Questions tagged [key-size]

Key size is the size measured in bits of the key used in a cryptographic algorithm.

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Bruteforcing a symmetric cipher

I don't understand how we could bruteforce a symmetric cipher. Let's take AES with a key size of $128$ as an example. It means that there are $2^{128}$ possible keys, and as many ways to decrypt a ...
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Calculating symmetric key bit strength

16 byte key where each byte is in range 0-255, generated using cryptograhic PRNG will be believed to have 128 bit strength. What would be a bit strength of a key generated using same quality PRNG, ...
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Cryptography standards on key size

There are many limits on key size. As far as I know 56 bit in USA and 40 bits in India without license. On the other hand much higher 128 bit or 1024 or 4096 bit for banking and other purposes. So ...
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Chaining signatures of different parties

My question might be quite beginner, so please pardon my ignorance :) So, assume there are 10 parties, each with their own keypairs. There is a message $M$ that is passed from one party to the next. ...
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How to calculate time needed for decryption of 64-bit key

I am having trouble figuring out how long it takes to decrypt a 64-bit key, given that a computer can do 1 billion trials per second. I know that there are $2^{64} = 1.844 \times 10^{19}$ possible ...
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Implementation of a decryption mixnet, and problems with the size of the key

I've been studying decryption mixnets, in the context of e-voting and stealth networks. Let's describe it in a very simplified way. The concept is pretty simple. A message M is forwarded through ...
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“16-bit DES encryption algorithm”

I need to use encryption software from PSpice for my SPICE model. In a user guide on page 71 they claim to use a "16-bit DES encryption algorithm". According to the wiki DES is using a 64-...
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Is there any cryptographic scheme with block size more than 128 bit

I am asking this question out of curiosity if there are any cryptographic algorithm that has a block length more that 128 bit. I am new to cryptography and I didn't know any. AES 128, 192, 256 all ...
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Key strength comparison: symmetric key vs RSA/DH key

I came across different reputable sources quoting different equivalent symmetric key strengths for RSA/DH keys. This NIST paper (page 67) states the following offer corresponding security strenghts (...
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Symmetric algorithm effective key length

If we have a symmetric algorithm with key length $m$ bit, and we do a 5 time encryption with it. How much will it be its effective key length.
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Do ciphers with a key size of 64 bits still have use under very limited attack models?

If we have a very performance critical interactive session, like a video game, running on a trusted platform (video game console). If our goal is to prevent exfiltration of up to date information (...
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The order of reading bits in blocks

Let's say I have a cryptographic algorithm that encrypts on 128-bit blocks and makes 20 rounds. Each round has its own keys (one of 72 keys per round). We read blocks before each round. But we're ...
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How to calculate RSA Key Size correctly starting from 384 bits to 15360 bits or beyond 15360 bits

Hello fellow experts here, I am new to cryptography. Recently I looked into RSA Key Size (Microsoft RSA library), it actually describes that the minimal key length required is 384 bits and maximum ...
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How to properly cypher 16 bytes message containing a CRC checksum?

This question arose from a new context under early developments. If cryptographic operations are not well chosen or badly sequenced, please do notice it along your answer or comments: I am a layman in ...
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What is the current security level of an algorithm?

I was reading a paper of some years ago about a cryptography and a phrase got my attention. We want to ensure a security level of at least $2^{80}$ I know that $2^{80}$ was used as rule of thumb ...
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RSA encryption secure mode, plaintext length limit vs. key length

I have two questions about RSA encryption to confirm: Assume use RSA 2048-bit key pair, what is the secure encryption mode? Are ECB / OAEPWithSHA-256AndMGF1Padding and ECB / OAEPWithSHA-...
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Disk storage of RSA and DSA keys

I have generated one RSA-2048 signing key and one DSA-2048 signing key, using gpg command gpg --full-generate-keys I would expect the key to have size 2048 bits, ...
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Why the output of elliptic curve based cryptosystems is smaller than the ordinary public key cryptosystems?

I am trying to understand how much the output of elliptic curve based cryptosystems (for example elliptic curve ElGamal) is smaller than the ordinary public key cryptosystems. I know that the ...
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Use large key size for RC4 to avoid RC4 bias

I saw a question on StackOverflow where RC4 was initialized by a 1024 bit key (with 2048 the maximum key size, if I'm not mistaken). Will such a large key size possibly solve any of the bias of the ...
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Prove that for key with $n$ dimensions, the order of the key is $k!$

I need to prove, that for a key with $n$ dimensions, they order of the key would be $n!$ and to prove that, I need to use mathematical induction: $$\text{Let n = 1} \Rightarrow {1} \text{ if there ...
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Why are AES keys increments of 64-bits?

Why are AES keys increments of 64-bits? Rijndael, which subsequently became AES, allowed key increments in 32-bits (128, 160, 192, 224, and 256 bits). However, AES made it 128, 192, or 256. My guess ...
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Given algorithms A and B with 128bit & 256bit variants, is A128 AND B128 keys better, equal, or less strength than either A256, or B256?

I'm not comparing an algorithm specifically because I'm interested in the generic aspect of key lengths. If I'm wrong to do that then I could bring up particular sponge functions to use. The idea is ...
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Key size of a repeating key XOR-encrypted message using Hamming distance

To find possible key sizes for an encrypted message, I break the message into blocks with length s, ...
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Requirements for RSA key parameters

Recently I'm working with a chinese vendor for POS devices and their devices use 2048bit RSA keys for signing binaries. I had to generate a public/private pair (so I can sign my own binaries) and I ...
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Are all sizes of RSA keys possible? [duplicate]

I mistakenly thought that RSA keys could only be powers of two(1024, 2048, 4096 etc.) but a few days ago read about a 1536-bit and 1160-bit RSA key. I am wondering is it possible to have an RSA key of ...
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How many keys in columnar transposition

In a book I am reading it says that the message Common sense is not so common. (which has 30 characters, space and punctuation included) has a range of possible ...
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Are short ElGamal keysizes acceptable (1024-bit or lower) in cases where security is only necessary in a short timeframe

I am working on an efficient mental poker framework. I have implemented a functional and secure commutative encryption scheme based on ElGamal as described in: http://groups.csail.mit.edu/cis/theses/...
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Effect of longer key on DES security

I am reading a book on cryptography and the author states that one of the complaints of the research community was that DES key length was chosen to be too short. I am trying to depict how DES would ...
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Recommended key size for DKIM

What is the recommended key length for DKIM? I'm currently thinking about a 1024-bit key vs. a 2048-bit one. From the crypto point of view for RSA, 2048 or 4096 bits is clearly recommended--no ...
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Security of ciphersuite and key

Is anyone able to cite resources that can be based on choosing a cipher suite? In my case, for a VPN server (OpenVPN) I chose a set of ciphers: TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 It provides 128 ...
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Why is the NIST recommendation for the private key exponent so much smaller than the modulus?

NIST recommends a 256-bit private key exponent for DLP with a 3072-bit modulus. This question answered how the modulus was chosen/calculated, however, why isn't the private key size closer to the ...
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When does the SIS (Short Integer Solution) Lattice-problem start becoming easy (According to the parameters size)?

SIS (Short Integer Solution) Problem : Given $m$ uniformly random vectors $a \in Z_q^n$, grouped as the columns of a matrix $A \in Z_q^{n.m}$, find a nonzero integer vector $z \in Z^m$ with $||z|| \...
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How is the recommended NIST modulus for DLP chosen/calculated?

NIST recommends a 256-bit private key exponent for DLP with a 3072-bit modulus. From this answer it appears that the range of private key numbers is derived by calculating a prime modulus via $2⋅p$ ...
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Maximum security strength in bits of ISAAC cipher?

Wikipedia claims key length can be very big in this cipher, so I assume it can offer a million bits of security provided entropy of key is the same? Of course I can SHA-256 hash the key to allow any ...
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Security strength of JPBC Type A curve compared to SecP curve

I recently encountered some problems when learning about the JPBC library. Does the curve generated by (J)PBC using the method typeAcurvegenerator(160,512) and the ...
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I need help determining the best encryption options based on System.Security.Cryptography in .NET

I asked a question here, and received a great summary but was redirected here. Covering the answers of the post, it was noted and suggested that: Use of plain (CBC) mode. They suggested to use GCM ...
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Length of password requirement using openssl aes-256-cbc

I am using the following OpenSSL command to AES 256 encrypt a file: ...
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Guessing the key in AES256-GCM? [duplicate]

I assume that my case is weird but I've the following information: IV: 0x263e or 0x3e26 Auth tag: 0x25 AES256-GCM encrypted payload: 0x4eec96df534ade4c013a AES256-GCM decrypted payload: ...
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How many bytes of data does AES 256 encrypt at one time?

Since the block size of AES 256 is 256, how would we calculate the bytes of data AES 256 encrypts at one time?
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80-bit collision resistance because of 80-bit x87 registers?

This is just a curious question, and it probably doesn't belong here anyway, and I'm just being bold asking it here. 80-bit used to be considered an adequate level of security, Skipjack and SHA1 ...
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Extracting Zip using Only the AES Key

I have set myself a little challenge, to see if I can decrypt my own text file from with a ZIP file... The AES Key from my encrypted ZIP is all I have managed to extract, how do I decrypt the ...
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Is it required to use a random IV for AES-CBC with random key per message? [duplicate]

I'm developing a program to encrypt and decrypt a file with AES-256/CBC in Java. And I want it to be safe enough. In my case, I generated random AES key for each file to encrypt and decrypt them. My ...
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Why does Laravel only support AES-256-CBC?

Modern Laravel uses OpenSSL to provide AES-256-CBC encryption along with a MAC. However, I was under the impression that this is not a particularly secure approach. Why does Laravel only support AES-...
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How secure is a 4 digit seed?

When I Use a 4 digit random number(e.g. 4468) as seed for a (manual) Stream cipher and straddle it to the length of the plaintext using a lagged fibonnacci generator, can this seed be found by brute ...
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385 views

AES-256-CBC with random IV - storing same plaintext as same ciphertext

I am encrypting some information stored in a column of a MySQL database. The column can contain repeated values, let's say the table has 7 rows and the column to be encrypted has the following values:...
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cryptographic accumulators: accumulator size vs. max. number of set members?

Here's a basic question about cryptographic accumulators, or at least ones based on fixed-size accumulator values (such as RSA ones based on modulo arithmetic), that is strangely not even mentioned in ...
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How Secure is gpg Command Using Symmetric AES-256 From Being Cracked

How secure is any data encrypted using the following command: gpg -o *encrypted_output_file_name* --symmetric --cipher-algo AES256 *file_to_be_encrypted* Can ...
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Key, plaintext block and ciphertext block permutations question

Question: If a cipher’s key size is $k$ bits and its block size is $b$ bits, how many possible keys are there, how many possible plaintext blocks are there, and how many possible ciphertext blocks are ...
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Why is Diffie-Hellman Insecure If Order of the Generator Has Only Small Prime Factors?

In this post from security SE, Tom Leek mentioned that, for Diffie-Hellman to be secure order of the group $g$ should have a prime factor at least $2k$ bits long, where $k$ is the security parameter. ...
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How many bits should I request from PBKDF2 to create a strong password?

I'm building a tool which generates passwords by hashing a service name with a master key. PBKDF2 was primarily chosen due to availability in the Web Crypto API. What would be a secure value for the ...

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