Prints out signature algorithm, as well as type and the length of the public key for a DER formated certifacted on STDIN

cert-type-length.go

package main

import (
        "crypto/ecdsa"
        "crypto/rsa"
        "crypto/x509"
        "fmt"
        "io/ioutil"
        "log"
        "os"
)

func main() {
        b, err := ioutil.ReadAll(os.Stdin)
        if err != nil {
                log.Fatal(err)
        }

        cert, err := x509.ParseCertificate(b)
        if err != nil {
                log.Fatal(err)
        }

        var length int
        switch v := cert.PublicKey.(type) {
        case *rsa.PublicKey:
                length = v.N.BitLen()
        case *ecdsa.PublicKey:
                length = v.Curve.Params().BitSize
        default:
                length = 0
        }

        fmt.Printf("SignatureAlgorithm: %-15v\tPublicKeyAlgorithm: %-15v\tPublicKeyLength: %d\n", cert.SignatureAlgorithm, cert.PublicKeyAlgorithm, length)
}

check.sh

for url in apple.com twitter.com netflix.com google.com facebook.com instagram.com; do 
  cipher=$(echo "" | openssl s_client -connect $url:443 -servername $url |& openssl x509 -outform der | go run main.go)
  printf "%-30s -> %s\n" "$url" "$cipher"; 
done