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Fix DKIM signing for multipart messages #45

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merged 2 commits into from
Jul 1, 2024
Merged

Fix DKIM signing for multipart messages #45

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9918cb8
Update go-mail library to v0.4.2
wneessen Jul 1, 2024
1ab85ff
Add random boundary generation to DKIM middleware
wneessen Jul 1, 2024
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22 changes: 19 additions & 3 deletions dkim/dkim.go
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,7 @@ import (
"bytes"
"crypto"
"crypto/ed25519"
"crypto/rand"
"crypto/x509"
"encoding/pem"
"errors"
Expand Down Expand Up @@ -75,14 +76,19 @@ func NewFromEd25519Key(k []byte, sc *SignerConfig) (*Middleware, error) {

// Handle is the handler method that satisfies the mail.Middleware interface
func (d Middleware) Handle(m *mail.Msg) *mail.Msg {
ibuf := bytes.Buffer{}
_, err := m.WriteToSkipMiddleware(&ibuf, Type)
// If no boundary is set for the mail.Msg we need to set our own fixed boundary, otherwise
// a new boundary will bet generated after the middleware has been applied and therfore
// the body hash will be altered
// TODO: Add a GetBoundary() method to go-mail, so we don't override a already set boundary
m.SetBoundary(randomBoundary())
ibuf := bytes.NewBuffer(nil)
_, err := m.WriteToSkipMiddleware(ibuf, Type)
if err != nil {
return m
}

var obuf bytes.Buffer
if err := dkim.Sign(&obuf, &ibuf, d.so); err != nil {
if err := dkim.Sign(&obuf, ibuf, d.so); err != nil {
return m
}
br := bufio.NewReader(&obuf)
Expand Down Expand Up @@ -157,3 +163,13 @@ func extractDKIMHeader(br *bufio.Reader) (string, error) {
}
return "", nil
}

// randomBoundary generates boundary in case no boundary is set yet
func randomBoundary() string {
var buf [30]byte
_, err := io.ReadFull(rand.Reader, buf[:])
if err != nil {
panic(err)
}
return fmt.Sprintf("%x", buf[:])
}
2 changes: 1 addition & 1 deletion go.mod
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,6 @@ go 1.16
require (
github.com/ProtonMail/gopenpgp/v2 v2.7.5
github.com/emersion/go-msgauth v0.6.8
github.com/wneessen/go-mail v0.4.1
github.com/wneessen/go-mail v0.4.2
golang.org/x/text v0.16.0
)
4 changes: 2 additions & 2 deletions go.sum
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Original file line number Diff line number Diff line change
Expand Up @@ -27,8 +27,8 @@ github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+
github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
github.com/wneessen/go-mail v0.4.1 h1:m2rSg/sc8FZQCdtrV5M8ymHYOFrC6KJAQAIcgrXvqoo=
github.com/wneessen/go-mail v0.4.1/go.mod h1:zxOlafWCP/r6FEhAaRgH4IC1vg2YXxO0Nar9u0IScZ8=
github.com/wneessen/go-mail v0.4.2 h1:wISuU9LOGqrA7pxy7OipRtwoExXTzuGKmAjb8gYwc00=
github.com/wneessen/go-mail v0.4.2/go.mod h1:zxOlafWCP/r6FEhAaRgH4IC1vg2YXxO0Nar9u0IScZ8=
github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
Expand Down
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