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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2
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1answer
28 views

Can we use the authentication tag as Nonce / IV for the next message?

Let's assume we're in some scenario requiring transfer of large amounts of data. This means we can only use AES-GCM chunk-for-chunk as its maximal size is restricted to a few GiBs. This means we have ...
2
votes
1answer
28 views

Using scrypt to generate key + IV/nonce together

Is there any security issue in using scrypt for Key + IV/nonce generation? In other words, can I safely use only a salt for scrypt and derive the nonce along with the key? For example: I have data I ...
3
votes
1answer
78 views

Secure method of encrypting data within a database

I'm designing a program which makes queries to a database stored locally which could potentially contain a lot of sensitive information. As such the information must be kept secure as possible from ...
2
votes
1answer
29 views

MDC-2 recommended IV values?

I'm currently reading Menezes' "Handbook of Applied Cryptography", and in it, when describing the MDC-2 cryptographic hash function, has the following line: Choose the 64-bit non-secret constants ...
16
votes
2answers
2k views

Why should I use an Initialization Vector (IV) when I have unique keys?

I took a look at “Why, or when, to use an Initialization Vector?” but my question is not the same. I have unique keys encrypting each plaintext (in CBC mode, AES-256) and I do not use a key to ...
0
votes
0answers
8 views

Does we need IV if we're generating a new Symmetric key for every message? [duplicate]

We need to encrypt individual messages, for every message we: Generate a new AES key Encrypt the message with the key (AES/CBC/PKCS5Padding) Encrypt the symmetric key with with a public key ...
1
vote
1answer
50 views

AES-CBC pre-determined IV vs. null IV

Is there any security advantage to using a pre-determined IV in CBC mode over a null IV? I'm implementing a license key system similar to this article on CodeProject, but I'm confused by the authors ...
2
votes
1answer
71 views

How bad it is using the same IV twice with AES/GCM?

I understand that initialization vectors should not be used twice when using AES/GCM. I am using a counter as initialization vector. Every time I send out a new packet (I am developing an UDP based ...
1
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1answer
47 views

Ciphertext and tag size and IV transmission with AES in GCM mode

I am completely new to using AES in GCM mode of operation, and I have not a very large background in cryptography as well. I have been playing with OpenSSL trying to encrypt and decrypt some messages. ...
11
votes
3answers
2k views

Is using a predictable IV with CFB mode safe or not?

While writing this answer, I noted that NIST SP 800-38A says that (emphasis mine): "For the CBC and CFB modes, the IVs must be unpredictable. In particular, for any given plaintext, it must not be ...
-3
votes
1answer
86 views

OTP - Reuse key BUT add IV, is it secure enough?

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! I have already asked a similar question and now I can continue to this question about adding a "extra key" = IV. My last question ...
1
vote
1answer
64 views

Derive cipher IV and cipher Key using PBKDF2 with random salt?

It is said that cipher IV does not have to be secret and the only secret component of the encryption scheme should be a cipher key. Question: is it safe to generate IV using PBKDF2 function, which ...
1
vote
1answer
71 views

Attacking CBC with predictable but encrypted IV

Let P be a secure block cipher, eg AES-128. Let's say a server has a CBC encryption oracle which uses an attacker-selected yet unique nonce to generate the IV for each message = P(key, nonce). The ...
15
votes
2answers
6k views

What is the main difference between a key, an IV and a nonce?

What are the main differences between a nonce, a key and an IV? Without any doubt the key should be kept secret. But what about the nonce and the IV? What's the main difference between them and their ...
0
votes
1answer
51 views

how does an initialization vector work? [duplicate]

Can somebody please explain how an initialization vector works. My current understanding is that it is used to prevent 2 of the same messages looking identical after encryption, but isn't this the ...
3
votes
3answers
2k views

How to break AES/CBC/PKCS5 when key and IV are reused?

I'm doing a code review for a crypto solution that reuses the same key with a constant IV. I want to demonstrate that this is not the right way to do things by figuring out the key and decrypting all ...
0
votes
2answers
57 views

Looking for encryption algorithm not subject to known-plaintext attack with IV reuse

I've encountered an interesting problem where we can basically say the following: We need to encrypt messages, but we have no room to store IVs. We can synthesize IVs; however an attacker would be ...
5
votes
1answer
902 views

What are the constraints for an IV using AES in CBC mode?

I'm designing a protocol for use into a VPN software. The VPN frames are encapsulated into AES-256 CBC encrypted frames. I understand that IVs must be uniquely used for each message encrypted with ...
1
vote
1answer
49 views

Are there equivalent IVs in DES/CBC?

I'm playing around with the CryptoPP library with DES/CBC and I've noticed that for some sets of data, if I decrypt the ciphertext with Key1, IV1, I get a good cleartext result -- but if I decrypt the ...
-7
votes
2answers
152 views

OTP - Reusing key IS SECURE! PROVED! [duplicate]

EDIT: This is not a duplicate, in this I have explained WHY this should be secure and not if it is secure, so please stop down-vote if you haven't read everything. I have questioned before about my ...
0
votes
1answer
304 views

What do I use as the encryption key and initialization vector in AES cfb128

I'm writing a program that can encrypt a file using AES cfb128 (using Openssl and C++). The scenario of the program is this: Person A visits computer, encrypts a file they make, takes away a key ...
3
votes
2answers
197 views

Why would an Initialization Vector be supplied externally?

My software uses a 3rd party encryption appliance. One of the capabilities they allow is for the client software to supply an IV while doing CBC encryption. Why would they not generate a random ...
-1
votes
1answer
134 views

credit card number encryption using aes-ctr mode

I want to encrypt credit card numbers. I want to apply AES-CTR mode. Is it suitable for that? How can I store nonce and counter values for an individual credit card number? How can I send the ...
-1
votes
2answers
162 views

Remove padding (CBC) from decrypted text [closed]

I have a bit problem with padding. Everything goes fine when I encrypt the text BUT when I decrypt I see some extra characters. Sometime's one character sometimes more and I dont know how to remove ...
4
votes
2answers
432 views

How do we compute IV+1 in CTR mode?

This may be a very simple question, but I have not found info about this in any place. My question is about CTR mode: When it says $IV+1$… How do we make this operation? For example, if I have the IV ...
2
votes
0answers
79 views

What are the steps to decrypt a TLS 1.1 record?

My question is related to another question in Cryptography about TLS 1.1 and 1.2. I have read both RFC 2246 The TLS Protocol Version 1.0 and RFC 4346 The TLS Protocol Version 1.1. What I know is that ...
1
vote
2answers
119 views

IV's for different AES encryption modes

I wanted to know if my understanding is correct! I have been reading up on aes encryption and modes(specifically CTR and CBC) and it took me sometime to understand the concept of IV. If the IV is ...
0
votes
1answer
90 views

How do I communicate the value of the initialization vector to the end user? Should it be part of the encrypted message?

I am taking a cryptography class and our first homework is to implement a 32-bit block cipher. I implemented a simple block-cipher that uses CBC. Currently, my implementation reads both the 32-bit IV ...
0
votes
1answer
42 views

With wrong IV at receiver side, the CFB in better than OFB?

Assume the receiver have a wrong IV (initialization vector), in the CFB mode only the first block of plaintext is wrong but in OFB mode the second and all blocks will be affected. Is that correct? ...
2
votes
1answer
115 views

BEAST attack confusion

I understand that BEAST is a CPA using javascript injected onto the browser's webpage. Apparently the thing that BEAST exploits is the fact that the IVs are predictable. What I'm confused about is why ...
2
votes
1answer
52 views

Effect of CFB IV reuse

If an Initialization Vector (IV) is reused (under the same encryption key) in Cipher Feedback Mode (CFB), what is the effect upon security? I know there is some negative effect upon security, but I ...
0
votes
2answers
162 views

(Re-)Using deterministic IV in CTR mode / How to: deterministic AES

I am aware of the requirement of an IV to be unique in CTR mode (Why must IV/key-pairs not be reused in CTR mode?). However I wonder if I can use an IV depending on the plaintext deterministically. ...
-2
votes
1answer
79 views

What is Initialization vector (IV) [closed]

I am not the best cryptologer and therefore I have some questions so I learn more and get better. Heres the questions: What is Initialization vector (IV)? MUST I use it or not?
9
votes
4answers
2k 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 ...
15
votes
1answer
2k views

Why do new versions of TLS use an explicit IV for CBC suites?

SSL 3.0 and TLS 1.0 used an insecure scheme to generate implicit IVs when encrypting records in CBC mode: they used the last part of the previous record, a value that can be predicted by the attacker. ...
3
votes
1answer
277 views

Possible CPA or CCA attack when using AES-CBC mode under the following situation?

Both client and server know a shared key in advance. Both sides us EVP_BytesToKey() derive a pair of same key and same IV. Then, client and server start transferring data encrypted by AES-CBC mode ...
4
votes
1answer
135 views

What's the consequence of having a short IV? Is one mode better in that case?

I've read lots about null-length IVs being bad for most modes. In a scenario where passing a 128-bit IV along with each message isn't feasible, how would generating the IV from a smaller passed-along ...
4
votes
3answers
1k views

Difference between a nonce and IV

I know the generic difference between a nonce and an IV. I am specifically looking for a clarification on these terms as used in the "Evaluation of Some Blockcipher Modes of Operation" by Phil ...
2
votes
1answer
159 views

Format of NONCE in Initialization Vector (IV)

When we talk about a Number used ONCE (NONCE) in Initialization Vector (IV), is it required to use numbers only? Is is possible to use letters or special characters?
9
votes
2answers
2k views

Why is CBC with predictable IV considered insecure against CPA

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 is uses, the attacker can ...
4
votes
3answers
336 views

Is it secure to use Diffie-Hellman key agreement to generate a nonce?

I have a system, using AES, in one of the modes that uses a nonce and authentication. We have a pre-shared key, and to agree about initial nonce we could use Diffie-Hellman, using the resulting ...
1
vote
1answer
116 views

Adding an IV to an AES implementation

I have an embedded project that requires AES, I seem to have found an AES implementation that fits the bill here: http://www.literatecode.com/aes256, but it does not include an IV. Are there any ...
1
vote
1answer
408 views

CBC-MAC length extension attack with IV simulation

I'm doing Matasano's challenges and struggling with second part of 49th problem where I'm asked to do the length extension attack with CBC-MAC without IV manipulation. There is a hint that I can ...
4
votes
3answers
958 views

What algorithm would give the shortest ciphertext for very short plaintexts?

I have to encrypt some very short messages (approx. 5 characters) and I would like the ciphertext to be as short as possible. I am currently using AES but the initialization vector (IV) is making my ...
1
vote
2answers
79 views

Key cracking: Prefer many small texts over one large text?

If an attackers sets out to crack the symmetric key of e.g. AES-CTR, would they prefer to have access to many small cryptotexts or one large cryptotext? I.e. is it more interesting for the attacker to ...
3
votes
1answer
222 views

Why must IV be sent with each packet?

I was reading about Encrypt-then-MAC and everywhere I go it seems people include the IV with the ciphertext generated for each message then MAC that and send all the information concatenated. Why do ...
1
vote
1answer
511 views

Value of “counter” when decrypting AES in CTR mode?

If – when using AES in CTR mode – you decide to use the setup where you combine the IV and the block count value into a single value, as suggested here, the first 12 bytes are your IV and the last 4 ...
-4
votes
3answers
462 views

IV's from Crypto++ AutoSeededRNG always ends the same: Problem with the PRNG? [closed]

I am using a AutoSeededRNG from Crypto++ to generate IVs for use in CBC encryption. I am encoding the IVs using Base64 for future use (decryption). I notice that ...
2
votes
3answers
984 views

Problems with using AES Key as IV in CBC-Mode

I'm a pentester and currently analysing a web application which are using some strange encryption scheme. The point is: They encrypt using AES-128, generate a (not cryptographic secure) key and use ...
1
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1answer
89 views

Is it possible to deduce the IV from CBC ciphered data, without knowing the key?

The question came up here, which left me thinking: Is it possible to deduce the IV from CBC ciphered data, without knowing the key? And if not, why is it considered a bad idea to create an IV by, for ...