Cryptography

Questions tagged [initialization-vector]

Ask Question

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.

295 questions
Newest
Active
Bountied
Unanswered
Filter by
Sorted by
Tagged with
3
votes
1answer
49 views

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 ...
2
votes
2answers
59 views

Size of IV in AES-GCM according to RFC 4106

RFC 4106 specifies about nonce. It contains a salt of size 4 octets and an iv of size 8 octets. Further, RFC specifies that salt is assigned at the beginning of the security associations which is ...
2
votes
1answer
94 views

IV generation best practice for AES-256 CBC

I saw some SWIFT code that generates IV for AES 256 from selecting 16 characters from a-zA-Z0-9 space. Is this secure? Sufficiently secure? What is the best practice to generate IV for AES 256? Will ...
2
votes
1answer
101 views

Finding the IV values of SHA-256 given all message blocks

Given all message blocks $w[i],i \in 0:63$ and assume that $n<128$ (arbitrary) bits $x_1,x_2,...,x_n$ of the IV values are unknown (e.g., $h_7$ bits are unknown) while other IV values coincide with ...
2
votes
1answer
36 views

Longer IV generation from a single block IV for ICBC

I was reading a question about ICBC here and it mentioned that you would need a $s \cdot n$-bit $IV$ if you would use $s$ "stripes", where $n$ is the blocksize. Say that we don't like transmit that ...
2
votes
1answer
45 views

Reusing IV but still generating different code?

I'm in a beginner's cryptography class and I'm trying to figure out if I'm doing something wrong, or if I just don't understand why something is the way it is. I created a simple .txt file of 124 ...
2
votes
3answers
839 views

Does the Initialization Vector in DES have to be 8 bytes long?

I was experimenting around with DES and decided to implement an IV (Initialization Vector) for it. I noticed that in DES, which is 56 bits and 8 parity bits, the IV would be 8 bytes in length. Does ...
3
votes
2answers
337 views

Given the key, the plain text and the cipher text can I calculate the IV used in CBC mode?

If I have the plain text, the ciphertext and the key for an AES-128 CBC operation, can I determine the IV, even if I don't know the padding (assuming the padding follows one of the more common formats)...
2
votes
1answer
36 views

Security implications of not concatenating a 1 to the IV when using GCM

When using GCM, The padding string $0^{31}||1$ is appended to the IV. I know that this is done to avoid the repetition of $E_K(0^n)$ which is used as key for the GHash. But what would be the security ...
0
votes
2answers
181 views

How to generate a 128 bit IV from a 32 bit value for AES-128 OFB

I have no clue how to determine suitable 128 bit IV (initialization vector) from a 32 bit IV. Encryption AES-128 OFB. The 32 bit IV has value 0x9a23773c (...
1
vote
1answer
129 views

How does reusing IV for OFB mode breaks the scheme

Consider a Plaintext P1 and Ciphertext P2, which is known to the attacker. If the attacker knows that the IV used in encrypting P1 in OFB mode is the same used to encrypt another plaintext P2, how can ...
2
votes
2answers
197 views

using different IV and SALT with AES-CBC but same KEY

I'm working on this project where a client can send a message, now obviously sending it in plainText is not very smart. So I decided to Encrypt it with AES-CBC. Now, each time I encrypt something, ...
1
vote
1answer
44 views

Is it safe to compute HMAC(Base64(IV) || “,” || Base64(CipherText)) instead of HMAC(IV || CipherText)?

Let || be the concatenation operator. Let CipherText = AES(Key1, IV, Message). Let us assume AES is used in CBC mode. I want ...
2
votes
3answers
167 views

AES Cipher Block Chaining 128 bit message

I understand that for AES CBC you need to split the plaintext up into blocks and perform XOR'ing using the previous blocks calculations etc. However, if your message is exactly 128 bits long, do you ...
3
votes
1answer
114 views

Best practices for IV generation

What are the best practices for IV generation for AES and other algorithms? Is RNG enough? What if I cannot use RNG and need to use a variable that is related to some characteristic of the ...
0
votes
0answers
42 views

Is it possible to encrypt a message stream with the same IV each time and for it to be secure?

I know we should ideally never reuse the IV (Depending upon the mode of encryption used), but is it possible to have a protocol which uses the same IV for the message stream and is as safe as one ...
1
vote
1answer
84 views

Attacking Double DES (OFB Mode) given the initialization vector and not much else? [closed]

I'm given a Plaintext/Ciphertext pair, a Ciphertext to break, and the IV. One thing of note is that the same IV is used for both DES Encryptions, so $$C = E_{K_2}(E_{K_1}(P, IV), IV)$$ I have limited ...
0
votes
1answer
43 views

Can I use a fixed IV with AES-GCM if I only encrypt unique plaintext values? [duplicate]

My use case guarantees that all plaintext values are unique. In this case, is it safe to use a fixed IV with AES-GCM to carry our encryption/decryption?
0
votes
1answer
94 views

Is the AES-GCM encryption using the SHA256 hash of the plaintext as IV secure?

I want to encrypt a list of unique values and I want the property of when I encrypt the same value I get the same ciphertext (determinism). The adversary only observes the ciphertexts of a unique set ...
3
votes
1answer
335 views

AES-CBC streaming configuration IV usage

I am interested in the implications of using AES-CBC in a streaming configuration. Reading the specifications of a few protocols I notice that when using AES-CBC they include IV + ciphertext + HMAC ...
0
votes
1answer
70 views

It is the IV shared in CBC mode?

I don't know if the IV in CBC mode is equal in both sides of the encryption and decryption operations. I know that the IV must be unpredictable, but has it to be MACed in the encryption side to be ...
1
vote
1answer
881 views

AES-GCM cipher - Nonce vs IV

I am using a Python library called PyCryptodome, which offers the following API for AES-GCM ciphers: https://pycryptodome.readthedocs.io/en/latest/src/cipher/aes.html As you see, IV is not ...
2
votes
3answers
729 views

What happens if you increment MAX counter in AES-CTR?

Suppose you use a IV/counter = ffffffffffffffffffffffffffffffffin AES-CTR. What will happen if you encrypt the next block, and thereby increment the counter by one? ...
0
votes
1answer
114 views

Signal Protocol Header key encryption initialization vector

In Signal Protocol when you use a Double Ratchet you have 2 options: Normal encryption = header + ciphertext Encrypted header encryption = ...
3
votes
2answers
97 views

Why BouncyCastleAesCbcBytesEncryptor is using a salt and an initialization vector?

I'm using the class BouncyCastleAesCbcBytesEncryptor from Spring Security. One of the constructor has the following signature: ...
0
votes
2answers
283 views

IVs in WEP encryption

First, I'm pretty new to the world of encryption. As I understand it, in WEP, the plaintext and CRC are XOR'd with the IV and the key (or more accurately, the key/stream, which is produced by a pseudo-...
0
votes
0answers
97 views

Is it possible to recover the key to a decrypted file? [duplicate]

Is it possible to recover the key to a decrypted file if you have the initialization vector and it uses RijndaelManaged in CBC mode? If so how? The file I want to recover the key from is a xml that ...
8
votes
3answers
1k views

Can a zero nonce be safely used with AES-GCM if the key is random and never used again?

I could generate a random nonce and prepend it to the ciphertext, but storage space is at a premium and the only constraint AES-GCM has on the nonce (if I'm reading correctly) is that the same nonce ...
0
votes
0answers
43 views

What is the most secure way to encrypt certain properties in logs

I would like to encrypt certain data before logging it. Currently, I use a private key and a static IV. Looking at generating a suitable IV I am concerned about the overhead in generating CSPRNG ...
0
votes
1answer
50 views

Randomly initialised global counter used to encrypt the kth message with IV = IV + k mod 2^n

The use of an increasing IV is not secure for a block cipher. That is, using a random IV for the first message then IV + 1 for the second , IV + 2 for the 3rd etc. How can I construct an attack to ...
2
votes
1answer
421 views

IPsec : transmission of Initialization Vector

I am currently carrying scholar research about IPsec protocol, and I have a question regarding the IP Encapsulating Security Payload (ESP). Is the initialization vector of operation mode transmitted ...
1
vote
1answer
115 views

IV Re-use and Chosen Plaintext against 56bit Blowfish (CBC)

I am looking at a very old protocol which uses Blowfish to encrypt packets with a constant 8-byte IV in CBC mode. Assuming I have: The ability to arbitrary encrypt known plaintexts The IV I know ...
1
vote
1answer
201 views

AES-GCM cipher tag and IV size, while attempting to render encrypted ciphertext useless by removing them

I'm using AES in GCM mode of operation for encryption/decryption & authentication of segments of data in a file. The layout of each segment can be summerized by this diagram. Each segment is ...
0
votes
1answer
227 views

how to compute IV with AES CTR if key, plaintext and ciphertext are known?

Given $E_k$, which a block-cipher using the (known) key $k$, and a plaintext-ciphertext pair $(p,c)$ where $c$ is the encryption of $p$ using CTR mode, can the initialization vector be recovered using ...
0
votes
2answers
241 views

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 ...
1
vote
1answer
289 views

Alter plaintext through IV in block cipher AES in CBC mode

IV: 69bb375aa919c72aa561dd7b7ffacf66 Ciphertext: "c28ea025d10186510855d083747d6435c808d9857075abd9bfc54b094e60eaf3" Plaintext: "SEND ENCRYPTED DATA" I want to be able to change the resulting ...
2
votes
2answers
2k views

AES-256 GCM IV guidelines

If I use for example AES-256 (GCM), and my message is bigger than 256 bit (broken into smaller 256 bit blocks for encryption), should the IV change for every 256 bits of the message?
1
vote
1answer
244 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:...
1
vote
1answer
78 views

Why can´t an attacker find the key if he has the plain text, the IV and the ciphertext? [duplicate]

I am reading a book about web security and they are now talking about AES CBC. After reading the chapter I was wondering, can an attacker compute my secret key if he has access to the IV, the plain ...
1
vote
2answers
107 views

With AES-GCM, may I use multiple tags per key?

In my implementation of AES-GCM, the key might change only once per minute. However, I wish to calculate a new tag every 6us, to reduce latency (since you have to buffer up a GCM "packet" before ...
2
votes
2answers
117 views

Safely erasing encrypted data

My secret message is encrypted in a byte buffer with AES-128 in CBC mode. The first 16 bytes are the IV and the message follows contiguously. If I want to securely delete this message is it enough ...
2
votes
1answer
228 views

Is an IV useless for encrypting database IDs?

In my scenario I need to build a pseudo-anonimization service: a machine that given a plainID return a chiperID and vice-versa. <...
4
votes
1answer
207 views

Crypto-shredding a file by erasing the IV instead of erasing the Key

Imagine an authenticated, encrypted file system, which uses AES-256-CTR to encrypt a 64 KB file sector, then uses HMAC-SHA256 to authenticate the 64 KB file sector (including the IV). IVs are 128-bit, ...
1
vote
1answer
560 views

Simulation of Chosen Plaintext Attack on CBC, Predictable IV with OpenSSL

I would like to simulate the CBC IV attack where the IV is predictable. It's described in the answer to this question: chosen plaintext attack on CBC, predictable iv (Only "Yes" and "No" are valid ...
0
votes
1answer
204 views

Recovery of private key in AES-CBC from two ciphertexts with different IV, but identical plantext

I have a system that encrypts messages for a given user using key K using AES-CBC in response in an external stimulus. Each message has a randomly generated IV. The user never decodes these messages,...
1
vote
2answers
111 views

Encryption using deterministic CSPRNG as secure as CSPRNG

As a beginner it seems that a scheme derived from a CSPRNG should be as secure as that CSPRNG. Is this a correct assumption? Are there restrictions or known special cases? A rough outline would be: ...
2
votes
1answer
393 views

Does it matter how the IV and XOR are applied for a single AES-128 block?

I want to encrypt 128 bits of data. I understand the problem with ECB, so I generate a 128-bit Initialization Vector to use for encryption and send with the encrypted data. Is there a "best" way to ...
1
vote
2answers
488 views

Can I find the IV of a single block of SHA256, given the plaintext and digest?

Each 512-bit block of SHA256 takes an initialization vector (IV) and message schedule and returns a digest. Knowing the message schedule and resulting digest, is it feasible to reverse the algorithm ...
1
vote
1answer
1k views

Decrypting an encrypted aes 256 cbc text with random IV, decrypts the string [duplicate]

This may be a basic question but bear with me. I started encrypting a text with aes 256 cbc mode generating a random iv of 16 bytes and a key. ...
1
vote
2answers
142 views

Encrypting current time using 3DES as a signature

I came across a peculiar system for generating "signatures" ("signatures" is within quotes because this is a bad use of 3DES) in the wild. It works as follows: a symmetric key is generated and used ...

1
2 3 4 5 6