# All Questions

3 views

### Constructing set membership proof for private set

Is it possible to construct a set membership proof to show $\delta \in \Psi$ where $\delta$ is publicly known and $\Psi$ should stay only known to the prover? It seems rather impossible but I would ...
46 views

### About Primitive roots mod n in Diffie-Hellman

I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers mod n). In some crypto papers and documents I've read that 'g' needs to be a primitive root mod n ('g' order ...
37 views

### How to decrypt a PGP message with only the two primes and the public exponent?

I'm trying to decrypt a PGP Message that is encrypted with an RSA key, but I only have this information: Public exponent: 65537 Prime 1: ...
149 views

### PGP String to Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
22 views

### My attempt of solving socialist millionaire. Is it good?

I've come up with an algorithm to solve the socialist millionaire problem, but I'm not sure if the algorithm is secure. I wasn't able to find any flaw in it, but it seems too simple to be secure, so ...
25 views

### Can you identify this algorithm?

We are attempting to integrate our application in to a third party system. To do this we need to pass encrypted passwords in to this system. I have decompiled the assembly and looking at the code it ...
5 views

### AES Encryption using CBC/PKCS5 padding in python while decrypting in java it is given below error

Can any one help me while encrypting using CBC/PKCS5 padding in python while decrypting in java it is given below error javax.crypto.BadPaddingException: Decryption error at ...
141 views

### Sharing a secret key between many users

I would like to know if there is any security issue in sharing a secret key (of an asymmetric cryptography) between several users. I know that this secret key is no longer "secret", so it's no longer ...
6 views

### What is padding PKCS5? How to encrypt the text data using IV key AES/CBC/PKCS5 in Python

hi am new to python coding,can anyone please give me exact information rearding PCKS5 padding and then about the encryption using IV key AES/CBC/PKCS5 in Python
31 views

### security in format preserving encryption

In format preserving encryption an attacker knows the format and data type of the plain text. The format of the plain text and cipher text are same. usually cipher text are unreadable form. then how ...
12 views

### Differences between HMAC and HKDF in a specific case

I want to use a key derivation function to derive a key to another one. I think HKDF is the easiest solution in my case. The following picture gives a clear definition of it : ...
76 views

### Fast PKI for embedded device

We are creating a device with a small microcontroller (20 MHz CPU 16 KiB RAM). We need some way to securely send signed files to device (only signature, no encryption necessary). An external company ...
31 views

### DPA Attack on HMAC SHA-256

I have read the paper "Differential Power Analysis of HMAC SHA-2 in the Hamming Weight Model" (http://www.di.ens.fr/~belaid/articleHMAC.pdf) and I want to understand the DPA Attack. In section 3.2.1 ...
55 views

### Can AES be considered as Perfectly Secure?

I am studying about the AES encryption standard, and as I know from the theory there is no known weaknesses today about this block-cipher. I would like to find out or at least to understand what ...
20 views

### What is the right notion of security to use for file encryption?

It seems that several file encryption systems do NOT use authenticated encryption. (E.g. gpg --symmetric and boxcryptor as far as I can determine). I understand that this is generally considered ...
22 views

### Is there a mental poker algorithm that does not rely on commutative encryption?

The algorithm for mental poker that I saw on Wikipedia and everywhere else relies on an encryption algorithm such that $E_k(E_j(P)) = E_j(E_k(P))$, but I can't find a modern and secure algorithm for ...
75 views

### Is it practical to use a stream cipher in a block cipher mode?

My idea is to use a stream cipher encrypting 16 bytes at a time as a primative block cipher in a mode of operation such as CBC mode. Is this practical or useful in any way?
23 views

### Why does OMAC2 exist?

The specification for OMAC has the following to say about OMAC2: For OMAC2, we adopted u−1 instead of u2 as Cst2. It requires one right shift to compute L· u−1 instead of one left shift to compute ...
107 views

### Why don’t all AES encryption tools produce the same key from the same password?

Alice and Bob meet regularly. They have agreed face-to-face a 128 bit password which they want use to encrypt/decrypt emails written between them. They decide to use 256-bit AES. Alice wrote her ...
32 views

### PGP public RSA key format

I have been trying to use Go (I could post the code, but I think I posted enough already...) to generate a PGP RSA key. However every time I try to encrypt something with it, something fails. However, ...
200 views

### VKO GOST R 34.10-2001 (described in RFC4357), Key Agreement Algorithm. Looking for its implementation/detailed description/examples

VKO GOST R 34.10-2001 was described in RFC4357 Page 7 But the description is very poor. Here it is: This algorithm creates a key encryption key (KEK) using 64 bit UKM, the sender's private key, ...
15 views

### Encoding info for different SaaS users [on hold]

My company is developing a management software and we want it to be SaaS. Now we face a crucial question: how do we ensure our clients that we cannot access their data from the server? Which is the ...
65 views

### What is the difference between H(M) and H3(M, s, IDA)? [on hold]

What is the difference between H(M) and H3(M, s, IDA)? I am aware of Hash function with a Message and a Key, but there are three parameters in: H3(M, s, IDA). Here M is the message, s is the key, ...
27 views

### What are these: b04bmtpf b00k8fdx b052hdnr b04d4p0b [on hold]

I'm trying to understand how the BBC sets its URLS. Each program on the BBC has a url like http://www.bbc.co.uk/programmes/b04bmtpf or http://www.bbc.co.uk/programmes/b04d4p0b Where the last 8 ...
26 views

### Is end to end email encryption possible without unique domain/subdomain for each user? [on hold]

Lets say Alice@gmail.com wants to send message to Bob@secureMail.com Alice <--> gmail.com <--> secureMail.com <--> Bob We know gmail.com can read the unencrypted message. Is it possible for ...
25 views

### Reducing the degree of polynomial descripting a block cipher [on hold]

Any one knows about Reducing the degree of polynomial descripting a block cipher? Regards.
2k views

### How to attack a classical cipher using known partial plaintext?

I have a ciphertext generated by a classical cipher. I do not know what was cipher used to generate it. I do however have the beginning of the plaintext. What are the cryptanalysis approaches for ...
51 views

### Operation modes of block ciphers how are used?

I am studying about different operation modes of block ciphers my question isn't something specific to that, but is how these operation modes are used in cryptography? I have this picture here ...
86 views

### Assemble RSA keys from components

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 ...
40 views

### Does the encryption algorithm DES perform random permutations? If so how is information not lost?

"Before round 1 begins, all 64 bits of an incoming message and all 56 bits of the secret key are seperately permuted (shuffled)" My question is this : Is the shuffling of the bits performed randomly? ...
24 views

I'm quite new to the topic and read a bit about poodle and padding oracle. I quite understand the "regular" padding oracle attack, substituting the last byte of block(n-1) to determine the last byte ...
45 views

### One-time-pad with multiplication [on hold]

Does a one-time-pad with multiplication instead of xor between the message and the key introduces security problems?
288 views

### Effective security of block cipher – equal the key size, or half the key size?

The Wikipedia “Key Size” article states: The security of an algorithm cannot exceed its key length (since any algorithm can be cracked by brute force), but it can be smaller. … … … Most ...
38 views

### Non-interactive zero-knowledge proof for discrete logarithm without random oracle

Is there any non-interactive zero-knowledge proof for discrete logarithm without random oracle over the group $\mathbb Z_p$?
63 views

### Do hand-based hash functions / MACs exist?

Is there research on a hash function or a MAC that can be executed without computers? I know there's a lot of history on hand-based ciphers and the OTP can easily be excecuted by hand. (By using ...
3k views

### Why hash the message before signing it with RSA?

The diagram below illustrates the process of digitally signing a message with RSA: As diagram shows, the message is first hashed, and the signature is then computed on the hash, rather than on the ...
241 views
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### How to prove that someone encrypted a specific (large) chunk of data

Alice encrypts her data with HER secret key. Then she sends the encrypted data to Bob who should encrypt it with HIS secret key. Caroline should then eventually get this double encrypted data. ...
68 views

### Improving on a clocked PRNG

I recently developed a PRNG from scratch with a little inspiration from the initialization function used in the HC stream cipher. The state ($S$) of the basic version is an array of 5 bytes and uses ...
132 views

### Looking for C++/Python Open Source code library for cryptanalysis of classical ciphers [on hold]

I've done a significant amount of coding over the years working on classical ciphers (e.g., Chaocipher, D'Agapeyeff). My main programming languages today are C++ and Python, although there was a time ...
41 views

### Why is public key cryptography not widely used in governments? [on hold]

Are there any practical limitations? Govt driving license, passport, SSN could be digitally signed making it easy for anyone to validate. They can have a qr code in them which can be easily validated ...
188 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 ...
45 views

### Using ECB as encryption mode, but encrypted messages are unique

As I understand, ECB should not be used as encryption mode unless you are encrypting single blocks of data which are always unique and only are encrypted once. I have a collection of ids represented ...
232 views

### What does a stream cipher provide that cannot be obtained with AES CTR mode operation?

I can precompute the key stream for the CTR mode operation and the encryption at that point is similar to a stream cipher. So why are there stream ciphers still used and proposed after RC4? Recently ...
71 views

### Would this be a plausible authenticated encryption scheme using nested encryption?

[This is was the most promising out of an incrementally developed set of (mostly flawed, to some degree) schemes I posted here, but I was told I should post each one separately] This scheme is highly ...
52 views

### One time pad in CBC mode?

I have been searching about if it is more secure to use CBC mode in OTP but I can't find anywhere where people have sad that it is more secure. Question: Is CBC mode in OTP more secure? Because I ...
77 views

### Finding public exponent e

I'm trying to create an algorithm to find the public exponent e given a plain (non-CRT) private key that doesn't include the public exponent, i.e. I've only got $n$ and $d$. A question has already ...
2k views

### Is it possible to make time-locked encrytion algorithm?

I'm not sure if what I'm asking is even a valid question but here goes. Would it be possible to add a mechanism to an encryption algorithm that would mean it had to be a certain time of the day or a ...
31 views

### Bilinear pairing arithmetic - cryptographic accumulators

For calculating accumulated values for set of elements chosen randomly from say ${ e_1 ,e_2,...e_n}\varepsilon X$ we use the formula $acc= g^{f(e,s)}$ where $f(e,s)= (e_1+s)(e_2+s).....(e_n+s)$ ...