stupidgcm: add our own thin wrapper around openssl gcm

...complete with tests and benchmark.

This will allow us to get rid of the dependency to spacemonkeygo/openssl
that causes problems on Arch Linux
( https://github.com/rfjakob/gocryptfs/issues/21 )

1 files changed, 154 insertions, 0 deletions

diff --git a/internal/stupidgcm/stupidgcm_test.go b/internal/stupidgcm/stupidgcm_test.go
new file mode 100644
index 0000000..dfd495d
--- /dev/null
+++ b/internal/stupidgcm/stupidgcm_test.go
@@ -0,0 +1,154 @@
+package stupidgcm
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/hex"
+	"testing"
+)
+
+// Get "n" random bytes from /dev/urandom or panic
+func randBytes(n int) []byte {
+	b := make([]byte, n)
+	_, err := rand.Read(b)
+	if err != nil {
+		panic("Failed to read random bytes: " + err.Error())
+	}
+	return b
+}
+
+// TestEncryptDecrypt encrypts and decrypts using both stupidgcm and Go's built-in
+// GCM implemenatation and verifies that the results are identical.
+func TestEncryptDecrypt(t *testing.T) {
+	key := randBytes(32)
+	sGCM := New(key)
+	authData := randBytes(24)
+	iv := randBytes(16)
+	dst := make([]byte, 71) // 71 = random length
+
+	gAES, err := aes.NewCipher(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	gGCM, err := cipher.NewGCMWithNonceSize(gAES, 16)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Check all block sizes from 1 to 5000
+	for i := 1; i < 5000; i++ {
+		in := make([]byte, i)
+
+		sOut := sGCM.Seal(dst, iv, in, authData)
+		gOut := gGCM.Seal(dst, iv, in, authData)
+
+		// Ciphertext must be identical to Go GCM
+		if bytes.Compare(sOut, gOut) != 0 {
+			t.Fatalf("Compare failed for encryption, size %d", i)
+			t.Log("sOut:")
+			t.Log("\n" + hex.Dump(sOut))
+			t.Log("gOut:")
+			t.Log("\n" + hex.Dump(gOut))
+		}
+
+		sOut2, sErr := sGCM.Open(dst, iv, sOut[len(dst):], authData)
+		if sErr != nil {
+			t.Fatal(sErr)
+		}
+		gOut2, gErr := gGCM.Open(dst, iv, gOut[len(dst):], authData)
+		if gErr != nil {
+			t.Fatal(gErr)
+		}
+
+		// Plaintext must be identical to Go GCM
+		if bytes.Compare(sOut2, gOut2) != 0 {
+			t.Fatalf("Compare failed for decryption, size %d", i)
+		}
+	}
+}
+
+// TestCorruption verifies that changes in the ciphertext result in a decryption
+// error
+func TestCorruption(t *testing.T) {
+	key := randBytes(32)
+	sGCM := New(key)
+	authData := randBytes(24)
+	iv := randBytes(16)
+
+	in := make([]byte, 354)
+	sOut := sGCM.Seal(nil, iv, in, authData)
+	sOut2, sErr := sGCM.Open(nil, iv, sOut, authData)
+	if sErr != nil {
+		t.Fatal(sErr)
+	}
+	if bytes.Compare(in, sOut2) != 0 {
+		t.Fatalf("Compare failed")
+	}
+
+	// Corrupt first byte
+	sOut[0]++
+	sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
+	if sErr == nil || sOut2 != nil {
+		t.Fatalf("Should have gotten error")
+	}
+	sOut[0]--
+
+	// Corrupt last byte
+	sOut[len(sOut)-1]++
+	sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
+	if sErr == nil || sOut2 != nil {
+		t.Fatalf("Should have gotten error")
+	}
+	sOut[len(sOut)-1]--
+
+	// Append one byte
+	sOut = append(sOut, 0)
+	sOut2, sErr = sGCM.Open(nil, iv, sOut, authData)
+	if sErr == nil || sOut2 != nil {
+		t.Fatalf("Should have gotten error")
+	}
+}
+
+// $ go test -bench .
+// PASS
+// Benchmark4kEncStupidGCM-2	   50000	     25622 ns/op	 159.86 MB/s
+// Benchmark4kEncGoGCM-2    	   10000	    116544 ns/op	  35.15 MB/s
+// ok  	github.com/rfjakob/gocryptfs/internal/stupidgcm	3.775s
+func Benchmark4kEncStupidGCM(b *testing.B) {
+	key := randBytes(32)
+	authData := randBytes(24)
+	iv := randBytes(16)
+	in := make([]byte, 4096)
+	b.SetBytes(int64(len(in)))
+
+	sGCM := New(key)
+
+	for i := 0; i < b.N; i++ {
+		// Encrypt and append to nonce
+		sGCM.Seal(iv, iv, in, authData)
+	}
+}
+
+func Benchmark4kEncGoGCM(b *testing.B) {
+	key := randBytes(32)
+	authData := randBytes(24)
+	iv := randBytes(16)
+	in := make([]byte, 4096)
+	b.SetBytes(int64(len(in)))
+
+	gAES, err := aes.NewCipher(key)
+	if err != nil {
+		b.Fatal(err)
+	}
+	gGCM, err := cipher.NewGCMWithNonceSize(gAES, 16)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	for i := 0; i < b.N; i++ {
+		// Encrypt and append to nonce
+		gGCM.Seal(iv, iv, in, authData)
+	}
+}