Questions tagged [cbc]
Cipher block chaining (CBC) is a method for encrypting large amounts of data with a block cipher that can only encrypt fixed length plaintexts. When used with an unpredictable initialization vector (IV), it is secure against chosen plaintext attacks (CPA-secure).
489
questions
0
votes
1
answer
127
views
Collision Security
Question concerning collision issue in CBC-mode:
If we are using CBC mode with AES for 1 message, the birthday paradox indicates that we risk a collision after 2^(n/2) so 2^64 plaintext of 128 bits of ...
Algorithm123
0
votes
0
answers
101
views
Meet-in-the-middle attack (different block cipher modes)
Does a meet-in-the-middle attack on depend on the used modes for block ciphers?
encryption: $C_i$ = $D_{K2}$($D_{K1}$($E_{K1}$($P_i$ $\oplus$ $C''_{i-1}$))) $\oplus$ $C'_{i-1}$ and $IV_1$ = $C''_0$ = ...
- 31
1
vote
0
answers
31
views
Meet-in-the-middle attack (on custom encryption scheme) [duplicate]
This is a question I had from an exercise session.
Exercise:
First we do DES in CBC encryption mode using a key $K_1$ and $IV_1 = O^n$.
Then we do DES in ECB decryption mode using $K_1$. And then DES ...
- 31
0
votes
1
answer
86
views
Symmetric encryption construction (meet-in-the-middle attack)
This is a question I had from an exercise session.
First we do DES in CBC encryption mode using a key $K_1$ and $IV_1 = O^n$.
Then we do DES in ECB decryption mode using $K_1$. And then DES in CBC ...
- 31
1
vote
1
answer
473
views
Cipher Block Chaining - How do you change the plaintext of all blocks?
I've just read about CBC encryption and decryption and was wondering how you can change every plaintext block?
Let's say you have an initialization vector, 3 ciphertext blocks, know each block-cipher-...
- 113
0
votes
1
answer
347
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 = ...
- 324
1
vote
1
answer
827
views
How does the CBC Padding Oracle Attack work in General?
Right now we don't have a single generalized question asking how the CBC padding oracle attack works. We have e.g. this one and this one but the former is distracted by the concrete values being ...
- 45.7k
1
vote
2
answers
2k
views
What are the implications of XORing ciphertext with plaintext?
I was intrigued by this question: Does adding complexity mean a more secure cipher?
And it led me to wonder: What are the implications (if any) of XORing a ciphertext with the original plaintext ...
- 117
2
votes
1
answer
448
views
Reverse the order of encryption and decryption in CBC mode. Does this work?
To encrypt a message, one uses the algorithm for doing a CBC decryption. To decrypt a message, one uses the algorithm for doing a CBC encryption. Does this work?
- 21
1
vote
0
answers
138
views
How to implement correctly a "secure" authentication protocol? [closed]
Due to my lack of knowledge in this matter I am facing some problems to identify which features are sign of a bad implementation of a symmetric authorization application.
As I am concerned the system ...
- 47
0
votes
0
answers
280
views
How to change the known ciphertext so the known plaintext is changed in AES CBC mode?
I already read a blog about the padding oracle and also some posts about how to change the plaintext but it didn't work out.
So I have the encrypted cookie (AES_CBC):
...
- 111
5
votes
2
answers
1k
views
What's the reason for Monte Carlo tests for block ciphers?
NIST specifies that implementations were required to create Monte Carlo test vectors for ECB and CBC mode for the AES competition.
What's the reason for these tests? The only thing I can think of is ...
- 91.9k
1
vote
1
answer
359
views
What is the Risk of Rotating Keys
This may be a difficult question
So, $C_1$ = AES-GCM($k_1$, nonce, message) where nonce = HMAC(key,message). $C_2$ = AES-CBC($k_2$, iv, $C_1$).
Now, a security breach occurs. The adversary obtains ...
- 11
2
votes
1
answer
253
views
How do i approach file encryption using encrypt-then-mac? [duplicate]
I'm programming a cryptographic application that encrypts files, locked with the password the user supplies. It's not intended to be used in production. It's a project for me to learn more about ...
- 23
0
votes
2
answers
123
views
Randomly initialised global counter used to encrypt the kth message with $\operatorname{IV} = \operatorname{IV} + k \hspace{5mm} mod \hspace{5mm} 2^n$ [duplicate]
The use of an increasing IV is not secure for a block cipher. That is, using a random IV for the first message then $\operatorname{IV} + 1$ for the second , $\operatorname{IV}+ 2$ for the 3rd etc. How ...
- 1
1
vote
1
answer
374
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 ...
- 111
4
votes
1
answer
5k
views
Length of password requirement using openssl aes-256-cbc
I am using the following OpenSSL command to AES 256 encrypt a file:
...
- 143
11
votes
0
answers
2k
views
Why does the Signal protocol use AES/CBC instead of AES/GCM?
AES/GCM has obviously proved itself to be better than AES/CBC. Unless the key is re-used with the same initialization vector (see disadvantages of GCM). More information on its advantages against CBC ...
- 324
0
votes
0
answers
1k
views
Aes brute force when part of data known [duplicate]
I have buffer of 16 bytes that encrypt with AES 128 cbc with IV =000000......(all IV is 0)
I have the encrypted buffer, and I know 7 bytes from 16 bytes before the encryption , I dont know the key .
...
- 101
0
votes
2
answers
4k
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
2
votes
1
answer
931
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 ...
- 63
3
votes
1
answer
3k
views
AES-CBC Padding: Why always attach 16x 0x10 pad?
Why do we have to always attach a 16x 0x10 pad even though the last block is already at block-length?
- 165
1
vote
1
answer
710
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:...
- 13
2
votes
1
answer
570
views
Plaintext Size Limit for ECIES with AES-128 CBC mode
Using the ECIES (Elliptic Curve Integrated Encryption Scheme), is there a limit size of plaintext? (what is the maximum allowed number of bytes to be encrypted with ECIES).
- 127
1
vote
1
answer
8k
views
Decrypt simple CBC with XOR
I have searched and my problem is exactly the same as shown here:
Decrypt simple CBC message with known IV using XOR encryption
However, when I implement the solution it doesn't work, neither does ...
- 23
2
votes
2
answers
184
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 ...
- 193
17
votes
1
answer
27k
views
Bit Flipping Attack on CBC Mode
To perform a bit flipping attack, the previous block is modified by using XOR. This results in an altered plaintext. However, now the ciphertext of the previous block is altered, hence it will result ...
- 311
3
votes
1
answer
438
views
Security of AES after key expansion 4-MB with ECB and CBC
My question is,
how does the security depend or change if I encrypt with AES-128 in total 4-MB of Data?
With Electronic Code Book Mode and
Cipher Block Chaining Mode ?
Does an adversary still ...
- 31
2
votes
2
answers
1k
views
The attacker model of the Lucky13 attack in TLS
Lucky13 is a timing attack against the MAC in the CBC MAC-then-encrypt ciphersuites. In the attack's page:
The attacks involve detecting small differences in the time at which
TLS error messages ...
- 407
2
votes
2
answers
875
views
Replacement for XOR in CBC?
In CBC mode, the XOR operation is used to combine the previous encrypted block with the current plaintext, to be used as the block to encrypt. Apart from other known disadvantages inherent to the mode ...
- 121
1
vote
1
answer
1k
views
What happens if CBC-mode uses the same IV for all processes?
In Cipher Block Chaining (CBC) mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted. What happens if I use the same IV instead of the previous ciphertext ...
1
vote
2
answers
2k
views
CBC related TLS cipher suites to be disabled in the server side
I understand the TLS cipher suites using CBC mode are susceptible to timing attacks. From that understanding it seems that the cipher suites using GCM (CTR-based) are safe to use considering they don'...
- 508
1
vote
1
answer
441
views
With DES, is ECB encryption mode equivalent to CBC with null IV for short data blocks?
I got to this by experimentation, but can someone maybe provide an explanation for this?
- 277
1
vote
1
answer
1k
views
How is a PRP different from PRF? Both can be inverted to get the same input
PRP is said to be a bijective function which means that there is a one-to-one mapping with the output. And hence the output can be inverted using the decryption algorithm to get the same input.
...
- 508
-5
votes
1
answer
391
views
AES without mode operation
i have field in database. ex: field name. this field maybe more than 16 byte. how to encrypt data more than 16 byte without cbc, etc?
any function or another ways to do this?
- 9
5
votes
1
answer
4k
views
Is DES secure under CBC?
I know DES is outdated, but will is is secure in CBC mode? Can anyone help me understand why not?
- 51
3
votes
1
answer
4k
views
Why can't decrypt with OpenSSL if salt changed (for CBC and ECB)
A file encrypted with OpenSSL (with, for example, AES 256-bit mode CBC) using the Linux command
openssl enc -aes-256-cbc -in texte -out encrypted_texte -k password
...
- 33
1
vote
1
answer
89
views
What happens if the plaintext $m1$ from the first block of CBC is known to adversary?
The adversary is has unlimited access to the encryption oracle. My thinking is that upon receiving the ciphertext C = $<c_0,c_1,c_2...,c_n>$ it will just use $c_0$ to XOR it with $F_k(m_1)$ to ...
0
votes
1
answer
880
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
1
answer
1k
views
Which block cipher mode to use?
I am working on securing a chat application, and I am not sure about which block cipher mode I should use. I am aware that I should avoid ECB as it's insecure, but what about CBC? I have watched ...
- 11
1
vote
1
answer
3k
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.
...
- 113
2
votes
1
answer
4k
views
Is AES-CBC mode not secure against chosen cipher-text attacks even if the IV is not predictable?
I've seen questions where people have asked if AES-CBC mode is vulnerable to chosen cipher-text attacks if the IV is predictable.
But is it guaranteed to be secure against chosen cipher text attacks ...
- 211
2
votes
2
answers
267
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 ...
- 33
2
votes
1
answer
726
views
Cipher Block Chaining (CBC) encryption in SSL
Is cipher block chaining (CBC) mode used in SSL encryption? If block reordering is already protected by SSL and TCP sequence numbers, what added advantage does CBC provide?
- 123
2
votes
2
answers
2k
views
Cipher Block Chaining Ciphertext Alteration
I am new to cryptography. My professor's slides say that "Disadvantage: altered ciphertext only influences two blocks" for the CBC. However, since we xor the ciphertext from the previous block and the ...
- 319
6
votes
2
answers
2k
views
Choice of padding scheme to prevent CBC padding oracle attacks?
I was watching a lecture about the padding oracle attack on CBC mode block ciphers, where the padding scheme used was PKCS#7.
My question is can padding oracle attacks be prevented (without any use ...
- 161
1
vote
2
answers
119
views
How to provide partial confidentiality and full integrity for a protocol message?
I want to provide confidentiality and integrity for a protocol. I don't want to encrypt the entire protocol message. I do not want to encrypt the header and timestamp of the protocol message, but I ...
- 461
0
votes
1
answer
335
views
Can I use PKCS#5 with CBC? [duplicate]
As far as I know there are two padding mechanisms, which are PKCS 5 and 7. Which one should be used for CBC?
- 461
5
votes
3
answers
6k
views
When do I need to use CBC and HMAC?
As I know CBC does not provide integrity for the message, thus HMAC is used to provide integrity for CBC message. Also, I hear about CBC-MAC which can provide integrity and confidentiality. Which one ...
- 461
1
vote
1
answer
434
views
Can blocks in AES-CBC ciphertext be manipulated in such a way that plaintext becomes shuffled?
Say we have a sequence of N 16-byte plaintext blocks encrypted using AES in CBC mode, with an IV, resulting in N+1 16-byte ciphertext blocks. Can this ciphertext be manipulated in such a way that, ...
- 115