1
vote
2answers
316 views

Kryptos : K2. What is the origin of the “abscissa” keyword?

I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4. Similar to the "palimsest" keyword for K1, the keyword "abscissa" for K2 was determined by brute-force. To better ...
4
votes
1answer
213 views

Why is feed-forward mechanism used in hash functions?

The compression function of SHA-1 when used in Davies-Meyer mode adds its input to the chaining values at the final step. For the first message block, the IV is used as the input and in the next step, ...
1
vote
1answer
248 views

Decryption a chunk of file with AES

We are having a requirement to store large files (~1GB) encrypted and decrypt them when reading. We are looking to use AES-CTR or AES-GCM mode to encrypt the data. There are scenarios where we want to ...
1
vote
1answer
98 views

Question about use of IV in this cipher

Main cipher objective : Generate a keyed CSPRN stream, that does not expose useful information about the state of the CSPRNG, and xor this with the plaintext. To prevent an attacked who could somehow ...
1
vote
1answer
2k views

How do I derive the time complexity of encryption and decryption based on modular arithmetic?

I want to calculate the time complexity of two encryption and decryption algorithms. The first one (RSA-like) has the encryption $$ C := M^e \bmod N $$ and decryption $$ M_P := C^d \bmod N. $$ ...
2
votes
1answer
291 views

Using Chi-Square for Vigenère Cipher

I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenère cipher. I came across a website that describes the Chi-Square statistics in a ...
3
votes
2answers
209 views

How is the x coordinate of a “point at infinity” encoded in a Secp256k1 signature?

I'm testing an implementation of Bitcoin, which uses the curve Secp256k1 for ECDSA, and I want to see how it handles the point at infinity ($0$) if present in a signature. For example, r could be the ...
5
votes
1answer
184 views

Questions on rank-attacks in Multivariate Cryptography

While reading this article on rank attacks on STS (a public-key scheme based on Multivariate Quadratic (MQ) equations), I stumbled upon some claims that I've also seen in other presentations on ...
1
vote
0answers
42 views

School exercise on untrusted channel comunication [duplicate]

Possible Duplicate: Why is H(k||x) not a secure MAC construction? I've the following problem: two parties, A and B, share a secret key Kab. M is a plaintext message, H an unkeyed hash ...
1
vote
0answers
227 views

RSA and One Time Password (OTP) service

What is the expert cryptographic opinion on the following? Assume that there is a web server and a client on web page. User on the Client calls an OTP web service on the server which: creates a RSA ...
1
vote
1answer
140 views

Do practical key-less cryptosystems exist?

Hopefully the question isn't too broad or off. Basically, are there any practical, and by practical I mean secure enough that a ciphertext only attack is infeasible, key-less cryptosystems? For ...
2
votes
2answers
301 views

What are the differences between proofs based on simulation and proofs based on games?

what are the main pros and cons of proving the "security" of a crypto scheme under simulation proofs instead of game based proofs?
2
votes
0answers
168 views

Creating colliding x509 certificates: Crafting RSA moduli step

I am trying to generate 2 x509 certificates with the same signature but different values in the common name field, based on md5 collisions, as it was specified in this paper (page 7). Now I have ...
3
votes
1answer
580 views

What is a smart card?

In many cryptographic protocols, some information is transmitted within smart cards. So, what is a smart card? Is it a physical card? What are they used for in cryptographic protocols?
0
votes
2answers
289 views

Cryptographic Symmetric Stream Cipher

Let me know a cryptographic symmetric stream cipher system with only two functions say S() and P() and it should satisfy the ...
2
votes
1answer
97 views

Using UMAC with stream cypher

I understand that most stream ciphers, due to being applied with a simple XOR, are specially fragile against data tampering, and must be used with some MAC mechanism. So I am investigating the use of ...
3
votes
2answers
340 views

Theoretical pi-based stream cipher

Let's pretend that all digits of pi are known and arbitrarily long sequences of digits are trivial to get. Further, some mathematician proves that there are no patterns in pi. We could create a stream ...
2
votes
1answer
125 views

Discrete log analog of ECM factoring algorithm?

Anecdotally, most factoring algorithms have a corresponding variant algorithm that can be used to attack the discrete log problem using similar ideas. Is there an analog of the elliptic curve (ECM) ...
1
vote
0answers
72 views

How to create a public-key certificate for RSA Web of trust?

How to create a public-key certificate for RSA Web of trust? I have (for exemple) two public / private key pair (obviously). They all need to sign each other certificate. How to create the ...
1
vote
1answer
126 views

How can encryption software accept password lengths which are not one of the AES key lengths?

AES comes with key sizes of 128, 192, and 256 bit. But in Truecrypt or other crypto software we can use passwords of different length, even less than 128 bit or more than 256 bit. How is this ...
4
votes
1answer
355 views

Hashing passwords with a salt - why use different salt for everyone?

Given a database where we have usernames and passwords, we want to secure users' passwords by hashing them. We should not use only username and passwords in this hash, as someone having data from ...
4
votes
1answer
128 views

How much do we trust KEA1 Assumption?

Let $$(g,h=g^s,q)$$ be a tuple such that $g$ is a generator for a group $\mathbb{G}$ of ord $q$ and $s$ is uniformly random in $\mathbb{Z}_q$. The KEA1 Assumption saies that for any adversary ...
1
vote
1answer
137 views

Generating non-supersingular elliptic curves for symmetric pairings

I am looking into the application of pairings in CPABE in particular. I've notice that the scheme uses a supersingular curve as the basis of the pairing. Looking through Ben Lynn's thesis for the ...
2
votes
2answers
117 views

GGM PRG construction: Why do we need to change keys all the time with underlying PRG

When constructing a PRF that has n bit input using the GGM PRG, why do we always have to recursively run the PRG using its previous output as a seed key n times. Instead, why don't we run the PRG n ...
3
votes
1answer
183 views

How to find an element of high-order in an RSA group?

Is this even possible? The RSA group is not cyclic, so usually you wouldn't find a generator for accessing all group elements. What happens if you use the RSA group in a scenario where you want that ...
1
vote
1answer
77 views

What is the most secure way to let Alice “input” her private key, transfer it to the server and decrypt the message?

What is the most secure way to let Alice "input" her private key, transfer it to the server and decrypt the message? (Then destroy the private key on the server) Every connection is using SSL. ...
-2
votes
1answer
186 views

What is the most paranoid way to exchange messages? [closed]

I'm looking for a way for Alice to send a message or a file to Bob in the most paranoid way possible (over the internet). It can be asymmetric or symmetric. But According to some articles, AES ...
-1
votes
1answer
107 views

Cryptographic Primitive Method

Is there any cryptographic primitive bijective (one-to-one and onto) function for creating cryptographic tools like symmetric encryption/decryption, Hash code generator, MAC, HMAC and Random number ...
2
votes
3answers
146 views

Secure communication between multiple peers on a public channel

I am wondering how can I secure communications between multiple peers over a public channel, like an IRC channel. With two peers it is easy - they exchange their encryption keys and decrypt the ...
4
votes
3answers
213 views

What is a block cipher?

I have read about block ciphers, but I do not understand the topic completely. Is a block cipher a way to send data or a way to encrypt data? How is the data divided into multiply blocks before it ...
-1
votes
1answer
160 views

Same Size Crypto Algorithm?

I need to know there is any algorithm that crypts data in same size, Any knowledge appriciated! Thank you!
3
votes
1answer
141 views

Why does Rijndael with a 256-bit block require the bottom two rows to be shifted one more space than usual?

From Wikipedia: For a 256-bit block, the first row is unchanged and the shifting for the second, third and fourth row is 1 byte, 3 bytes and 4 bytes respectively. Why the change? Is there any ...
2
votes
1answer
105 views

Hashing a password with the password?

I was wondering if hashing a password with the password would be a good way of encrypting the password. So, the user must know his/her password to get the same result as the one in the database. Also, ...
6
votes
3answers
406 views

Initialize a PRNG with a password

Let's assume that we have a secure PRNG. Is it "safe" to initialize it with password, or seed based on a password like SHA256(password)? If yes, is it "safe" to generate an RSA or DSA key from it? ...
4
votes
2answers
292 views

In the Paillier cryptosystem, is there a method to judge whether an encrypted number is less than 0 (without the private key)

Or, is there a cryptosystem that is both order-perserving and additive homomorphic?
2
votes
2answers
391 views

RSA private key format for Mega

I've been trying to reverse engineer Mega's (mega.co.nz) API calls. And stopped on the step where client needs to decrypt session id with provided RSA key. I can get key data, but I have no idea how ...
5
votes
1answer
124 views

How to generate a key using any m passwords out of total n?

My application requires an AES-256 key K for some secure operation. In order to avoid saving this key in application, I have implemented following scheme: There ...
1
vote
1answer
191 views

Understanding padding oracles - is an attack plausible in my scenario?

I have a scheme that, long story short, uses AES in CBC mode to encrypt third-party credentials for user accounts with a password-derived key. It's been mentioned that the use of CBC mode is a ...
11
votes
1answer
506 views

Is Encrypt+HMAC stronger than AEAD?

There are a few posts that I've come across that seem to infer that using regular encryption and a MAC might be better than using the newer AEAD (ie: AES/GCM) modes. ...
7
votes
2answers
165 views

Encrypting or HMACing password digests

Assuming I'm using bcrypt to digest passwords, is any additional security gained by either encrypting or HMACing the resulting digests? By requiring a key to compare password hashes, I would expect ...
2
votes
1answer
128 views

Non-cryptographic hash function as MAC for stream ciphers

I understand that for a stream cipher to be useful, there must be a way to verify that the message was not tampered with (bits were flipped by an attacker). So, instead of using some cryptographic ...
2
votes
2answers
162 views

Does it take brute force to find a pair of plaintext and ciphertext that each follow a certain condition, given an AES encryption key?

Suppose that I have an AES key $K$, and I'm instructed to find a plaintext such that the first 32 bits of the plaintext are some string of bits $S_1$, and the last 32 bits of the ciphertext once the ...
2
votes
1answer
89 views

Discrete logs on elliptic curve with embedding degree 3 with the 'MOV' attack

The curve $E(\mathbb{F}_{47}):y^2=x^3+x+38$ has order $61$ and $61|47^3-1$ so the embedding degree of $E$ is $3$ and therefore the MOV attack, presumably using some sort of distortion map and a ...
1
vote
1answer
71 views

Two files encrypted with related data versus one file

I have some code that takes a list of credit-card numbers, splits the number into two chunks, one chunk is 8 characters long, the other chunk is the remainder. Each series of chunks is saved into ...
4
votes
5answers
860 views

Any efficient text-based steganographic schemes?

While there are sophisticated and efficient steganographic schemes with images as cover available, I am yet ignorant of the existence of any fairly efficient and secure schemes with texts as cover. ...
5
votes
1answer
205 views

Security for IV in AES-GCM mode

I'd like to use AES-GCM instead of HMAC for authentication and privacy in a token used in a web application, but I'm unsure how to securely tag each token with an IV. Is it safe for me to prepend the ...
4
votes
2answers
268 views

Modulus for elliptic curve point multiplication

I want to implement a point multiplication ($k \cdot P$) operation on FPGA. I have a BN curve $y^2=x^3+2$, and a scalar value $k$. The $x$ and $y$ coordinates of point $P$ are of 256 bits. In the ...
4
votes
1answer
164 views

Why work in a subgroup QR(n) of an RSA group $Z^*_n$?

I sometimes read in papers that a (sub-)group generator $g$ is taken from $\mathrm{QR}(n)$ instead of $\mathbb{Z}^*_n$, where $n = p \cdot q$ and $p$ and $q$ are prime. Is there a reason for this? ...
1
vote
0answers
272 views

How compared encryption algorithm in terms of efficiency

I doing to compare two algorithm cryptography. first algorithm is RSA cryptography and second algorithm is El Gamal elliptic curve cryptography. now I want a way to compare between two algorithm by ...
4
votes
1answer
111 views

Any implication of a Yale result to security of quantum cryptology?

Quantum key distribution depends, if I don't err, on (irreversible) damages done by MITM's measurements on qbits. Now news.yale.edu/2013/01/11/new-qubit-control-bodes-well-future-quantum-computing ...

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