Add fuzz testing for CryptoAEADAES256GCM

Add tests for all encryption and decryption functions.
Uses random data from gofuzz (see GoKillers#1).

cryptoaead/crypto_aead_aes256gcm_test.go

@@ -0,0 +1,70 @@
+package cryptoaead
+
+import (
+	"testing"
+	"bytes"
+	"github.com/google/gofuzz"
+)
+
+var testCount = 1000000
+
+type Test struct {
+	Message    []byte
+	Ad         []byte
+	Key        [32]byte
+	Nonce      [12]byte
+}
+
+func TestCryptoAEADAES256GCM(t *testing.T) {
+	// Skip the test if unsupported on this platform
+	if !CryptoAEADAES256GCMIsAvailable() {
+		t.Skip()
+	}
+
+	// Test the key generation
+	if len(CryptoAEADAES256GCMKeyGen()) != CryptoAEADAES256GCMKeyBytes() {
+		t.Error("Generated key has the wrong length")
+	}
+
+	// Fuzzing
+	f := fuzz.New()
+
+	// Run tests
+	for i := 0; i < testCount; i++ {
+		var c, m, ec, mac []byte
+		var err int
+		var test Test
+
+		// Fuzz the test struct
+		f.Fuzz(&test)
+
+		// Detached encryption test
+		c, mac, err = CryptoAEADAES256GCMEncryptDetached(test.Message, test.Ad, test.Nonce[:], test.Key[:])
+		if err != 0 {
+			t.Errorf("Detached encryption failed for %+v", test)
+			t.FailNow()
+		}
+
+		// Encryption test
+		ec, err = CryptoAEADAES256GCMEncrypt(test.Message, test.Ad, test.Nonce[:], test.Key[:])
+		if err != 0 || !bytes.Equal(ec, append(c, mac...)) {
+			t.Errorf("Encryption failed for %+v", test)
+			t.FailNow()
+		}
+
+		// Detached decryption test
+		m, err = CryptoAEADAES256GCMDecryptDetached(c, mac, test.Ad, test.Nonce[:], test.Key[:])
+		if err != 0 || !bytes.Equal(m, test.Message) {
+			t.Errorf("Detached decryption failed for %+v", test)
+			t.FailNow()
+		}
+
+		// Decryption test
+		m, err = CryptoAEADAES256GCMDecrypt(ec, test.Ad, test.Nonce[:], test.Key[:])
+		if err != 0 || !bytes.Equal(m, test.Message) {
+			t.Errorf("Decryption failed for %+v", test)
+			t.FailNow()
+		}
+	}
+	t.Logf("Completed %v tests", testCount)
+}