加密前：

加密后，直接无法加载ab，所以无法正常看到ab内容。

using UnityEngine;
using UnityEditor;
using System.IO;
public static class AssetBundleDemoTest
{
    [MenuItem("Tools/打包!")]
    public static void Build()
    {
        //注意:StreamingAssets文件夹需手动创建
        //参数:打包路径(Assets/StreamingAssets文件夹)、打包方式、打包平台(运行平台)
        BuildPipeline.BuildAssetBundles(Application.streamingAssetsPath, BuildAssetBundleOptions.ChunkBasedCompression,
            EditorUserBuildSettings.activeBuildTarget);

        //刷新编辑器
        AssetDatabase.Refresh();
    }
    [MenuItem("Tools/加密AB")]
    public static void EncryptAB()
    {
        string[] filePaths = Directory.GetFiles(Application.dataPath + "/StreamingAssets");
        foreach (string filePath in filePaths)
        {
            byte[] bytes = File.ReadAllBytes(filePath);
            byte[] newBytes = new byte[bytes.Length + 8];
            for (int i = 0; i < bytes.Length; i++)
            {
                newBytes[8 + i] = bytes[i];
            }
            File.WriteAllBytes(filePath, newBytes);
        }
    }
}

测试代码如下，加载名为"prefab_ab"的AB包，并加载名为"Cube"的资源，是一个预制体。

关于资源加载详情：【Unity】资源加载方式大全_streamingassets manifest-CSDN博客

利用public static AssetBundle LoadFromFile(string path, uint crc, ulong offset);API从磁盘加载AB包，其中crc填0，代表没有任何CRC校验，offset填加密所使用的偏移量8（你可以改，但一定和加密时偏移量一样。） 

using System.Collections.Generic;
using UnityEngine;

public class AssetBundleTest : MonoBehaviour
{
    Dictionary<string, GameObject> resourcesDict = new Dictionary<string, GameObject>();
    void Start()
    {
        GameObject goPrefab = LoadResourceByResourceNameFromAb("prefab_ab", "Cube");
        if (goPrefab != null)
        {
            GameObject go = GameObject.Instantiate(goPrefab);
        }
    }

    private GameObject LoadResourceByResourceNameFromAb(string abName, string resourceName)
    {
        if (!resourcesDict.ContainsKey(abName + "|" + resourceName))
        {
            //加载ab包 本地加载方式 一个名为apple的ab包文件
            AssetBundle assetBundle = AssetBundle.LoadFromFile(Application.streamingAssetsPath + "/" + abName, 0, 8);
            if (assetBundle != null)
            {
                //加载源资源时先加载依赖资源
                //1.加载位于StreamingAssets目录下的StreamingAssets包
                AssetBundle streamingAssetsBundle = AssetBundle.LoadFromFile(Application.streamingAssetsPath + "/StreamingAssets", 0, 8);
                if (streamingAssetsBundle == null)
                {
                    Debug.Log("streamingAssetsBundle is not exist!");
                    return null;
                }
                //加载StreamingAssets包下的AssetBundleManifest文件(可打开StreamingAssets.manifest文件看第三行的名字就是它)
                AssetBundleManifest assetBundleManifest = streamingAssetsBundle.LoadAsset<AssetBundleManifest>("AssetBundleManifest");
                //获取abName包的全部依赖名称!即StreamingAssets.manifest文件的指定Info为abName的Dependencies的数组内容
                string[] deps = assetBundleManifest.GetAllDependencies(abName);
                //加载abName包的全部依赖资源
                for (int i = 0; i < deps.Length; i++)
                {
                    //Debug.Log("依赖资源名称" + deps[i]);
                    //因为依赖名称是一个相对路径，例如:StreamingAssets下的pp文件夹的m2资源是写为 pp/m2，所以加载是没问题
                    AssetBundle.LoadFromFile(Application.streamingAssetsPath + "/" + deps[i], 0, 8);
                }
                //加载源资源
                GameObject go = assetBundle.LoadAsset<GameObject>(resourceName);
                if (go != null)
                {
                    resourcesDict.Add(abName + "|" + resourceName, go);
                    return go;
                }
                else
                {
                    Debug.LogWarning("abNmae:" + abName + ",resourceName:" + resourceName + " is not exist!");
                    return null;
                }
            }
            else
            {
                Debug.LogWarning("abNmae:" + abName + " is not exist!");
                return null;
            }
        }
        else
        {
            GameObject go = null;
            resourcesDict.TryGetValue(abName + "|" + resourceName, out go);
            return go;
        }
    }
}