Encryption is the process of transforming plaintext using a cipher into ciphertext to make it unreadable to anyone except those possessing the key. Decryption is the process of transforming that ciphertext back into plaintext, using the key.

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File using same key on XOR cipher. Using CBC [closed]

I have some files that are encrypted using an unknown key and it's using the CBC method to encrypt the files. When I XOR two files together the first two bytes are always the same, but different for ...
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Concatenated Key Question - Poly-alphabetic Substitution and Columnar Transposition

I am working on a degree module, and have been tasked with designing an Encryption/Decryption algorithm. I hope to receive some help with a couple of questions, if possible. Apologies if terminology ...
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36 views

RC6 Key Size Understanding

I need help to understand how RC6 works. Many sites show that the maximum key size of RC6 is 2040 bits (255 Bytes). I can also have 0..255 rounds and 4 times 32bits words in the 128bit block variant ...
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How to encrypt an image with logistic chaotic map?

I need to encrypt color images, using logistic chaotic map. Could you please recommend an algorithm for this? All the articles that I've found on the Internet are completely unclear.
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19 views

AES - Size of T-Boxes and obtaining T-Box values

In article "A high performance ST-Box based unified AES encryption/decryption architecture on FPGA" (http://www.sciencedirect.com/science/article/pii/S0141933115001945) two 32Kb dual-port BRAMs are ...
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Is pseudo-random letter insertion secure?

Is pseudo-random letter insertion a secure mechanism? I mean by expanding the key or taking two parameters in the encryption function, you select positions in the text at which to insert random ...
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1answer
66 views

How can public key not reverse encryption if the algorithm is known? [duplicate]

I've been reading about WhatsApp getting "end-to-end" encryption, and when reading about it, I've notice something. If I want to send a message from cell $A$ to cell $B$, since there's a public key, ...
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92 views

Combining multiple PRGs together

Got some theoretical questions about PRGs to solve (given by lecturer for self-learning, no score involved). Tried to find on the internet but couldn't figure out how to solve them, so I will mention ...
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19 views

Filling in MD5 input variables

I have a majority of an input string(as well as the total length) and the output for an MD5 hash. Is there a way to calculate the remaining input bytes that I am missing?
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CryptDB data re-encryption and onion layers

From the CryptDB paper , I understoond that the onion layers once decrypted are not re-encrypted. Only columns which are queried infrequently will be re-encrypted to higher onion layers. But if we ...
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Unpredictable value rotation

I have very vey basic skills in cryptography, it's hard for me to explain clearly my problem so I will start with an example. Estimote beacons have a security function called secure UUID, once ...
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73 views

Is it safe to use the same IV for multiple encryptions in AES CBC mode when you are always encrypting random bytes?

I am generating random bytes (16 or 32 bytes at a time), and I want to encrypt them using a 128 bit AES key in CBC mode. Am I really weakening this horribly if I am reusing the same IV and key each ...
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How to make the range of modulo $p$ to $[-\frac{p}{2};\frac{p}{2}]$?

I am using NTL (A Library for doing Number Theory) to implement a FHE (Fully Homomorphic Encryption) scheme. In general, the range of modulo p is $[-\frac{p}{2};\frac{p}{2}]$ in FHE scheme. However, ...
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Is there something wrong with my decryption using key=9, mod 26?

I am new to cryptography and have started looking at some basic encryption. I have the following question to answer: Decrypt the the following encrypted quotation using ...
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2answers
58 views

How to prove a symmetric encryption scheme provides perfect secrecy?

I learned in class that in order to achieve perfect secrecy, the source of the plaintext $\mathcal{P}$ needs to be independent from the source of the encryption key $\mathcal{K}$. We also learned that ...
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102 views

How do I create a secure encryption scheme using addition?

You have a 4 number long PIN code with each number ranging from 0 to 9 which you wish to encrypt. You are then given a random 4 digit number ranging from 0 to 9999, which when added to the original ...
3
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1answer
127 views

How to reverse engineer a cryptography algorithm if some input-output pair is known.

I am trying to reverse engineer an unknown encryption algorithm. By this, I mean I dont know what kind of algorithm is used to encrypt the words. But I know some input-output pairs. From this point ...
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71 views

Trusted Third Party Cryptanalysis Labs?

There's no doubt that third party cryptanalysis is an essential part of the crypto ecosystem. It's how we know that there's some degree of practical "goodness" to a new algorithm or protocol. Unlike ...
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Does composing multiple substitution ciphers improve security?

Will using two substitution ciphers one after the another be more secure than using single substitution cipher?
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37 views

How SAM modules secure transactions?

As you know SAM Modules are used mainly in the electronic payment industry. Due to the low security of key storing in general storage devices or MCUs, Manufacturers used SAM modules for secure storing ...
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Are there any crypography schemes which rely on Graph Isomorphism not being in P?

Are there any cryptography schemes having correctness relying on Graph Isomorphism not being in P? If I should ask this question in the CS Theory area, I will migrate it. Thanks.
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80 views

A block cipher whose key changes after each block

I have been reading about various block cipher modes of operation, and all of them seem to treat the block cipher (including it's key and key schedule) as a sort of immutable black box. I would like ...
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21 views

If you receive a message with a digital signature, how do you know what verification key to use and the verification algorithm?

Really, I'm asking how do you know who sent it? My confusion has arisen from the following scenario... Problems with Signing-then-encrypting. If Alice digitally signed some data and then encrypted ...
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16 views

CCA on PKCS#5 using error feedback

My question is about attacking PKCS#5 with CCA using the error feedback. What we learnt in class about PKCS#5: CBC requires padding to whole block boundary PKCS#5: standard padding If ...
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60 views

What are the possible security issues when exporting a plaintext database to a file like this?

Say I have plaintext database with key-value pairs of usernames and passwords. Then I iterate through the database, encrypt the passwords, and write the username and encrypted password pairs to file ...
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Can error correcting codes be used to guess this plaintext?

I pick a finite set of messages, perhaps the set of integers $M = \lbrace n \in \mathbf{Z} \, : \, 0 \leq n\lt10 \rbrace$, which you are then allowed to encode in any way you want (some form of error ...
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49 views

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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469 views

Why is it a bad idea to use a UTF-8 derived symmetric key?

Given a cryptographically secure series of octets, it is often useful to display this information or store it in a database in a textual format such as hexadecimal. Why would it be incorrect to take ...
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124 views

What's the safest TrueCrypt algorithm and hash?

I have an encrypted file container inside my NTFS pendrive. The root folder Write permission is blocked for everyone. A folder inside it has all permissions unblocked. The dummy file of TrueCrypt is ...
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68 views

In case M is small is it possible to recover the message

In the plain RSA encryption, suppose $N$ is 1024 bits and the public key $e = 17$. Is it secure to use this setting to encrypt very small message, say $3 \leq m \leq 9$? In other words, is it possible ...
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64 views

Single public key for NaCL signing and encryption?

Bob wants to use NaCL (specifically the Python NaCL library) to both a) sign some publically available plaintext for anybody to authenticate as being written by Bob and b) encrypt some other secret ...
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154 views

How is this for security? [closed]

I have a function in a C++ program that uses a incrementing integral pattern within a algebraic formula. Each time there' a new character inserted, it uses this ...
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62 views

Breaking One Time Pad with CCA

I was taught that: although OTP is CPA secure, it is not the case with CCA. I'm trying to figure how to break OTP with CCA by showing how it fails the IND test. ...
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Use Smart Card to decrypt files

So I'm trying to figure out the feasibility of using a Smart Card to decrypt files in an offline scenario. I wish to sync encrypted files to a mobile phone with a Smart Card reader case. The files ...
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How to identify the difference between two cryptographic schemes in terms of security?

I am currently working on a project, that requires using encryption libraries namely (LibScarab and FHEW). I want to know how can I compare the two schemes in terms of security (I already compared ...
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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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Detecting Encryption in Real-Time

Is there anyway to detect encryption in real-time through a common signature or pattern recognition. Say, a file is being encrypted using an AES-256 cipher, if I have access to the file stream - can ...
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How should I implement a secure recovery of encryption?

I want to create a system to host as securely as possible encrypted data in a way that not even the system can know the content of the data, but that it could be recovered. I would like to know how ...
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Authenticated encryption with Enc-Sign-Mac

I've given a CPA secure private key encryption scheme, an unforgeable private key MAC scheme and an unforgeable public key signature scheme. I want to combine them to protect confidentiality, ...
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35 views

Can I open a file in plaintext (already decrypt) but the cipher doesn't change?

I want to create an app that encrypts a file and saves it to the Dropbox. Thus, I open and edit this file, I want the file is already decrypted, but the encrypted file that stored in Dropbox still in ...
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I homebrewed an algorithm. Is it secure?

This is a bit of a cross-posted question which I first asked at StackOverflow, however I was not satisfied with stackoverflow, so I came here for an in depth answer. I, as they say, "rolled my own ...
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Finding sum of two encrypted numbers

Let's consider such process: Two emitents emit two (integer) secret numbers independently They encrypt (encode) these number in such a way that no-one (except emitent) can decode these numbers. ...
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1answer
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SHA encyption (help me) [closed]

OK, so I am a real noob at cryptography stuff and I have a set of files. One is a string that I am trying to decrypt, and the other has this SHA: 4534e95cb5f001719a6119a092459dc826965d60 Can I use ...
3
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1answer
86 views

Authenticated encryption with Signatures

I've given a CPA secure private key encryption scheme (wich gets to a CCA secure scheme or better to an authenticated encryption scheme, when i combine it with a given MAC) and a unforgeable public ...
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101 views

Homomorphic system that allows Hamming distance computation?

How can I work out Hamming distance between two binary vectors securely? I would like to know how I can apply homomorphic techniques here.
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1answer
74 views

Combining public key signature schemes and private key encryption

I'm working on my bachelor thesis and I have some questions. I want to combine a CPA-secure private key encryption scheme and some unforgeable public key signature scheme (in my case some sanitizable ...
3
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1answer
70 views

Is RSA encryption without padding secure with NIST Key Establishment schemes?

NIST SP800-56B standard (addressing IFC-based Key Establishment schemes) defines some key establishment (KE) schemes using the RSASVE primitive in which the common secret $Z$ is encrypted with RSA-EP ...
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28 views

Recryption of ciphertext with a different key

Let's have $P$ some sensitive piece of data and $K_1$a secret value, both known to Alice, but not to Bob. $K_1(P)$ means $P$ encrypted using $K_1$. Alice sends $K_1(P)$ to Bob. Bob keeps the value of ...
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459 views

How is the message digest related to Signatures and Encryption?

I was studying about 'Data Security' and I found out this one thing confusing. What is an message digest? I got it is the hash of the message. Is the message here referring to the plaintext or ...
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238 views

How secure is a client-side javascript encrypter?

A friend of mine needed help with her website and asked how to send me her login information securely. I've never known how to do this, so I figured now was the time to learn. After some googling, I ...