From 9dc89517ee8e790441b59d05f36b55a8bfbcc93a Mon Sep 17 00:00:00 2001
From: fiatjaf <fiatjaf@gmail.com>
Date: Mon, 27 Jan 2025 16:33:54 -0300
Subject: [PATCH] nip44: remove size limits.

implements https://github.com/nostr-protocol/nips/pull/1907
---
 nip44/nip44.go      | 40 +++++++++++++++++++++++++---------------
 nip44/nip44_test.go | 23 +++++++++++++++++++++++
 2 files changed, 48 insertions(+), 15 deletions(-)

diff --git a/nip44/nip44.go b/nip44/nip44.go
index 1590613..9a8d52c 100644
--- a/nip44/nip44.go
+++ b/nip44/nip44.go
@@ -21,10 +21,6 @@ import (
 
 const version byte = 2
 
-const (
-	MaxPlaintextSize = 0xffff // 65535 (64kb-1) => padded to 64kb
-)
-
 var zeroes = [32]byte{}
 
 type encryptOptions struct {
@@ -65,14 +61,22 @@ func Encrypt(plaintext string, conversationKey [32]byte, applyOptions ...func(op
 
 	plain := []byte(plaintext)
 	size := len(plain)
-	if size == 0 || size > MaxPlaintextSize {
-		return "", fmt.Errorf("plaintext should be between 1b and 64kB")
+	if size == 0 {
+		return "", fmt.Errorf("plaintext can't be empty")
 	}
 
 	padding := calcPadding(size)
-	padded := make([]byte, 2+padding)
-	binary.BigEndian.PutUint16(padded, uint16(size))
-	copy(padded[2:], plain)
+	var padded []byte
+
+	if size < (1 << 16) {
+		padded = make([]byte, 2+padding)
+		binary.BigEndian.PutUint16(padded[0:2], uint16(size))
+		copy(padded[2:], plain)
+	} else {
+		padded = make([]byte, 6+padding)
+		binary.BigEndian.PutUint32(padded[2:6], uint32(size))
+		copy(padded[6:], plain)
+	}
 
 	ciphertext, err := chacha(cc20key, cc20nonce, []byte(padded))
 	if err != nil {
@@ -95,7 +99,7 @@ func Encrypt(plaintext string, conversationKey [32]byte, applyOptions ...func(op
 
 func Decrypt(b64ciphertextWrapped string, conversationKey [32]byte) (string, error) {
 	cLen := len(b64ciphertextWrapped)
-	if cLen < 132 || cLen > 87472 {
+	if cLen < 132 {
 		return "", fmt.Errorf("invalid payload length: %d", cLen)
 	}
 	if b64ciphertextWrapped[0:1] == "#" {
@@ -112,7 +116,7 @@ func Decrypt(b64ciphertextWrapped string, conversationKey [32]byte) (string, err
 	}
 
 	dLen := len(decoded)
-	if dLen < 99 || dLen > 65603 {
+	if dLen < 99 {
 		return "", fmt.Errorf("invalid data length: %d", dLen)
 	}
 
@@ -139,13 +143,19 @@ func Decrypt(b64ciphertextWrapped string, conversationKey [32]byte) (string, err
 		return "", err
 	}
 
-	unpaddedLen := binary.BigEndian.Uint16(padded[0:2])
-	if unpaddedLen == 0 || unpaddedLen > MaxPlaintextSize || len(padded) != 2+calcPadding(int(unpaddedLen)) {
+	unpaddedLen := int(binary.BigEndian.Uint16(padded[0:2]))
+	offset := 2
+	if unpaddedLen == 0 {
+		unpaddedLen = int(binary.BigEndian.Uint32(padded[2:6]))
+		offset = 6
+	}
+
+	if unpaddedLen < 1 || len(padded) != offset+calcPadding(unpaddedLen) {
 		return "", fmt.Errorf("invalid padding")
 	}
 
-	unpadded := padded[2:][:unpaddedLen]
-	if len(unpadded) == 0 || len(unpadded) != int(unpaddedLen) {
+	unpadded := padded[offset : offset+unpaddedLen]
+	if len(unpadded) == 0 || len(unpadded) != unpaddedLen {
 		return "", fmt.Errorf("invalid padding")
 	}
 
diff --git a/nip44/nip44_test.go b/nip44/nip44_test.go
index ff526d0..a1b93c9 100644
--- a/nip44/nip44_test.go
+++ b/nip44/nip44_test.go
@@ -3,6 +3,7 @@ package nip44
 import (
 	"crypto/sha256"
 	"encoding/hex"
+	"strings"
 	"testing"
 
 	"fiatjaf.com/nostr"
@@ -1053,3 +1054,25 @@ func hexDecode32Array(hexString string) (res [32]byte, err error) {
 	_, err = hex.Decode(res[:], []byte(hexString))
 	return res, err
 }
+
+func TestEncryptDecryptLargePayload(t *testing.T) {
+	sk1, err := nostr.SecretKeyFromHex("0000000000000000000000000000000000000000000000000000000000000001")
+	require.NoError(t, err)
+	pub1 := nostr.GetPublicKey(sk1)
+
+	sk2, err := nostr.SecretKeyFromHex("0000000000000000000000000000000000000000000000000000000000000002")
+	require.NoError(t, err)
+
+	convKey, err := GenerateConversationKey(pub1, sk2)
+	require.NoError(t, err)
+
+	plaintext := strings.Repeat("a", 10_000_000)
+
+	ciphertext, err := Encrypt(plaintext, convKey)
+	require.NoError(t, err)
+
+	decrypted, err := Decrypt(ciphertext, convKey)
+	require.NoError(t, err)
+
+	require.Equal(t, plaintext, decrypted)
+}