4
votes
1answer
94 views

Changing encryption key without revealing the original key

Say that Alice encrypts a $\text{plaintext}$ with $\text{key}_{m}$ and gives the $\text{ciphertext}_m$ to Bob. Alice wants to send several gigabytes of $\text{plaintext}$ to Eve but she is on a mobile ...
2
votes
1answer
72 views

Does Mersenne Twister generate homogeneous numbers?

I have been assigned to generate 15000+ homogeneous and uniform random numbers for a work. I have been searching if Mersenne Twister generate homogeneous distribution of numbers but I don't find ...
2
votes
1answer
55 views

Design for file transfers to a new party

I'm pondering a problem of how to enable transfers of files from clients to people that does not yet have an application/account/keys yet. Here's my current thought for Alice wanting to send Bob ...
10
votes
0answers
191 views

AMD and RDRAND instruction

The latest AMD programmer manuals, dated June 2015, include the RDRAND instruction in the instruction set. For completeness, it lacks ...
0
votes
0answers
54 views

Detecting Software Changes - Verifying untampered code

This question assumes an environment devoid of any internet connections, the software in questions operates in a non-connected environment on a single machine. I have a piece of software that may be ...
3
votes
3answers
114 views

Fast forwarding hash functions

We know that a good hash function is a one way/trapdoor function. Easy to calculate one way, harder to work out a previous state. I was wondering if anyone knew a good hashing system that allowed ...
3
votes
2answers
195 views

Memory-hard proof-of-work: are they ASIC-resistant?

Is a memory-hard proof-of-work scheme necessarily resistant to speedups from custom ASICS? Background: Bitcoin uses a proof-of-work scheme based on SHA256 hashing. The scheme is compute-bound. ...
2
votes
0answers
34 views

Hiding the identity of a party within the Kerberos authentication scheme

In the Kerberos authentication protocol, as described here: would it be safer to replace step (1) with: $$ A \rightarrow T : A, E_{K_A{_{T}}}(B, N_A) $$ so that a passive adversary does not know ...
3
votes
1answer
98 views

Can a billion elliptic curve keys be generated on a laptop in less than an hour?

I want my application to generate an EC key pair. The first four bytes of the sha256 hash of the public key should contain a known IP address. As hashes are one-way functions, I need to brute force ...
2
votes
1answer
49 views

How to detect changes in data while preserving confidentiality (under constraints)?

Suppose party $A$ has two pieces of data, $X$ and $Y$, either of which may change separately, or they may change together. Given the following constraints: $A$ knows its current $X$ and $Y$ but has ...
0
votes
2answers
160 views

Secure Key exchange using javacard applet

I am working on a javacard applet project where i need... Secure communication between two applets let say there is applet A and applet B. Let say both applet has their own RSA key pairs. Now I ...
9
votes
2answers
1k views

Does an encrypted random sequence conserve its “randomness”?

If you have a random uniform sequence of bits $A$ generated by a TRNG with good performance of randomness tests (eg Dieharder, NIST, Kolmogorov complexity, chi-square, etc) and perform an encryption ...
4
votes
1answer
52 views

State level “Weak Diffie-Hellman” working for SRP too?

I've read about the "Weak Diffie-Hellman" attack (paper, website), where a resourceful entity like a state can pre-compute values for known primes to aid solving the discrete logarithm problem for ...
1
vote
0answers
106 views

Solving Vigenére with unknown alphabet

I'm trying to decrypt a cipher that I suppose has been encrypted with Vigenére. However I came about the following thought: The cipher consists of characters from ...
2
votes
1answer
40 views

Proving the security of a one-way function with partially known input

Let's say we have a construction like in this question: We have a OWF $h(.)$, a secret salt TXT, and a counter starting at 1, and we compute ...
0
votes
0answers
32 views

Number of qubits and breaking hashes [duplicate]

Noting D-Wave's press release on a 1000 qubits quantum computer had me wondering... Does the number of qubits nonlinearly change the speed/rate at breaking a SHA256 hash? If someone makes a say ...
2
votes
1answer
40 views

Data Switching and Information Leakage

Hypothesis: Let $z,a$ be uniformly random elements of a field $\mathbb{F}_p$ where $p$ is a large prime number. Also, let $(-z)$ be additive inverse of $z$. I have a fixed secret value $x$. I mask ...
3
votes
1answer
322 views

Deciphering “easy” ciphers without hints

I've been keen on IT Security for a long time now and I've learned a lot about networking & security. However trying a "decryption challenge" I'm lacking what I think is basic ...
0
votes
1answer
74 views

Why does TLS 1.2 use GCM with additional SHA hash? [duplicate]

I am studying the cipher suites provided by TLS 1.2 and found an interesting question. TLS 1.2 adopts GCM for encryption and SHA256 or SHA384 for hash (e.g. TLS_RSA_WITH_AES_128_GCM_SHA256). But, GCM ...
0
votes
0answers
103 views

Values of p and q when e = 3 (RSA)?

I am doing a paper on textbook RSA (this is for high school btw) and in my example I need two very large primes, but I want my $e = 3$. Is there a short way to calculate the values of $p$ and $q$ ...
1
vote
1answer
257 views

SHA256: Padding a 512 bits length message

I am currently implementing the SHA256 hash-algorithm for a "custom-built" embeded-device. Obviously I have a problem with message padding. The routine I wrote does not work with message whose size ...
3
votes
2answers
167 views

HMAC key storage for a web app?

If one is going to use an HMAC, I.E: http://php.net/manual/en/function.hash-hmac.php, where exactly are they storing the key? Without some sort of secure storage (i.e not in a local file or code), I ...
2
votes
1answer
158 views

Can a file encrypted with one tool be decrypted with different tool? [closed]

I'm new to cryptography and I'm trying implement a file encryption feature into a Python program but I'm running into a big issue...what is needed for someone else to decrypt the file?! Obviously, I ...
1
vote
0answers
55 views

Properly storing an E-mail Password

I'm creating a messaging application that will use an outlook account to send an email. However, I'm unsure about the proper steps to store the e-mail password on the user's computer. Suppose I had ...
2
votes
1answer
226 views

RSA Signature Verification Implementation on Cortex M0

I have to implement RSA Signature Verification procedure (RSA-2048) on a Cortex M0 based MCU. My budget is 15kB Flash and 2-4kB Flash RAM. Is it even possible to do RSA on a low end MCU based on ...
3
votes
1answer
158 views

Concrete example of Weil Pairing

I am trying to find a concrete example of the Weil Pairing. What I have done until now is that I took $E=(x-1)(x-2)(x-3)$ over $F_5$. I took $E[2]=\{\infty,(1,0),(2,0),(3,0)\}$. I know that there ...
0
votes
0answers
85 views

public/private key: is it possible to have master public/private key

This may be a very primitive question which might not be possible but I have this question to understand. Assume Yahoo provides a messenger where yahoo users can chat in secure way (end-end ...
1
vote
3answers
136 views

Adding dummy bytes to ciphertext

I was wondering if interleaving the resulting crypted data with dummy bytes placed at random positions but known in advance by the peers could improve security (no matter the algorithm and strength ...
2
votes
0answers
50 views

can pairings only be used with elliptic curves?

As far as I understand one big advantage of ECC is that we can use pairings on the group of torsion points of the curve. I was wondering if it is possible to construct pairings from general finite ...
2
votes
0answers
69 views

Scale-Invariant DGHV Scheme - Decryption

I have just started reading the Scale-Invariant Fully Homomorphic Encryption over the Integers paper and I'm a bit confused about something: When decrypting the ciphertext: $c = r + (m+2r^*) \cdot ...
3
votes
1answer
159 views

How to clock a linear feedback shift register?

I have some trouble understanding what happens when a LFSR is clocked. I have tried many examples but I do not get the correct result. Can anyone point out my errors? I have the following polynomial: ...
0
votes
2answers
53 views

How hard to solve the given mod problem

Let c = a.b mod p where p is n bit prime number (e.g. 128 or 160 bit prime number); a - random number between 1 and (p-1); b - random number between 1 and (p-1); Given c, a and p, how hard to ...
1
vote
1answer
44 views

Is there a standard prefix random padding scheme?

Is there a standardized padding scheme which is prefix instead of postfix and that uses random bytes except for the first byte which would be the length of the padding?
3
votes
1answer
89 views

Is there any benefit of changing the AES-CCM encryption key periodically even if the Nonce space is not exhausted yet?

I would like an answer that could be sustained by a mathematical proof. Let's say I'm using AES-CCM to encrypt a lot of messages, and I always use a different nonce. I know that when the nonce space ...
4
votes
1answer
66 views

Should the signature be prefix or postfix to the message in the sign-then-encrypt scheme?

Let's assume we have a message $M$ and it's signature $S$ and that $|$ is the concatenation operator. Should we encrypt $S|M$ or $M|S$? Does it even matter?
0
votes
1answer
63 views

How can I turn this cipher into a perfect cipher by altering only its encryption algorithm?

Given a toy cipher that picks a key, k, from the key space of {00,01,10} and a message,m, from the same set {00,01,10} and encrypts using E = m ⊕ k. How can I change the encryption function E in ...
2
votes
1answer
380 views

What is required to decrypt an encrypted file?

At the risk of sounding stupid and being laughed at...I must ask this question. What is required to decrypt an encrypted file? Obviously you need the appropriate key to decrypt, but is any other ...
0
votes
2answers
73 views

The benefit of PBKDF2 for big keyfile?

The man page of cryptsetup says: Whenever a passphrase is added to a LUKS header (luksAddKey, luksFormat), the user may specify how much the time the passphrase processing should consume. The ...
2
votes
1answer
242 views

Given a linear block-cipher,how can an attacker decrypt any plaintext value encrypted,using 128 chosen ciphertexts

Given the linear block cipher $\operatorname{LinearCipher}(k, p) = c$ $$\operatorname{LinearCipher}(k, p_1 \oplus p_2) = \operatorname{LinearCipher}(k, p_1) \oplus \operatorname{LinearCipher}(k, ...
2
votes
0answers
25 views

Raw /dev/random output for keymat [duplicate]

Noob question: It is my understanding that the raw output from non-blocking /dev/random (where the kernel's entropy_avail estimate is equal to or greater than the number of random bits required) ...
2
votes
1answer
133 views

Very short signatures? (eg: 48bits?)

Our application requires some 'mild' form of 'proof of origin' for the tokens we issue (~200 bytes), however, the value of each is trivial. The requirement is to provide 'tamper resistance' rather ...
2
votes
1answer
207 views

ECDH or RSA more secure for symmetric key wrapping?

Suppose a message is encrypted with a symmetric block cipher with a random key. RSA is often used to wrap the symmetric key using the recipient's public key. In this case, the size of the message is ...
0
votes
3answers
55 views

Does a padding oracle have the encryption key? Where in real life do I see such an oracle?

So after some searching, I kinda know the attack procedure of altering bit by bit. But I'm still confused how this is possible. If I understand it correctly, the attacker never has the key, or tries ...
0
votes
1answer
21 views

Why many passes at file removal? [closed]

Why file removal tools offer gost 2 passes and British 3 passes or even gutman 35 passes options? In which case the single pseudo random pass is not enough?
2
votes
0answers
54 views

Using a product of a series of curve25519 scalars as a private key

There are a few systems like the GNU Name System and the Sphinx mixnet packet format that employ a series of curve25519 scalars all multiplied together as a private key. Are there any caveats to ...
3
votes
3answers
838 views

For any hash value, is there an infinite number of inputs that hash to it?

Bruce Schneier writes (back in 2005) in a post on cryptanalysis of SHA-1: SHA-1 produces a 160-bit hash. That is, every message hashes down to a 160-bit number. Given that there are an ...
1
vote
1answer
223 views

Testing hash functions for collision resistance

I was hoping to implement a software that allows testing a user-defined hash function for cryptographic properties (Meant to pique interest in cryptographic hash function for a school showcase), as ...
1
vote
2answers
147 views

MD5 Collision Attack Explained

In one of my assignments, I came across this line Due to MD5’s length-extension behavior, we can append any suffix to both messages and know that the longer messages will also collide. This lets ...
6
votes
1answer
95 views

Encoding scalar values to points on Ed25519

I'm interested exploring key derivation and threshold signature protocol that require point arithmetic (addition) on the private scalar values and $S$ values of the signatures in ed25519. ...
4
votes
2answers
100 views

Weakness of SRP after server compromise

From SRP section 3: The host stores user passwords as triplets of the form { <username>, <password verifier>, <salt> } Password entries ...

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