Score:1

How to calculate ECDSA compressed public key in HEX?

pl flag
ah_

I am given the ECDSA public key x and y coordinates below, calculate the compressed public key in HEX:

PubKey.X :

61702053028733271054209908027052318932346644879827564097906752978487519734153

PubKey.Y :

107222915356196552656214196479588207773590978294786246589469812962187242002272

How do I find the Compressed PubKey?

For example, say Alice generates a private key ‘a' (currently these kinds of keys are 2,000 to 4,000 bits long for security), and Bob generates a private key 'b’. Knowing g and n, Alice can calculate her public key as ga mod n, and Bob his public key as gb mod n, and, given a sufficiently large n (again 2,000 to 4,000 bits) it's impossible for anyone to figure out what a or b are without brute-force checking all the possibilities g1 mod n, g2 mod n, … etc.

From there, Alice and Bob can exchange their public keys knowing it won’t expose their private keys, and then they can use the properties of exponentiation to derive the same secret value:

sv = (ga)b mod n = (gb)a mod n
Maarten Bodewes avatar
in flag
Everything after "How do I find the Compressed PubKey?" seems to be a bad description of ECDH with key sizes and problem description more like RSA than ECDH. What have you actually tried and read?
knaccc avatar
es flag
This question is gibberish, and there is no reason for the ripemd tag
fgrieu avatar
ng flag
The question asks to perform [sec1v2 §2.3.3](https://www.secg.org/sec1-v2.pdf#subsubsection.2.3.3). Step 2.2.1 applies. The only part where a computer is useful is converting PubKey.X to hexadecimal.
I sit in a Tesla and translated this thread with Ai:

mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.