# Tagged Questions

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 is PuTTYgen-created RSA public exponent(e) not in {3,17,65537}?

As far as I know, RSA public exponent(e) should be one of {3,17,65537}. However, I found PuTTYgen-created RSA public exponent(e) is 0x25(37) by default,as follows, (PuTTYgen version: 0.66) I am ...
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### CPA on theoretical OTP with CBC mode

Body of question Note: this is THEORETICAL exercise. I understand OTP and CBC does not get along. I have to find a CPA on CBC enc-mode using OTP as the encryption algorithm, s.t a new key is ...
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### How do you prove an encryption scheme is IND-CPA or IND-CCA?

I know for proving a scheme is not IND-CPA or not IND-CCA you can construct an Adversary which has an unfair advantage in an experiment/game, but how would you prove a scheme is IND-CPA or IND-CCA?
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### How to increment the counter value for CTR mode?

I am testing CTR mode on STM32 board. I want to know how the auto increment of counter happens and what is the method to follow if I have to increment the counter manually.
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### Is this PRG secure?

$G$ is a safe PRG in range $\{0,1\}^n\rightarrow\{0,1\}^{n+1}$. Let us define $G'(S)=G(S\oplus G(S)_{1,...,n})$, s.t. $G(S)_{1,...,n}$ is the first n bits of $G(S)$. Is $G'(S)$ a secure PRG? ...
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### How to find HEXA value of String [closed]

This may be very easy thing, but i am just unable to understand this. I have a string "Hi", and in HEXA its written like this ...
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### Rotate values in predefined manner

I want to create a Server S1, that publish a different value every 10 minutes on the internet. The value looks something like f7826da6-4fa2-4e98-8024-bc5b71e0893e. ...
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### How can I show RSA OAEP IND-CPA secure

How can I show, that RSA with OAEP is IND-CPA secure by using G,H one way function?
20k views

### What is the difference between CBC and GCM mode?

I am trying to learn more about GCM mode and how it differs between CBC. I already know that GCM provides a MAC which is used for message authentication. From what I have read, and seen code ...
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### Why are MACs not included when defining Protocols?

I see often in literature related to cryptographic protocols that MACs (Message Authentication Codes) are not included in protocol definitions. For example: ...
4k views

### Why is CBC with predictable IV considered insecure against chosen-plaintext attack?

I just learned that using CBC encryption with an IV which is predictable is not secure. From what I understand, using certain plain texts, and then guessing the IV that it uses, the attacker can ...
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### How much weaker is AES-64 than AES-128?

It's hard to say exact QC specs, but let's assume we have decent a quantum computer using Grover's algorithm that is able to half AES-128 keyspace to that of AES-64. How long will a bruteforce attack ...
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### Should RSA primes p and q differ in length by “a few digits”?

When generating RSA keys in the original RSA paper it is stated: to gain additional protection against sophisticated factoring algorithms, p and q should differ in length by a few digits Why is ...
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### What are the pros and cons of SIP media encryption types SRTP, ZRTP, and DTLS?

I'm just getting used to SIP for my first time using Linphone. Which encryption is better and why? My Settings > Network > Media Encryption has the options of SRTP, ZRTP, and DTLS.
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### Why do cryptographic hashing and symmetric encryption use different functions?

Something about encryption and hashing has always bothered me. Given a cryptographically secure hash function $H$, I can produce an arbitrarily long key from any seed $s$ by recursively applying $H$ ...
12k views

### The modulus of RSA public key

I am studying the RSA cryptosystem. The public key consists of $(n, e)$, the modulus (product of two large primes), and the encryption exponent. I want to separate the modulus $n$ and exponent $e$. A ...
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### If I have the unencrypted text and the encrypted text, can I calculate the key?

If I have the unencrypted text and the encrypted text, can I calculate the key? It seems logical based on my limited knowledge of encryption that I should be able to... but it also seems like too ...
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### Encrypting using “Cryptography.HMACSHA1”, how to decrypt (VBA)

I have an encryption routine that works very well in VBA. But now I need to program the decryption routine, and I'm stuck. For encryption I'm using HMACSHA1 and transferring the encrypted byte to base ...
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### How is the base64 encoded signature in Craig Wright's proof constructed?

Mr. Craig S. Wright might be Satoshi Nakamoto - the inventor of bitcoin. He is currently proving the case. But how is the base64 encoded proof, that is published by himself on his blog post ...
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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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### Fully or partially Decrypting Data with Multiple keys

Is there any good paper or research carried out till now that a data is encrypted by a single key or onwer(user) and their are 2 or more decryption keys. One key can decrypt the entire data. Other ...
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### Algorithm to rotate values in a predefined manner

I will start with an example. Some beacon like estimote Beacons use something called secure ID. The ID transmitted by the beacon change every 10 minutes autonomously without contacting the server. ...
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### Triple DES with 2 keys

Suppose triple DES is performed by choosing two keys $K_1$ and $K_2$ and computing $C = T (T (T (L, K_1), K_2), K_2)$. How to attack this modified version with a meet-in-the-middle attack, in which ...
407 views

### To what extent is WhatsApp's statement on secure messaging realistic?

As those of you who use WhatsApp Messenger probably know, with their recent update chats and calls are now encrypted. Here's what WhatsApp claims: Messages you send to this chat and calls are now ...
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### Is this cascading encryption, and is my security weakened as a result?

I'm trying to understand what is, and what is not, considered cascading encryption. All of the posts and conversations I've read over the past few days discourage the practice, including this article. ...
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### Determining an encryption key when ciphertext and algorithm are known

I would like to know how I can tell that I have successfully performed an exhaustive search attack on an encrypted message. Here are the conditions: key is 40 bit I am aware of the cipher text and ...
102 views

### How to calculate plaintext from modpower cipher

Let $a$ be the plaintext message, $e$ be a small prime exponent (such as 11, 13, 17 etc.), $b$ be cipher text and $n$ be a large modulo (non-prime). Suppose that: \$b \equiv a^e \space mod \...
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### How secure is the OTR protocol?

I am using Adium and wondering how secure it is. I believe it uses AES-256 (I do not understand what that means) by default. It also requests that users exchange fingerprints with each other before ...
787 views

### How can mega store my login details and still be secure?

I understand how Mega's encryption works. For a quick summary of all those in the future looking for an answer on this... here is how it works: Upon first signing up for an account you make a ...
442 views

### Security of tokenization of plain text conversations - cryptanalysis

I came across a marketing video here. They claim to perform AES encryption and tokenization of sensitive data, at the corporate gateway, before it leaves the company firewall destined for the public ...
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### Which cryptography technique does not increase the size of the plain data?

I want to encrypt some data(text/voice/video) but it is essential that the size of the cipher data remains the same as the plain data. Which techniques can I use, and how secure are these techniques ...
2k views

### Can someone explain the ECB Penguin?

I've seen the ECB Penguin used to demonstrate why ECB is not a recommended method of encryption, but I do not understand how this translates to text or passwords. Aren't the people who create these ...
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### Key derivation using the main AES encryption key and some plain text

I am using AES 128 bit encryption in java. I have an encryption key and 10 digit plain text. I want to derive a key for HMAC using the AES encryption key and the 10 digit plain text. This plain text ...
220 views

### Different tools return different ciphertext value for equal input

I have a Luna G5 Safenet HSM and I want to encrypt a text file containing testtest with 3DES-ECB algorithm. So in the first step ...
212 views

### What are the constraints on using GCM with a tag size of 96 and 128 bits

Say we want to use AES (or any other secure 128 bit block cipher) with GCM and a tag size of 96 or 128 bits. I'm assuming an AES key size of 128 bits and an IV size of 96 bits (the default). NIST ...
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### DES hardware implementation of substitution lookup table [ ReWorked ]

I'm a crypto enthusiastic and student of cryptography. I'm developing a project with other students titled "A hardware implementation of a DES cryptography for educational purposes", our idea was to ...
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### 4 x E = D in Simplified AES how it's possible?

Can anyone explain how it's possible through hexadecimal or Binary 4 x E= D
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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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### How is a per round key generated in DES algorithm?

I am reading over a slide that I found online regarding the DES algorithm for encryption and I am a little confused about the per round key generation. From the slide below, I understand that each per ...
6k views

### Layman's explanation of encryption backdoors

Some times I read about "backdoors" in encryption algorithms in the media. I'd like to understand what such a backdoor actually consist of. Is it: a) a hidden weakness in the math formulas that ...
4k views

### Why is the IV passed in the clear when it can be easily encrypted?

The initialization vector (IV) is exclusive or'd against the plain text before encryption for the first block sent in order to prevent an attacker from learning that duplicate message blocks are being ...
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### Can we use merely permutation to hide a message?

This question is related to this: When all shares of a secret are given to adversary as a permuted matrix I think the below question is a simplified version of that. Assume we have a 40-bit ...
746 views

### Precisely how does CBC mode use the initialization vector? [duplicate]

As I understand it, AES in CBC mode does an XOR of the 128-bit initialization vector and the first 128 bits of plain text. Is this correct? I am using the PHP 5.3 openssl extension in aes-256-cbc ...
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### Data in frequency modulated audio [closed]

I'd like to have a peek at the firmware of a piece of Hardware. Its firmware is available as a .wav file to be uploaded via audio jack. https://drive.google.com/open?id=0B6S_PcWWM1YlQnNwT2FSMnFzVE0 ...
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### KFB mode - key feedback

Please, could someone explain to me how the Key feedback mode (KFB) mode works and what the IV in output block stands for? And what properties does the "constant input" has to provide? Should it be ...
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### Deciphering and encrypting using Vigenére square for kids?

Is Vigenére cipher the most basic form of enrypting or is there another simpler way? I'd like to expose my niece to it.
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### Why is hybrid encryption more effective than other encryption scheme?

Currently I am learning about Hybrid Encryption but I was not able to find any good study material. Below is my understanding: One of the reason why we use ...
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### Example describing Baek and Zheng’s threshold identity-based decryption scheme

I am trying to work through an example of Baek and Zheng’s “threshold identity-based decryption scheme” and I tried a lot to solve this, but somewhere I’m doing something wrong. I hope someone can ...