From 994071243fc80990cf09e820b671006e9bd31c76 Mon Sep 17 00:00:00 2001
From: Gab <24553253+gabrix73@users.noreply.github.com>
Date: Thu, 13 Aug 2026 14:04:30 +0200
Subject: Separate active YAMN code from Katzenpost PoC

---
 katzenpost/dispatcher/envelope.go | 45 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 katzenpost/dispatcher/envelope.go

(limited to 'katzenpost/dispatcher/envelope.go')

diff --git a/katzenpost/dispatcher/envelope.go b/katzenpost/dispatcher/envelope.go
new file mode 100644
index 0000000..b9ff7b8
--- /dev/null
+++ b/katzenpost/dispatcher/envelope.go
@@ -0,0 +1,45 @@
+package dispatcher
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"net/mail"
+	"strings"
+)
+
+const MaxEnvelopeBytes = 64 * 1024
+
+// Envelope is the only application payload accepted by the dispatcher. Message
+// must already be a complete YAMN transport envelope, not user supplied mail.
+type Envelope struct {
+	EntryAddress string `json:"entry_address"`
+	Message      []byte `json:"message"`
+}
+
+func (e Envelope) Validate(allowedDomains map[string]struct{}) error {
+	if len(e.Message) == 0 || len(e.Message) > MaxEnvelopeBytes {
+		return fmt.Errorf("invalid YAMN envelope size")
+	}
+	if bytes.Contains(e.Message, []byte("\r")) {
+		return errors.New("YAMN envelope must use LF line endings")
+	}
+	address, err := mail.ParseAddress(e.EntryAddress)
+	if err != nil || address.Address != e.EntryAddress {
+		return errors.New("invalid entry remailer address")
+	}
+	parts := strings.Split(address.Address, "@")
+	if len(parts) != 2 || parts[0] == "" || parts[1] == "" {
+		return errors.New("invalid entry remailer address")
+	}
+	if _, ok := allowedDomains[strings.ToLower(parts[1])]; !ok {
+		return errors.New("entry remailer domain is not allowed")
+	}
+	if !bytes.HasPrefix(e.Message, []byte("To: "+e.EntryAddress+"\n")) {
+		return errors.New("YAMN envelope recipient does not match entry remailer")
+	}
+	if !bytes.Contains(e.Message, []byte("-----BEGIN REMAILER MESSAGE-----\n")) {
+		return errors.New("invalid YAMN envelope")
+	}
+	return nil
+}
-- 
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