3
votes
1answer
48 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 ...
0
votes
0answers
34 views

Does bad IV generation weaken CBC? [duplicate]

Let's say that I generate an IV like so: dd if=/dev/urandom of=iv.bin bs=16 count=1 Let's also say that /dev/urandom has been ...
3
votes
3answers
448 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 ...
1
vote
1answer
71 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 ...
1
vote
1answer
189 views

Encrypting firmware with AES and no IV [closed]

I have an embedded device with a AES CBC engine on it that is used to ensure the integrity of the firmware. I know that CBC mode requires unique IVs to be any good, but I'm unsure if it makes a large ...
1
vote
2answers
179 views

AES-CBC and IV — Encrypting multiple blocks of a file with the same IV?

I have large files which are broken into blocks of 512 KB and uploaded to a server. In my DB I store the IV, and the user knows the security key themselves. When downloading, I use the same IV and ...
3
votes
3answers
431 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 ...
3
votes
1answer
225 views

Generating an IV for ESP 3DES-CBC

I have an application written in C, running in Linux. It uses IPsec (ESP) (manually putting the IPSec packet together) to send certain packets. The algorithm used ...
3
votes
2answers
420 views

Encrypted counter as IV in CBC mode encryption using same key

I'm currently working with a secure transport protocol that defines the IV to be a counter (incremental nonce) to be encrypted with the same key. This is a followup to a protocol that did not provide ...
3
votes
0answers
54 views

CBC with random prefix but no IV - secure? [duplicate]

I'm looking at a datagram-based protocol that encrypts a payload. The payload is encrypted with AES or blowfish in CBC mode, and the result is then authenticated with a HMAC. To save space, the ...
13
votes
2answers
837 views

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

I took a look at this question. My question is not the same. I've unique keys encrypting (in CBC mode, AES-256) each plaintext, i.e. I do not use a key to encrypt more than one plaintext. Is it ...
2
votes
2answers
228 views

IV Security Clarification

After doing lots of reading on SO and other websites relating to AES cryptography, I am trying to understand the security issues surrounding IV's. There seems to be a lot of confusion and ...
2
votes
1answer
163 views

Can prepending “junk” be equivalent to an IV when encrypting using CBC?

We are encrypting a small positive integer (1-1000) with a constant key using AES256 encryption. We are considering two approaches to make this secure; use an initial vector (which we then need to ...
4
votes
1answer
538 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 ...
2
votes
2answers
864 views

Validating successful decryption in AES

I have a program which uses AES-256 in CBC mode to encrypt and decrypt files. As I have quickly realized, AES will even use an incorrect passphrase to decrypt data, which leaves me with no way to ...
3
votes
0answers
108 views

CBC with fixed IV but changing data [duplicate]

Possible Duplicate: Using CBC with fixed IV I am using AES in CBC mode. For some reasons I have some issues for transmiting the IV. So I am using a fixed IV. If the first 128bits of the ...
2
votes
0answers
173 views

Why not use CBC, not send IV, and assume first plaintext block is garbage? [duplicate]

Possible Duplicate: Using CBC with fixed IV Forgive me if this has been asked before, I looked but haven't seen any answers that suit. Is there any danger in using CBC, encrypting a ...
10
votes
5answers
1k views

Using CBC with a fixed IV and a random first plaintext block

What if, instead of using CBC mode in the normal way with a random IV, I used this approach: Use a fixed IV (like a block of 0's). Before encrypting, generate a random block and prepend it to the ...
4
votes
1answer
2k views

Why, or when, to use an Initialization Vector?

i'm trying to figure out when an Intialization Vector (IV) should be used. There are anecdotal reports that WEP was broken because of weak IV's. It's also claimed that if two pieces of plaintext are ...
5
votes
2answers
2k views

Is AES in CBC mode secure if a known and/or fixed IV is used?

I have a need to encrypt credentials for a third-party app used by a secured internal app. Over on ITSec.SE, I was helpfully shown a scheme to encrypt the third-party credentials based on a hash of ...
8
votes
2answers
1k 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
990 views

Why does CBC decryption with a wrong IV still give readable results?

While developing some code that uses the .NET AesManaged algorithm, I made some mistakes but was surprised at the results. My encryption was correct. I was generating a random IV block and writing ...
11
votes
1answer
791 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. ...
1
vote
2answers
3k views

Initialization vector length insufficient in AES

I use AES with AES/CBC/PKCS5Padding with the following encryption and decryption code sections in Java: ...
6
votes
1answer
3k views

How do I correctly derive a Key and IV?

Mainly I'm trying to understand how to correctly create the Key and IV for use with the .NET Implementation of AES (AesManaged class). This encryption code will be used in conjunction with existing ...
9
votes
1answer
3k views

Can CBC ciphertext be decrypted if the key is known, but the IV not?

Let's say that there is a binary file encrypted with AES in CBC mode (i.e. using a key and initialization vector). If key is known, but IV is not, is it easy to fully decrypt the file? How hard is ...
8
votes
3answers
969 views

Is it okay to use a hash of a timestamp as the IV for AES?

The message format includes a datetime field in the clear. Is it okay to also use this field (or some hash thereof) as the initialization vector? In this case, CBC is the mode being used.