \oplus 𝑥_2,𝑥_1,⋅⋅⋅,x_n.$ Prove that ...
1
vote
1answer
40 views

Monoalphabetic cipher using different languages in the same plaintext

Today I learned the principle of the monoalphabetic cipher. It's simple to decrypt a ciphertext written all in the same language (english for example) because I can use the syntactic properties as ...
1
vote
2answers
72 views

Decrypt affine cipher given encryption key [duplicate]

i have a ciphertext C=TLNJG formed using the equation c=(7p+11) mod 27,c equivalent to numerical equivalent character of ciphertext and p the plaintext how do i ...
1
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1answer
34 views

Composite vs Prime Order Groups in Attribute Based Encryption

Reading about Accountability in ABE currently and the paper "White-box traceable ciphertext-policy attribute-based encryption supporting flexible attributes" when comparing its system with an existing ...
1
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1answer
29 views

Secret key agreement by public discussion from common information

There is a paper: U. M. Maurer, Secret key agreement by public discussion from common information, IEEE Trans. Inf. Theory, 39(3) 733-742 of 1993, with an IMHO fairly impressive title but having ...
1
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1answer
90 views

What is the importance of 1 < d < φ(n) and 0 ≤ m < n in RSA?

I'm a first year Maths undergraduate and we have recently gone onto RSA. I understand the majority of the algorithm using Fermat's Theorem etc. From the algorithm stated on Wikipedia: 4) Choose ...

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