check spf, dmarc, dkim

emailheader.go

package main 

import (
	"fmt"
	"net"
	"regexp"
	"encoding/base64"
	"crypto/x509"
	"crypto/rsa"
	// "math/big"
	"errors"
)

func LookupSPF(domain string) (string, error) {
	txtRecords, err := net.LookupTXT(domain)
	if err != nil {
		return "", err
	}

	for _, record := range txtRecords {
		match, _ := regexp.MatchString("^v=spf1.*", record)
		if match == true {
			return record, nil
		}
	}

	return "", nil
}

func LookupDMARC(domain string) (string, error) {
	dmarcDomain := "_dmarc." + domain
	txtRecords, err := net.LookupTXT(dmarcDomain)
	if err != nil {
		return "", err
	}

	for _, record := range txtRecords {
		match, _ := regexp.MatchString("^v=DMARC1.*", record)
		if match == true {
			return record, nil
		}
	}

	return "", nil
}
func LookupDKIM(domain string) (string, error) {
	dmarcDomain := "dkim._domainkey." + domain
	txtRecords, err := net.LookupTXT(dmarcDomain)
	if err != nil {
		return "", err
	}

	for _, record := range txtRecords {
		re := regexp.MustCompile(`v=DKIM1; k=rsa; p=(.*)$`)
		result := re.FindStringSubmatch(record)
		if len(result) > 1 {
			return result[1], nil
		} 
	}
	return "", errors.New("no dkim cert found")
}
func testPublicKey(k string) error {
	key, _ := base64.StdEncoding.DecodeString(k)
	re, err := x509.ParsePKIXPublicKey(key)
	pub := re.(*rsa.PublicKey)
	if err != nil {
		fmt.Println(err)
		return err
	}
	fmt.Println(pub.E, " ", pub.N)
	//why is this 32 bit not 2048 etc
	fmt.Println("bits: ", len(pub.N.Bits()))
	return nil
}

func main() {
	domain := "ryanair.com"
	result, err := LookupSPF(domain)
	if err != nil {
		fmt.Println("err: ", err)
	} else {
		fmt.Println("result: ", result)
	}
	result, err = LookupDMARC(domain)
	if err != nil {
		fmt.Println("err: ", err)
	} else {
		fmt.Println("result: ", result)
	}
	result, err = LookupDKIM(domain)
	if err != nil {
		fmt.Println("err: ", err)
	} else {
		fmt.Println("result: ", result)
		testPublicKey(result)
	}
	
}