# Tag Info

17

In short: You must authenticate the IV. Which particular attacks apply if you don't depends on the block cipher mode; I will give two common examples. In CTR mode, an attacker who fiddles with the IV can forge authenticated messages, but the content of the corresponding plaintext is beyond his control (since he doesn't know the key). Depending on the ...

9

Both an AES-128 key (as defined by FIPS 197), and a TDES Keying Option 2 key (as defined by FIPS SP-800-67) are 128-bit bitstrings. Similarly, both an AES-192 key and a TDES Keying Option 1 key are 192-bit bitstrings. The differences are: In AES, all bits of a key matter to the result; in TDES, 1 bit out of 8 (the lower-order bit of each byte in ...

5

First, it's not said that AES is unbreakable, merely that none of the currently known attacks reduce the computational cost to a point where it's feasible. The current best attack on AES-128 takes 2^126.1 operations, if we had a computer (or cluster) several million times more efficient than any current computer and could operate at the thermodynamic ...

4

Your fault attack scenario correspond to this paper : A Differential Attack Technique Against SPN Structures with Application to AES and KHAZAD (Piret & Quisquater - CHES 2003) This paper describe how to retrieve four bytes of the last round key with at least two pairs of ciphertext/faultytext. Each pair of ciphertext $C$ and faultytext $C^*$ could be ...

4

The Encrypt then MAC is done in general in order to be sure to decrypt into the correct plaintext, without risking of parsing a non-authentic plaintext message. If you don't MAC the IV, then Mallory (attacker that can tamper with messages as a man-in-the-middle) can modify the IV and your MAC will be still validated as good. So you will decrypt into an ...

2

There are some differences between the keys of AES and 3DES. However I do think that your colleagues are more interested in the security of the primitive itself. The AES block cipher is rather more secure than triple DES. If a 128 bit triple DES key is created the amount of effective key bits - the bits actually used in the protocol - is 112 bits. This is ...

2

None of Twofish, Serpent and AES are currently known as broken, so as far as security is concerned, you can use any of them. AES has a slight advantage because it's very widely used, so if it gets broken you're more likely to hear about it and get relevant software updates quickly. The Snowden postings haven't changed much as far as cryptography usage is ...

2

No, that's not really possible without blatant flaws of the implementation. Modern modes of operation of ciphers are resistent to attacks even if you know many pairs of plaintext and ciphertext - and the IV is public knowledge. Knowing it is the normal case. You also didn't mention what operation mode was used. Well, of course you could brute force the key, ...

2

Welcome to crypto SE. I guess, you are referring to the mix columns operation from the point of view with polynomials over $GF(2^8)$. A detailed explanation of this can be found at Wikipedia. It is a quite unusual structure, but it behaves just like you would consider any $GF$. The columns are first considered as polynomial, or better: as coefficients ...

2

Yes, there are modes of operation that achieve the property that you are describing. For example, the Propagating Cipher Block Chaining (PCBC) mode of operation: This mode is similar to CBC but the output for each block is propagated to the input of the next one, so a small error will propagate indefinitely, both for encryption and decryption. There may ...

2

Based on your description, you will not be able to recover the original encrypted file. Since you specify that you used a password and do not indicate the use of an IV, my assumption is that you did, in fact, use a passphrase rather than a secret key. When you encrypt a file with a passphrase, OpenSSL assumes that it is a low-entropy string unsuitable for ...

1

The standard approach is to have the sender pick his nonce (either randomly, or as a counter), and send it with the packet. The decryptor then knows what nonce to use to decrypt, because it's right there. Because nonces aren't assumed to be secret, this works.

1

AES is asymmetrical in this regard. It is down to the key schedule, which generates a sequence of round keys from an initial key. In a modern desktop environment, the round key sequence is simply generated before encryption/decryption starts, so the difference in speed is minimal. In a memory-constrained environment like a smartcard, this may not be ...

1

Take a look at this article it explains the IV can be publicly known once you have encrypted your data. Is using (and storing) a different iv for each file sufficient? (Am I correct in thinking that I'd need to store the iv with the encrypted data?) Yes, as a matter of fact i would not recommend using an IV twice, just for safety. Is this safe? ...

1

Initialization Key hash function hashstring Configuration: E is Rijndael with a block size and key size of 256 bits Input: keystring Output: hash The keystring is padded up with bytes valued zero and split up in blocks of 256 bits $S_0$ to $S_n$; The key blocks $K_0$ to $K_n$ are generated, where $K_0$ consist of $S_0$. The following blocks - if any, ...

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