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-rw-r--r--internal/stupidgcm/stupidgcm.go15
-rw-r--r--internal/stupidgcm/stupidgcm_test.go39
2 files changed, 53 insertions, 1 deletions
diff --git a/internal/stupidgcm/stupidgcm.go b/internal/stupidgcm/stupidgcm.go
index 5cc6c3c..54915df 100644
--- a/internal/stupidgcm/stupidgcm.go
+++ b/internal/stupidgcm/stupidgcm.go
@@ -55,7 +55,17 @@ func (g stupidGCM) Seal(dst, iv, in, authData []byte) []byte {
if len(in) == 0 {
log.Panic("Zero-length input data is not supported")
}
- buf := make([]byte, len(in)+tagLen)
+
+ // If the "dst" slice is large enough we can use it as our output buffer
+ outLen := len(in) + tagLen
+ var buf []byte
+ inplace := false
+ if cap(dst)-len(dst) >= outLen {
+ inplace = true
+ buf = dst[len(dst) : len(dst)+outLen]
+ } else {
+ buf = make([]byte, outLen)
+ }
// https://wiki.openssl.org/index.php/EVP_Authenticated_Encryption_and_Decryption#Authenticated_Encryption_using_GCM_mode
@@ -115,6 +125,9 @@ func (g stupidGCM) Seal(dst, iv, in, authData []byte) []byte {
// Free scratch space
C.EVP_CIPHER_CTX_free(ctx)
+ if inplace {
+ return dst[:len(dst)+outLen]
+ }
return append(dst, buf...)
}
diff --git a/internal/stupidgcm/stupidgcm_test.go b/internal/stupidgcm/stupidgcm_test.go
index eb322f2..4d37d08 100644
--- a/internal/stupidgcm/stupidgcm_test.go
+++ b/internal/stupidgcm/stupidgcm_test.go
@@ -73,6 +73,45 @@ func TestEncryptDecrypt(t *testing.T) {
}
}
+// 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) {
+ key := randBytes(32)
+ sGCM := New(key, false)
+ authData := randBytes(24)
+ iv := randBytes(16)
+
+ gAES, err := aes.NewCipher(key)
+ if err != nil {
+ t.Fatal(err)
+ }
+ gGCM, err := cipher.NewGCMWithNonceSize(gAES, 16)
+ if err != nil {
+ t.Fatal(err)
+ }
+ 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]
+
+ sOut := sGCM.Seal(dst, iv, in, authData)
+ dst2 := make([]byte, 16)
+ gOut := gGCM.Seal(dst2, iv, in, authData)
+
+ // Ciphertext must be identical to Go GCM
+ if !bytes.Equal(sOut, gOut) {
+ 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))
+ }
+ }
+}
+
// TestCorruption verifies that changes in the ciphertext result in a decryption
// error
func TestCorruption(t *testing.T) {