All Questions

54 views

Smart Card choice for PKI implementation

I'm seeking to implement a national digital signature standard on a smart card. I feel like this is a good place to ask if anybody is acquainted with a hardware supplier offering smart cards that ...
24 views

Using a straight password for encryption and authentication

Assume we have a password like 3buNCh_7kaRmencrEst3. Now suppose we have two parties who know this password. We a have communication scheme that uses the password ...
24 views

MAC is constructed by hashing and then encrypting

Suppose the MAC is constructed by hashing and then encrypting, that is $MAC(m, k2)=E_{k2}(H(m))$ where H is a public hash function. There can be several alternatives in how the transmitted message is ...
14 views

Testing the first 40 bit sequence for A5/1 if all registers initialized to 1

I have an assignment where my instructor asked to generate the first 40 bits for an A5/1 algorithm if all registers are initialized to '1' initially . I have implemented the algorithm successfully ...
39 views

signature, hashing schemes

I have 20 friends. we create message(s) (1...i) and tar them up with a file messages.hashes(1..i). We sign these tars with our ...
8 views

SAM module in Payment transactions & cryptogram key storing

As you know because of low security factors,General MCU's are not appropriate choice for storing Transaction or cryptograms keys.Therefor embedded systems developers used SAM modules for secure ...
38 views

Find SHA256(secret||data) using SHA256(secret) and data

I need to find the SHA256 hash of s string like this: "part1-part2". I know the SHA256(part1), length of part1 and I know part2, but I don't know what is the contents of part1. Is there any chance I ...
24 views

What is transaction capacity of a POS using 3DES DUKPT?

I am looking for the transaction capacity of a Point-Of-Sale device using 3DES DUKPT. Once all keys derived from the future key set are exhausted (1M or 500K?), how will the POS be reloaded with a new ...
23 views

key hierarchy management and master key

I have this equation, $E_{K_{as}}(E_{K_{bs}}(K_{ab}))$ which means $K_{ab}$ is encrypted by $K_{bs}$ then whole packet is encrypted by $K_{as}$. I think the key structure is $K_{as}$ is the master ...
19 views

Can you have partial cryptographic obfuscation (without a trusted setup)?

Cryptographic Obfuscation is a powerful cryptographic technique. My question is, can you do it partially? Instead of obfuscating an algorithm completely, you can have an algorithm with a couple of ...
19 views

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Composing hash functions

Suppose there is a cryptographic hash function $H : \{0,1\}^* \to \mathbb G$. Now, we want to define a hash function $H' : \{0,1\}^* \to \mathbb G \times \mathbb G$. My first idea is to define $H'$ ...
29 views

Length extension attacks or prefix attacks on HMAC

Why HMACs are not vulnerable to length extension attacks or prefix attacks? (As commented by @codesinchaos, That's a different construction. So it's related, but no duplicate of Why is ...
18 views

McEliece variants that support signatures

Besides the Niederreiter cryptosystem, are there any other variants that support digital signatures? Can any of them sign arbitrary signatures unlike the Niederreiter cryptosystem? What are the key ...
22 views

Concatenated Key Question - Poly-alphabetic Substitution and Columnar Transposition

I am working on a degree module, and have been tasked with designing an Encryption/Decryption algorithm. I hope to receive some help with a couple of questions, if possible. Apologies if terminology ...
36 views

Is pseudo-random letter insertion secure?

Is pseudo-random letter insertion a secure mechanism? I mean by expanding the key or taking two parameters in the encryption function, you select positions in the text at which to insert random ...
25 views

generate unpredictable value with a shared key

Is there any function that taek a key to generate (un)predictable value ? I hope you will more understand more what I mean with this example f take in input an array, a key and a round number ...
30 views

Key size limitations due to software compatibility?

At the moment, much popular encryption-based software routinely handles up to 4096 bit keys and standard usage is broadly migrating from 1024 to 2048 bit keys. Hashes widely used are MD5/SHA1/SHA256 ...
18 views

Filling in MD5 input variables

I have a majority of an input string(as well as the total length) and the output for an MD5 hash. Is there a way to calculate the remaining input bytes that I am missing?
14 views

Can XTS + checksum be used for authenticated encryption?

Is it possible to use XTS+a checksum for authenticated encryption? Specifically, it seems like a good $n$ bit checksum applied before encryption should ensure that any change to the ciphertext ...
18 views

Is it okay to use Threefish-512 in ECB mode with Poly1305 MAC to protect some AES keys?

A person has some independent AES-GCM-SIV keys they need to protect as part of a hypothetical protocol or product, where it is publically known that it is in fact AES-GCM-SIV keys that are being ...
21 views

If you receive a message with a digital signature, how do you know what verification key to use and the verification algorithm?

Really, I'm asking how do you know who sent it? My confusion has arisen from the following scenario... Problems with Signing-then-encrypting. If Alice digitally signed some data and then encrypted ...
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18 views

Do users need to know decryption scheme in Identity-based broadcast encryption?

I have a question related to identity-based broadcast encryption: For decryption, there are different decryption schemes. Does the user need to know that scheme, or does the system firmly define the ...
50 views

Lightest symmetric, fixed key, “Format preserving Encryption” algorithm?

message m = 49 bit string key k = any format but fixed Ciphertexts should be 49 bits long. Are there several "Format Preserving Encryption" algorithms? I want an algorithm that is as light as ...
21 views

Value of security through amiguity?

Let's say that you have a symmetric cipher which takes in an 8 bit plain text value and a key, and generates cipher text which can be decoded using the key to get the original plain text value. Since ...
31 views

autocorrelation and entropy of historical ciphers

I'm learning cryptography and come across historical ciphers such as vigenere cipher,hill cipher,random substitution and etc.I'm using cryptool for learning purposes and I have a question in mind.I've ...
36 views

ECIES is must with Symmetric?(ECIES-AES or ECIES-TDES)

I can't understand the ECIES algorithm. I saw two different ECIES algorithms: Using only Public key Key generation: $A_{pri} : n_A$ $A_{pub} : n_A G$ $B_{pri} : n_B$ $B_{pub} : n_B G$ ...
7 views

calculating n-gram lists and spaces in ciphertext

I'm doing an analysis on a block of ciphertext message with 27 characters(including spaces).Now do the spaces need to be taken into account when performing the digram and trigram analysis?because the ...
38 views

If I send a signed email, how does the end user get the public key?

I am sending a signed email using Python and smtplib. I have successfully signed the email using this example: ...
28 views

Recryption of ciphertext with a different key

Let's have $P$ some sensitive piece of data and $K_1$a secret value, both known to Alice, but not to Bob. $K_1(P)$ means $P$ encrypted using $K_1$. Alice sends $K_1(P)$ to Bob. Bob keeps the value of ...
28 views

Encoding issue - PKCS#11 CKM_RSA_PKCS wrapping unwrapping EME-PKCS1-v1_5

I am trying to figure out why I am not able to get compatible format of EME-PKCS1-v1_5 3DES key encrypted by public RSA key. I need to send to a third party 3DES key encrypted using their public RSA ...
19 views

What is the benefit of artificially padding messages?

For ECB, CBC, and CFB, padding is required when the plaintext does not fill out a complete multiple of the block size. However, I have heard that is good practice to pad all messages, even if the ...
27 views

how MitM compute server secret number in logjam

I would like to know how man in the middle can compute the server secret number if the prime is 512 bit in length and if knowing ($g$) parameter as in the following figure help him or not? is the man ...
58 views

Why is it so hard to make a good KDF?

Why are we stuck with only 2-3 KDF functions since KDFs don't imply mathematically conceiving a cryptographic primitive like the inner workings of AES or SHA but instead build a system out of existing ...
27 views

i have encrypted a file using aescrypt and took memory image while the file was being encrypted and hence have the key that was used for encryption in the image but not the password, can i decrypt the ...
50 views

I am trying to understand how AES works

I am trying to understand how AES encryption operates. I am trying to run through the steps on paper to understand. So far, I am creating a simple example. I have the plain text "MESSAGE TESTTEXT" ...
33 views

Using quadratic residue to learn the sign of a field element

Given $x' \in \{-x, x\} \bmod q$ (where $q$ could be any prime of my choice), $s$ is a random element in the field, $y = x'\cdot s$ and $y' = \pm\sqrt{(x\cdot s)^2}\bmod q$ (i.e., both solutions to ...
23 views

MISTY1 encryption/ extension tricks

I'm trying to understand MISTY1 encryption algorithm but i faced some problems in key scheduling part : Key scheduling part consists of the following operations. for i = 0, ..., 7 do EK[i] = ...
In order to prevent known plaintext attack in case of block cipher, a simple randomization technique can be used: $E(M||R)$, here $R$ is a random bit sequence which is only available to the sender.The ...