Panic on short RC4Cipher.XORKeyStream output

cng/rc4.go

@@ -47,6 +47,10 @@ func (c *RC4Cipher) XORKeyStream(dst, src []byte) {
 	if c.kh == 0 || len(src) == 0 {
 		return
 	}
+	// rc4.Cipher.XORKeyStream throws an out of bond panic if
+	// dst is smaller than src. Replicate the same behavior here.
+	_ = dst[len(src)-1]
+
 	if subtle.InexactOverlap(dst[:len(src)], src) {
 		panic("crypto/rc4: invalid buffer overlap")
 	}

cng/rc4_test.go

@@ -8,10 +8,12 @@ package cng_test
 
 import (
 	"bytes"
+	"crypto/cipher"
 	"fmt"
 	"testing"
 
 	"github.com/microsoft/go-crypto-winnative/cng"
+	"github.com/microsoft/go-crypto-winnative/internal/cryptotest"
 )
 
 type rc4Test struct {
@@ -138,6 +140,13 @@ func TestRC4Block(t *testing.T) {
 	}
 }
 
+func TestRC4Stream(t *testing.T) {
+	cryptotest.TestStream(t, func() cipher.Stream {
+		c, _ := cng.NewRC4Cipher(golden[0].key)
+		return c
+	})
+}
+
 func benchmarkRC4(b *testing.B, size int64) {
 	buf := make([]byte, size)
 	c, err := cng.NewRC4Cipher(golden[0].key)

internal/cryptotest/block.go

@@ -10,8 +10,6 @@ import (
 	"testing"
 )
 
-// This file is a copy of https://github.com/golang/go/blob/9e9b1f57c26a6d13fdaebef67136718b8042cdba/src/crypto/internal/cryptotest/block.go.
-
 type MakeBlock func(key []byte) (cipher.Block, error)
 
 // TestBlock performs a set of tests on cipher.Block implementations, checking

internal/cryptotest/stream.go

@@ -0,0 +1,241 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cryptotest
+
+import (
+	"bytes"
+	"crypto/cipher"
+	"crypto/subtle"
+	"fmt"
+	"strings"
+	"testing"
+)
+
+// Each test is executed with each of the buffer lengths in bufLens.
+var (
+	bufLens = []int{0, 1, 3, 4, 8, 10, 15, 16, 20, 32, 50, 4096, 5000}
+	bufCap  = 10000
+)
+
+// MakeStream returns a cipher.Stream instance.
+//
+// Multiple calls to MakeStream must return equivalent instances,
+// so for example the key and/or IV must be fixed.
+type MakeStream func() cipher.Stream
+
+// TestStream performs a set of tests on cipher.Stream implementations,
+// checking the documented requirements of XORKeyStream.
+func TestStream(t *testing.T, ms MakeStream) {
+
+	t.Run("XORSemantics", func(t *testing.T) {
+		if strings.Contains(t.Name(), "TestCFBStream") {
+			// This is ugly, but so is CFB's abuse of cipher.Stream.
+			// Don't want to make it easier for anyone else to do that.
+			t.Skip("CFB implements cipher.Stream but does not follow XOR semantics")
+		}
+
+		// Test that XORKeyStream inverts itself for encryption/decryption.
+		t.Run("Roundtrip", func(t *testing.T) {
+
+			for _, length := range bufLens {
+				t.Run(fmt.Sprintf("BuffLength=%d", length), func(t *testing.T) {
+					rng := newRandReader(t)
+
+					plaintext := make([]byte, length)
+					rng.Read(plaintext)
+
+					ciphertext := make([]byte, length)
+					decrypted := make([]byte, length)
+
+					ms().XORKeyStream(ciphertext, plaintext) // Encrypt plaintext
+					ms().XORKeyStream(decrypted, ciphertext) // Decrypt ciphertext
+					if !bytes.Equal(decrypted, plaintext) {
+						t.Errorf("plaintext is different after an encrypt/decrypt cycle; got %s, want %s", truncateHex(decrypted), truncateHex(plaintext))
+					}
+				})
+			}
+		})
+
+		// Test that XORKeyStream behaves the same as directly XORing
+		// plaintext with the stream.
+		t.Run("DirectXOR", func(t *testing.T) {
+
+			for _, length := range bufLens {
+				t.Run(fmt.Sprintf("BuffLength=%d", length), func(t *testing.T) {
+					rng := newRandReader(t)
+
+					plaintext := make([]byte, length)
+					rng.Read(plaintext)
+
+					// Encrypting all zeros should reveal the stream itself
+					stream, directXOR := make([]byte, length), make([]byte, length)
+					ms().XORKeyStream(stream, stream)
+					// Encrypt plaintext by directly XORing the stream
+					subtle.XORBytes(directXOR, stream, plaintext)
+
+					// Encrypt plaintext with XORKeyStream
+					ciphertext := make([]byte, length)
+					ms().XORKeyStream(ciphertext, plaintext)
+					if !bytes.Equal(ciphertext, directXOR) {
+						t.Errorf("xor semantics were not preserved; got %s, want %s", truncateHex(ciphertext), truncateHex(directXOR))
+					}
+				})
+			}
+		})
+	})
+
+	t.Run("AlterInput", func(t *testing.T) {
+		rng := newRandReader(t)
+		src, dst, before := make([]byte, bufCap), make([]byte, bufCap), make([]byte, bufCap)
+		rng.Read(src)
+
+		for _, length := range bufLens {
+
+			t.Run(fmt.Sprintf("BuffLength=%d", length), func(t *testing.T) {
+				copy(before, src)
+
+				ms().XORKeyStream(dst[:length], src[:length])
+				if !bytes.Equal(src, before) {
+					t.Errorf("XORKeyStream modified src; got %s, want %s", truncateHex(src), truncateHex(before))
+				}
+			})
+		}
+	})
+
+	t.Run("Aliasing", func(t *testing.T) {
+		rng := newRandReader(t)
+
+		buff, expectedOutput := make([]byte, bufCap), make([]byte, bufCap)
+
+		for _, length := range bufLens {
+			// Record what output is when src and dst are different
+			rng.Read(buff)
+			ms().XORKeyStream(expectedOutput[:length], buff[:length])
+
+			// Check that the same output is generated when src=dst alias to the same
+			// memory
+			ms().XORKeyStream(buff[:length], buff[:length])
+			if !bytes.Equal(buff[:length], expectedOutput[:length]) {
+				t.Errorf("block cipher produced different output when dst = src; got %x, want %x", buff[:length], expectedOutput[:length])
+			}
+		}
+	})
+
+	t.Run("OutOfBoundsWrite", func(t *testing.T) { // Issue 21104
+		rng := newRandReader(t)
+
+		plaintext := make([]byte, bufCap)
+		rng.Read(plaintext)
+		ciphertext := make([]byte, bufCap)
+
+		for _, length := range bufLens {
+			copy(ciphertext, plaintext) // Reset ciphertext buffer
+
+			t.Run(fmt.Sprintf("BuffLength=%d", length), func(t *testing.T) {
+				mustPanic(t, "output smaller than input", func() { ms().XORKeyStream(ciphertext[:length], plaintext) })
+
+				if !bytes.Equal(ciphertext[length:], plaintext[length:]) {
+					t.Errorf("XORKeyStream did out of bounds write; got %s, want %s", truncateHex(ciphertext[length:]), truncateHex(plaintext[length:]))
+				}
+			})
+		}
+	})
+
+	t.Run("BufferOverlap", func(t *testing.T) {
+		rng := newRandReader(t)
+
+		buff := make([]byte, bufCap)
+		rng.Read(buff)
+
+		for _, length := range bufLens {
+			if length == 0 || length == 1 {
+				continue
+			}
+
+			t.Run(fmt.Sprintf("BuffLength=%d", length), func(t *testing.T) {
+				// Make src and dst slices point to same array with inexact overlap
+				src := buff[:length]
+				dst := buff[1 : length+1]
+				mustPanic(t, "invalid buffer overlap", func() { ms().XORKeyStream(dst, src) })
+
+				// Only overlap on one byte
+				src = buff[:length]
+				dst = buff[length-1 : 2*length-1]
+				mustPanic(t, "invalid buffer overlap", func() { ms().XORKeyStream(dst, src) })
+
+				// src comes after dst with one byte overlap
+				src = buff[length-1 : 2*length-1]
+				dst = buff[:length]
+				mustPanic(t, "invalid buffer overlap", func() { ms().XORKeyStream(dst, src) })
+			})
+		}
+	})
+
+	t.Run("KeepState", func(t *testing.T) {
+		rng := newRandReader(t)
+
+		plaintext := make([]byte, bufCap)
+		rng.Read(plaintext)
+		ciphertext := make([]byte, bufCap)
+
+		// Make one long call to XORKeyStream
+		ms().XORKeyStream(ciphertext, plaintext)
+
+		for _, step := range bufLens {
+			if step == 0 {
+				continue
+			}
+			stepMsg := fmt.Sprintf("step %d: ", step)
+
+			dst := make([]byte, bufCap)
+
+			// Make a bunch of small calls to (stateful) XORKeyStream
+			stream := ms()
+			i := 0
+			for i+step < len(plaintext) {
+				stream.XORKeyStream(dst[i:], plaintext[i:i+step])
+				i += step
+			}
+			stream.XORKeyStream(dst[i:], plaintext[i:])
+
+			if !bytes.Equal(dst, ciphertext) {
+				t.Errorf(stepMsg+"successive XORKeyStream calls returned a different result than a single one; got %s, want %s", truncateHex(dst), truncateHex(ciphertext))
+			}
+		}
+	})
+}
+
+// TestStreamFromBlock creates a Stream from a cipher.Block used in a
+// cipher.BlockMode. It addresses Issue 68377 by checking for a panic when the
+// BlockMode uses an IV with incorrect length.
+// For a valid IV, it also runs all TestStream tests on the resulting stream.
+func TestStreamFromBlock(t *testing.T, block cipher.Block, blockMode func(b cipher.Block, iv []byte) cipher.Stream) {
+
+	t.Run("WrongIVLen", func(t *testing.T) {
+		t.Skip("see Issue 68377")
+
+		rng := newRandReader(t)
+		iv := make([]byte, block.BlockSize()+1)
+		rng.Read(iv)
+		mustPanic(t, "IV length must equal block size", func() { blockMode(block, iv) })
+	})
+
+	t.Run("BlockModeStream", func(t *testing.T) {
+		rng := newRandReader(t)
+		iv := make([]byte, block.BlockSize())
+		rng.Read(iv)
+
+		TestStream(t, func() cipher.Stream { return blockMode(block, iv) })
+	})
+}
+
+func truncateHex(b []byte) string {
+	numVals := 50
+
+	if len(b) <= numVals {
+		return fmt.Sprintf("%x", b)
+	}
+	return fmt.Sprintf("%x...", b[:numVals])
+}