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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Why does applying 56-bit DES twice only give 57 bits of security?

Given two 56-bit keys, $k_1$ and $k_2$, why does $E_{k_1}(E_{k_2}(M))$ only give 57 bits of security? So basically I'm unsure why it only gives 57 bits of security; I understand that one key will ...
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What are the links between Cryptography and Algebraic Topology?

I have asked "What are application of Cryptography in Algebraic Topology". But I want to know whether are there any relation between Algebraic Topology and Cryptography. Are there any application of ...
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17 views

suitable method for encryption and decryption [on hold]

I want to encrypt and store important data in mysql so that no one else can access its original form and I want to decrypt those data whenever required. Which encryption scheme is suitable for this ...
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35 views

What type of encryption is this? [on hold]

I need to know what type of encrpytion is this, ed6467d63c907d220447b00bf875e4e017702ff5
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37 views

Is authentication length always a subset of encryption length?

Do in all the use cases, if I have to encrypt and authenticate, encrypt-then-authenticate or authenticate-then-encrypt, like in IPSEC, SSL or SSH or others, if I were to do these operations to a ...
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42 views

Why is the call to RSA_generate_key_ex() failing sometimes? [on hold]

I'm trying to randomly generate a pair of RSA asymmetric keys, however with my current implementation, the RSA_generate_key_ex() method seems to hang forever. I'm unable to extract an error code ...
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18 views

Does it make sense to have multiple values of authentication and cipher offsets while encrypting a packet?

Consider a packet with N segments. cofsset(cipher offset - from where one must cipher) lies in arbitrary Segment "A". aoffset (authentication offset - from where one must authenticate) lies in ...
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107 views

Is chaotic encryption secure?

I know this sounds too broad. But I noticed that there was a chapter on chaotic crypto in the recent Handbook of Information and Communication Security Editors: Stavroulakis, Peter, Stamp, Mark (Eds.) ...
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1answer
72 views

Benefit of using random key in Shamir's Secret Sharing

I am implementing Shamir's Secret Sharing, and I find that in (t,n)-threshold scheme, the shares are just using 1,2,3...,n as the key to form the shares ...
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83 views

Decryption using Key and vector. [closed]

Decrypt the enclosed text using not so advanced encryption technique. Key is “abcdefgh” and vector is “abcdefgh”. ÷ó*ÁÛýÁ n9†“Ü,YÓ©?†]žÀ
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117 views

How to decrypt the text using the key and vector? [closed]

Decrypt the enclosed text using not so advanced encryption technique. Key is “abcdefgh” and vector is “abcdefgh”. ÷ó*ÁÛýÁ n9†“Ü,YÓ©?†]žÀ
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42 views

Why is plain ElGamal not secure?

Why is plain ElGamal not secure? What is the proof behind it?
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37 views

What’s the output of two round Feistel network [closed]

What’s the output of two round Feistel network, 1) when input is 132||032 (L0 is 32 bit 1, R0 is 32 bit 0)? 2) when input is input is 064(L0 is 32 bit 0, R0 is 32 bit 0)?
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1answer
80 views

How does the Blowfish algorithm key initialization work

I'm having some trouble understanding the Blowfish encryption algorithm. From the Wikipedia article... The secret key is then, byte by byte, cycling the key if necessary, XORed with all the ...
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75 views

Axolotl ratchet crypto protocol in plain English [on hold]

I have been trying to read and understand https://github.com/trevp/axolotl/wiki but there's too much technical wording which I can't understand. From what other developers tell me it's the safest ...
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63 views
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1answer
48 views

Encryption & Decryption of Video using RSA [closed]

I need code in java for Encrypt & Decrypt any file using RSA Algorithm. I have code which takes a text file read data from it and then encrypt it. but I need program to encrypt mp3, mp4 any file.
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1answer
60 views

How to encrypt a vector $e\in Z^{m}$ using LWE

I have a vector $e \in Z^{m}$, now I want to encrypt it by using LWE (Learning With Errors). Because in LWE, we have to encrypt of a bit $\{0,1\}$. How can I encrypt a vector $e \in Z^{m}$? Thank you ...
2
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1answer
100 views

Encrypt entire payload or only confidential parts of payload?

In cases where a large complex data structure contains elements that are a mix of confidential and not-so-confidential data, what would be the pros & cons of: encrypting the entire structure ...
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1answer
72 views

Creating a random password based off of a prime number

So I am making an application that basically creates strings that must be encrypted before they are stored on a user's device. If the user blindly starts running the application without creating a ...
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1answer
51 views

How does the certificate authority generate a signature F?

E=encrypt(K,M) - is message M encrypted with key K gives encrypted text E M=decrypt(K,E) - is encrypted text E decrypted with key K gives message M KCA−pub,KCA−priv - is the private-public key pair ...
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1answer
107 views

Decrypted RSA 64 bit encryption using modulus and private exponent. Got gobbledygook [Verify] [closed]

As part of an experiment, I was given a .enc RSA (encrypted) file that was most likely generated using openssl. I had the public key, I factored it, obtained the private exponent, and decrypted the ...
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1answer
138 views

How to decrypt a '.enc' file that has been encrypted with RSA using a public key?

While solving a CTF challenge online, I came across a situation where I needed to decrypt a '.enc' file that has been encrypted using someone's public key. The ...
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1answer
29 views

DSA: Authentication and assurance of authorized parties

When dealing with Asymmetric cryptographic algorithms, usually the sender of the critical data asks the listener for a Public Key for encrypting the data and sending them. This is while the private ...
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3answers
75 views

Is the keystream transmitted with the ciphertext when a stream cipher is used?

When a stream cipher is used and a keystream is generated to be XOR'ed with the plaintext, is the keystream sent with the ciphertext so that the receiver knows how to decrypt it? Or does the ...
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1answer
106 views

Is there a need to encrypt data when send over https? [closed]

I was monitoring web traffic from my Android mobile using Man in the middle proxy. I installed certificate signed from my server in my mobile and I could see all applications sending sensitive ...
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72 views

In what countries am I now allowed to talk about technical details of cryptography? [closed]

I hope this is the correct place to post this, otherwise I'm sorry. The OpenSSL Legality section states: OR EVEN JUST COMMUNICATING TECHNICAL DETAILS ABOUT CRYPTOGRAPHY SOFTWARE IS ILLEGAL IN ...
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16 views

how do i encrypt a user input using shared secret and then decrypt it using ECDH? [migrated]

i am using diffie helman key exchange method. i have got the keys and shared secret. however now am unable to encrypt the user input and generate the cypher text. any suggestions? my code till now is ...
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1answer
86 views

How to encypt/decrypt messages after ECDH key agreement

I am using Diffie-Helman key exchange to generate the shared secret. But how will can a message be encrypted using this shared key?
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1answer
315 views

What are the vulnerabilities of this homemade encryption algorithm?

I decided to program a relatively trivial encryption algorithm in my downtime. This algorithm takes a seed from a user (supports floating point seeds), and then adds 1 to the seed for every iteration ...
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1answer
148 views

Is it safe to encrypt random data using ECB mode?

If I have 48 random bytes, is it safe to encrypt them using ECB mode? Or is there still a good reason to use another mode like CTR, CBC, etc.? Context is this: I am creating something like a TLS ...
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21 views

Device intercommunication with commands

I want to create a smart house project, and in that i bought some simple RF modules. Those modules don't support crypto out of the box but i want to connect them to a device that i would program to ...
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1answer
205 views

Cryptography system by combining a block cipher and a stream cipher

I have to come up with a design for a cryptography system by combining a block cipher and a stream cipher. I can't seem to come up with anything on my own. Can someone point me in the right direction ...
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2answers
124 views

Prove that if we redefine the key space, we can assume Gen chooses a key uniformly

I am working on problem 2.1 in Introduction to Modern Cryptography 2nd edition by Katz and Lindell. 2.1) Prove that by redefining the key space, we may assume that the key generation algorithm ...
2
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1answer
85 views

Stacked LFSR - why not used?

New to cryptographic, weak in math. I have designed a PRG which consist of 33 LFSR's, each 32 bits wide. I use one of the LFSR's as "selector", using the 5 LSB from this register to select one of ...
2
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1answer
936 views

Practical brute-force attack on 128 bit encryption

In brute-force attack calculations cryptographers say we should assume an attacker will find the key after $2^{(n/2)}$ tries. If n=128, then n/2=64. We know that this is practical (A 64 bit key is ...
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1answer
50 views

Key sizes supported by 3DES

I read about 3DES encryption but I don't understand exactly what the specific meaning of key size is. For example I found that 3DES supports 64, 128, 192, and 256 bits key size. What are all the ...
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45 views

common ways / methods to try to break a SP network

I have a very little cryptography background (but a relatively solid maths background) so my below question is very general. Basically I have been given a SP network with an output to reverse. I ...
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1answer
75 views

NTRU Encryption

It's using Euclidian inverse. Can you show it step by step? $$N=7, q=11, a = 3+2X^2 -3X^4 +X^6$$ the inverse of $a \pmod {11}$ is $$A=-2+4X+2X^2 +4X^3 -4X^4 +2X^5 -2X^6$$ How do we compute $A$?
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Are modes of operation algorithms practical?

I took a cryptography class back in college, and now that I am working my 1st career one of the things currently on my plate is coming up with an algorithm to encrypt data before it's placed on the ...
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feistel structure? why decryption is so easy with reverse order of subkey

I am doing an assignment on writing own encryption and decryption algorithm..so i come across feistel structure...can someone explain to me why we only use reverse order of key in decrpytion and we ...
0
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1answer
72 views

Is it safe to use PBEWithMD5AndDES?

I'm encrypting some of my (not so much important) files with PBEWithMD5AndDES. Is it a strong method or it can be de-crypt easily without knowing my selected ...
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1answer
61 views

How are RSA and ElGamal compatible in PGP?

I'm starting to play with PGP and I don't understand how if your key pair is RSA you can encrypt a message for someone whose key is for example ElGamal. How does the asymmetric key exchange work if ...
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1answer
50 views

Is it safe to encrypt data by simply randomizing chunks based on a permutation?

Say I want to encrypt the following text: "Today is March the 22nd, 2015". And say want to encrypt 8-byte blocks of data using the following permutation [6,3,0,1,5,7,2,4] to swap characters at those ...
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21 views

Choosing a cipher in SSH

When and how do the client/server agree on what cipher and MAC will be used during an SSH connection?
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97 views

Coding of unsigned int to prevent guessing next ID

Suppose we are assigning records an unsigned integer ID from a N-bit space (say 32-bit) in a sequential manner. Is there a way we can code this ID before showing it to the public such that someone ...
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1answer
57 views

Is it safe to prefix the a key with a known value?

Almost every encryption algorithm is based on a secret key. I wonder when the algorithm is considered safe, does that also imply that I can prefix (or suffix) the key with a known value, as long as ...
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1answer
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ECDSA for encryption

ECDSA keys are much shorter than RSA keys, but typically only used for signing, not encryption. Is there an accepted way of doing this? (https://bitcointalk.org/index.php?topic=196378.0 ...
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81 views

MAC in SSH packet encryption, benefits to not including it?

What are the benefits to not including MAC in a SSH packet encryption? I understand what the MAC is there for, but if it was not included would there be an advantage? Is the MAC somewhat redundant ...
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Composition of non-perfect encryption keys

Definition 1: A key $k$ is called perfect if it is uniformly distributed from the adversary's point of view; a key $k$ is called $ε$-perfect, if its distribution has an $ε$ trace (statistical) ...