Cryptography Stack Exchange Community Digest

Top new questions this week:

Does this RSA decryption scheme make sense?

A custom file format has a header encrypted with a 2048-bit RSA public key. I need to decrypt it using a 2048-bit RSA private key. The header has 48 bytes, and according to the scheme I got for the ...

rsa public-key openssl key-size output-size  
user avatar asked by Maksym Shcherban Score of 9
user avatar answered by Ilmari Karonen Score of 10

Prove that what's running inside a black box is code that has been released publicly

Suppose someone has a black box, which is running some program. This box has some internal states, and we can observe the outputs it produces. Now someone comes along and claims the release the source ...

user avatar asked by nialv7 Score of 5
user avatar answered by kodlu Score of 7

Encrypting a symmetric key which requires 2 keys to decrypt?

Let's say a device has 2 private keys and service has the 2 corresponding public keys. Is there an efficient way to encrypt a symmetric key from the service side utilizing the 2 public keys, such that ...

user avatar asked by Bakudo81 Score of 5
user avatar answered by knaccc Score of 5

Why is forward secrecy needed at X3DH?

In the official documentation of the X3DH Algorithm (link) is made an analysis about the forward secrecy. Forward secrecy would be an uselful property if we would repeat the protocol multiple times. ...

user avatar asked by p_1092131280 Score of 5

Do we need the quantum random oracle model (QROM)?

I am currently studying the proof of the Dilithium signature in the quantum random oracle model (QROM). I am curious to hear if anyone have any thoughts on the importance of having proofs in the QROM ...

post-quantum-cryptography lattice-crypto random-oracle-model quantum-cryptography dilithium  
user avatar asked by Rory Score of 4
user avatar answered by Daniel S Score of 4

Where does signing/decrypting take place on a YubiKey 5 for PGP private key?

I have found similar question for PIV (and not PGP) I assume PIV and OpenPGP would work in similar ways. I also assumes that the GPG private key never leaves the Yubikey. If these assumptions are ...

encryption pgp decryption  
user avatar asked by AlexVal Score of 4
user avatar answered by knaccc Score of 3

Why does FIDO2/WebAuthn really need to generate a separate key-pair for each site?

I understand that FIDO2/WebAuthn generates a separate key-pair for each web-site (domain), and only allows a specific key-pair to be used for authentication on the same web-site (domain) who ...

public-key authentication key-generation  
user avatar asked by Uwe Kohl Score of 3
user avatar answered by Taylor R Campbell Score of 2

Greatest hits from previous weeks:


I have three questions: Would you use HMAC-SHA1 or HMAC-SHA256 for message authentication? How much HMAC-SHA256 is slower than HMAC-SHA1? Are the security improvements of SHA256 (over SHA1) enough to ...

hash hmac sha-256 sha-1 sha-2  
user avatar asked by Mario Score of 34

Can I remove newlines in a public key?

Can I remove new lines from the RSA public key file to get a one line string? So the question is if the key looks like this AAA BBB CCC or ...

rsa public-key keys encoding ssh  
user avatar asked by xpepermint Score of 43
user avatar answered by otus Score of 31

How is XOR used for encryption?

I am a programmer, so when I hear XOR, I think about the bitwise operator (e.g. 0110 ^ 1110 = 1000). The mention of "XOR" comes ...

encryption xor  
user avatar asked by IQAndreas Score of 29
user avatar answered by Nova Score of 28

How does one implement the Inverse of AES' MixColumns

I got an answer in the related question about Mixcolumn for encryption, but how about decryption? what will I do? Because it said that I will used this: During decryption the Mix Column the ...

encryption aes  
user avatar asked by goldroger Score of 4

If WhatsApp cannot read our message, how can the media forwarding happen in an instant?

WhatsApp says even the photos shared on its platform are end-to-end encrypted. When WhatsApp says encrypted I assume the data is encrypted in my device and then sent across to the recipient. When we ...

user avatar asked by 0xAB1E Score of 104
user avatar answered by fgrieu Score of 129

What's the appeal of using ChaCha20 instead of AES?

I read about ChaCha20 being used in TLS by Google, SSH, and towards standardization in general. What's the appeal of using something other than AES, what with AES receiving dedicated CPU instructions ...

tls chacha  
user avatar asked by JDĹ‚ugosz Score of 60
user avatar answered by Ruggero Score of 70

What is the difference between a digest and a hash function?

I was wondering about the difference between these two terms... What is the difference between a digest and a hash function?

hash terminology  
user avatar asked by sekmo Score of 86
user avatar answered by Awn Score of 103

Can you answer these questions?

Secure permutation of $E(\mathbb{F}_q)$ as a set for an elliptic curve $E$ over a finite field $\mathbb{F}_q$

Let $E$ be an elliptic curve over a finite field $\mathbb{F}_q$. For simplicity, let the group $E(\mathbb{F}_q)$ be of prime order. Assume that I know how to construct an efficiently computable ...

elliptic-curves protocol-design implementation cryptocurrency protocol-analysis  
user avatar asked by Dimitri Koshelev Score of 1

Why pairing domains are subgroups of the r-torsion group?

In pairing based cryptography (PBC) we restrict the pairing domains to be subgroups of the $r$-torsion group $E[r]$. This arises two questions to me: Why do we restrict them to subgroups of $E[r]$? ...

elliptic-curves pairings  
user avatar asked by Bean Guy Score of 1

Doing a chosen ciphertext attack against an unknown cipher

I am trying to attack an unknown cipher. I can do a chosen ciphertext attack on a file that is encrypted with this cipher. I changed 8 bytes of the encrypted input file at the offset 0x000308c0, the ...

cryptanalysis attack chosen-ciphertext-attack  
user avatar asked by Flole Score of 1
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