Cryptography Stack Exchange
Cryptography Stack Exchange

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).

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).

CBC finally is removed from TLS 1.3.

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CBC mode with predictable IV ok if key is only used once?

Someone told me recently that using CBC mode with a predictable (e.g. all 0) IV is reasonably secure if a key is only used for encryption one time. I've gone through a couple of examples of chosen plaintext attacks against CBC mode with a…
Swashbuckler
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In CBC mode if 2 cipher blocks are same then is CBC still secure?

I was going through this question Why is it said that if we have a duplicate ciphertext block it can leak our information? and I was just wondering if there is a $P_i \oplus P_j= C_{i−1}\oplus C_{j−1}$ relationship, is CBC still secure? How does…
Aish2410
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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?
randomjsmash
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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 present plaintext, before encryption; it seems…
Ninja Bug
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Is it dangerous to use plaintext as IV in CBC?

Is it dangerous to use plaintext as IV in CBC? For example: I want to encrypt $p1$, $p2$ with CBC. However I use $p2$ as the IV for CBC purposes. What would be the risk of not using a IV based on random number(s)?
tony
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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 the encryption, my question is what happens if…
Alonso
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Question about Cipher Block Chaining(CBC)

I'm studying at the moment the CBC Encryption method,and I was asked in an excercise how many bits would be wrong after decryption if during the transmission 2 bits are interchanged. My guess is that the whole bits are wrong due to how CBC works, am…
vc73
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CBC byte flipping attack

I'm learning how CBC works but i don't understand when altering the first 2 bytes of the ciphered text why the 1rst block and ONLY the first 2 bytes of the second block are altered. The first 2 bytes of the cypher text are altered using a xor…
Nadim Hajj
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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
BugsBuggy
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CBC-MAC using predictable IV

Imagine you have a string of plaintext (a), IV (ai) and the MAC (am) for the plaintext (a). How can you generate a MAC (bm) for a different string of plaintext (b) - using an IV (ib) of your choice, using the same key - which you don't know and…
user58341
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Implications of reversing CBC encryption

What would be the security implications if we reverse CBC encyption? Here is a picture of CBC encryption: Here is a picture of CBC decryption: My guess is that the encryption would work if we ran the decryption process for encryption and encryption…
mrQWERTY
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Proof that counter mode of operation and CBC mode are CPA secure when pseudorandom permutations?

I know counter mode can be CPA secure, when used with block ciphers modeled as random permutations. If we use pseudo-random permutations, is it still CPA secure? Is there a proof? How about CBC mode? When used with block ciphers modeled as…
user3754216
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