3
votes
1answer
77 views

Yao's Garbled circuit: Does Bob ever see the circuit?

I asked a question about whether the circuit structure for Yao's garbled circuit needs to be rearranged. I understand from Yehuda Lindell's response that the circuit structure itself does not need to ...
3
votes
1answer
61 views

What are the pros and cons of SIP media encryption types SRTP, ZRTP, and DTLS?

I'm just getting used to SIP for my first time using Linphone. Which encryption is better and why? My Settings > Network > Media Encryption has the options of SRTP, ZRTP, and DTLS.
1
vote
0answers
51 views

Encrypting/Decrypting using RSA and AES; standards?

I'm looking for a standard way of encrypting and signing a message using RSA and AES. I understand that in pseudo code the actions taking place are like this: Alice's actions for sending a secret, ...
2
votes
1answer
59 views

How to find collisions in a hash function knowing its coefficent?

Say I have a simple hash function where $x$ is a sequence of integers: $$h(x)=(a_1\cdot x_1+...+ a_n\cdot x_n) \bmod N=\sum_i a_i\cdot x_i \bmod N$$ where $a_1,a_2,a_3,...,a_n$ is the coefficient ...
2
votes
0answers
27 views

Proving CCA security for scheme constructed from secure PRP

We have a $PRP : \{0,1\}^{3n} \rightarrow \{0,1\}^{3n}$ and encryption scheme constructed from this $PRP$. $E_k(x\|r\|0^n)$, where $r$ is randomly chosen from $\{0,1\}^n$ and $0^n$ is a block of ...
0
votes
1answer
72 views

Diffie-Hellman: Calculating the private key from the public key with Java

I have the task to calculate the private key from the given public key and have the hint that the secret exponent lies in the range from $-2^{31} < e < 2^{31}$. To find the exponent I ...
0
votes
1answer
44 views

DROWN Attack - Which is the SSLv2 vulnerability exploited?

In order to get the session key used in TLS communication, an attacker must capture X TLS handshakes based on RSA key encryption, and switch to a server supporting SSLv2 protocol, and sharing the same ...
1
vote
1answer
55 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 ...
3
votes
2answers
81 views

Why are MACs not included when defining Protocols?

I see often in literature related to cryptographic protocols that MACs (Message Authentication Codes) are not included in protocol definitions. For example: ...
6
votes
1answer
95 views

Noise in Homomorphic encryption

What is the noise in homomorphic encryption schemes? (or where does the noise come from, I see that its inbuilt in the scheme and is not a side channel or disturbance noise) Is it also due to the ...
2
votes
1answer
307 views

An example of of an information theoretically secure protocol that is not cryptographically secure

Does there exist a protocol $\pi$ for some functionality $F$ which is information theoretically secure protocol that is not cryptographically secure for some threshold number of corrupt parties? ...
2
votes
1answer
50 views

How do you prove an encryption scheme is IND-CPA or IND-CCA?

I know for proving a scheme is not IND-CPA or not IND-CCA you can construct an Adversary which has an unfair advantage in an experiment/game, but how would you prove a scheme is IND-CPA or IND-CCA?
3
votes
2answers
71 views

RSA: select $e$ given $n$ and $\varphi(n)$

I have a question for a course I am doing. In an RSA question, it asks "Is it possible to select $e$ in such a way that it coincides with the corresponding private key $d$? If it is possible, provide ...
0
votes
0answers
25 views

A question about pseudo random generators with seed that starts with a 0

Given that G is prg, is the following always a prg? G'(s)=G(0•s) I know that if there was a random bit instead of the leading 0 it was a prg, but I don't know about the leading 0. Thanks a lot
4
votes
2answers
56 views

Yao's Garbled Circuit- Why does Alice need to rearrange the circuit?

My understanding of Yao's Garbled Circuit (based mostly on this summary) is as follows: Alice creates a garbled circuit based on the function f to be computed. She then hard-codes her input into the ...
7
votes
1answer
191 views

How many qubits are required to break RSA 2048 or 4096 with a universal quantum computer?

So in the news this week, IBM have created a universal quantum computer with 5 fully functional qubits. Logic and Moore's law dictates they will be able to scale this up to a lot more qubits within a ...
-4
votes
1answer
68 views

How to find $e$ when $p,q,d$ are given?

I have solved till here ..... $$n=p*q$$ $$n=5*11$$ $$\varphi(n)=(p-1)*(q-1)=4*10=40$$ Now, how to find $e$, when $d$ is given as $27$ and message for encryption is $\text{abcdefghij}$. We have to take ...
4
votes
1answer
49 views

How can bit slicing be constant time, when Mix Columns is in the cipher

I'm reading about bit-slicing techniques, and one thing about it caught my mind. The strength with bit sliced implementations are (apart from that they are fast) that they are running in constant ...
0
votes
0answers
47 views

Attacking AES-CTR mode with known prefix [duplicate]

My question is the following: Consider a 128-bit AES-CTR mode encryption on a plain-text $m$ . The structure of $m$ is constant. First comes a string, let's say : "JustSomeText\" followed by 5 ...
1
vote
1answer
49 views

BB84 quantum protocol

In BB84 protocol, when Alice and Bob make key distribution, what is the private thing? They select randomly bases and then make a measurement according to these bases. Used bases are private? I mean ...
7
votes
2answers
218 views

Should HMAC-SHA3 be preferred over H(C(k,M))?

If I understand correctly SHA-3 (Keccak) is resistant against more attacks than SHA-2. This would make it possible - again if I understand correctly - to use SHA-3 with a simpler scheme than HMAC. ...
0
votes
0answers
39 views

MD5 - Length extension

I am currently trying to get a working understanding of MD5 length extension. I have been following the first exercise located here: https://www.cis.upenn.edu/~cis331/proj1.pdf (it looks like the ...
0
votes
1answer
529 views

Are there attacks on AES with 16-bit keys? [closed]

Are there known attacks on AES that uses a 16-bit key? Assuming the data can be 95MB size, and that I can request the same data over and over. For example, can someone explain to me how this code ...
1
vote
2answers
28 views

Validating subset of a password

Is anyone aware of an algorithm/method that allows me to validate just a few letters (or other characters) from a password. For example, the application asks for the 2nd, 3rd, 6th and 9th letters from ...
5
votes
2answers
138 views

Why do cryptographic hashing and symmetric encryption use different functions?

Something about encryption and hashing has always bothered me. Given a cryptographically secure hash function $H$, I can produce an arbitrarily long key from any seed $s$ by recursively applying $H$ ...
1
vote
1answer
51 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.
5
votes
1answer
46 views

In Fortuna, can I use ChaCha20 instead of a block cipher and Blake2b instead of iterated SHA256?

In the Fortuna CSPRNG, can I use ChaCha20 instead of a block cipher and Blake2b instead of double SHA256, and still retain security? My hypothesis is "yes" because: The block cipher's only use is ...
0
votes
2answers
72 views

Encrypting using “Cryptography.HMACSHA1”, how to decrypt (VBA)

I have an encryption routine that works very well in VBA. But now I need to program the decryption routine, and I'm stuck. For encryption I'm using HMACSHA1 and transferring the encrypted byte to base ...
4
votes
1answer
38 views

Why ssh-gen makes difference between PEM and PKCS8?

Correct me if I am wrong, but PKCS8 is format to store private key info. It could be binary-enoded (DER) or Base64 encoded (<...
-2
votes
1answer
90 views

Decrypting an RSA message given $a^2 \equiv 1 \pmod n$

I need help with a practice problem for an upcoming test. I've learned the answer to the problem is "well done", but don't know how to get there. Any help is greatly appreciated. Suppose that the ...
2
votes
1answer
62 views

SipHash's (non-)collision resistance

I'm very new to cryptography, and I need help understanding the security claims made in Aumasson and Bernstein's paper on the SipHash. In particular, I'm trying to understand the following statement ...
1
vote
0answers
37 views

Does a password that's cracked someone's account increase the chances of cracking someone else's account?

For every find in password that cracks someone's account, does that particular password have a higher probability of cracking someone else's account more than a brute force dictionary choice? How ...
5
votes
2answers
172 views

Should RSA primes p and q differ in length by “a few digits”?

When generating RSA keys in the original RSA paper it is stated: to gain additional protection against sophisticated factoring algorithms, p and q should differ in length by a few digits Why is ...
0
votes
0answers
21 views

Securely register a client in server using AES an RSA

I've designed the following protocol to send the client's public key to the server. Initially, the client knows server's public key, but the server does not know the client's public key. client ...
0
votes
1answer
47 views

How to use the hardcoded server's public key to register a client application?

I'm designing the security for a smartphone app that can be used to make car reservations. Clients have to register them with their driver's licence through the application and can then book a car. ...
4
votes
1answer
62 views

What is the branch number of this matrix?

We have the following matrix: $$\begin{pmatrix}0&1&1&1\\ 1&0&1&1\\ 1&1&0&1\\ 1&1&1&0\end{pmatrix}$$ What is the branch number? Is this a MDS marix?
1
vote
3answers
66 views

How to generate many passwords from one passphrase, so that knowledge of one password does not compromise the others?

The limitations are: it should be a function. passphrase is so weak, that if hash of it is known (or big part of hash), then it can be brute forced. I want to get N passwords from one passphrase. ...
1
vote
1answer
57 views

A question about fully homomorphic encryption (FHE)

Hypothesis: We define the messages on a field $\mathtt{F}_p$, where $p$ is a large prime number. I am considering a dynamic outsourced private data scenario. Assume we have 3 messages: $m_1=2, ...
4
votes
1answer
55 views

Prove that the following MAC is insecure

I am trying to prove that the following MAC is insecure, but I don't know how to exploit the properties of the pseudorandom function $F$ involved: Gen generates a uniform $k \in \{0, 1\}^n$. To ...
1
vote
0answers
54 views

Is it possible to enumerate the possible RSA keys? [duplicate]

As far as I understand ECDSA keys are smaller than RSA because all of the value of the ECDSA (up to a high number) are valid private keys. Is there any method of compressing RSA keys, based on some ...
4
votes
1answer
72 views

Statistical tests for PRNG that generates a sequence which is not binary

Is there a pratical application to PRNG that generates a sequence which is not a binary one? A ternary, quaternary sequence, for instance. If so, how can we test this? Is there any alternative test ...
1
vote
1answer
48 views

How is the base64 encoded signature in Craig Wright's proof constructed?

Mr. Craig S. Wright might be Satoshi Nakamoto - the inventor of bitcoin. He is currently proving the case. But how is the base64 encoded proof, that is published by himself on his blog post ...
3
votes
1answer
73 views

ECFP harder than ECDLP ?

Given two points $P$ and $Q = \sum_{i=1}^{n} x_i.P$ over $E_p(a, b)$ for $x_1,x_2,...,x_n \in \mathbb F_p$. The Elliptic Curve Factorization Problem (ECFP) is to find the points $x_1.P,x_2.P,...,x_n.P$...
1
vote
0answers
44 views

Is there any symmetric key cipher (block or stream cipher) providing partial decryption? [duplicate]

symmetric key cipher (block or stream cipher) providing partial decryption of data at some points. Although the entire data has not been decrypted, the data decrypted to that specific point should be ...
0
votes
0answers
18 views

Why does HS1-SIV use the universal hash function the second time?

HS1-SIV uses HS1-Hash twice: once with the message as input, and the second time with the authentication tag as input. The second use seems somewhat strange to me: assuming that the core is a strong ...
0
votes
0answers
41 views

Hash function with good performance on extremely short messages

Are there randomized almost universal hashes that are fast for extremely short messages (usually <10 bytes)? Edit: This is for hash tables, so it only needs to be hard enough to break to make the ...
0
votes
0answers
28 views

PHP Apple News HASH HHMAC

I am having a problem generating the signature key in PHP as describred in the Apple nes API documentation found here: https://developer.apple.com/library/ios/documentation/General/Conceptual/...
0
votes
0answers
34 views

TLS 1.2 PRF Cipher Suite Specification

I am upgrading our assembler SSL/TLS implementation to support TLS 1.2 and am reviewing RFC5246 specification for TLS 1.2. It states that the PRF is now part of the cipher suite specification but ...
1
vote
0answers
29 views

Algorithm to rotate values in a predefined manner

I will start with an example. Some beacon like estimote Beacons use something called secure ID. The ID transmitted by the beacon change every 10 minutes autonomously without contacting the server. ...
1
vote
2answers
63 views

Converting a 5-bit s-box to its bit-sliced format

I'm currently trying to convert a 5-bit sbox (the one from this cipher: http://primates.ae/wp-content/uploads/primatesv1.02.pdf) to its bit-sliced format (i.e. to a boolean network). Most papers ...

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