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21 de jul. de 2022 · AES-256 GCM encryption uses about the same number of AES operations as AES-256 CBC (often, 1 more), for a given amount of encrypted data. Reasons AES-256 GCM could be faster are limited to: if the implementation uses parallelization, or is otherwise better optimized; a sizable portion of the plaintext is treated as Authenticated Data (explained ...
GCM and CBC modes internally work quite differently; they both involve a block cipher and an exclusive-or, but they use them in different ways. In CBC mode, you encrypt a block of data by taking the current plaintext block and exclusive-oring that wth the previous ciphertext block (or IV), and then sending the result of that through the block cipher; the output of the block cipher is the ...
GCM should be considered superior to CCM for most applications that require authenticated encryption. Because of the authentication that happens, GCM is not susceptible to the bit flipping and other attacks that can be mounted against counter mode or other stream modes.
GCM is defined for the tag sizes 128, 120, 112, 104, or 96, 64 and 32. Note that the security of GCM is strongly dependent on the tag size. You should try and use a tag size of 64 bits at the very minimum, but in general a tag size of the full 128 bits should be preferred.
13 de dez. de 2022 · 2. AES-GCM uses CTR mode internally but adds authentication, which detects when someone modifies (tampers with) the ciphertext. It also supports authentication of associated data (e.g. file headers, a counter, other metadata). GCM is faster than doing CTR-then-HMAC or similar and saves people implementing that combination themselves.
17 de ago. de 2023 · An IV is concatenated with the counter, followed by the creation of a cipher using an AES key, which is then XORed with the plaintext. Please suggest some additional vulnerabilities related to AES-GCM, assuming the attacker may have knowledge about the structure/content of plaintext and the value of the initialization vector (IV).
26 de jan. de 2017 · 3. The first three are counter mode AES, the cipher is AES and the mode is counter. 128,192,256 refers to the block (and key) size which is used. The larger block sizes also have a different number of rounds: 10, 12 or 14 respectively. There are also differences in how the round keys are derived.
10 de mai. de 2018 · AES-GCM is an authenticated encryption algorithm. Encrypt-then-Authenticate is one specific construction that achieves this general definition and is indeed preferable to Authenticate-then-Encrypt, which is why GCM internally does encrypt-then-authenticate and so AES-GCM achieves the same security definition as CBC-then-HMAC.
3 de jul. de 2021 · $\begingroup$ GCM doesn't make AES any more secure. It protects data integrity but when it comes to breaking encryption, GCM, which is in fact just CTR, is not harder to break than CBC. Also GCM limits the IV to 96 bits, instead of 128 bits and when using CTR, an IV collision is deadly, whereas the same collision is way less likely for CBC and way less critical should it ever happen. $\endgroup$
19 de jun. de 2022 · Newer TLS cipher suites (introduced in TLS 1.2) do authenticated encryption using an authenticated encryption primitive, such as a block cipher in GCM or CCM mode, or ChaCha20+Poly1305. The authentication primitive takes care of everything with a single key.
