The 2024 Developer Survey results are live! See the results

# Tag Info

### What's the difference between RSA and Diffie-Hellman?

Diffie-Hellman Key Exchange Problem: We have a symmetric encryption scheme and want to communicate. We don't want anybody else to have the key, so we can't say it out loud (or over a wire). Solution/...
• 861
Accepted

### What's the difference between RSA and Diffie-Hellman?

In practice, in situations like TLS, public key encryption will be used to encrypt a secret for encrypting the actual messages, as part of a hybrid cryptosystem. This is done because Asymmetric ...
• 19.7k

### Why is this not a viable key exchange algorithm?

I've simplified the Alice random bytes to ARB and Bob random bytes to BRB. Then the protocol follows as; Alice knows $key$ and $ARB$ and sends $$C_1 = key \oplus ARB$$ Bob knows $C_1$ and $BRB$ and ...
• 49.2k
Accepted

### What is a ratchet?

A ratchet is simply a device that only moves forward, one step at a time, much like fastening a tie rib (which is a ratchet device). So if you've got a state value in the past you can calculate all ...
• 93.6k

### Summarize the mathematical problem at the heart of breaking a Curve25519 public key

Six-word summary: the elliptic-curve discrete log problem. $\newcommand{\F}{\mathbb{F}}\newcommand{\Z}{\mathbb{Z}}$Summary with math: Given $x(A)$ and $x(P)$ for two points $A$ and $P$ on the elliptic ...
• 48.9k
Accepted

### After ECDH with Curve25519, is it pointless to use anything stronger than AES-128?

The reasoning is wrong, because the scaling of attacks on AES is qualitatively different from the scaling of attacks on X25519. A successful multi-target attack on a system using AES-128—that is, an ...
• 48.9k

### What is the key size currently used by RSA and Diffie-Hellman for secure communication over Internet?

A good overview on that matter can always be found on https://keylength.com, which summarises many publications with recommendations for key lengths. Especially NIST SP-800-38 yields good data for ...
• 2,528
Accepted

### What is the key size currently used by RSA and Diffie-Hellman for secure communication over Internet?

Currently (as of 2017-05-11) 2048-bit keys are most popular for use with RSA, and 2048 bit keys should also be used with classic Diffie-Hellman. These offer about the same security as a symmetric ...
• 2,297
Accepted

### DDH Assumption Not Holding

Here's the issue; the size of the multiplicative group is $p-1$; if $p>2$, then $p-1$ is even. What this means is that we can divide the group into two equal sized halves, the "even" elements (...
• 149k
Accepted

### Could Diffie-Hellman protocol serve as a zero-knowledge proof of knowledge of discrete logarithm?

This is an interesting question. In fact, cryptographers have been using this exact protocol on many occasions, and there are two important reasons to prefer Schnorr over this protocol in most ...
• 20.6k

### Why do we use groups, rings and fields in cryptography?

Kindly, let me know what was the actual problem which leads us to use groups in cyptogrpahy? Well, we use groups and other similar mathematical constructs because: We found there are problems that ...
• 149k
Accepted

### Does perfect forward secrecy (using DH or ECDH) imply quantum resistance?

No it does not. Perfect forward secrecy implies that even if you retrieve the private key of the asymmetric key pair that you cannot read any of the past or future messages within a connection. It is ...
• 93.6k
Accepted

### What are the differences between ephemeral-static ECDH and static-static ECDH?

Static static Diffie-Hellman isn't that commonplace. It uses two static key pairs (where both the public and private keys are static, not just the public key) to establish the secret. Generally those ...
• 93.6k