Reputation: 137
I am generating a KeyPair for ECC from curve 'secp128r1' using openssl
Steps I followed :
first I generated a private key using the command
openssl ecparam -genkey -name secp128r1 -noout -out private.pem
then i viewed the corresponding public key using the command
openssl ec -in private.pem -text -noout
which showed an output as :
read EC key
Private-Key: (128 bit)
priv:
00:9f:bf:2b:bd:06:86:3a:a1:bc:7c:3e:90:57:40:
f4:bc
pub:
04:04:ce:24:34:d4:cb:f2:58:94:2f:8a:5f:06:d7:
3f:ed:5a:50:ef:fb:cc:b7:49:62:16:62:9e:aa:d5:
30:a8:a5
ASN1 OID: secp128r1
I want explicitly x and y components from the public key generated here, please can anyone suggest the correct way of doing this ?
The above public key is 264 bits long, hence cannot take(/split) it as is
Thanks
Upvotes: 10
Views: 18869
Reputation: 878
If anyone wants to do this in nodejs, as i did when needing to share public Keys (jwk) for other people/apps to verify my signatures... here is a quick way to derive the X and Y coordinates from an secp256k1 public key:
import base64url from 'base64url';
function getCoordinatesFromSecp256k1PublicKey(uncompressedHexPubKey: string) {
const publicKeyBuff = Buffer.from(uncompressedHexPubKey, 'hex');
const pubKeyCoordsBuff = publicKeyBuff.slice(1); // First byte just signals that it is uncompressed. TRASH!
const halfLen = Buffer.byteLength(pubKeyCoordsBuff) / 2; // should be 32;
const x = pubKeyCoordsBuff.slice(0, halfLen);
const y = pubKeyCoordsBuff.slice(halfLen, Buffer.byteLength(pubKeyCoordsBuff) + 1);
return {
x: base64url.fromBase64(x.toString('base64')),
y: base64url.fromBase64(y.toString('base64'))
};
}
This way you can return your JWK data thusly:
const { x, y } = getCoordinatesFromSecp256k1PublicKey(pubKey);
JSON.stringify(
{
use: 'sig',
kid: 'my-keyid',
alg: 'ECDSA',
kty: 'EC',
crv: 'P-256',
x,
y,
},
null,
2
)
Upvotes: 1
Reputation: 2500
Pub:
04:04:ce:24:34:d4:cb:f2:58:94:2f:8a:5f:06:d7:
3f:ed:5a:50:ef:fb:cc:b7:49:62:16:62:9e:aa:d5:
30:a8:a5
0x04
indicates uncompressed form04:ce:24:34:d4:cb:f2:58:94:2f:8a:5f:06:d7:3f:ed
5a:50:ef:fb:cc:b7:49:62:16:62:9e:aa:d5:30:a8:a5
UPD. Found this website that contains further details.
Upvotes: 18