# Tag Info

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AES-GCM uses single block cipher operation and can be processed in parallel, therefore it should be faster. CTR+HMAC requires block cipher and hash function, which usually can't be processed in parallel. Also it requires 2 keys. It is often miss-implemented (MAC-than-encrypt or MAC-and-encrypt, using single key). Cipher-text length is the same for same ...

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AES-GCM encrypts the plaintext in the Counter Mode. GHASH operates on the resulting ciphertext, so no weakness in GHASH could compromise the confidentiality of plaintext. The GCM authentication is not as strong as that of SHA-256, in particular on short tags. If the tag is $\tau$-bit, an adversary can forge the tag after $2^{\tau/2}$ attempts given the ...

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Because AES CBC does not provide authenticated encryption, this leads to many interesting attacks, which allow to modify or guess plaintext. Such attacks as BEAST or Lucky 13 are based on this vulnerability of AES CBC. Some details about this attacks you can find here.

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I don't see any reason to expect this to provide integrity (INT-PTXT or INT-CTXT). In fact, if $R1,R2$ were known to the attacker, I can show that in general it does not provide integrity: there exist some encryption algorithms that are IND-CPA secure but where your scheme does not provide integrity. (e.g., any stream cipher.) This sounds like a ...

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If you don't mind that the ciphertext is longer than the plaintext, GCM is perfectly fine for storage encryption. Every time you write a block to disk, choose a fresh nonce and write the resulting ciphertext to disk. (You can ask for even stronger security properties, but then everything gets more expensive. Basically, build a tree structure for tags. Reads ...

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Yes, as long as you obey all the total usage limits and choose the IV appropriately (see below). Whilst IV is a general term for any initialisation vector the recent trend has been to use the term 'IV' to refer to a random vector, and "nonce" (a contraction of "n-umber used once") to refer to an input vector that need not be random, but cannot be repeated. ...

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IV (initial value or initialization vector) is a vague term that describes some kind of starting value for a mode of operation that is known to both parties, and generally sent in the clear with the encrypted data (and known to the attacker) IVs in many modes of operation have specific requirements to that mode. In some modes the requirement is that is ...

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You could, however the one part that doesn't translate in an obvious manner is the Galois field representation; you would need to pick a field representation for $GF(2^{256})$ and $GF(2^{512})$, because those have not be predefined for those sizes. Here's the issue; GCM does field multiplications internally; that is, it takes two $N$-bit vectors (where $N$ ...

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As far as I can see you would have (at least) to define a wider polynomial for the multiplication over the GF(256) or GF(512) respectively (See point 2.5 Multiplication). It is unclear if you can do that without touching the overall security of the algorithm. I would not rely on the security of these modified algorithms without extensive research of the ...

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