128 lines
2.8 KiB
Go
128 lines
2.8 KiB
Go
package dkim
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import (
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"crypto/rsa"
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"crypto/x509"
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"encoding/base64"
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"net"
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"strings"
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)
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// pubKeyRep represents a parsed version of public key record
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type pubKeyRep struct {
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Version string
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HashAlgo []string
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KeyType string
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Note string
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PubKey rsa.PublicKey
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ServiceType []string
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FlagTesting bool // flag y
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FlagIMustBeD bool // flag i
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}
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func newPubKeyFromDnsTxt(selector, domain string) (*pubKeyRep, error) {
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txt, err := net.LookupTXT(selector + "._domainkey." + domain)
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if err != nil {
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if strings.HasSuffix(err.Error(), "no such host") {
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return nil, ErrVerifyNoKeyForSignature
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} else {
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return nil, ErrVerifyKeyUnavailable
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}
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}
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// empty record
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if len(txt) == 0 {
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return nil, ErrVerifyNoKeyForSignature
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}
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pkr := new(pubKeyRep)
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pkr.Version = "DKIM1"
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pkr.HashAlgo = []string{"sha1", "sha256"}
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pkr.KeyType = "rsa"
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pkr.ServiceType = []string{"all"}
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pkr.FlagTesting = false
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pkr.FlagIMustBeD = false
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// parsing, we keep the first record
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// TODO: if there is multiple record
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p := strings.Split(txt[0], ";")
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for i, data := range p {
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keyVal := strings.SplitN(data, "=", 2)
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val := ""
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if len(keyVal) > 1 {
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val = strings.TrimSpace(keyVal[1])
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}
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switch strings.ToLower(strings.TrimSpace(keyVal[0])) {
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case "v":
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// RFC: is this tag is specified it MUST be the first in the record
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if i != 0 {
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return nil, ErrVerifyTagVMustBeTheFirst
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}
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pkr.Version = val
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if pkr.Version != "DKIM1" {
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return nil, ErrVerifyVersionMusBeDkim1
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}
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case "h":
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p := strings.Split(strings.ToLower(val), ":")
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pkr.HashAlgo = []string{}
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for _, h := range p {
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h = strings.TrimSpace(h)
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if h == "sha1" || h == "sha256" {
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pkr.HashAlgo = append(pkr.HashAlgo, h)
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}
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}
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// if empty switch back to default
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if len(pkr.HashAlgo) == 0 {
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pkr.HashAlgo = []string{"sha1", "sha256"}
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}
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case "k":
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if strings.ToLower(val) != "rsa" {
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return nil, ErrVerifyBadKeyType
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}
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case "n":
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pkr.Note = val
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case "p":
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rawkey := val
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if rawkey == "" {
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return nil, ErrVerifyRevokedKey
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}
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un64, err := base64.StdEncoding.DecodeString(rawkey)
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if err != nil {
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return nil, ErrVerifyBadKey
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}
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pk, err := x509.ParsePKIXPublicKey(un64)
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pkr.PubKey = *pk.(*rsa.PublicKey)
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case "s":
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t := strings.Split(strings.ToLower(val), ":")
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for _, tt := range t {
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if tt == "*" {
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pkr.ServiceType = []string{"all"}
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break
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}
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if tt == "email" {
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pkr.ServiceType = []string{"email"}
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}
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}
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case "t":
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flags := strings.Split(strings.ToLower(val), ":")
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for _, flag := range flags {
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if flag == "y" {
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pkr.FlagTesting = true
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continue
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}
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if flag == "s" {
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pkr.FlagIMustBeD = true
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}
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}
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}
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}
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// if no pubkey
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if pkr.PubKey == (rsa.PublicKey{}) {
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return nil, ErrVerifyNoKey
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}
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return pkr, nil
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}
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