Why does encrypted AssetBundle fail LoadFromFile?

LoadFromFile expects raw Unity bundle format. Encrypted bytes are unrecognized. Decrypt into a Stream then call LoadFromStream.

In-memory or streaming decrypt?

Small bundles: read into byte[] and LoadFromMemory. Large bundles: CryptoStream wrapping the file FileStream and LoadFromStream — saves memory.

CTR streams; can decrypt random ranges. CBC requires sequential read. For seekable bundle access (some load patterns), CTR is preferred.

Fix: Unity Encrypted AssetBundle Stream Load Fails

Quick answer: Wrap encrypted file in CryptoStream, then AssetBundle.LoadFromStream(cryptoStream).

Custom-encrypted bundle deployed. LoadFromFile fails “not a valid asset bundle”. Bytes are encrypted; Unity can’t parse.

The Fix

using System.Security.Cryptography;

var aes = Aes.Create();
aes.Key = key;
aes.IV  = iv;

using var file = File.OpenRead(path);
using var crypto = new CryptoStream(file, aes.CreateDecryptor(), CryptoStreamMode.Read);

var bundle = AssetBundle.LoadFromStream(crypto);

CryptoStream decrypts on-demand as Unity reads. Small memory footprint. AsyncOp variant exists for non-blocking.

Verifying

Encrypted file loads. Without crypto: corrupt error. With wrong key: corrupt or stub assets.

“CryptoStream wrap. LoadFromStream. Encrypted clean.”

Related Issues

For AssetBundle dedup, see dedup. For decompression stutter, see stutter.

CryptoStream. Bundle loads.