The Stack Overflow podcast is back! Listen to an interview with our new CEO.

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).

Filter by
Sorted by
Tagged with
1
vote
1answer
246 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?
1
vote
1answer
266 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. ...
-5
votes
1answer
97 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?
3
votes
1answer
1k 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I know DES is outdated, but will is is secure in CBC mode?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?
3
votes
1answer
2k 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 ...
1
vote
1answer
73 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
1answer
158 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
1answer
333 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 ...
1
vote
1answer
798 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
1answer
825 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 ...
1
vote
2answers
90 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
vote
1answer
346 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?
1
vote
2answers
530 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 ...
3
votes
2answers
927 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 ...
1
vote
2answers
64 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 ...
0
votes
1answer
215 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?
3
votes
3answers
2k 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 ...
1
vote
1answer
147 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, ...
0
votes
1answer
78 views

Encryption / Decryption method secure

I was wondering whether this encryption / decryption flow is very solid / secure. I encrypt the data using AES CBC 256 bit with an static IV. When the user logs in with his Firebase account (first ...
0
votes
2answers
221 views

TLS1.2 AES 128 CBC Encrypted Data size is not a multiple of block size [closed]

I know that TLS ciphers such as TLS_RSA_WITH_AES_128_CBC_SHA transmit data as shown https://tools.ietf.org/html/rfc5246#section-6.2.3.2. From my understanding the ciphertext MUST be a multiple of the ...
4
votes
0answers
201 views

AES key reuse between CTR and CBC

The question Given the same plaintext content that is encrypted two times. One time with AES-CTR and the other time with AES-CBC. Both times with the same AES key but with different IVs. What are ...
2
votes
1answer
287 views

Is it safe to use unauthenticated AES CBC when encrypting random bytes?

I am studying an application with an AES crypto implementation that works that like the following: PBKDF2 is used with X iterations and SHA-256 to generate a 256-bit "master key" from a user-provided ...
-1
votes
1answer
723 views

How can you change this message which is in block cipher AES-256 in CBC?

Given is the secret message encrypted with AES-256 in CBC mode 5a04ec902686fb05a6b7a338b6e07760 14c4e6965fc2ed2cd358754494aceffa The first 16 Byte is the initial ...
3
votes
1answer
91 views

Propagating CBC insecure Authenticated Encryption

why is Propagating CBC (PCBC) insecure for authenticated encryption? I received the hint that I should feed a message of length $n$ and a message of length $n-1$ to it, but I don't really get what the ...
2
votes
2answers
85 views

How much data do I leak if I use the first bytes of a file as AES-CBC IV?

I found a piece of code that uses the first 16 bytes of the input file as IV. This immediately set off some flags in my head, but I have no idea how bad it really is. So, how bad is it? Obviously we'...
3
votes
2answers
1k views

Are TLS 1.2 AES-CBC and AES-GCM Authenticated Encryption ciphersuites?

In the answer of the following post: Why was AES CBC removed in TLS 1.3?, I quote the following from the chosen answer: After the Lucky13 attack (a timing oracle caused by MAC-then-encrypt), it ...
0
votes
2answers
162 views

Modification of block cipher in CBC mode

I know that CBC is not secure against data modification. Can someone explain to me by illustrating at an example how I could change the last block if I have the encryption of "0"? Thanks in advance
2
votes
1answer
2k views

AES-CBC then SHA vs AES-GCM for encrypting and authenticating a web token

I am trying to have something like JWT but kinda ad hoc and encrypted. The token itself is simply a stringified JSON that contains the user ID and Unix timestamp. Now, I tried to use AES-128-GCM, ...
0
votes
1answer
114 views

CBC first block malleability

Let $m_1 = \underbrace{ \{0,1\}^n \times \cdots \times \{0,1\}^n }_{L\text{ times}}$ be a message of space $\mathcal{M}^L$, where $\mathcal{M} = \{0,1\}^n$. Let $c_1$ be the encryption of $m_1$ ...
0
votes
1answer
243 views

CBC-MAC using predictable IV

Imagine you have a string of plaintext (a), IV (ai) and the MAC (am) for the plaintext (<...
3
votes
2answers
465 views

Is CBC block cipher mode susceptible to reordering attacks?

Regarding reordering attacks, is CBC block cipher as vulnerable as ECB? why? If CBC can prevent reordering attacks (that is, after reordering, the decrypted plaintext will make nonsense so the ...
8
votes
4answers
3k views

Are there any benefits to using ECB over CBC?

From what I have understood about ECB and CBC, CBC is far better as it doesn't reveal any pattern. There have been several questions here about how ECB is bad: Should I use ECB or CBC encryption mode ...
5
votes
2answers
982 views

Can AES-CBC be safely used in combination with RSA, or must it be CBC-MAC?

The plan is to encrypt files using an AES-256 in CBC mode secret key. The secret key itself will be encrypted with a RSA 2048-bit public key. Is using AES-CBC sufficiently secure if used in ...
2
votes
1answer
530 views

Is zero IV with AES-CBC safe if CPA is not possible and indistinguishability is not an issue?

Is using zero IVs with AES-CBC safe, if chosen-plaintext attack (CPA) is not possible and ciphertext indistinguishability is not an issue? Practical example: ...
2
votes
2answers
593 views

AES CBC: how shall i get to know with AES CBC method, the received Cipher Text is padded or not [closed]

Algorithm: AES - CBC mode with PKCS7 padding KeyValue: 10a58869d74be5a374cf867cfb473859 IV: ...
3
votes
1answer
698 views

CBC - Cipher-text stealing decryption

(I asked in stackoverflow and I should ask my question here not there, sorry about that) The graph shows CBC- with cipher-text stealing and (b) is the block length. The output cipher-text is c1,...,...
-2
votes
2answers
551 views

ciphertext stealing and CTR

Why Does CTR mode encryption not use ciphertext stealing?
0
votes
1answer
520 views

CMAC Generation : If input payload length is not aligned in 16 bytes, what are the possible side effects?

While searching for answers ,I understand that RFC AES-CMAC 4493 is suggested by NIST to overcome if payload is not aligned in 16 bytes. I would like to know what drawbacks/insecure caused by AES-...
2
votes
3answers
9k views

Can we calculate AES-CBC-PKCS7 ciphertext length based on the length of the plaintext?

I am currently using AES256 in CBC mode with PKCS7 Padding to encrypt some data. It seems like the output size is not always a power of two, which was what I expected. Is it possible to calculate the ...
1
vote
2answers
1k views

CBC Mode error during encryption

In CBC mode I know that if i get a corrupted Ci* block than Pi and Pi+1 will be wrong during the decryption, but i believe that this happens only when Ci* is not envolved during the feedback stage at ...
1
vote
1answer
142 views

Cut through mode for TLS AES-CBC / SHA ciphersuite

I am looking at RFC5246 and it seems that AES-CBC/SHA cipher suites cannot be implemented in a cut-through mode. Let's suppose that received record spans two segments. As i understood HMAC ...
3
votes
1answer
581 views

Cryptopals challenge 2.11: Distinguish ECB and CBC encryption

I'm going through the Matasano crypto challenges (also known as cryptopals) and I recently got stuck in the following challenge: http://cryptopals.com/sets/2/challenges/11 The goal of the challenge ...
4
votes
1answer
670 views

In a AES-CBC + HMAC architecture, Is it secure to send a second IV in a message to a device incapable of producing satisfactory random numbers?

There are many threads here explaining the need of a random and unpredictable IV for the AES-CBC. I am building a home automation system with security for a school project where a Raspberry Pi ...
1
vote
1answer
1k views

Get IV from Key, Clear and Cipher text in AES-256 CBC

Newbie question here but can I get the IV if I know the Key, plain text and chiper text ? (I thought that if I encrypt 16 first bytes of clear with the key and 16 first bytes of cipher text as IV it ...
0
votes
1answer
296 views

Given an AES-CBC encrypted string, IV, and plain text, how can I compute the key?

If I have the AES-CBC encrypted string along with the IV and the plain text before encryption, how can I compute the key which was used for encryption?
1
vote
1answer
220 views

How HMAC is calculated for TLS AES_128_CBC_SHA

The RFC 5246 defines generic block cipher as follow: struct { opaque IV[SecurityParameters.record_iv_length]; ...
2
votes
1answer
80 views

Would a simplified CBC-MAC be safe?

Would using the ciphertext of the previous block as key instead of XOR:ing the block and encrypting with the normal key work? Normally it's done like this: What if we instead do this: Seems like it ...
0
votes
2answers
475 views

In use of AES CBC, can a cipher text signature be replaced with appending a known string to the plain text?

Would appending a known string to the end of plain text then validating the string after decrypting adequately verify the authenticity of the cipher text?
2
votes
1answer
109 views

calculate ESS IV initialization vector for aes- bc essiv encryption

I want to do block level encrypton on my ext4 image file system with aes-cbc-essiv How can I find/calculate the the ESSIV needed for encryption?
2
votes
3answers
495 views

Do I need to generate unique IV for CBC encryption of a file if I encrypt multiple blocks of data?

The situation is that I download a mp3 file (song) and I encrypt blocks of data (4096 bites for example). The output of every encryption operation I save it in a new file. When I play the song (...