Fix a small issue with updating the block index

For the reader, we should only update the block index once we've
successfully read a block.

1 files changed, 6 insertions, 2 deletions

diff --git a/internal/cryptoutil/oae2.go b/internal/cryptoutil/oae2.go
index 2819852..4e667b7 100644
--- a/internal/cryptoutil/oae2.go
+++ b/internal/cryptoutil/oae2.go
@@ -60,7 +60,6 @@ func (o *oae2) nonce(nonce []byte, lastBlock bool) error {
 		return errors.New("counter overflowed (64 bits??)")
 	}
 	binary.BigEndian.PutUint64(nonce[noncePrefixSize:], o.i)
-	o.i++
 	if lastBlock {
 		nonce[gcmNonceSize-1] = 1
 	}
@@ -73,6 +72,7 @@ func (o *oae2) encryptBlock(out, block []byte, lastBlock bool) ([]byte, error) {
 		return nil, err
 	}
 	encrypted := o.aead.Seal(out, nonce, block, o.additionalData)
+	o.i++
 	o.additionalData = nil
 	return encrypted, nil
 }
@@ -83,8 +83,12 @@ func (o *oae2) decryptBlock(out, block []byte, lastBlock bool) ([]byte, error) {
 		return nil, err
 	}
 	decrypted, err := o.aead.Open(out, nonce, block, o.additionalData)
+	if err != nil {
+		return nil, err
+	}
+	o.i++
 	o.additionalData = nil
-	return decrypted, err
+	return decrypted, nil
 }
 
 // An EncryptingWriter encrypts data in segments using the STREAM construction