1 files changed, 152 insertions, 0 deletions
diff --git a/internal/stupidgcm/common_test.go b/internal/stupidgcm/common_test.go
new file mode 100644
index 0000000..28f3308
--- /dev/null
+++ b/internal/stupidgcm/common_test.go
@@ -0,0 +1,152 @@
+package stupidgcm
+
+import (
+	"bytes"
+	"crypto/cipher"
+	"encoding/hex"
+	"testing"
+)
+
+// testEncryptDecrypt encrypts and decrypts using both stupidgcm and Go's built-in
+// GCM implementation and verifies that the results are identical.
+func testEncryptDecrypt(t *testing.T, c1 cipher.AEAD, c2 cipher.AEAD) {
+	if c1.NonceSize() != c2.NonceSize() {
+		t.Fatal("different NonceSize")
+	}
+	if c1.Overhead() != c2.Overhead() {
+		t.Fatal("different Overhead")
+	}
+
+	authData := randBytes(24)
+	iv := randBytes(c1.NonceSize())
+
+	dst := make([]byte, 71) // 71 = arbitrary length
+
+	// Check all block sizes from 1 to 5000
+	for i := 1; i < 5000; i++ {
+		in := make([]byte, i)
+
+		c1out := c1.Seal(dst, iv, in, authData)
+		c2out := c2.Seal(dst, iv, in, authData)
+
+		// Ciphertext must be identical to Go GCM
+		if !bytes.Equal(c1out, c2out) {
+			t.Fatalf("Compare failed for encryption, size %d", i)
+			t.Log("c1out:")
+			t.Log("\n" + hex.Dump(c1out))
+			t.Log("c2out:")
+			t.Log("\n" + hex.Dump(c2out))
+		}
+
+		c1out2, sErr := c1.Open(dst, iv, c1out[len(dst):], authData)
+		if sErr != nil {
+			t.Fatal(sErr)
+		}
+		c2out2, gErr := c2.Open(dst, iv, c2out[len(dst):], authData)
+		if gErr != nil {
+			t.Fatal(gErr)
+		}
+
+		// Plaintext must be identical to Go GCM
+		if !bytes.Equal(c1out2, c2out2) {
+			t.Fatalf("Compare failed for decryption, size %d", i)
+		}
+	}
+}
+
+// Seal re-uses the "dst" buffer it is large enough.
+// Check that this works correctly by testing different "dst" capacities from
+// 5000 to 16 and "in" lengths from 1 to 5000.
+func testInplaceSeal(t *testing.T, c1 cipher.AEAD, c2 cipher.AEAD) {
+	authData := randBytes(24)
+	iv := randBytes(c1.NonceSize())
+
+	max := 5016
+	// Check all block sizes from 1 to 5000
+	for i := 1; i < max-16; i++ {
+		in := make([]byte, i)
+		dst := make([]byte, max-i)
+		dst = dst[:16]
+
+		c1out := c1.Seal(dst, iv, in, authData)
+		dst2 := make([]byte, 16)
+		c2out := c2.Seal(dst2, iv, in, authData)
+
+		// Ciphertext must be identical to Go GCM
+		if !bytes.Equal(c1out, c2out) {
+			t.Fatalf("Compare failed for encryption, size %d", i)
+			t.Log("sOut:")
+			t.Log("\n" + hex.Dump(c1out))
+			t.Log("gOut:")
+			t.Log("\n" + hex.Dump(c2out))
+		}
+	}
+}
+
+// testInplaceOpen - Open re-uses the "dst" buffer it is large enough.
+// Check that this works correctly by testing different "dst" capacities from
+// 5000 to 16 and "in" lengths from 1 to 5000.
+func testInplaceOpen(t *testing.T, c1 cipher.AEAD, c2 cipher.AEAD) {
+	authData := randBytes(24)
+	iv := randBytes(c1.NonceSize())
+
+	max := 5016
+	// Check all block sizes from 1 to 5000
+	for i := 1; i < max-c1.NonceSize(); i++ {
+		in := make([]byte, i)
+
+		c2ciphertext := c2.Seal(iv, iv, in, authData)
+
+		dst := make([]byte, max-i)
+		// sPlaintext ... stupidgcm plaintext
+		c1plaintext, err := c1.Open(dst[:0], iv, c2ciphertext[c1.NonceSize():], authData)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Plaintext must be identical to Go GCM
+		if !bytes.Equal(in, c1plaintext) {
+			t.Fatalf("Compare failed, i=%d", i)
+		}
+	}
+}
+
+// testCorruption verifies that changes in the ciphertext result in a decryption
+// error
+func testCorruption(t *testing.T, c cipher.AEAD) {
+	authData := randBytes(24)
+	iv := randBytes(c.NonceSize())
+
+	in := make([]byte, 354)
+	out := c.Seal(nil, iv, in, authData)
+	out2, sErr := c.Open(nil, iv, out, authData)
+	if sErr != nil {
+		t.Fatal(sErr)
+	}
+	if !bytes.Equal(in, out2) {
+		t.Fatalf("Compare failed")
+	}
+
+	// Corrupt first byte
+	out[0]++
+	out2, sErr = c.Open(nil, iv, out, authData)
+	if sErr == nil || out2 != nil {
+		t.Fatalf("Should have gotten error")
+	}
+	out[0]--
+
+	// Corrupt last byte
+	out[len(out)-1]++
+	out2, sErr = c.Open(nil, iv, out, authData)
+	if sErr == nil || out2 != nil {
+		t.Fatalf("Should have gotten error")
+	}
+	out[len(out)-1]--
+
+	// Append one byte
+	out = append(out, 0)
+	out2, sErr = c.Open(nil, iv, out, authData)
+	if sErr == nil || out2 != nil {
+		t.Fatalf("Should have gotten error")
+	}
+}