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package dkim
import (
"crypto/rsa"
"crypto/x509"
"encoding/base64"
"io/ioutil"
"mime/quotedprintable"
"net"
"strings"
)
// PubKeyRep represents a parsed version of public key record
type PubKeyRep struct {
Version string
HashAlgo []string
KeyType string
Note string
PubKey rsa.PublicKey
ServiceType []string
FlagTesting bool // flag y
FlagIMustBeD bool // flag i
}
// DNSOptions holds settings for looking up DNS records
type DNSOptions struct {
netLookupTXT func(name string) ([]string, error)
}
// DNSOpt represents an optional setting for looking up DNS records
type DNSOpt interface {
apply(*DNSOptions)
}
type dnsOpt func(*DNSOptions)
func (opt dnsOpt) apply(dnsOpts *DNSOptions) {
opt(dnsOpts)
}
// DNSOptLookupTXT sets the function to use to lookup TXT records.
//
// This should probably only be used in tests.
func DNSOptLookupTXT(netLookupTXT func(name string) ([]string, error)) DNSOpt {
return dnsOpt(func(opts *DNSOptions) {
opts.netLookupTXT = netLookupTXT
})
}
// NewPubKeyRespFromDNS retrieves the TXT record from DNS based on the specified domain and selector
// and parses it.
func NewPubKeyRespFromDNS(selector, domain string, opts ...DNSOpt) (*PubKeyRep, verifyOutput, error) {
dnsOpts := DNSOptions{}
for _, opt := range opts {
opt.apply(&dnsOpts)
}
if dnsOpts.netLookupTXT == nil {
dnsOpts.netLookupTXT = net.LookupTXT
}
txt, err := dnsOpts.netLookupTXT(selector + "._domainkey." + domain)
if err != nil {
if strings.HasSuffix(err.Error(), "no such host") {
return nil, PERMFAIL, ErrVerifyNoKeyForSignature
}
return nil, TEMPFAIL, ErrVerifyKeyUnavailable
}
// empty record
if len(txt) == 0 {
return nil, PERMFAIL, ErrVerifyNoKeyForSignature
}
// parsing, we keep the first record
// TODO: if there is multiple record
return NewPubKeyResp(txt[0])
}
// NewPubKeyResp parses DKIM record (usually from DNS)
func NewPubKeyResp(dkimRecord string) (*PubKeyRep, verifyOutput, error) {
pkr := new(PubKeyRep)
pkr.Version = "DKIM1"
pkr.HashAlgo = []string{"sha1", "sha256"}
pkr.KeyType = "rsa"
pkr.FlagTesting = false
pkr.FlagIMustBeD = false
p := strings.Split(dkimRecord, ";")
for i, data := range p {
keyVal := strings.SplitN(data, "=", 2)
val := ""
if len(keyVal) > 1 {
val = strings.TrimSpace(keyVal[1])
}
switch strings.ToLower(strings.TrimSpace(keyVal[0])) {
case "v":
// RFC: is this tag is specified it MUST be the first in the record
if i != 0 {
return nil, PERMFAIL, ErrVerifyTagVMustBeTheFirst
}
pkr.Version = val
if pkr.Version != "DKIM1" {
return nil, PERMFAIL, ErrVerifyVersionMusBeDkim1
}
case "h":
p := strings.Split(strings.ToLower(val), ":")
pkr.HashAlgo = []string{}
for _, h := range p {
h = strings.TrimSpace(h)
if h == "sha1" || h == "sha256" {
pkr.HashAlgo = append(pkr.HashAlgo, h)
}
}
// if empty switch back to default
if len(pkr.HashAlgo) == 0 {
pkr.HashAlgo = []string{"sha1", "sha256"}
}
case "k":
if strings.ToLower(val) != "rsa" {
return nil, PERMFAIL, ErrVerifyBadKeyType
}
case "n":
qp, err := ioutil.ReadAll(quotedprintable.NewReader(strings.NewReader(val)))
if err == nil {
val = string(qp)
}
pkr.Note = val
case "p":
rawkey := val
if rawkey == "" {
return nil, PERMFAIL, ErrVerifyRevokedKey
}
un64, err := base64.StdEncoding.DecodeString(rawkey)
if err != nil {
return nil, PERMFAIL, ErrVerifyBadKey
}
pk, err := x509.ParsePKIXPublicKey(un64)
if pk, ok := pk.(*rsa.PublicKey); ok {
pkr.PubKey = *pk
}
case "s":
t := strings.Split(strings.ToLower(val), ":")
for _, tt := range t {
tt = strings.TrimSpace(tt)
switch tt {
case "*":
pkr.ServiceType = append(pkr.ServiceType, "all")
case "email":
pkr.ServiceType = append(pkr.ServiceType, tt)
}
}
case "t":
flags := strings.Split(strings.ToLower(val), ":")
for _, flag := range flags {
flag = strings.TrimSpace(flag)
switch flag {
case "y":
pkr.FlagTesting = true
case "s":
pkr.FlagIMustBeD = true
}
}
}
}
// if no pubkey
if pkr.PubKey == (rsa.PublicKey{}) {
return nil, PERMFAIL, ErrVerifyNoKey
}
// No service type
if len(pkr.ServiceType) == 0 {
pkr.ServiceType = []string{"all"}
}
return pkr, SUCCESS, nil
}
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