How to show the public key for a website certificate - ssl

Question

I've created a Go program to connect to a website and get the certificates it uses. I'm not sure how to get the correct representation of the public key.
I can fetch the certificate and I can type check on Certificate.PublicKey. Once I understand it's rsa.PublicKey or ecdsa.PublicKey I'd need to print the hex representation of it.
switch cert.PublicKey.(type) {
case *rsa.PublicKey:
logrus.Error("this is RSA")
// TODO: print hex representation of key
case *ecdsa.PublicKey:
logrus.Error("this is ECDSA")
// TODO: print hex representation of key
default:
fmt.Println("it's something else")
}
I'd expect it to print something like:
04 4B F9 47 1B A8 A8 CB A4 C6 C0 2D 45 DE 43 F3 BC F5 D2 98 F4 25 90 6F 13 0D 78 1A AC 05 B4 DF 7B F6 06 5C 80 97 9A 53 06 D0 DB 0E 15 AD 03 DE 14 09 D3 77 54 B1 4E 15 A8 AF E3 FD DC 9D AD E0 C5

Answer 1

it seems you are asking for the sha1 sum of the certificates involved.
here is a working example that asks for a host:port and prints the sums of the certificates involved
package main
import (
"crypto/sha1"
"crypto/tls"
"fmt"
"log"
"os"
)
func main() {
if len(os.Args) != 2 {
log.Panic("call with argument of host:port")
}
log.SetFlags(log.Lshortfile)
conf := &tls.Config{
//InsecureSkipVerify: true,
}
fmt.Printf("dialing:%s\n", os.Args[1])
conn, err := tls.Dial("tcp", os.Args[1], conf)
if err != nil {
log.Println(err)
return
}
defer conn.Close()
for i, v := range conn.ConnectionState().PeerCertificates {
//edit: use %X for uppercase hex printing
fmt.Printf("cert %d sha1 fingerprint:%x \n", i, sha1.Sum(v.Raw))
}
}
run as:
./golang-tls www.google.com:443
dialing:www.google.com:443
cert 0 sha1 fingerprint:34781c3be98cf958f514aecb1ae2e4e866effe34
cert 1 sha1 fingerprint:eeacbd0cb452819577911e1e6203db262f84a318
for general notions on SSL i have found this stackexchange answer to be extremely valuable.