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// reader.go largerly mimics github.com/emersion/go-gpgmail, with changes made
// to interface with the gpg package in aerc
package gpg
import (
"bufio"
"bytes"
"fmt"
"io"
"mime"
"strings"
"git.sr.ht/~rjarry/aerc/lib/crypto/gpg/gpgbin"
"git.sr.ht/~rjarry/aerc/models"
"github.com/emersion/go-message/textproto"
)
type Reader struct {
Header textproto.Header
MessageDetails *models.MessageDetails
}
func NewReader(h textproto.Header, body io.Reader) (*Reader, error) {
t, params, err := mime.ParseMediaType(h.Get("Content-Type"))
if err != nil {
return nil, err
}
if strings.EqualFold(t, "multipart/encrypted") && strings.EqualFold(params["protocol"], "application/pgp-encrypted") {
mr := textproto.NewMultipartReader(body, params["boundary"])
return newEncryptedReader(h, mr)
}
if strings.EqualFold(t, "multipart/signed") && strings.EqualFold(params["protocol"], "application/pgp-signature") {
micalg := params["micalg"]
mr := textproto.NewMultipartReader(body, params["boundary"])
return newSignedReader(h, mr, micalg)
}
var headerBuf bytes.Buffer
_ = textproto.WriteHeader(&headerBuf, h)
return &Reader{
Header: h,
MessageDetails: &models.MessageDetails{
Body: io.MultiReader(&headerBuf, body),
},
}, nil
}
func Read(r io.Reader) (*Reader, error) {
br := bufio.NewReader(r)
h, err := textproto.ReadHeader(br)
if err != nil {
return nil, err
}
return NewReader(h, br)
}
func newEncryptedReader(h textproto.Header, mr *textproto.MultipartReader) (*Reader, error) {
p, err := mr.NextPart()
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to read first part in multipart/encrypted message: %w", err)
}
t, _, err := mime.ParseMediaType(p.Header.Get("Content-Type"))
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to parse Content-Type of first part in multipart/encrypted message: %w", err)
}
if !strings.EqualFold(t, "application/pgp-encrypted") {
return nil, fmt.Errorf("gpgmail: first part in multipart/encrypted message has type %q, not application/pgp-encrypted", t)
}
metadata, err := textproto.ReadHeader(bufio.NewReader(p))
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to parse application/pgp-encrypted part: %w", err)
}
if s := metadata.Get("Version"); s != "1" {
return nil, fmt.Errorf("gpgmail: unsupported PGP/MIME version: %q", s)
}
p, err = mr.NextPart()
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to read second part in multipart/encrypted message: %w", err)
}
t, _, err = mime.ParseMediaType(p.Header.Get("Content-Type"))
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to parse Content-Type of second part in multipart/encrypted message: %w", err)
}
if !strings.EqualFold(t, "application/octet-stream") {
return nil, fmt.Errorf("gpgmail: second part in multipart/encrypted message has type %q, not application/octet-stream", t)
}
md, err := gpgbin.Decrypt(p)
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to read PGP message: %w", err)
}
cleartext := bufio.NewReader(md.Body)
cleartextHeader, err := textproto.ReadHeader(cleartext)
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to read encrypted header: %w", err)
}
t, params, err := mime.ParseMediaType(cleartextHeader.Get("Content-Type"))
if err != nil {
return nil, err
}
if md.IsEncrypted && !md.IsSigned && strings.EqualFold(t, "multipart/signed") && strings.EqualFold(params["protocol"], "application/pgp-signature") {
// RFC 1847 encapsulation, see RFC 3156 section 6.1
micalg := params["micalg"]
mr := textproto.NewMultipartReader(cleartext, params["boundary"])
mds, err := newSignedReader(cleartextHeader, mr, micalg)
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to read encapsulated multipart/signed message: %w", err)
}
mds.MessageDetails.IsEncrypted = md.IsEncrypted
mds.MessageDetails.DecryptedWith = md.DecryptedWith
mds.MessageDetails.DecryptedWithKeyId = md.DecryptedWithKeyId
return mds, nil
}
var headerBuf bytes.Buffer
_ = textproto.WriteHeader(&headerBuf, cleartextHeader)
md.Body = io.MultiReader(&headerBuf, cleartext)
return &Reader{
Header: h,
MessageDetails: md,
}, nil
}
func newSignedReader(h textproto.Header, mr *textproto.MultipartReader, micalg string) (*Reader, error) {
micalg = strings.ToLower(micalg)
p, err := mr.NextPart()
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to read signed part in multipart/signed message: %w", err)
}
var headerBuf bytes.Buffer
_ = textproto.WriteHeader(&headerBuf, p.Header)
var msg bytes.Buffer
headerRdr := bytes.NewReader(headerBuf.Bytes())
fullMsg := io.MultiReader(headerRdr, p)
_, _ = io.Copy(&msg, fullMsg)
sig, err := mr.NextPart()
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to read pgp part in multipart/signed message: %w", err)
}
md, err := gpgbin.Verify(&msg, sig)
if err != nil {
return nil, fmt.Errorf("gpgmail: failed to read PGP message: %w", err)
}
if md.Micalg != micalg && md.SignatureError == "" {
md.SignatureError = "gpg: header hash does not match actual sig hash"
}
return &Reader{
Header: h,
MessageDetails: md,
}, nil
}
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