v2: Fixed block size with padding (#3)

README.md

@@ -1,16 +1,18 @@
 # pull-secretstream
 
-replacement for [`pull-box-stream`](https://github.com/dominictarr/pull-box-stream) using libsodium's [secretstream](https://libsodium.gitbook.io/doc/secret-key_cryptography/secretstream)
+Replacement for [`pull-box-stream`](https://github.com/dominictarr/pull-box-stream) using libsodium's [secretstream](https://libsodium.gitbook.io/doc/secret-key_cryptography/secretstream)
 
-## example
+Uses a fixed ciphertext block size. (By default: 512 bytes.)
+
+## Example
 
 ```js
 const { randomBytes } = require('crypto')
 const pull = require('pull-stream')
-const { KEYBYTES, createEncryptStream, createDecryptStream } = require('pull-secretstream')
+const { KEY_SIZE, createEncryptStream, createDecryptStream } = require('pull-secretstream')
 
-// generate a random secret, `KEYBYTES` bytes long.
-const key = randomBytes(KEYBYTES)
+// generate a random secret, `KEY_SIZE` bytes long.
+const key = randomBytes(KEY_SIZE)
 
 const plaintext1 = Buffer.from('hello world')
 
@@ -34,3 +36,33 @@ pull(
   }),
 )
 ```
+
+## API
+
+### `createEncryptStream(key, ciphertextBlockSize = DEFAULT_BLOCK_SIZE)`
+
+Returns a "through" pull-stream that:
+
+- first sends the secretstream header,
+- then encrypts incoming plaintext as secretstream ciphertext (of a fixed block size, padding if necessary),
+- and when done, sends a secrestream message marked as the final.
+
+### `createDecryptStream(key, ciphertextBlockSize = DEFAULT_BLOCK_SIZE)`
+
+Returns a "through" pull-stream that:
+
+- first recives the secretstream header,
+- then decrypts incoming secretstream ciphertext as plaintext (unpadding if necessary),
+- and is done when a secretstream message marked as final is received.
+
+### `DEFAULT_BLOCK_SIZE`
+
+512 bytes
+
+### `KEY_SIZE`
+
+32 bytes
+
+### `getPlaintextBlockSize(ciphertextBlockSize)`
+
+`cipherBlockSize` - 17 bytes (secretstream's additional data)

examples/readme.js

@@ -1,9 +1,9 @@
 const { randomBytes } = require('crypto')
 const pull = require('pull-stream')
-const { KEYBYTES, createEncryptStream, createDecryptStream } = require('../')
+const { KEY_SIZE, createEncryptStream, createDecryptStream } = require('../')
 
-// generate a random secret, `KEYBYTES` bytes long.
-const key = randomBytes(KEYBYTES)
+// generate a random secret, `KEY_SIZE` bytes long.
+const key = randomBytes(KEY_SIZE)
 
 const plaintext1 = Buffer.from('hello world')
 

package.json

@@ -27,13 +27,15 @@
   },
   "homepage": "https://github.com/ahdinosaur/pull-secretstream#readme",
   "dependencies": {
+    "bl": "^6.0.8",
     "debug": "^4.3.4",
     "pull-cat": "^1.1.11",
     "pull-header": "^0.0.0",
     "pull-map-last": "^1.0.0",
     "pull-reader": "^1.3.1",
     "pull-stream": "^3.7.0",
     "pull-through": "^1.0.18",
-    "sodium-secretstream": "^1.1.0"
+    "sodium-secretstream": "^1.1.0",
+    "sodium-universal": "^4.0.0"
   }
 }

src/index.js

@@ -1,9 +1,13 @@
-const { KEYBYTES, HEADERBYTES, Push, Pull } = require('sodium-secretstream')
+const { KEYBYTES, HEADERBYTES, ABYTES, Push, Pull } = require('sodium-secretstream')
+const { BufferList } = require('bl')
 const pull = require('pull-stream/pull')
 const pullCat = require('pull-cat')
 const pullHeader = require('pull-header')
 const pullThrough = require('pull-through')
 const createDebug = require('debug')
+const { sodium_pad, sodium_unpad } = require('sodium-universal')
+
+const DEFAULT_BLOCK_SIZE = 512 // bytes
 
 createDebug.formatters.h = (v) => {
   return v.toString('hex')
@@ -12,18 +16,26 @@ createDebug.formatters.h = (v) => {
 const debug = createDebug('pull-secretstream')
 
 module.exports = {
-  KEYBYTES,
+  KEY_SIZE: KEYBYTES,
+  DEFAULT_BLOCK_SIZE,
   createEncryptStream,
   createDecryptStream,
+  getPlaintextBlockSize,
+}
+
+function getPlaintextBlockSize(ciphertextBlockSize = DEFAULT_BLOCK_SIZE) {
+  return ciphertextBlockSize - ABYTES
 }
 
-function createEncryptStream(key) {
+function createEncryptStream(key, ciphertextBlockSize = DEFAULT_BLOCK_SIZE) {
   if (key.length !== KEYBYTES) {
     throw new Error(`pull-secretstream/createEncryptStream: key must be byte length of ${KEYBYTES}`)
   }
-  const debugKey = key.slice(0, 2)
 
+  const debugKey = key.slice(0, 2)
   const encrypter = new Push(key)
+  const plaintextBlockSize = getPlaintextBlockSize(ciphertextBlockSize)
+  const plaintextBufferList = new BufferList()
 
   const sendHeader = () => {
     let hasSentHeader = false
@@ -42,13 +54,36 @@ function createEncryptStream(key) {
 
   const encryptMap = pullThrough(
     function encryptThroughData(plaintext) {
-      debug('%h : encrypting plaintext %h', debugKey, plaintext)
-      const ciphertext = encrypter.next(plaintext)
-      debug('%h : encrypted ciphertext %h', debugKey, ciphertext)
-      this.queue(ciphertext)
+      plaintextBufferList.append(plaintext)
+
+      // while we still have enough bytes to send full blocks
+      while (plaintextBufferList.length >= plaintextBlockSize) {
+        const plaintextBlock = plaintextBufferList.slice(0, plaintextBlockSize)
+        plaintextBufferList.consume(plaintextBlockSize)
+        debug('%h : encrypting block %h', debugKey, plaintextBlock)
+        const ciphertext = encrypter.next(plaintextBlock)
+        debug('%h : encrypted ciphertext %h', debugKey, ciphertext)
+        this.queue(ciphertext)
+      }
+
+      // send the remaining as a padded block
+      if (plaintextBufferList.length > 0) {
+        const plaintextLength = plaintextBufferList.length
+        const plaintextBlock = Buffer.alloc(plaintextBlockSize)
+        plaintextBufferList.copy(plaintextBlock, 0, 0, plaintextLength)
+        plaintextBufferList.consume(plaintextLength)
+        sodium_pad(plaintextBlock, plaintextLength, plaintextBlockSize)
+        debug('%h : encrypting padded block %h', debugKey, plaintextBlock)
+        const ciphertext = encrypter.next(plaintextBlock)
+        debug('%h : encrypted ciphertext %h', debugKey, ciphertext)
+        this.queue(ciphertext)
+      }
     },
     function encryptThroughEnd() {
-      const final = encrypter.final()
+      // send a block full of zeros with the final marker
+      const finalBlock = Buffer.alloc(plaintextBlockSize)
+      sodium_pad(finalBlock, 0, plaintextBlockSize)
+      const final = encrypter.final(finalBlock, Buffer.allocUnsafe(plaintextBlockSize + ABYTES))
       debug('%h : encrypter final %h', debugKey, final)
       this.queue(final)
       this.queue(null)
@@ -60,13 +95,15 @@ function createEncryptStream(key) {
   }
 }
 
-function createDecryptStream(key) {
+function createDecryptStream(key, ciphertextBlockSize = DEFAULT_BLOCK_SIZE) {
   if (key.length !== KEYBYTES) {
     throw new Error(`pull-secretstream/createDecryptStream: key must be byte length of ${KEYBYTES}`)
   }
-  const debugKey = key.slice(0, 2)
 
+  const debugKey = key.slice(0, 2)
   const decrypter = new Pull(key)
+  const plaintextBlockSize = getPlaintextBlockSize(ciphertextBlockSize)
+  const ciphertextBufferList = new BufferList()
 
   const receiveHeader = pullHeader(HEADERBYTES, (header) => {
     debug('%h : decrypter receiving header %h', debugKey, header)
@@ -75,13 +112,29 @@ function createDecryptStream(key) {
 
   const decryptMap = pullThrough(
     function decryptThroughData(ciphertext) {
-      debug('%h : decrypting ciphertext %h', debugKey, ciphertext)
-      const plaintext = decrypter.next(ciphertext)
-      debug('%h : decrypted ciphertext %h', debugKey, plaintext)
-      this.queue(plaintext)
-      if (decrypter.final) {
-        debug('%h : decrypter final', debugKey)
-        this.emit('end')
+      ciphertextBufferList.append(ciphertext)
+
+      // while we still have enough bytes for full blocks
+      while (ciphertextBufferList.length >= ciphertextBlockSize) {
+        const ciphertextBlock = ciphertextBufferList.slice(0, ciphertextBlockSize)
+        ciphertextBufferList.consume(ciphertextBlockSize)
+        debug('%h : decrypting block %h', debugKey, ciphertextBlock)
+        const plaintextBlock = decrypter.next(ciphertextBlock)
+        debug('%h : decrypted plaintext %h', debugKey, plaintextBlock)
+        const plaintextLength = sodium_unpad(
+          plaintextBlock,
+          plaintextBlock.length,
+          plaintextBlockSize,
+        )
+        const plaintext = plaintextBlock.slice(0, plaintextLength)
+        debug('%h : unpadded plaintext %h', debugKey, plaintext)
+        this.queue(plaintext)
+
+        if (decrypter.final) {
+          debug('%h : decrypter final', debugKey)
+          this.emit('end')
+          break
+        }
       }
     },
     function decryptThroughEnd() {

test/basics.test.js

@@ -2,11 +2,11 @@ const test = require('node:test')
 const assert = require('node:assert')
 const pull = require('pull-stream')
 const { randomBytes } = require('crypto')
-const { KEYBYTES, createEncryptStream, createDecryptStream } = require('../')
+const { KEY_SIZE, createEncryptStream, createDecryptStream } = require('../')
 
 test('test basic encryptStream and decryptStream', async (t) => {
   // generate a random secret, `KEYBYTES` bytes long.
-  const key = randomBytes(KEYBYTES)
+  const key = randomBytes(KEY_SIZE)
 
   const plaintext1 = Buffer.from('hello world')