解密成功是不是很难识别?

发布于 09-17 08:43 字数 98 浏览 7 评论 0原文

当我听说破解加密算法的方法时,我注意到通常关注的是如何快速解密以及如何减少搜索空间。然而,我总是想知道如何识别成功的解密,以及为什么这不会形成瓶颈。或者通常假设加密/解密对是已知的?

When I hear about methods for breaking encryption algorithms, I notice there is often focused on how to decrypt very rapidly and how to reduce the search space. However, I always wonder how you can recognize a successful decryption, and why this doesn't form a bottleneck. Or is it often assumed that a encrypted/decrypted pair is known?

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梦萦几度2024-09-24 08:43:24

来自 Cryptonomicon

两者之间有一个折衷方案
一方面,不是极端的
完全知道任何明文,
另一方面,知道这一切。
在属于的密码学中
婴儿床的标题。婴儿床是一个
有根据地猜测什么词或
短语可能出现在
信息。例如,如果您是
解密来自世界的德国信息
第二次世界大战,你可能会猜到
明文包含短语“HElL
希特勒”或“SIEG HELL”。你可能会选择
输出十个字符的序列
随机地说,“让我们假设
这代表希特勒万岁。如果那样的话
既然如此,那么这意味着什么
关于消息的其余部分?”

...

坐在他的办公室里
新鲜的 Arethusa 拦截,他去了
工作,使用 FUNERAL 作为婴儿床:如果这样
七个字母组成的组解密为
葬礼,那么剩下的是什么?
消息是什么样子的?胡言乱语?
好吧,这个七人组怎么样?
字母?

From Cryptonomicon:

There is a compromise between the two
extremes of, on the one hand, not
knowing any of the plaintext at all,
and, on the other, knowing all of it.
In the Cryptonomicon that falls under
the heading of cribs. A crib is an
educated guess as to what words or
phrases might be present in the
message. For example if you were
decrypting German messages from World
War II, you might guess that the
plaintext included the phrase "HElL
HITLER" or "SIEG HElL." You might pick
out a sequence of ten characters at
random and say, "Let's assume that
this represented HEIL HITLER. If that
is the case, then what would it imply
about the remainder of the message?"

...

Sitting down in his office with the
fresh Arethusa intercepts, he went to
work, using FUNERAL as a crib: if this
group of seven letters decrypts to
FUNERAL, then what does the rest of
the message look like? Gibberish?
Okay, how about this group of seven
letters?

彩扇题诗2024-09-24 08:43:24

一般来说,您对预期解密后的文件格式有所了解,并且大多数格式都提供了一种简单的方法来识别它们。例如,几乎所有二进制格式(例如图像、文档、zip 文件等)都具有易于识别的标头,而文本文件将仅包含 ASCII 或仅包含有效的 UTF-8 序列。

Generally, you have some idea of the format of the file you expect to result from the decryption, and most formats provide an easy way to identify them. For example, nearly all binary formats such as images, documents, zipfiles, etc, have easily identifiable headers, while text files will contain only ASCII, or only valid UTF-8 sequences.

蓝眸2024-09-24 08:43:24

在非对称加密中,您通常可以访问公钥。因此,任何对加密密文的解密都可以使用公钥重新加密,并与原始密文进行比较,从而揭示解密是否成功。

对称加密也是如此。如果您认为您已经解密了密码,那么您也必须认为您已经找到了密钥。因此,您可以使用该密钥来加密您的(可能是正确的)解密文本,并查看加密结果是否与原始密文相同。

In assymetric cryptography you usually have access to the public key. Therefore, any decryption of an encrypted ciphertext can be re-encrypted using the public key and compared to the original ciphertext, thus revealing if the decryption was succesful.

The same is true for symmetric encryption. If you think you have decrypted a cipher, you must also think that you have found the key. Therefore, you can use that key to encrypt your, presumably correct, decrypted text and see if the encrypted result is identical to the original ciphertext.

无所谓啦2024-09-24 08:43:24

对于密钥长度短于密文长度的对称加密,您保证无法生成所有可能的明文。您可能会在某种程度上猜到您的纯文本将采用什么形式 - 您可能知道它是图像还是 XML,或者如果您甚至不知道那么多,那么您可以假设您能够在其上运行file并且不获取“数据”。您必须希望只有少数密钥可以为您提供模糊的合理解密,并且只有一个与您正在寻找的形式相匹配。

如果您有示例纯文本(或部分纯文本),那么这会变得容易得多。

For symmetric encryption where the key length is shorter than the cipher-text length, you're guaranteed to not be able to produce every possible plain-text. You can probably guess what form your plain--text will take, to some degree -- you probably know whether it's an image, or XML, or if you don't even know that much then you can assume you'll be able to run file on it and not get 'data'. You have to hope that there are only a few keys which would give you even a vaguely sensible decryption and only one which matches the form you are looking for.

If you have a sample plain-text (or partial plain-text) then this gets a lot easier.

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