20

Applied cryptographers often see one of the three variants of AES, say AES-256, as a function: $$\begin{align}E:\ \{0,1\}^{256}\times\{0,1\}^{128}&\to\{0,1\}^{128}\\ (k,p)\quad &\mapsto c=E(k,p)\end{align}$$ such that: for all $k\in\{0,1\}^{256}$, encryption with key $k$ defined as follows $$\begin{align}E_k:\ \{0,1\}^{128}&\to\{0,1\}^{128}\\ p\...


3

I have a solution that may satisfy you Splitting the file into parts and chaining is a solution for you. To prevent the truncation we will use the associated data, that same for the first and last. Assume that you divide the file into $n$ parts each around 16KB ( need adjustments). Encrypt each of them with $\operatorname{AES-GCM}$ with the following ...


3

Under an ideal cipher model, every key implements a random permutation. A random wrong key that maps $x_1$ to $y_1$ thus maps $x_2\ne x_1$ to a random ciphertext $y_2'$ other than $y_1$. For a $b$-bit block cipher, there are $2^b-1$ such ciphertexts, thus the probability that $y_2'=y_2$ is $1/(2^b-1)$. The probability that an incorrect key survives two tests ...


2

I'm aware of only one official specification: NIST SP 800-38G, and recommend to ignore it. Rather, consider NIST SP 800-38Gr1-draft, still unofficial, if something next to a rubber stamp is badly needed. That draft changes both modes in the official specification, FF1 and FF3, fixing security issues: The minimal size of the input/output space is increased ...


1

It is a block cipher with block size 3. Therefore for a given known-plaintext, we can build the current key's action table that has $2^3=8$ values. We will use the decryption part $$P_i = D(C_i) \oplus C_{i-1} \oplus P_{i-1}$$ with $C_{0} \oplus P_{0} = IV$ with conversion $$D(C_i) = P_i \oplus C_{i-1} \oplus P_{i-1}$$ P_i 000 001 010 011 100 101 ...


1

Is he implicitly saying that [Cj-1 ⊕Pj-1] = Oj-1 Yes, this is true. ? If yes, why? Well, we know that: $$C_{j-1} = P_{j-1} \oplus E(K, O_{j-2})$$ (this is the first formula, replacing $j$ with $j-1$), and we know that: $$O_{j-1} = E(K, O_{j-2})$$ Combining the two, we get: $$C_{j-1} = P_{j-1} \oplus O_{j-1}$$ or, in other words: $$C_{j-1} \oplus P_{j-1} = ...


1

Almost all block cipher performs some types of substitution and permutation in every round function. For AES, ShiftRow, MixColumn, AddRoundKey are linear operations; only S-box operation is a nonlinear operation. If all operations in a round function are linear then there is no advantage of having multiple(10,12,14) iterative encryption rounds to produce the ...


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