Cryptography

Questions tagged [initialization-vector]

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Unique data used by block cipher modes of operation to randomize the output in order to achieve semantic security. Also for other similar constructs in other iterative algorithms.

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Safety of AES-256/CBC/PKCS#7 + randomization and reusage of IV

As a start, I'm by any means no expert or anything near that in cryptography. I know the very basic about this, enough to more or less choose a method to implement and then read about it so I knew ...
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layout scheme to store encrypted files

I'm working on a little hobby project to better understand crypto. https://app.gitbook.com/@noojee/s/dvault/ The aim is to make it easy to encrypt a set of files into a 'vault' and decrypt them at a ...
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HKDF with predefined IV

Can I generate from a randomly generated key let say three other keys via HKDF with predefined IVs, eg. Sha-256 of "apple", "banana", "pear"? My use-case is an app that ...
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CBC mode, fixed Key and IV but unique plaintexts

My transport channel is sufficiently tiny that I don't want to give up 16 bytes for an IV (AES block size). My environment is also resource constrained such that I have no RNG. I have read over and ...
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How to properly guarantee authentication, confidentiality, and replay-resistance for multiple messages using a pre-shared key?

I have a device that needs to communicate with another host and exchange fixed-length messages. All traffic should be encrypted and authenticated, and it should be resistant to replay attacks. ...
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189 views

CTR overlap with random IV

Problem: I'm slightly worried about counter repeats in CTR mode when using random IV. If you split it (like half IV, half counter), it increases chances of same IV (it is smaller) and limits message ...
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How to use nonce, counter, and IV in AES-256-CTR?

preface: i am not cryptographically savvy. there are similar questions on this board but they do not give the answer i need. how do i construct a valid IV, given a nonce? What does this have to do ...
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How can I decrypt AES-256 GCM with key with a IV that is missing?

I want to decrypt a file that has been encrypted using AES-256 in GCM mode in libressl. I have the key but I don't have the IV, is there any way I can still decrypt?
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Is 64-bit SHA-256 IV-based MAC for fixed-length messages reasonably secure?

I want to use truncate8(SHA256-nopad(IV=secret, message)) as a 64-bit MAC, where message is guaranteed to be exactly one hash ...
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Decrypting the same message with the same IV using aes-256-cbc

Is it safe to use the same IV when decrypting the exact same encrypted message. From my understanding, there is a security flaw when using the same IV for numerous different messages, as attackers can ...
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Secure AES IV with static salt

I have an (offline) shared secret key (symmetric) which is used to encrypt/decrypt data. Now this data belongs to a specific user which is known on the backend and frontend. My idea was to use the ...
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Do I need an inititalization vector if I don't care about message leaking?

In Safety of a private key when knowing the full content of an encrypted message in case of fixed initialization vector, an answer says using a fixed IV is bad practice since it allows statistical ...
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How to allow a partner to encrypt a message that I can decrypt without using a random initialization vector?

My company has a requirement to allow a partner vendor to log people into our web app via some kind of single sign on. We need this to be a simple process for them, not involving the use of ...
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Comparing the security when using fixed IV for CBC and CTR

Assuming that I'm using fixed IV's for CBC mode and CTR mode. I know that in CBC, the blocks depend on the previous ones and on CTR they are all independent. Yet with the same key and fixed IV, the ...
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Proving Security of a Tweakable Block Cipher in CBC Mode (Threefish)

I want to prove the security of a Tweakable Block Cipher in CBC Mode How does one prove the security of a Tweakable block cipher (ie Threefish) in CBC mode with a random IV and a constant (public) ...
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LibTomCrypt Documentation on LRW Mode/Tweakable Block Cipher - Apparent Contradiction?

In the LRW mode discussion on page 34/161 of the LibTomCrypt manual, available here for example https://opensource.apple.com/source/CommonCrypto/CommonCrypto-55010/Source/libtomcrypt/doc/...
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Finding the IV of AES CBC (CTF)

We have a python program that encrypts/decrypts plaintext given in hex to a cipher using AES CBC. We know that the IV is the same and is not going to change (it is stored in a file). How can we ...
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Is it safe to reuse an IV 100 times to a single key with AES CBC? [duplicate]

I have a unique 6 digit number that I am generating a IV from. I am trying to make it as unique as possible. From my programming, I am able to get it down to only have 100 duplicate IVs per unique 6 ...
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IV in RSA Encrypted Private Key

I have been provided an RSA encrypted private key which was generated in NodeJS (crypto) using the following: ...
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Where is the SIV in AES-GCM-SIV?

This is my understanding of Synthentic IVs You have 2 keys $K_1$ & $K_2$. $F$ is a PRF Instead of choosing a separate IV, you instead generate the IV from the PlainText. $IV = F(K_1, m)$ $c = E(...
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Is it necessary to use an IV in CBC mode when just encrypting one file? [duplicate]

As far as I know, CBC mode, even with a null IV, will encrypt identical plaintext blocks to unique ciphertext blocks within a single file. The purpose of an IV is to obscure the similarities between ...
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Deterministic Encryption - Generating IV from password key

I need to encrypt file and directory names/paths but I need the encryption to be deterministic. I need to sync the local files with a cloud storage provider so I can't use probabilistic encryption. ...
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290 views

AES CTR: Random IV

I want to use AES CTR with a random IV, as this would be the easiest way for me. I have a cryptographic module, that supports true random number generation. Due to compatibility, I must use AES CTR. ...
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With AES-CTR does the block input need to be implemented as nonce || counter?

I am looking at an AES-CTR implementation (WebCrypto) and it takes an initialization parameter count which is an array of 16 bytes. It then asks you to specify <...
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What would be the most recommended AES && RSA Keys for production?

While I am a front-end developer and not a security expert programmer, I am worry about the keys I am using for my AES && RSA encryption. Please help me to understand: Is the following keys ...
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Combining CTR and ECB modes to prevent attacks

In Reusing AES-CTR Keys and IVs for File Encryption, the OP was asking about a composite encryption scheme $$C_i = E_K\left(P_i \oplus E_K\left(IV + i\right)\right)$$ which is basically just a CTR ...
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Is it safe to use the CBC-MAC as a Initial Vector and Key Check Value in deterministic encryption?

I want to deterministically encrypt a short message <50 bytes with AES-128 CBC. I also want to be able to detect if the correct key is being used. Ciphertext and IV integrity will be guaranteed by ...
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658 views

Can you change an AES encrypted message if you control the IV?

Let's say that an attacker has the plaintext, the ciphertext and the IV of a specific message. If the attacker can control the ciphertext and the IV, could he forge valid plaintext? Let's say that the ...
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Changing a bit in IV of MD5

It is obvious that changing even one bit in data or IV (initialization vector) will change the hash value a lot. I want to know if, for example, changing a single bit within the $IV$ in MD5 can be ...
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The Rationale behind NIST's counter/LFSR recommendation on deterministic IV constructions on SP 800-38D

The NIST has a "SP 800-38D: Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC". This guideline is a base for AES-GCM from definition to security ...
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Can I use different IVs when encrypting identical plaintexts with identical keys with AES-CTR?

I would like to use AES-CTR to encrypt the same plaintext with the same key more than once (on different machines). I'm wondering whether I should try to use the same IV each time, or whether it's ...
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Why would you want to keep the Initialization Vectors Public?

So I was researching Initialization Vectors (IV) and even took a look at this thread... What is the main difference between a key, an IV and a nonce? ,but I was hoping that I could get some clarity. ...
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Safety of a private key when knowing the full content of an encrypted message in case of fixed initialization vector

When knowing the full content of the original message, will I be able to derive the private key from the encrypted message when the underlying encryption uses a fixed initialization vector? Meaning if ...
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63 views

Number message limits of Galois/Counter Mode (GCM) per key

In https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf page 27, it is said that ...the total number of blocks of plaintext and AAD that are protected by invocations of the ...
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Why SHA-512/256 when we already have SHA-384?

Both of them are just SHA-512 with different IV's and truncation. What's the point of having 2 of them? (Actually we have 3 of them as SHA-512/224 is the exact same thing.)
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Extending AES-GCM initialization vector

We all know that applications of crypto primitives like to not think about the management of nonces, and initialization vectors and often prefer to just set them to random values. This sometimes leads ...
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Why does SHA2-224 use different IV's than SHA2-256?

Given that it's otherwise just a truncation, I can guess that being able to compute the 224 value from the 256 value is an unwanted property, but that's just speculation.
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Multiple IV CBC

CBC's encryption is not paralelizable but I could divide a 64 block message in 4 16 block parts and encrypt those 4 parts separatly in parallel using a diferent IV for each one. Is this unsecure ? Is ...
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Find IV and the key ? AES with CFB or OFB

I have a question about the AES-128 and AES-256 encryption method. I need to encrypt 64-bit size data in and out. I want to encrypt them with AES. So I turned to AES-OFB or AES-CFB because these ...
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Is it okay to have no IV when using AES-CBC with unique keys, that are however derived from one shared key?

Given $\operatorname{AES-CBC}$ (128-bit), with $IV=0$ and unique encryption keys $$K_{Enc} = \operatorname{CMAC}(MK, \text{known_text})$$ where $MK$ is a shared symmetric 128-bit key and $\text{...
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348 views

Encryption with Web Crypto API (SubtleCrypto)

I want to end-to-end encrypt items in a stateless environment. These items have an identifier (random string). Now I want to add encryption by adding a random key. The URL could be ...
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JOSE: JWE CEK Initialization Vector Position or Reuse

So I am attempting to generate a JWE using an X25519 to encrypt the for the Content Encryption Key (CEK) and AES-256-GCM for the content. My issue however is that NaCl needs an IV (nonce in NaCl) for ...
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74 views

AES-256 CTR with ESSIV, is this correct?

I am having some problems encrypting disk using AES-256 in CTR mode, with ESSIV iv generation (I am aware of couple of flaws, although this mode is enough for now). What I have here is: ...
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Number of keystreams generated in Kreyvium for a single key/IV pair

Kreyvium employs 128-bit key and 128-bit IV. By a single initialization procedure using a key/IV pair, how many keystreams can be generated?
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ECRYPT Salsa20 Test Vectors Interpretation

I am currently implementing Salsa20 for my bachelor thesis. After having verified all the functions needed for the final encryption function with the given test data in the specification from DJB, I ...
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Crypto system design : How to design Encryption for Zero width characters

Zero width character's can be used to hide text in plain sight.I am building a system where user's can provide their secret message , cover message and a password (key) which I would encrypt and give ...
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Can Trivium ciphertext be decrypted by an adversary if the key is known, but the IV is not?

Suppose that the adversary is able to recover the key of Trivium cipher. But the associated IV is unknown to him. Will he be able to decrypt the ciphertexts without any complexity?
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What is the significance of IV in stream ciphers like Trivium?

In Trivium cipher, an 80-bit key and 80-bit IV (initialization vector) are used initially to set up the initial state. I would like to know, Role of IV in stream cipher? Can we make IV a secret ...
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When using CBC-ESSIV for disk encryption, why does the generation of IV require a hash then encryption instead of only one hash?

The CBC-ESSIV algorithm specifies how to calculate the IV to use for a given key (K) and sector number (S) as the following: $$\text{IV} = \operatorname{Enc}(\operatorname{Hash}(K) , S)$$ https://en....
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If I allow arbitrary initial hash values for SHA-256, what would be the weaknesses?

The initial hash values (IV) of SHA256 are fixed. However, let's say I modify the SHA256 hash function to allow the attacker to use arbitrary IVs rather than fixed IVs. What kind of weaknesses would ...

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