Latest Crypto related questions

Score: 0
AUser avatar
How can I validate certificate chain when CA certs held in Java Key Store
ca flag

Can someone please help me with the following, I googled before hand but did not find a blog outlining what I wanted to do, thanks in advance.

I have and internal test PKI (based on AD CS). I have imported the Root CA certificate and the Issuing CA Certificate (minus their private keys) into the CACerts java key store (keying the GUI tool "KeyStore Explorer 5.5.1"

I have a leaf (end-entity certifica ...

Score: 2
RLWE Explanation
cn flag

In RLWE, we often choose the following polynomial ring, where q is a prime, and n is a power of 2, e.g. $2^k$ $$\mathbb Z_q[X]/(X^n + 1)$$

We know that ${X^{2^k}} + 1$ is an irreducible polynomial under $Z$, because of Cyclotomic Polynomial, but in this question, Considering $$\mathbb Z_{17}[X]/(X^4 + 1)$$ $(X^4 + 1)$ can be factorized into $$\mathbb (X^2 + 4)(X^2 - 4) = X^4 - 16 = X^4 + 1$$ because ...

Score: 0
r3p1et avatar
Get issuerNameHash and issuerKeyHash of x509
th flag

I need to get the following out of x509 CA certificates:

  • the Hash of the DER encoded public key (excluding tag and length) of the subject public key field
  • the hash of the issuers distinguished name, that must be calculated over the DER encoding of the issuer's name field

I tried to use X509_issuer_name_hash and X509_pubkey_digest , but apparently they return not the results that I expect.

This  ...

Score: 2
Ankush Soni avatar
Scyther related questions for handling/splitting values and verifying hashes
fr flag

While implementing a protocol in Scyther, I need help with the following questions -

  1. How do we split a particular message/variable into two parts in Scyther? (For eg. if I have value R in my protocol that I need to divide into two parts say K1 and K2, how do I go about doing it in Scyther. I tried R=CONCAT(K1, K2) where all R, K1 and K2 are of the same type but I don't know whether it is the corre ...
Score: 0
Bob avatar
How to pack the inputs using hybrid encoding?
cn flag
Bob

I'm reading Gazelle. This paper proposes a matrix multiplication vector(encrypted) method using the SIMD property of RLWE-based FHE. It proposed a hybrid encoding. For $n_o \times n_i$ matrix, when $n_o < n, n_i <n$ where n is the slot count.

The author said that using the input packing, the number of $\text{SIMDScMult}$ and the hoisted rotation is $\frac{n_o\cdot n_i}{n}$. Without input packing,  ...

Score: 1
Sending encrypted message without public key from recipient (elgamal)
hk flag

assume Bob and Alice use Elgamal encryption scheme. Alice wants to send Bob a message, but does not know Bobs public key. Is there a way for Alice to find out Bobs public key by receiving multiple message pairs C1 (ephemeral key) and C2 (message) from Bob? Alice can easily decrypt Bobs messages, as from Bob to Alice the shared K is known by Alice. But Alices messages to Bob cannot be correctly decrypted ...

Score: 1
CrazyPhil avatar
How to crack sha256 used as streamcipher with known or guessable block
cn flag

Using SHA-256 as a stream cipher appears to bear cryptographic weaknesses, however, I am not quite sure how to implement them in decryption.

Assume that I have an encryption function using 64-byte blocks. I encrypt each of the blocks with the hash of the previous to produce my ciphertext. The weak link here is, that I know, or can guess the very first block of bytes.

In one of the posts linked below ...

Score: 1
How to create a key for AES in a 192 bit key length from a password?
mu flag

Let's say that I have a password. And it's secure. But it's a 10-character string.

So If I wanted to create an AES key for the 128-bit version of the algorithm I would just hash it using MD5. Or If I wanted the 256 version of the algorithm I would hash it with any of the 256 length hash functions such as Sha_256. But I have not been able to find any hashes (other than some named Tiger) that gener ...

Score: 0
Basic CS Insights avatar
Has anyone come across any Papers on Statistical analysis of Present cipher? Nist or Dieharder
ke flag

I need to Perform Statistical Analysis of Present. I choose NIST but I am getting underflow error even though I am taking 10 million bits.

Score: 0
How to import OpenPGP Card / YubiKey backup encryption key
lk flag

When I generate a new OpenPGP key on a YubiKey, it gives me the option to save a copy of the encryption key as a backup like so:

$ gpg --edit-card

Reader ...........: Yubico Yubikey NEO U2F CCID 00 00
Application ID ...: D2760001240102000006054943550000
Application type .: OpenPGP
Version ..........: 2.0
Manufacturer .....: Yubico
Serial number ....: 05494355
Name of cardholder: [not set]
Language ...

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