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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 partP_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} = ...