1
vote
1answer
51 views

In $\mathbb Z/p\mathbb Z$, is $(a+b\cdot r)$ a random value for fixed $a,b$ and random $r$?

Let $p$ be a prime number. Consider two fixed values $a,b\in\mathbb Z/p\mathbb Z$, where $b\neq0$, and a uniformly random value $r\leftarrow \mathbb Z/p\mathbb Z$. Is $v=a+b\cdot r$ a uniformly ...
0
votes
2answers
143 views

Assemble RSA keys from components [on hold]

I'm studying openpgp cryptography and struggling to understand some things. I can't use pgp tool for generating keys and ecryption, but have to write a simple app to generate keys, encrypt and decrypt ...
2
votes
2answers
30 views

Supersingular Isogeny Key Exchange broken?

Found this report detailing a quantum algorithm for computing isogenies between supersingular elliptic curves. http://cacr.uwaterloo.ca/techreports/2014/cacr2014-24.pdf with the quote ...
3
votes
1answer
119 views

Is it possible to track down copies of WW2-era codebooks?

I've got an academic curiosity regarding some of the old Japanese naval codes used during World War II specifically. I'm wondering if any of the codebooks from this era have been made available, or ...
1
vote
1answer
34 views

Random Function size

I am new to cryptography. I have question regarding the size of the set of random functions. I found the text from "Introduction to modern cryptography" by Katz and Lindell, in another thread which ...
2
votes
2answers
77 views

Client login without sending a password

I would love to have a system where the password is never send in plaintext (even with TLS) to authenticate a user. I've come up with this protocol, but I'd rather use something proven. Registration: ...
0
votes
0answers
22 views

Complement of information on software usage [on hold]

I recently asked this question on cryptography S.E. and was kind of surprised that the answer didn't contain technical explanations (what software to use, etc) that would have solved it. One user ...
5
votes
1answer
254 views

ECC considered secure in OpenSSL?

If I perform the following command: openssl ecparam -list_curves using my OpenSSL version (1.0.1f), it spits out the following supported curves: ...
3
votes
4answers
2k views

Why is RSA encryption significantly faster than decryption?

I am designing an implementation of RSA . I recorded computation times in Java by using System.currentTimeMillis(). It returned an encryption time of 0.05 ms and ...
1
vote
0answers
17 views

Is there an existing AE protocol with forward secrecy for embedded devices?

I'm working on an embedded device that is connected to a computer over an untrusted channel. According to my threat model I need authentication and encryption on the wire with perfect forward secrecy. ...
1
vote
0answers
34 views

Email: Degrees of Security [on hold]

It has been explained to me by IT that there is no such thing as totally secure email - but rather a spectrum. If systems are secured via https and SSL what degree of encryption/security are we ...
2
votes
1answer
468 views

Why does openssl BN_generate_prime return only a fraction of the safe primes within the given bit range?

I went into prime generation issues the last week and eventually calculated 10^7 primes using erik tews safeprimegen python wrapper for openssl. (https://github.com/eriktews/gensafeprime) (System: ...
1
vote
1answer
81 views

Pseudo Random Function

The definition of pseudo randomness that leads to pseudo random function talks about indistingishability of a key-ed function and a random function. i.e. The key-ed function family $\{F_k\}$ is PRF ...
4
votes
1answer
185 views

Changing SRP-6a message order

In SRP-6a, the public key $B$ of the server is normally sent after receiving the public key of the client $A$. Is it okay to send $B$ and $s$ after the client sends its username $I$, but before the ...
7
votes
2answers
699 views

Is SipHash cryptographically secure?

I'm evaluating different hash algorithms for use in my application. One of the kind of algorithms I am looking at are cryptographically secure ones to protect against DOS attacks. SipHash seems ...
4
votes
0answers
26 views

Additive homomorphic encryption scheme without change in operator

I'm looking for an additive homomorphic encryption that the addition operator (+) in its plaintext space be the same as addition operator in its ciphertext space. (Schemes like Paillier do addition in ...
3
votes
1answer
269 views

A fast non-cryptographic hash function that is “strong enough”?

I'm designing a simple one-time-password mechanism for authentication against a possibly-insecure server - i.e. I don't want to use symmetric shared secrets. The first idea that came into mind was ...
3
votes
2answers
684 views

Generate a unique 64 bit numeric database key without collisions at $2^{32}$ birthday threshold?

What is the best way to generate a unique 64 bit numeric database key from a string? For example: if the string is a URL, you could generate a 64 bit key using SipHash or by truncating a SHA256 hash ...
1
vote
1answer
62 views

Cryptanalysis of Marvin32 compared to SipHash

So I am curious about the security analysis of Marvin32, the randomized hash algorithm used in .NET (to prevent hash-table DoS). I found the source code here: ...
2
votes
1answer
70 views

Does SipHash have 64 bit (second) preimage security?

I was not able to find an explicit statement about the first and second preimage security of SipHash-2-4 or SipHash-4-8 anywhere. I think it should be 64 bits, but I'd feel safer if somebody who has ...
0
votes
0answers
35 views

Does anyone have an idea of what this is? [on hold]

I found this within an mp3 using audacity. Does anyone recognize this type of code?
4
votes
4answers
221 views

Computation indistinguishability questions

The definition I have is: Two probability ensembles $X = \{X_n\}_{n \in \mathbf{N}}$ and $X = \{Y_n\}_{n \in \mathbf{N}}$ are computationally indistinguishable if for every probabilistic ...
-1
votes
0answers
42 views

What is the recommended key length for digital signature? [on hold]

What is the recommended key length considered secure in order to sign a flash memory using PKCS #1.5? What is the main difference between PKCS#1 1.5 to 2.2?
5
votes
1answer
294 views

Timing Attack on RSA

So far I have researched on timing attack on RSA, We all know the ransomware named Cryptolocker it uses RSA 2048 bit encryption. Now is it possible to break the encryption using timing attack. I have ...
7
votes
1answer
1k views

Knowing pre-encryption data, can we find the private key CryptoLocker used?

One of our users seems to have been hit by CryptoLocker. As a result, he has a hard drive full of encrypted files. The ransom-ware claims to have used public key encryption on the files. If we know ...
0
votes
0answers
19 views

Knowing pre-encryption data, can we find the private key CryptoWall used?

I'm just repurposing a question already asked about Cryptolocker for CryptoWall: "If we know exact contents of some of the files prior to them being encrypted, would it be feasible to use those ...
1
vote
1answer
36 views

How can I handle the situation if key size is less than 64 bits in DES?

If the data is not a multiple of 64 bits, then I can use padding. I know that it is not secure. But if the key is less than or more than 64 bits, should I ask the user to enter the key again, or ...
1
vote
3answers
47 views

Digital signature algorithms within the European Union

I've just noticed that US NIST has accepted DSA as a digital signature standard. Does the European Union have a similar standard, specifying an algorithm to use when digitally signing messages? I ...
2
votes
2answers
211 views

Encryption of 8 bit of block data

I'm looking for a cryptographic algorithm that allows encrypting only 8 bits of data in a block. Is there any such algorithm that is considered secure? The reason I'm asking is because I have to ...
0
votes
1answer
24 views

What is the difference between a random oracle and a probabilistic algorithm? [on hold]

What is the difference between a random oracle and a probabilistic algorithm?
0
votes
0answers
11 views

Envelope Encryption with asymmetric keys vs KMS

In Envelope encryption a symmetric secret key is used to sign the data and then another key is used to encrypt the secret to produce an encrypted secret key. The encrypted messages is packaged with ...
1
vote
1answer
22 views

How to encrypt/decrypt data in an SPI BIOS FLASH

I need some info/suggestions about the cryptographic algorithm that make me sure that the executed bios by the CPU is an authenticated bios. The check has to be performed by a FPGA. I have SPI Flash ...
2
votes
2answers
798 views
0
votes
0answers
32 views

Is double encryption using AES using different key lengths (128 bit and then 256 bit) vulnerable? [duplicate]

I know that AES 256 bit is far more than enough to secure a file. I just want to know if there are any vulnerabilities or known attacks which can make such this combination less secure "double ...
0
votes
2answers
34 views

OTP same message encrypted twice (with different keys)

Lets say we have a message $m$ that we encrypt with two keys $k_1, k_2$ such that $k_1 \ne k_2$. This will produce two ciphertexts $c_1, c_2$ such that $c_1 = m \oplus k_1, c_2 = m \oplus k_2$. The ...
0
votes
0answers
33 views

How to build a secure cryptographic algorithm [on hold]

I need some info about the building of a cryptographic system. I would like to know the flow to follow and if there is some books or paper that covers this topic, because I know to concatenate ...
5
votes
1answer
940 views

CKM_RSA_PKCS vs CKM_RSA_X_509 mechanisms in PKCS#11

What is the exact difference between the CKM_RSA_PKCS and CKM_RSA_X_509 mechanisms in the PKCS#11 v2.20 specification (Please ...
4
votes
4answers
3k views

Diffie-Hellman and man-in-the-middle attacks

See here for the man-in-the-middle attack on Diffie-Hellman that I'm concerned about: What is Diffie-Hellman? How do we combat this? I have two questions: Is one solution for both Alice and Bob ...
1
vote
1answer
38 views

Why an upside down path on the evaluation of branching program on encrypted data?

Suggested by Ricky Demer in this post, I am reading the paper "Evaluating Branching Programs on Encrypted Data"(TCC 2007), which uses one-round strong OT protocol to implement homomorphic evaluation ...
3
votes
1answer
49 views

Recommended password complexity for SSH key encryption using AES-256-CBC

When protecting SSH private keys with password-based encryption, what would be a good minimum password complexity+length standard to make cracking the password too difficult to be worthwhile anytime ...
2
votes
1answer
79 views

Recovering key length from transposition block cipher ciphertext

First of all I would like to say hello to all StackExchange users. So far I've been stalking the forum for some time, now it's time to leave the shadows. In my master thesis I'm writing about ...
0
votes
1answer
34 views

Are there any encryption schemes that enable to permute homomorphically?

According to the Barrington's theorem, any circuit in NC1 can be converted to a branching program, whose main operation is the composition of permutations (along with the choosing of permutations ...
0
votes
1answer
36 views

Why the $IV$ used in Merkle-Damgard has to be fixed to a specific value?

I just can't figure out why on earth the $IV$ in Merkle-Damgard has to be fixed (that's what the Katz-Lindell book says)? Because even if you choose it randomly from say $\{{0,1}\}^n$ then the ...
12
votes
3answers
2k views

Why does the padding in Merkle–Damgård hash functions like MD5 contain the message length?

I understand the need for padding in MD5. But why do we append the message length to the padding? I heard it strengthens the hash but how? Please provide an example if possible and how it applies to ...
1
vote
2answers
30 views

Is there a partially homomorphic quantum secure public key cryptosystem with IND-CCA1 security?

I recentely asked "IND-CCA1 RSA padding?" about whether there is a IND-CCA1 secure variant of RSA. The original version of the question also allowed usage of ECC which would allow usage of ElGamal, ...
0
votes
1answer
27 views

Request for review: known plaintext mitigation by rotation and xor encoding

When using structured data inside a plaintext (such as gzip headers, xml, etc.) they generate known plaintext which may be useful in cracking the ciphertext. So I had these two ideas on how to make ...
0
votes
0answers
26 views

how to do AES decryption knowing the key (matasano) [on hold]

I'm doing the challenge in matasano and I'm doing something wrong cause I don't understand what to do. All I want to do for now is to decrypt the first block (128 bits) and then I will code the rest ...
1
vote
2answers
39 views

El-Gamal signature with two messages

Alice uses an ElGamal signature with base the group $Z^*_{107}$ and parameter $g=3$ of order $q=53$.The private key of Alice is some $x \in \{0,1,.....,52\}$ and the public key of her is $y=10$. To ...
0
votes
1answer
23 views

Modular reduction for NIST prime P256— understanding the data

I am working on a project where I need to implement elliptic curve cryptography, I am struggling from a long time in order to understand the working and the process. Modular finite field arithmetic, ...
1
vote
1answer
34 views

Triple-DES DUKPT CBC PIN variant vs Data variant

Does any know the difference between triple des dukpt decryption algorithm with PIN variant and Data variant? I have done Triple DES DUKPT PIN variant, which generate session key from KSN and BDK. ...

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