攻防世界- MISC新手區–第11題–base64隱寫

下載之后解壓，是stego.txt

打開stego.txt

顯然是base64編碼之后的結果，base64解碼，我還百度翻譯了一下，也沒什么發現。

于是想辦法，因為沒有MISC的基礎，就去看了WP，知道是base64隱寫。于是查閱資料了解了一下。

base64隱寫的原理

（1）起因：
俄羅斯有個叫 Olympic_ctf 的 CTF, 在 2014 年有道 misc 題是關于 Base64 的隱寫題.

大意就是給了你一段字符串, 讓你找 flag.
這里放上字符串, 便于讀者實驗

U3RlZ2Fub2dyYXBoeSBpcyB0aGUgYXJ0IGFuZCBzY2llbmNlIG9m IHdyaXRpbmcgaGlkZGVuIG1lc3NhZ2VzIGluIHN1Y2ggYSB3YXkgdGhhdCBubyBvbmV= LCBhcGFydCBmcm9tIHRoZSBzZW5kZXIgYW5kIGludGVuZGVkIHJlY2lwaWVudCwgc3VzcGU= Y3RzIHRoZSBleGlzdGVuY2Ugb2YgdGhlIG1lc3M= YWdlLCBhIGZvcm0gb2Ygc2VjdXJpdHkgdGhyb3VnaCBvYnNjdXJpdHkuIFS= aGUgd29yZCBzdGVnYW5vZ3JhcGh5IGlzIG9mIEdyZWVrIG9yaWdpbiBhbmQgbWVhbnMgImNvbmNlYW== bGVkIHdyaXRpbmciIGZyb20gdGhlIEdyZWVrIHdvcmRzIHN0ZWdhbm9zIG1lYW5pbmcgImNv dmVyZWQgb3IgcHJvdGVjdGVkIiwgYW5kIGdyYXBoZWluIG1lYW5pbmcgInRvIHc= cml0ZSIuIFRoZSBmaXJzdCByZWNvcmRlZCB1c2Ugb2YgdGhlIHRlcm0gd2FzIGluIDE0OTkgYnkgSm9o YW5uZXMgVHJpdGhlbWl1cyBpbiBoaXMgU3RlZ2Fub2dyYXBoaWEsIGEgdHJlYV== dGlzZSBvbiBjcnlwdG9ncmFwaHkgYW5kIHN0ZWdhbm9ncmFwaHkgZGlzZ8== dWlzZWQgYXMgYSBib29rIG9uIG1hZ2ljLiBHZW5lcmFsbHksIG1lc3P= YWdlcyB3aWxsIGFwcGVhciB0byBiZSBzb21ldGhpbmcgZWxzZTogaW1hZ2VzLCBhcnRp Y2xlcywgc2hvcHBpbmcgbGlzdHMsIG9yIHNvbWUgb3R= aGVyIGNvdmVydGV4dCBhbmQsIGNsYXNzaWNhbGx5LCB0aGUgaGlkZGVuIG1lc3NhZ2UgbWF5IGJlIGluIGludmm= c2libGUgaW5rIGJldHdlZW4gdGhlIHZpc2libGUgbGluZXMgb2YgYSBwcml2YXRlIGxldHRlci4NCg0KVGhl IGFkdmFudGFnZSBvZiBzdGVnYW5vZ3JhcGh5LCBvdmVyIGNy eXB0b2dyYXBoeSBhbG9uZSwgaXMgdGhhdCBtZXNzYWdlcyBkbyBub3QgYXR0cmFjdCBhdHRlbnRpb25= IHRvIHRoZW1zZWx2ZXMuIFBsYWlubHkgdmlzaWJsZSBlbmNyeXB0ZWQgbWVzc2FnZXOXbm8gbWF0dGVyIF== aG93IHVuYnJlYWthYmxll3dpbGwgYXJvdXNlIHN= dXNwaWNpb24sIGFuZCBtYXkgaW4gdGhlbXNlbHZlcyBiZSBpbmNyaW1pbmF0aW5nIP== aW4gY291bnRyaWVzIHdoZXJlIGVuY3J5cHRpb24gaXMgaWxsZWdhbC4gVGhlcmVmb3JlLH== IHdoZXJlYXMgY3J5cHRvZ3JhcGh5IHByb3RlY3RzIHRoZSBjb250ZW50cyBvZj== IGEgbWVzc2FnZSwgc3RlZ2Fub2dyYXBoeSBjYW4gYmUgc2FpZCB0byBwcm90ZWN0IGJ= b3RoIG1lc3NhZ2VzIGFuZCBjb21tdW5pY2F0aW5nIHBhcnRpZXMuDQoNClN0ZWdhbm9ncmFwaHkgaW5jbHW= ZGVzIHRoZSBjb25jZWFsbWVudCBvZiBpbmZvcm1hdGlvbiB3aXRoaW4gY29t cHV0ZXIgZmlsZXMuIEluIGRpZ2l0YWwgc3RlZ2Fub2dyYXBoeSwgZWxlY3Ryb25pYyBjb21tdW5pY2F0aW9u cyBtYXkgaW5jbHVkZSBzdGVnYW5vZ3JhcGhpYyBjb2RpbmcgaW5zaZ== ZGUgb2YgYSB0cmFuc3BvcnQgbGF5ZXIsIHN1Y2ggYXMgYSBkb2N1bWVudCBmaWxlLCBpbWFnZSBmaWx= ZSwgcHJvZ3JhbSBvciBwcm90b2NvbC4gTWVkaWEg ZmlsZXMgYXJlIGlkZWFsIGZvciBzdGVnYW5vZ3JhcGhpYyB0cmFuc21pc3Npb+== biBiZWNhdXNlIG9mIHRoZWlyIGxhcmdlIHNpemUuIEFzIB== YSBzaW1wbGUgZXhhbXBsZSwgYSBzZW5kZXIgbWlnaHQgc3RhcnQgd2l0aCBh biBpbm5vY3VvdXMgaW1hZ2UgZmlsZSBhbmQgYWRqdXN0IHRoZSBjb2xvciBvZiBldmVyeSAxMDB0aCBwaXhlbCD= dG8gY29ycmVzcG9uZCB0byBhIGxldHRlciBpbiB0aGUgYWxwaGFiZXQsIGF= IGNoYW5nZSBzbyBzdWJ0bGUgdGhhdCBzb21lb25lIG5vdCBzcGVjaWZpY2FsbHkgbG9va2luZyBm b3IgaXQgaXMgdW5saWtlbHkgdG8gbm90aWNlIGl0Lg0KDQpUaGU= IGZpcnN0IHJlY29yZGVkIHVzZXMgb2Ygc3RlZ2Fub2dyYXBoeSBjYW4gYmUgdHJ= YWNlZCBiYWNrIHRvIDQ0MCBCQyB3aGVuIEhlcm9kb3R1cyBtZW50aW9ucyB0d28gZXhhbXBsZXMgb+== ZiBzdGVnYW5vZ3JhcGh5IGluIFRoZSBIaXN0b3JpZXMgb2Yg SGVyb2RvdHVzLiBEZW1hcmF0dXMgc2VudCBhIHdhcm5pbmcgYWJvdXQgYSB= Zm9ydGhjb21pbmcgYXR0YWNrIHRvIEdyZWVjZSBieSB3 cml0aW5nIGl0IGRpcmVjdGx5IG9uIHRoZSB3b29kZW4gYmFja2luZyBvZiBhIHdheCB0YWJsZXQgYmVm b3JlIGFwcGx5aW5nIGl0cyBiZWVzd2F4IHN1cmZhY2UuIFdheCB0YWJsZXRzIHdlcmUgaW4gY29tbW9uIHVzZV== IHRoZW4gYXMgcmV1c2FibGUgd3JpdGluZyBzdXJmYWNlcywgc29tZXRpbWX= cyB1c2VkIGZvciBzaG9ydGhhbmQuIEFub3RoZXIgYW5jaWVudCBleGFtcGxlIGlzIHRoYXQgb9== ZiBIaXN0aWFldXMsIHdobyBzaGF2ZWQgdGhlIGhlYWQgb2YgaGlzIG1vc3QgdHJ1c3RlZCBz bGF2ZSBhbmQgdGF0dG9vZWQgYSBtZXNzYWdlIG9uIGl0LiBBZnRlciBoaXMgaGFpciBoYWQgZ5== cm93biB0aGUgbWVzc2FnZSB3YXMgaGlkZGVuLiBUaGUgcHVycG9zZSB3YXMgdG+= IGluc3RpZ2F0ZSBhIHJldm9sdCBhZ2FpbnN0IHRoZSBQZXJzaWFucy4NCg0KU3RlZ2Fub2dyYXBoeSBoYXMgYm== ZWVuIHdpZGVseSB1c2VkLCBpbmNsdWRpbmcgaW4gcmVjZW50IGhpc3RvcmljYWwgdGltZXMgYW5kIHT= aGUgcHJlc2VudCBkYXkuIFBvc3NpYmxlIHBlcm11dGF0aW9ucyBhcmUgZW5kbGVzcyBhbmT= IGtub3duIGV4YW1wbGVzIGluY2x1ZGU6DQoqIEhpZGRlbiBtZXNzYWdlcyB3aXRoaW4gd2F4IHRh YmxldHM6IGluIGFuY2llbnQgR3JlZWNlLCBwZW9wbGUgd3JvdGUgbWV= c3NhZ2VzIG9uIHRoZSB3b29kLCB0aGVuIGNvdmVyZWQgaXQgd2l0aCB3YXggdXBvbiB3aGljaCBhbiBpbm5vY2Vu dCBjb3ZlcmluZyBtZXNzYWdlIHdhcyB3cml0dGVu Lg0KKiBIaWRkZW4gbWVzc2FnZXMgb24gbWVzc2VuZ2VyJ3MgYm9keTogYWxzbyB1c2VkIGluIGFuY2llbt== dCBHcmVlY2UuIEhlcm9kb3R1cyB0ZWxscyB0aGUgc3Rvcnkgb1== ZiBhIG1lc3NhZ2UgdGF0dG9vZWQgb24gYSBzbGF2ZSdzIHNoYXZlZCBoZWFkLCBoaWRkZW4gYnkgdGhl IGdyb3d0aCBvZiBoaXMgaGFpciwgYW5kIGV4cG9zZWQgYnkgc2hhdmluZyBoaXMgaGVhZM== IGFnYWluLiBUaGUgbWVzc2FnZSBhbGxlZ2VkbHkgY2FycmllZCBhIHdhcm5pbmcgdG8gR3JlZWNlIGFib5== dXQgUGVyc2lhbiBpbnZhc2lvbiBwbGFucy4gVGh= aXMgbWV0aG9kIGhhcyBvYnZpb3VzIGRyYXdiYWNrcyz= IHN1Y2ggYXMgZGVsYXllZCB0cmFuc21pc3Npb24gd2hpbGUgd2FpdGluZyBmb3IgdGhlIHP= bGF2ZSdzIGhhaXIgdG8gZ3JvdywgYW5kIHRoZSByZXN0cmljdGlvbnMgb3== biB0aGUgbnVtYmVyIGFuZCBzaXplIG9mIG1lc3M= YWdlcyB0aGF0IGNhbiBiZSBlbmNvZGVkIG9uIG9uZSBwZXJzb24= J3Mgc2NhbHAuDQoqIEluIFdXSUksIHRoZSBGcmVuY2ggUmVzaXN0YW5jZSBzZW50IHNvbWUgbWVzc2FnZXMgd2== cml0dGVuIG9uIHRoZSBiYWNrcyBvZiBjb3VyaWVycyD= dXNpbmcgaW52aXNpYmxlIGluay4NCiogSGlkZGVuIG1lc3NhZ2VzIG9uIHBhcGVyIHdy aXR0ZW4gaW4gc2VjcmV0IGlua3MsIHVuZGVyIG90aGVyIG1lc3NhZ2Vz IG9yIG9uIHRoZSBibGFuayBwYXJ0cyBvZiBvdGhlct== IG1lc3NhZ2VzLg0KKiBNZXNzYWdlcyB3cml0dGVuIGluIE1vcnNlIGNvZGUgb24ga25pdHRpbmcgeWFybiBhbmQg dGhlbiBrbml0dGVkIGludG8gYSBwaWVjZSBvZiBjbG90aGluZyB3b3K= biBieSBhIGNvdXJpZXIuDQoqIE1lc3NhZ2VzIHdyaXR0ZW4gb24gdGhlIGJhY2sgb5== ZiBwb3N0YWdlIHN0YW1wcy4NCiogRHVyaW5nIGFuZCBhZnRlcm== IFdvcmxkIFdhciBJSSwgZXNwaW9uYWdlIGFnZW50cyB1c2VkIHBob3RvZ3JhcGhpY2FsbHkgcO== cm9kdWNlZCBtaWNyb2RvdHMgdG8gc2VuZCBpbmZvcm1hdGlvbiBiYWNrIGFuZH== IGZvcnRoLiBNaWNyb2RvdHMgd2VyZSB0eXBpY2FsbHkg bWludXRlLCBhcHByb3hpbWF0ZWx5IGxlc3MgdGhhbiB0aGUgc2l6ZSBvZiB0aGUgcGVyaW9kIHByb2R= dWNlZCBieSBhIHR5cGV3cml0ZXIuIFdXSUkgbWljcm9kb3RzIG5lZWRlZCB0byBiZSBlbWJlZGRlZB== IGluIHRoZSBwYXBlciBhbmQgY292ZXJlZCB3aXRoIGFuIGFkaGVzaXZlIChzdWNoIGFzIGNvbGxvZGlvbikuIFR= aGlzIHdhcyByZWZsZWN0aXZlIGFuZCB0aHVzIGRldGVjdGFibGUg Ynkgdmlld2luZyBhZ2FpbnN0IGdsYW5jaW5nIGxpZ2h0LiBBbHRlcm5hdGl2ZSB0ZWNobmlxdWVzIGluY2x1ZGVk IGluc2VydGluZyBtaWNyb2RvdHMgaW50byBzbGl0cyBjdXQgaW50byB0aGUgZWRnZSBvZv== IHBvc3QgY2FyZHMuDQoqIER1cmluZyBXb3JsZCBXYXIgSUksIGEgc3B5IGZvciB= SmFwYW4gaW4gTmV3IFlvcmsgQ2l0eSwgVmVsdmFsZWW= IERpY2tpbnNvbiwgc2VudCBpbmZvcm1hdGlvbiB0byBhY2NvbW1vZGF0aW9= biBhZGRyZXNzZXMgaW4gbmV1dHJhbCBTb3V0aCBBbWVyaWO= YS4gU2hlIHdhcyBhIGRlYWxlciBpbiBkb2xscywgYW5kIG== aGVyIGxldHRlcnMgZGlzY3Vzc2VkIGhvdyBtYW55IG9mIHRoaXMgb3IgdGhhdCBkb2xs IHRvIHNoaXAuIFRoZSBzdGVnb3RleHQgd2FzIHRoZSBkb2xsIG9yZGVycywgd2hpbGUgdGhl IGNvbmNlYWxlZCAicGxhaW50ZXh0IiB3YXMgaXRzZWxmIGVuY2+= ZGVkIGFuZCBnYXZlIGluZm9ybWF0aW9uIGFib3V0IHNoaXAgbW92ZW1lbnRzLF== IGV0Yy4gSGVyIGNhc2UgYmVjYW1lIHNvbWV3aGF0IGZh bW91cyBhbmQgc2hlIGJlY2FtZSBrbm93biBhcyB0aGX= IERvbGwgV29tYW4uDQoqIENvbGQgV2FyIGNvdW50 ZXItcHJvcGFnYW5kYS4gSW4gMTk2OCwgY3JldyBtZW1iZW== cnMgb2YgdGhlIFVTUyBQdWVibG8gKEFHRVItMikgaW50ZWxsaWdlbmNlIHNoaXAgaGVsZCBhcyBwcm== aXNvbmVycyBieSBOb3J0aCBLb3JlYSwgY29tbXVuaWNhdGVkIGluIHNpZ25= IGxhbmd1YWdlIGR1cmluZyBzdGFnZWQgcGhvdG8gb3Bwb3J0 dW5pdGllcywgaW5mb3JtaW5nIHRoZSBVbml0ZWQgU3RhdGVzIHRoZXkg d2VyZSBub3QgZGVmZWN0b3JzIGJ1dCByYXRoZXIgd2VyZSBiZWluZyBoZWxkIGNh cHRpdmUgYnkgdGhlIE5vcnRoIEtvcmVhbnMuIEluIG90aGVyIHBob3Rv cyBwcmVzZW50ZWQgdG8gdGhlIFVTLCBjcmV3IG1lbWJlcnMgZ2F2ZSAidGhlIGZpbmdlciIgdG8g dGhlIHVuc3VzcGVjdGluZyBOb3J0aCBLb3JlYW5zLCBpbiBhbiBhdHRlbXB0IHRvIE== ZGlzY3JlZGl0IHBob3RvcyB0aGF0IHNob3dlZCB0aGVtIHNtaQ== bGluZyBhbmQgY29tZm9ydGFibGUuDQoNCi0tDQpodHRwOi8vZW4ud2lraXBlZGlhLm9yZw== L3dpa2kvU3RlZ2Fub2dyYXBoeQ0K

（2）復習base64編碼

BASE64 是一種編碼方式, 是一種可逆的編碼方式.
編碼后的數據是一個字符串, 包含的字符為: A-Za-z0-9+/
共 64 個字符：26 + 26 + 10 + 1 + 1 = 64
其實是 65 個字符, = 是填充字符.

64 個字符需要 6 位二進制來表示
2^5=32
2^6=64
表示成數值為 0~63.

比如, 字符串"Rascals"經過 Base64 編碼后變為"UmFzY2Fscw=="

上面的 圖，完整展示了為什么轉化后面會多出兩個=，原因是后面補了兩個000000

概括來說，出現等號是因為：
需在原數據二進制值后面添加零, 使其字節數是 6 的倍數.
然后, 在編碼后的字符串后面添加 1 個或 2 個等號"=", 表示所添加的零值字節數.

按照上面的邏輯，同理：
長度為 3 個字節的數據經過 Base64 編碼后就變為 4 個字節 38=64

（3）base64隱寫原理

從Base64編碼的原理可得Base64解碼的過程：

丟掉末尾的所有‘=’； 每個字符查表轉換為對應的6位索引，得到一串二進制字符串； 從頭開始，每次取8位轉換為對應的ASCII字符，如果不足8位則丟棄。

以上面剛才用到的例子：

做解析：
UmFzY2Fscw== 首先丟掉末尾的== ，得到UmFzY2Fscw
然后 每個字符查表轉換為對應的6位索引

后面的完整過程如下：

在解碼的過程中中，會有部分數據被丟棄（即不會影響解碼結果），這些數據正是我們在編碼過程中補的0
也就是說，如果我們在編碼過程中不全用0填充，而是用其他的數據填充，仍然可以正常編碼解碼，因此這些位置可以用于隱寫。

解開隱寫的方法就是將這些不影響解碼結果的位提取出來組成二進制串，然后轉換成ASCII字符串。

（4）base64隱寫腳本（解密）

python腳本：

d='''U3RlZ2Fub2dyYXBoeSBpcyB0aGUgYXJ0IGFuZCBzY2llbmNlIG9m IHdyaXRpbmcgaGlkZGVuIG1lc3NhZ2VzIGluIHN1Y2ggYSB3YXkgdGhhdCBubyBvbmV= LCBhcGFydCBmcm9tIHRoZSBzZW5kZXIgYW5kIGludGVuZGVkIHJlY2lwaWVudCwgc3VzcGU= Y3RzIHRoZSBleGlzdGVuY2Ugb2YgdGhlIG1lc3M= YWdlLCBhIGZvcm0gb2Ygc2VjdXJpdHkgdGhyb3VnaCBvYnNjdXJpdHkuIFS= aGUgd29yZCBzdGVnYW5vZ3JhcGh5IGlzIG9mIEdyZWVrIG9yaWdpbiBhbmQgbWVhbnMgImNvbmNlYW== bGVkIHdyaXRpbmciIGZyb20gdGhlIEdyZWVrIHdvcmRzIHN0ZWdhbm9zIG1lYW5pbmcgImNv dmVyZWQgb3IgcHJvdGVjdGVkIiwgYW5kIGdyYXBoZWluIG1lYW5pbmcgInRvIHc= cml0ZSIuIFRoZSBmaXJzdCByZWNvcmRlZCB1c2Ugb2YgdGhlIHRlcm0gd2FzIGluIDE0OTkgYnkgSm9o YW5uZXMgVHJpdGhlbWl1cyBpbiBoaXMgU3RlZ2Fub2dyYXBoaWEsIGEgdHJlYV== dGlzZSBvbiBjcnlwdG9ncmFwaHkgYW5kIHN0ZWdhbm9ncmFwaHkgZGlzZ8== dWlzZWQgYXMgYSBib29rIG9uIG1hZ2ljLiBHZW5lcmFsbHksIG1lc3P= YWdlcyB3aWxsIGFwcGVhciB0byBiZSBzb21ldGhpbmcgZWxzZTogaW1hZ2VzLCBhcnRp Y2xlcywgc2hvcHBpbmcgbGlzdHMsIG9yIHNvbWUgb3R= aGVyIGNvdmVydGV4dCBhbmQsIGNsYXNzaWNhbGx5LCB0aGUgaGlkZGVuIG1lc3NhZ2UgbWF5IGJlIGluIGludmm= c2libGUgaW5rIGJldHdlZW4gdGhlIHZpc2libGUgbGluZXMgb2YgYSBwcml2YXRlIGxldHRlci4NCg0KVGhl IGFkdmFudGFnZSBvZiBzdGVnYW5vZ3JhcGh5LCBvdmVyIGNy eXB0b2dyYXBoeSBhbG9uZSwgaXMgdGhhdCBtZXNzYWdlcyBkbyBub3QgYXR0cmFjdCBhdHRlbnRpb25= IHRvIHRoZW1zZWx2ZXMuIFBsYWlubHkgdmlzaWJsZSBlbmNyeXB0ZWQgbWVzc2FnZXOXbm8gbWF0dGVyIF== aG93IHVuYnJlYWthYmxll3dpbGwgYXJvdXNlIHN= dXNwaWNpb24sIGFuZCBtYXkgaW4gdGhlbXNlbHZlcyBiZSBpbmNyaW1pbmF0aW5nIP== aW4gY291bnRyaWVzIHdoZXJlIGVuY3J5cHRpb24gaXMgaWxsZWdhbC4gVGhlcmVmb3JlLH== IHdoZXJlYXMgY3J5cHRvZ3JhcGh5IHByb3RlY3RzIHRoZSBjb250ZW50cyBvZj== IGEgbWVzc2FnZSwgc3RlZ2Fub2dyYXBoeSBjYW4gYmUgc2FpZCB0byBwcm90ZWN0IGJ= b3RoIG1lc3NhZ2VzIGFuZCBjb21tdW5pY2F0aW5nIHBhcnRpZXMuDQoNClN0ZWdhbm9ncmFwaHkgaW5jbHW= ZGVzIHRoZSBjb25jZWFsbWVudCBvZiBpbmZvcm1hdGlvbiB3aXRoaW4gY29t cHV0ZXIgZmlsZXMuIEluIGRpZ2l0YWwgc3RlZ2Fub2dyYXBoeSwgZWxlY3Ryb25pYyBjb21tdW5pY2F0aW9u cyBtYXkgaW5jbHVkZSBzdGVnYW5vZ3JhcGhpYyBjb2RpbmcgaW5zaZ== ZGUgb2YgYSB0cmFuc3BvcnQgbGF5ZXIsIHN1Y2ggYXMgYSBkb2N1bWVudCBmaWxlLCBpbWFnZSBmaWx= ZSwgcHJvZ3JhbSBvciBwcm90b2NvbC4gTWVkaWEg ZmlsZXMgYXJlIGlkZWFsIGZvciBzdGVnYW5vZ3JhcGhpYyB0cmFuc21pc3Npb+== biBiZWNhdXNlIG9mIHRoZWlyIGxhcmdlIHNpemUuIEFzIB== YSBzaW1wbGUgZXhhbXBsZSwgYSBzZW5kZXIgbWlnaHQgc3RhcnQgd2l0aCBh biBpbm5vY3VvdXMgaW1hZ2UgZmlsZSBhbmQgYWRqdXN0IHRoZSBjb2xvciBvZiBldmVyeSAxMDB0aCBwaXhlbCD= dG8gY29ycmVzcG9uZCB0byBhIGxldHRlciBpbiB0aGUgYWxwaGFiZXQsIGF= IGNoYW5nZSBzbyBzdWJ0bGUgdGhhdCBzb21lb25lIG5vdCBzcGVjaWZpY2FsbHkgbG9va2luZyBm b3IgaXQgaXMgdW5saWtlbHkgdG8gbm90aWNlIGl0Lg0KDQpUaGU= IGZpcnN0IHJlY29yZGVkIHVzZXMgb2Ygc3RlZ2Fub2dyYXBoeSBjYW4gYmUgdHJ= YWNlZCBiYWNrIHRvIDQ0MCBCQyB3aGVuIEhlcm9kb3R1cyBtZW50aW9ucyB0d28gZXhhbXBsZXMgb+== ZiBzdGVnYW5vZ3JhcGh5IGluIFRoZSBIaXN0b3JpZXMgb2Yg SGVyb2RvdHVzLiBEZW1hcmF0dXMgc2VudCBhIHdhcm5pbmcgYWJvdXQgYSB= Zm9ydGhjb21pbmcgYXR0YWNrIHRvIEdyZWVjZSBieSB3 cml0aW5nIGl0IGRpcmVjdGx5IG9uIHRoZSB3b29kZW4gYmFja2luZyBvZiBhIHdheCB0YWJsZXQgYmVm b3JlIGFwcGx5aW5nIGl0cyBiZWVzd2F4IHN1cmZhY2UuIFdheCB0YWJsZXRzIHdlcmUgaW4gY29tbW9uIHVzZV== IHRoZW4gYXMgcmV1c2FibGUgd3JpdGluZyBzdXJmYWNlcywgc29tZXRpbWX= cyB1c2VkIGZvciBzaG9ydGhhbmQuIEFub3RoZXIgYW5jaWVudCBleGFtcGxlIGlzIHRoYXQgb9== ZiBIaXN0aWFldXMsIHdobyBzaGF2ZWQgdGhlIGhlYWQgb2YgaGlzIG1vc3QgdHJ1c3RlZCBz bGF2ZSBhbmQgdGF0dG9vZWQgYSBtZXNzYWdlIG9uIGl0LiBBZnRlciBoaXMgaGFpciBoYWQgZ5== cm93biB0aGUgbWVzc2FnZSB3YXMgaGlkZGVuLiBUaGUgcHVycG9zZSB3YXMgdG+= IGluc3RpZ2F0ZSBhIHJldm9sdCBhZ2FpbnN0IHRoZSBQZXJzaWFucy4NCg0KU3RlZ2Fub2dyYXBoeSBoYXMgYm== ZWVuIHdpZGVseSB1c2VkLCBpbmNsdWRpbmcgaW4gcmVjZW50IGhpc3RvcmljYWwgdGltZXMgYW5kIHT= aGUgcHJlc2VudCBkYXkuIFBvc3NpYmxlIHBlcm11dGF0aW9ucyBhcmUgZW5kbGVzcyBhbmT= IGtub3duIGV4YW1wbGVzIGluY2x1ZGU6DQoqIEhpZGRlbiBtZXNzYWdlcyB3aXRoaW4gd2F4IHRh YmxldHM6IGluIGFuY2llbnQgR3JlZWNlLCBwZW9wbGUgd3JvdGUgbWV= c3NhZ2VzIG9uIHRoZSB3b29kLCB0aGVuIGNvdmVyZWQgaXQgd2l0aCB3YXggdXBvbiB3aGljaCBhbiBpbm5vY2Vu dCBjb3ZlcmluZyBtZXNzYWdlIHdhcyB3cml0dGVu Lg0KKiBIaWRkZW4gbWVzc2FnZXMgb24gbWVzc2VuZ2VyJ3MgYm9keTogYWxzbyB1c2VkIGluIGFuY2llbt== dCBHcmVlY2UuIEhlcm9kb3R1cyB0ZWxscyB0aGUgc3Rvcnkgb1== ZiBhIG1lc3NhZ2UgdGF0dG9vZWQgb24gYSBzbGF2ZSdzIHNoYXZlZCBoZWFkLCBoaWRkZW4gYnkgdGhl IGdyb3d0aCBvZiBoaXMgaGFpciwgYW5kIGV4cG9zZWQgYnkgc2hhdmluZyBoaXMgaGVhZM== IGFnYWluLiBUaGUgbWVzc2FnZSBhbGxlZ2VkbHkgY2FycmllZCBhIHdhcm5pbmcgdG8gR3JlZWNlIGFib5== 2/2 dXQgUGVyc2lhbiBpbnZhc2lvbiBwbGFucy4gVGh= aXMgbWV0aG9kIGhhcyBvYnZpb3VzIGRyYXdiYWNrcyz= IHN1Y2ggYXMgZGVsYXllZCB0cmFuc21pc3Npb24gd2hpbGUgd2FpdGluZyBmb3IgdGhlIHP= bGF2ZSdzIGhhaXIgdG8gZ3JvdywgYW5kIHRoZSByZXN0cmljdGlvbnMgb3== biB0aGUgbnVtYmVyIGFuZCBzaXplIG9mIG1lc3M= YWdlcyB0aGF0IGNhbiBiZSBlbmNvZGVkIG9uIG9uZSBwZXJzb24= J3Mgc2NhbHAuDQoqIEluIFdXSUksIHRoZSBGcmVuY2ggUmVzaXN0YW5jZSBzZW50IHNvbWUgbWVzc2FnZXMgd2== cml0dGVuIG9uIHRoZSBiYWNrcyBvZiBjb3VyaWVycyD= dXNpbmcgaW52aXNpYmxlIGluay4NCiogSGlkZGVuIG1lc3NhZ2VzIG9uIHBhcGVyIHdy aXR0ZW4gaW4gc2VjcmV0IGlua3MsIHVuZGVyIG90aGVyIG1lc3NhZ2Vz IG9yIG9uIHRoZSBibGFuayBwYXJ0cyBvZiBvdGhlct== IG1lc3NhZ2VzLg0KKiBNZXNzYWdlcyB3cml0dGVuIGluIE1vcnNlIGNvZGUgb24ga25pdHRpbmcgeWFybiBhbmQg dGhlbiBrbml0dGVkIGludG8gYSBwaWVjZSBvZiBjbG90aGluZyB3b3K= biBieSBhIGNvdXJpZXIuDQoqIE1lc3NhZ2VzIHdyaXR0ZW4gb24gdGhlIGJhY2sgb5== ZiBwb3N0YWdlIHN0YW1wcy4NCiogRHVyaW5nIGFuZCBhZnRlcm== IFdvcmxkIFdhciBJSSwgZXNwaW9uYWdlIGFnZW50cyB1c2VkIHBob3RvZ3JhcGhpY2FsbHkgcO== cm9kdWNlZCBtaWNyb2RvdHMgdG8gc2VuZCBpbmZvcm1hdGlvbiBiYWNrIGFuZH== IGZvcnRoLiBNaWNyb2RvdHMgd2VyZSB0eXBpY2FsbHkg bWludXRlLCBhcHByb3hpbWF0ZWx5IGxlc3MgdGhhbiB0aGUgc2l6ZSBvZiB0aGUgcGVyaW9kIHByb2R= dWNlZCBieSBhIHR5cGV3cml0ZXIuIFdXSUkgbWljcm9kb3RzIG5lZWRlZCB0byBiZSBlbWJlZGRlZB== IGluIHRoZSBwYXBlciBhbmQgY292ZXJlZCB3aXRoIGFuIGFkaGVzaXZlIChzdWNoIGFzIGNvbGxvZGlvbikuIFR= aGlzIHdhcyByZWZsZWN0aXZlIGFuZCB0aHVzIGRldGVjdGFibGUg Ynkgdmlld2luZyBhZ2FpbnN0IGdsYW5jaW5nIGxpZ2h0LiBBbHRlcm5hdGl2ZSB0ZWNobmlxdWVzIGluY2x1ZGVk IGluc2VydGluZyBtaWNyb2RvdHMgaW50byBzbGl0cyBjdXQgaW50byB0aGUgZWRnZSBvZv== IHBvc3QgY2FyZHMuDQoqIER1cmluZyBXb3JsZCBXYXIgSUksIGEgc3B5IGZvciB= SmFwYW4gaW4gTmV3IFlvcmsgQ2l0eSwgVmVsdmFsZWW= IERpY2tpbnNvbiwgc2VudCBpbmZvcm1hdGlvbiB0byBhY2NvbW1vZGF0aW9= biBhZGRyZXNzZXMgaW4gbmV1dHJhbCBTb3V0aCBBbWVyaWO= YS4gU2hlIHdhcyBhIGRlYWxlciBpbiBkb2xscywgYW5kIG== aGVyIGxldHRlcnMgZGlzY3Vzc2VkIGhvdyBtYW55IG9mIHRoaXMgb3IgdGhhdCBkb2xs IHRvIHNoaXAuIFRoZSBzdGVnb3RleHQgd2FzIHRoZSBkb2xsIG9yZGVycywgd2hpbGUgdGhl IGNvbmNlYWxlZCAicGxhaW50ZXh0IiB3YXMgaXRzZWxmIGVuY2+= ZGVkIGFuZCBnYXZlIGluZm9ybWF0aW9uIGFib3V0IHNoaXAgbW92ZW1lbnRzLF== IGV0Yy4gSGVyIGNhc2UgYmVjYW1lIHNvbWV3aGF0IGZh bW91cyBhbmQgc2hlIGJlY2FtZSBrbm93biBhcyB0aGX= IERvbGwgV29tYW4uDQoqIENvbGQgV2FyIGNvdW50 ZXItcHJvcGFnYW5kYS4gSW4gMTk2OCwgY3JldyBtZW1iZW== cnMgb2YgdGhlIFVTUyBQdWVibG8gKEFHRVItMikgaW50ZWxsaWdlbmNlIHNoaXAgaGVsZCBhcyBwcm== aXNvbmVycyBieSBOb3J0aCBLb3JlYSwgY29tbXVuaWNhdGVkIGluIHNpZ25= IGxhbmd1YWdlIGR1cmluZyBzdGFnZWQgcGhvdG8gb3Bwb3J0 dW5pdGllcywgaW5mb3JtaW5nIHRoZSBVbml0ZWQgU3RhdGVzIHRoZXkg d2VyZSBub3QgZGVmZWN0b3JzIGJ1dCByYXRoZXIgd2VyZSBiZWluZyBoZWxkIGNh cHRpdmUgYnkgdGhlIE5vcnRoIEtvcmVhbnMuIEluIG90aGVyIHBob3Rv cyBwcmVzZW50ZWQgdG8gdGhlIFVTLCBjcmV3IG1lbWJlcnMgZ2F2ZSAidGhlIGZpbmdlciIgdG8g dGhlIHVuc3VzcGVjdGluZyBOb3J0aCBLb3JlYW5zLCBpbiBhbiBhdHRlbXB0IHRvIE== ZGlzY3JlZGl0IHBob3RvcyB0aGF0IHNob3dlZCB0aGVtIHNtaQ== bGluZyBhbmQgY29tZm9ydGFibGUuDQoNCi0tDQpodHRwOi8vZW4ud2lraXBlZGlhLm9yZw== L3dpa2kvU3RlZ2Fub2dyYXBoeQ0K''' e=d.splitlines() binstr="" base64="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" for i in e :if i.find("==")>0:temp=bin((base64.find(i[-3])&15))[2:]#取倒數第3個字符，在base64找到對應的索引數（就是編碼數），取低4位，再轉換為二進制字符binstr=binstr + "0"*(4-len(temp))+temp #二進制字符補高位0后，連接字符到binstrelif i.find("=")>0:temp=bin((base64.find(i[-2])&3))[2:] #取倒數第2個字符，在base64找到對應的索引數（就是編碼數），取低2位，再轉換為二進制字符binstr=binstr + "0"*(2-len(temp))+temp #二進制字符補高位0后，連接字符到binstr str="" for i in range(0,len(binstr),8):str=str+chr(int(binstr[i:i+8],2)) #從左到右，每取8位轉換為ascii字符，連接字符到字符串 print(str) #結果是 Base_sixty_four_point_five轉換為

輸出：

得到flag就是flag{Base_sixty_four_point_five}

總結

base64隱寫解密，以后碰到直接用腳本，先成為腳本小子（小白沒辦法）

總結

以上是生活随笔為你收集整理的20220207-CTF-MISC-第11题--- base64隐写--附带脚本的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。