-1
votes
1answer
92 views

How to use the key from a Diffie Hellman exchange? [closed]

I watched a YouTube video about Diffie-Hellman called "Diffie-Hellman Key Exchange", and it said after doing some modulo operations with the public modulus and generator and the random private ...
5
votes
2answers
240 views

Adding tweak to a block cipher

I know there are XEX, XTS and other ways to add tweak to block cipher without modifying cipher itself. However they are quite slow and/or complex. If we assume we have a secure block cipher round ...
0
votes
1answer
275 views

Bouncy Castle and Salsa 20 [closed]

I want to use Salsa 20 in Java, so I downloaded Bouncy Castle, and... it makes no sense to me. I've got it working, but most of my choices were essentially random. But I can't see there anything ...
1
vote
0answers
60 views

Forward Secrecy with pseudorandom functions

Let $H_1$, $H_2$ be keyed hash functions (e.g. $H_i(x) = SHA_{256}(s_i||x)$ for pseudorandom $s_1$, $s_2$). Let $s_n = H_1^k(s_0)$, $k_n = H_2(s_n)$, where $s_0$ is a secret (pseudorandomly chosen ...
3
votes
0answers
61 views

online Vickrey auction using remote coin flip

Is there any published work on implementing a online auction, which uses "remote coin flip" to prevent auctioneer cheating when choosing winner and bid value? Is there any possible way to use remote ...
2
votes
0answers
125 views

How to compute the decompositions used in fast FHE bootstrapping?

Leo Ducas and Daniele Micciancio's recent paper "FHE Bootstrapping in less than a second" gave an exciting result that one can compute the `atom operation' of Fully Homomorphic Encryption (i.e. ...
1
vote
1answer
118 views

Is it possible to 'fake' time for TOTP? (Time-based One-time Password)

TOTP (Time-based One-Time Password) Algorithm is used in Two factor authentication. I understand the algorithm and that current time is used as a variable to generate a token. Wiki page for reference: ...
0
votes
1answer
179 views

Encrypt a Zip File with Caesar Cipher

I'm trying to understand, why the Filesize of a Caesar Cipher encrypted foo.txt.zip File is smaller than a Caesar cipher encrypted foo.txt File. For example: Foo.txt size: 90bytes foo.txt.Caesar.enc ...
1
vote
1answer
286 views

How can convert affine to Jacobian coordinates?

I have a point in affine coordinates: $(x,y)$. What should I do when I want to convert to $(X,Y,Z)$ in Jacobian coordinates? I need it for calculating ECC in a prime field.
4
votes
1answer
818 views

Where did the SHAKEs come from in SHA3?

Where did SHAKE128 and SHAKE256 originate from? I am trying to find them in the original Keccak documentation but can't find them. Is it some special mode of Keccak referenced in the documentation? ...
1
vote
2answers
492 views

How do RSA and ElGamal key sizes compare?

I have a rather silly question regarding the comparison of RSA with ElGamal over integers. If you want to compare their performance in the same level of security, does the modulus of both of them need ...
1
vote
1answer
85 views

SpongeWrap without padding and frame bit

Assuming all inputs are same length as rate except last can be shorter. Is it necessary to pad every input (not just last) to sponge for authenticated encryption to be secure? Is this just, because ...
3
votes
1answer
311 views

Is it possible to demonstrate that md5(x) != x for any x?

I am looking for an easy to follow explanation, if possible, that demonstrates/proves the validity (or not!) of this assertion: for any X, md5(X) != X (being X any string of 32 hex characters)
1
vote
1answer
389 views

Using C_Sign to create a PKCS7 signature

I am using the PKCS#11 function C_Sign to sign some data. The output I get is just a signature. How do I get it in PKCS#7 format - i.e. ASN1 with signature and certificate (for detached) or ASN1 with ...
3
votes
1answer
586 views

How does MD5 process text which is shorter than 512 bits

MD5 processes a 512-bit block and produces a 128-bit (16 byte) message digest often expressed as 32-digit hexadecimal value For example if I hash the word "how" using MD5 , I get the following hash ...
1
vote
1answer
120 views

Block Cipher Modes

I have a question here asking the following: Why do block ciphers need the use of blocking modes? To encrypt messages larger than the size of the block. To avoid having the same block ...
2
votes
1answer
387 views

Serpent 256bit key wrong round keys

Assume that we have this 256bit key: 15FC0D48 D7F8199C BE399183 4D96F327 10000000 00000000 00000000 On first 0-7 keys we can't apply formula wi=(wi-8 xor wi-5 xor wi-3 xor wi-1 xor phi xor ...
0
votes
0answers
101 views

Bit level permutation

Could anyone explain how secure is bit level permutation? What is the most serious threat against the security of this kind of cipher? Thank you
5
votes
1answer
784 views

Security analysis of Spritz?

Recently, a new cipher called Spritz has been released by Ronald L. Rivest and Jacob Schuldt. It should be a "drop-in replacement" for RC4. There are many differences to RC4, Spritz is "spongy" and ...
2
votes
1answer
312 views

Do Export Restrictions Still Apply To The Key Length of RC4?

I've just read a paper from 2004 which stated that the RC4 encryption algorithm was restricted to a 40 bit key size when exported from the USA; however the reference for this information (Applied ...
1
vote
1answer
94 views

Breaking RSA moduli

Let suppose that the sizes of factors $p$ and $q$ are $b$ bits. We construct two RSA numbers $n$, $n'$ of same sizes. Can we say that the duration to break these two numbers is two times the duration ...
0
votes
1answer
415 views

What is meaning of “Decipher the rest of the message by deducing additional words”?

I have an assignment in cryptography. I am not asking here answer, but meaning of question. This is a question : 2.4 The following ciphertext was generated using a simple substitution algorithm. ...
2
votes
2answers
1k views

Is .NET DESCryptoServiceProvider secure in this case?

I have the following piece of .NET code (see below). I know that DES is not quite secure, I saw that MSDN does not recommend using DES, only for compatibility with legacy programs. I also saw that ...
4
votes
2answers
4k views

How exactly does AES-NI work?

I am looking in to AES-NI which is now supported by many new CPU's and I have read a few papers which states that AES-CBC works faster with AES-NI, but I am unable to understand how exactly AES-NI ...
1
vote
1answer
294 views

How costly is to find millions of large prime numbers for RSA?

Consider I need to assign a large distinct prime number to each element in a large set. This must be deterministic so the function always gives me the same prime to the same value. What is the most ...
1
vote
1answer
194 views

RFC3447 OBJECT IDENTIFIER semantic

http://tools.ietf.org/html/rfc3447#appendix-B.1 ...
1
vote
0answers
366 views

how to find key matrix in hill cipher

I want to solve this problem but there are 3 known plaintext-ciphertext pairs. The key of Hill cipher is a 3*3 matrix as k=[k1,k2,3; k4,k5,k6; k7,k8,k9] where the unknown ...
3
votes
2answers
326 views

Do I need an IV to use AES-CTR as a CSPRNG?

I'm using AES128-CTR for generating pseudo-random values, which is considered secure for up to 1MB (at least from what I've read). I simply encrypt a 128-bit little-endian counter, starting from 0. ...
1
vote
1answer
194 views

Weak key schedule IDEA [closed]

Why was such a weak key schedule chosen for IDEA? The key schedule of IDEA works like this: Divide the key (128 bit) into 8 round keys, each 16 bit long. This are the first 8 "round" keys (6 keys per ...
1
vote
0answers
98 views

side channel attacks on AES

Say you have a web application that's performing AES encryption. What sorts of side channel attacks should one keep an eye out for? Timing attacks affect RSA more than symmetric ciphers in-so-far as ...
2
votes
1answer
87 views

Can adding nonces make challenge response authentications weaker?

In a custom protocol we want to replace an aged tiger32 based challenge response authentication. I suggested that we use something existing, so threw HMAC into the room. As per wikipedia it works as: ...
-2
votes
1answer
122 views

FEAL-4 Fk Function 4 Rounds

As I understood in FEAL-4 it needs 4 pair of round keys. Which means that we need to launch Fk function 4 times. My problem occurs starting the 2nd round. At the first round we have the original 64 ...
1
vote
3answers
203 views

Linear transformation proof

Ok, so I have this question and I honestly have no idea how to prove it. I know that the function is linear and I know it works for every possible combination, I just don't know how to prove it in an ...
0
votes
1answer
159 views

Session based AES with random key and static salt

I'm currently using aes to encrypt/decrypt messages to and from a web service. When the user establishes a session he sends a random generated secret via rsa public key. This secret is used to ...
2
votes
3answers
248 views

Does this guarantee a unique 32 bit Hash?

I came across some source code that loosely does the below in order to achieve a 32 bit hash. The input string is passed through MD5 to get 16 bytes Hash (as usual). Then the 16 bytes are split into ...
2
votes
3answers
567 views

Does AES CTR mode store header information in encrypted files?

According to the movable-type.co.uk website, In the ‘counter mode’ used in this implementation, a counter which changes with each block is first encrypted, and the result is bitwise xor’d with the ...
1
vote
0answers
87 views

advantages of hashing over elliptic curve signatures for a proof of work protocol

I'm trying to create a proof-of-work protocol for a proof-of-concept software, and it's basically something like this: ...
1
vote
1answer
68 views

Key escrow on indistinguishability games

Does it mean that when PPT attacker is breaking an indistinguishable based (equivalent with semantic security) game with non negligible probability that he is able to infer the secret keys either on ...
0
votes
1answer
204 views

Is this chat protocol safe?

I am in the design phase of a secure chat application at the moment. I am trying to make this as secure as possible. The Serverprovider should not have access to the messagedata. So my idea was the ...
1
vote
1answer
420 views

Fast AES-128 on 32 bits encryption

Suppose in AES-128, there are $5$ tables, namely Te0, Te1, Te2, Te3, Te0 which help in fast encryption on $32$ bits CPU. Each table contains 256 numbers, where each number is $4$ bytes. Te4's ...
1
vote
2answers
140 views

How to guarantee every plaintext is in a rainbow table?

This guide says that for a rainbow table or pre-computed hash chain, you can only get a probability that a plaintext is in a table, not a guarantee. Is there a way to guarantee every possible ...
1
vote
0answers
186 views

What does “nonlinear mapping” mean?

Page 15 of the Keccak reference (PDF) explains that the $Chi$ step mapping of the Keccak-f permutation in Keccak is defined to be “nonlinear mapping”. Without this, the complete permutation would be ...
2
votes
3answers
311 views

If a cipher has key length shorter than plaintext, then it is not perfectly secure

I am trying to verify the statement above. So far I only know that a One-Time-Pad is the only “perfectly secure” cipher. It has a key length which is exactly the same as the plaintext. I think the ...
3
votes
1answer
225 views

Why don't we use bcrypt and scrypt together?

Everyone is comparing bcrypt to scrypt. Bcrypt is proven, lots of cryptoanalysis and no vulnerabilities so far, but uses very low memory. While scrypt uses a lot of memory, but it's too early in its ...
1
vote
0answers
57 views

FEAL-4 Wrong outputs of Round Functions

On page 2 of this article, there is example of FEAL-4. At round 2, the input to F (Round Function) is 0x80800000. As F accepts only 4 bytes I divide the input by 2 so that (As I assume the result ...
1
vote
1answer
318 views

Number of keys for a monoalphabetic cipher

My teacher stated that… The number of possible keys (E) in a monoalphabetic cipher is $26$! My thinking: Every letter in the alphabet can be $25$ different letters hence it the number of ...
1
vote
0answers
110 views

Which mathematical operations does secp256k1 point multiplication use?

To convert a bitcoin private key to a public key, the secp256k1 point multiplication math is used. Could I – theoretically – convert a private key to a public key just using the four arithmetic ...
13
votes
2answers
12k views

How is XOR used for encryption?

I am a programmer, so when I hear XOR, I think about the bitwise operator (e.g. 0110 ^ 1110 = 1000). The mention of "XOR" comes ...
1
vote
0answers
323 views

Serpent Cipher 128bits (Example rounds on any plaintext/key)

Is there are any possibility to see trace(example) of Serpent Encryption/Decryption on concrete plaintext/key example, (not code implementation) or at least animation of steps. During reading of ...
2
votes
1answer
214 views

RC4 key schedule and algorithm design

I've looked up RC4 algorithm and it's seems easy enough but some parts of it seem random to me. In the key schedule part take for example the following part : ...

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