# Tagged Questions

usually secret information used as input to various kinds of cryptographic algorithms, like encryption, signature, MAC, to select the concrete transformation done by the algorithm.

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### How to choose key from string?

do you know any methods for choosing specific position in text for a key? Background: Lets suppose, that I want to encode message to friend: Text1 (not too long - max 1000 chars). I have made ...
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### How can I identify this (I think) symmetric encryption? [closed]

I'm working on a CTF and I'm trying to decrypt some cipher text. I've got a key and the cipher text, but I'm not sure how to determine the algorithm used. ...
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### AES Key Generation based on database guid

I am developing a .NET application spanning multiple servers who should all be able to decrypt data stored in a SQL database. My database is multi-company where each company has its own GUID. since ...
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### Updating the seed key of a PRNG while maintaining initial entropy?

Consider a seed key ($n$-bit long) is completely random and entropy of random variable is $n$ and PRNG is using deterministic algorithm and that that deterministic algorithm does not add any entropy ...
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### Deriving Minimum Description Length of Substitution Key

Given a plaintext: Now is the time for all good men to come to the aid of their country because the quick brown fox jumped over the lazy dog. and a substitution ciphertext: Mpe od yjr yo,r ...
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### Can we use more than one irreducible polynomial in AES?

I understand that the irr. poly is used to form the s-box (and inv. s-box), the key schedule and the mix columns. But could we use a different irr. poly for the mix columns and another for the key ...
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### How would an attacker perform an exhaustive key search on a block cipher using ECB mode?

Do you always assume from Kerchoff's principle, that the attacker has access to everything but the decryption key? That is, am I to assume that to perform an exhaustive key search, the attacker has a ...
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### Storing RSA private key

Currently I'm developing an application where users generate their own pair RSA keys in order to achieve a secure communication with my server. Also clients are able to communicate directly, sending ...
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### Why are there $q^2$ keys for each equivalence class in Pedersen-van Heyst Signature Scheme?

How do you know there are $q^2$ keys for each equivalence class in the Pedersen-van Heyst Signature Scheme? My textbook says this is "easy to see", however, I am not seeing it. Is it because in the ...
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### Symmetric : Generate new key from old ones

Symmetric keys should be refreshed regularly. Is is terribly wrong to first agree on $N$ independent keys and then generate the key $k_j$ with $j>N$ by computing some form of hash on the keys \$k_{...
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### Shannon theorem of perfect secrecy

From the class: Shannon Theorem: For a perfect encryption scheme, the number of keys is at least the size of the message space (number of messages that have a non-zero probability). Proof: ...
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### HMAC Secure Key Exchange?

Within RFC 2104 section 3 there is discussion around keys (below). How are these keys agreed upon/distributed? Practically speaking is asymmetric crypto a requirement to "bootstrap" and distribute ...
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### What is considered a “weak key” in AES?

I need to construct an AES key from an array of bytes (in Java), but I first I have to check if the key created from these bytes would be weak. Java can check for weakness for DES, but not for AES. ...
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### Decrypting a file encrypted with AESCRYPT using key instead of password

i have encrypted a file using aescrypt and took memory image while the file was being encrypted and hence have the key that was used for encryption in the image but not the password, can i decrypt the ...
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### AES key reuse and guessing the key

Bit of a noob question and a fair bit of Googling didn't help. I understand that the current encryption standard is AES256. A few questions Is the point of this (and other encryption techniques) to ...
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### Does a key derivation function always generate an even distribution of bits in the resulting key?

I am a student of crypto. During our study course, we went into the AES-128 algorithm. All the examples given used an initial key k, 128 bits and we only briefly touched on the key derivation of ...
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### How does a company like Apple keep its keys safe? [closed]

Whatever key is used to sign new iOS updates (for example) must be incredibly well-protected. How does a huge corporation like Apple keep those 4096 bits safe?! Same goes for SSL keys for websites ...
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### X509 converted to Encrypted and Signing keys

We have proprietary tool which takes a p12 file and generates a .key file. Inside the key file, I see two PEM formatted sections: Encrypting Certificate and Signing Certificate. When I open them on my ...
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### How common are weak RSA keys?

There exist certain attacks that can be used against RSA keys whose prime factors are of specific forms, such as one by Coppersmith. How common are these RSA keys? If you generate primes randomly, ...
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### Number of shifts in DES key schedule

In DES key schedule some rounds use one left shift while others use two left shifts. What is the reason behind this?
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### Confidentiality then Integrity with different keys

Can anyone describe how we can do what is said in the below sentence which is in Mark Stamp crypto slides (PPTX) on slide number 101 : Can do a little better - about 1.5 “encryptions” The whole ...
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### Can the key-complement property of DES be used against 3DES?

The comments in this recent question about the security of 3DES made me wonder if the key complement property of DES (which reduces its security by ~1 bit) can be used in the meet-in-the-middle attack ...
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### Why does a hacker need to crack the key to an encrypted file, instead of just brute forcing the password? [closed]

Most encryption softwares don't seem to have a trial limit. So why would a hacker need to crack the key, or even need to know the salt value, if he can just brute force the 6-8 digit password?
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### Choosing which is public vs private key

When I calculate two RSA keys, what if anything, would make any difference which I call the public vs which I call the private key?