我对cryptopp的部分解码有疑问。 使用AES 256 CTR;
编码来源：
CTR_Mode< AES >::Encryption e;
e.SetKeyWithIV(key, 32, iv);
string encrypt;
string a = "Example text to encoding";
encrypt.clear();
StringSource s(a, true,
new StreamTransformationFilter(e,
new StringSink(encrypt)
)
);
解码来源：
CTR_Mode<AES>::Decryption d;
d.SetKeyWithIV(key, 32, iv);
string x;
StringSource s1(encrypt, true,
new StreamTransformationFilter(d,
new StringSink(x)
)
);
工作正常。但我不知道如何只解密部分。例如，示例encrypt.begin()+10
部分解码：
CTR_Mode<AES>::Decryption d;
d.SetKeyWithIV(key, 32, iv);
d.DiscardBytes(5); //bit to skip
string todecrypt = encrypt.substr(5,10); // part of encrypted message
string x;
StringSource s1(todecrypt, true,
new StreamTransformationFilter(d,
new StringSink(x)
)
);
答案 0 :(得分：2)
如何在CTR模式下搜索并解密部分流？
使用Crypto++ Pipeline有点尴尬，因为Discard or Skip on a Source does not work as expected。您必须在当前实施下将Pump数据转换为＆＃34; no＆＃34; 。另请参阅Stack Overflow上的Skip'ing on a Source does not work as expected。
以下是使用AES / CTR并在流中搜索的示例。它需要执行一个＆＃34;两部分＆＃34;寻求。首先，它会丢弃名为Source的{{1}}上的字节。其次，它在名为cipher的加密对象的密钥流中寻找同步计数器。执行搜索后，通过调用enc来解密密码文本的其余部分，这将通过管道抽取剩余的数据。
PumpAll()结果如下：
#include "modes.h"
#include "aes.h"
using namespace CryptoPP;
int main(int argc, char* argv[])
{
string plain = "Now is the time for all good men to come to the aide of their country";
byte key[AES::DEFAULT_KEYLENGTH] = {0};
byte nonce[AES::BLOCKSIZE] = {0};
CTR_Mode<AES>::Encryption enc;
enc.SetKeyWithIV(key, sizeof(key), nonce, sizeof(nonce));
string cipher;
StringSource ss1(plain, true, new StreamTransformationFilter(enc, new StringSink(cipher)));
for(size_t i=0; i<cipher.size(); i++)
{
CTR_Mode<AES>::Decryption dec;
dec.SetKeyWithIV(key, sizeof(key), nonce, sizeof(nonce));
StringSource ss2(cipher, false);
ss2.Pump(i);
dec.Seek(i);
string recover;
StreamTransformationFilter stf(dec, new StringSink(recover));
// Attach the decryption filter after seeking
ss2.Attach(new Redirector(stf));
ss2.PumpAll();
cout << i << ": " << recover << endl;
}
return 0;
}
现在您已经看到了常规模式，以下是使用范围$ ./test.exe
0: Now is the time for all good men to come to the aide of their country
1: ow is the time for all good men to come to the aide of their country
2: w is the time for all good men to come to the aide of their country
3: is the time for all good men to come to the aide of their country
4: is the time for all good men to come to the aide of their country
5: s the time for all good men to come to the aide of their country
6: the time for all good men to come to the aide of their country
7: the time for all good men to come to the aide of their country
8: he time for all good men to come to the aide of their country
9: e time for all good men to come to the aide of their country
10: time for all good men to come to the aide of their country
11: time for all good men to come to the aide of their country
12: ime for all good men to come to the aide of their country
13: me for all good men to come to the aide of their country
14: e for all good men to come to the aide of their country
15: for all good men to come to the aide of their country
16: for all good men to come to the aide of their country
17: or all good men to come to the aide of their country
18: r all good men to come to the aide of their country
19: all good men to come to the aide of their country
20: all good men to come to the aide of their country
21: ll good men to come to the aide of their country
22: l good men to come to the aide of their country
23: good men to come to the aide of their country
24: good men to come to the aide of their country
25: ood men to come to the aide of their country
26: od men to come to the aide of their country
27: d men to come to the aide of their country
28: men to come to the aide of their country
29: men to come to the aide of their country
30: en to come to the aide of their country
31: n to come to the aide of their country
32: to come to the aide of their country
33: to come to the aide of their country
34: o come to the aide of their country
35: come to the aide of their country
36: come to the aide of their country
37: ome to the aide of their country
38: me to the aide of their country
39: e to the aide of their country
40: to the aide of their country
41: to the aide of their country
42: o the aide of their country
43: the aide of their country
44: the aide of their country
45: he aide of their country
46: e aide of their country
47: aide of their country
48: aide of their country
49: ide of their country
50: de of their country
51: e of their country
52: of their country
53: of their country
54: f their country
55: their country
56: their country
57: heir country
58: eir country
59: ir country
60: r country
61: country
62: country
63: ountry
64: untry
65: ntry
66: try
67: ry
68: y
对数据集进行的修改。
您不必须致电[5,10]，因为一旦执行XOR，恢复的文本就会就绪。其他模式可能需要调用stf.MessageEnd()。另请参阅Crypto ++ wiki上的Init-Update-Final。
MessageEnd()它产生：
StringSource ss2(cipher, false);
ss2.Pump(5);
dec.Seek(5);
string recover;
StreamTransformationFilter stf(dec, new StringSink(recover));
// Attach the decryption filter after seeking
ss2.Attach(new Redirector(stf));
ss2.Pump(10 - 5 + 1);
cout << "'" << recover << "'" << endl;
还有一点：
$ ./test.exe
's the '
它产生：
StringSource ss2(cipher, false);
ss2.Pump(5);
dec.Seek(5);
string recover;
StreamTransformationFilter stf(dec, new StringSink(recover));
// Attach the decryption filter after seeking
ss2.Attach(new Redirector(stf));
ss2.Pump(10 - 5 + 1);
cout << "'" << recover << "'" << endl;
ss2.Pump(1);
cout << "'" << recover << "'" << endl;
ss2.Pump(1);
cout << "'" << recover << "'" << endl;
之前我说＆＃34;使用Crypto++ Pipeline有点尴尬＆＃34; 。这就是我们想要做的所有事情，但我们现在无法做到：
$ ./test.exe
's the '
's the t'
's the ti'
关于Rob的评论＆＃34;您必须解密整个16字节的块...＆＃34; - 如果您正在使用其他模式，如CBC模式，那么你将不得不处理前面的纯文本或密文;你必须在街区上操作。 CBC模式及其链接属性需要它。
然而，点击率的设计略有不同。它的设计是可寻找的，它允许你在流中跳来跳去。在这方面，它很像OFB模式。 （CTR模式和OFB模式在生成密钥流的方式上有所不同。但是，对于使用纯文本或密文的密钥流，XOR都是异或的。）