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Questions tagged [cryptanalysis]

study of analyzing cryptographic systems in order to get information of the key or the message by finding weaknesses in the cryptographic algorithm.

The question on this tag should be related to one of the following subjects: Cryptanalysis methods, Cryptanalysis implementations. It should not contain question about: side channel attacks.

The quality of an attack is measured by 3 parameters:

  • Time: The amount of encryptions taken to attack. It can be splitted to time before attacking and online time.

  • Memory: Size of the needed memory.

  • Data: Amount of data needed to perform the attack. This can be known plaintext, chosen plaintexts, known ciphertext, etc.

44 questions
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Is it possible to reverse engineer AES256?

Imagine I have this: $cdata = AES_256($data, $pass); AES_256 implements the AES algorithm. If I know the content of $cdata and the content of $data and also have the AES_256() code, can I reverse engineer and find $pass?
acemtp
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Scoring a string based on how English-like it is

I'm not sure how exactly to word this question, so here's an example: string1 = "THEQUICKBROWNFOX" string2 = "KLJHQKJBKJBHJBJLSDFD" I want a function that would score string1 higher than string2 and a million other gibberish strings. Note the lack…
Seth
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How do brute force decryption attacks know when they've found the right solution?

How do brute-force attacks on encrypted data know when they've found the right key to decrypt the data? Is there a way to know that data's been decrypted, other than having a human looking at it? What if it's not human-friendly data?
user151841
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How key_derivation and key_verification functions are implemented of a 7-zip archive's encryption mechanism?

I am curious about how password recovery works for password protected files. And I want to know the exact flow of the 7-zip encryption mechanism. 7-zip uses AES-256 encryption algorithm in CBC mode, to encrypt files or a folder. The key is generated…
Gopal
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Isn't it difficult to recognize a successful decryption?

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…
Dimitri C.
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What is the difference between a multi-collision and a first or second pre-image attack on a hash function?

What is the difference between a multi-collision in a hash function and a first or second preimage. First preimage attacks: given a hash h, find a message m such that hash(m) = h. Second preimage attacks: given a fixed message m1, find a different…
Ethan Heilman
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Tools to practice cryptanalysis and cryptography techniques

I am looking for tools (preferably free) to practice various cryptoanalysis and cryptography techniques. Something along the lines of following two online tools but with more…
user1163441
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How to predict the next GUID from a given GUID?

I have sent 10000 mails to our customers and each mail had a link of the format http://example.com/LogIn?key={guid} Unfortunately the guid I sent were random guids (test data generated by Guid.NewGuid()) so the customers have all received invalid…
tobi
4
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1 answer

Security implications of storing the password hash along an encrypted AES key

I am using the PKCS#5 standard to generate a key using a random and unique salt and the user`s password in input. Consider this key as the "encryption" key. The "encryption" key is used to encrypt a random AES key. Each users have an AES key…
Normand Bedard
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What does the information of XOR of two cipher texts in one-time pad gives me?

So, we're told to not use the same key for one-time pad, because if an attacker knows the two cipher texts, he can get the XOR of the two plain texts. For example: Plain Text1: 0001011 Key : 1010110 Ciphertext : 1011101 Plain Text2:…
good_evening
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Get the AES key from an encrypted file using an already decrypted version of the same file

Is that even possible? The encrypted file uses AES-128 in CBC mode. I already have its decrypted version, but I don't know the key that was used to encrypt it, and I need it (I prefer to not say the reason). I know both files are the same because…
user1347938
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How do I recognise a string as Malbolge source code?

Suppose I was given a string that looks completely garbage, and I am asked to identify what it could possibly be, there are tell-tale signs that crypto-analysts use to form a set of hypotheses to be tested. Are there such signs for Malbolge? Take…
Morpheu5
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Regarding SAT Solvers and cnf files

I've been trying to use Cryptominisat (something similar will do) to formulate an attack on Piccolo, a lightweight block cipher, similar to AES. The equations are something like this: Z= z1|z2|...|z16, 1<= i<=16 Then, ui= (1+z(4i-3)) ^ (1+ z(4i-2))…
Rishav Mishra
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Conversion of equations to cnf, for using sat solvers

So I've to convert some equations which has been devised by a colleague of mine into the cnf file format, to use with some open source sat solvers. The equations are: S-boxes: y1= 1+x1+x2+x4+x1x2 y2= 1+x1+x2+x3+x3x2 y3=…
Rishav Mishra
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Why is it recommended to make crypto algorithms public?

Cryptography books say that you should expose your encryption/decryption algorithm to test it against attacks and cryptanalysis, and the non-exposed algorithm is not considered strong as it is not tested against attacks, but they say also that the…
Dorgham
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