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8

The answer is, yes, you can get FIPS certification even if you don't implement every approved cryptographical primitive, or if you don't implement every possible option of those primitives. When you undergo FIPS testing, they ask you to fill out an "information form" that asks for the details of what cryptography you claim to implement. These includes ...


7

The GCM authentication tag doesn't need to be encrypted. Just attach it to the ciphertext in the clear. A very quick intuitive justification: It's an authentication tag derived from the ciphertext, it doesn't contain any sensitive information itself. The security of the GCM model assumes the tag is left in the open. (The GCM spec, SP 800-38D, shows the ...


6

In the context of packet communications, it feels like it would be optimal to setup key and IV once and then use that single initialisation in some way for all packets on the same channel. It might be optimal for efficiency standpoint, but we also care about security; it isn't necessary very good for security. You mentioned that, with CBC mode, you can ...


5

In comparison against CBC mode and HMAC, GCM mode is quite commonly better alternative. But, I'll go to detail where it neccessarily is not. Just like Richie Frame, I also do not agree that CBC + HMAC is always the best comparison target. I've added few other details. Hope you find them useful. Against CBC and HMAC I'll discuss downsides first. The ...


4

I don't see any obvious way to do this without violating the security of GCM; at least, if you are at all concerned with an evesdropper (and if you're not, why are you encrypting at all?) Here is a distallation of your requirements: you want to have the sender send the ciphertext (including nonce, ciphertext and tag). Then, you want the sender to be able ...


4

To answer your question: yes, GMAC does have niche applications where it performs better than either HMAC or CMAC; however it might not make sense for you. First of all, you are correct in that GMAC requires an IV, and bad things happen if a particular IV value is reused; this rather rules out GMAC for some applications, and is a cost even for applications ...


4

AEAD modes like GCM are authenticated encryption with associated data; this setting only affects the associated data half of that. The ciphertext itself is still authenticated. The associated data portion is there to provide contextual information for the authentication of the ciphertext. Usually this data is something that's outside of direct control of the ...


4

eBACS, as given by CodesInChaos, is a great resource, and it provides much more data than I could hope to give in this answer. However, the page is not explicit about whether or not AES-NI was used — looking at the results, it doesn't seem so. For an extremely shallow analysis, but allowing us to know for-sure about hardware acceleration, we can use ...


3

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 $N$ ...


3

The usual mode for disk encryption is XTS (let's say the mode suggested by the NIST). AEAD cipher seems to be promissing but typically with the GCM you will have also to store an authentication tag per encrypted block which may lead to a complex implementation (but interesting). I believe that regarding at least integrity, there exist "new" file systems ...


2

Regarding GCM mode and the uniqueness of the nonce, it should be noted that EAX mode and OCB mode also require unique nonces. One potential problem EAX mode has, which neither GCM or CCM have, is that it is hard to implement it in such way that you can guarantee that the probability of nonce collisions is zero; only that it is acceptably low. OCB mode has ...


2

Here's a NodeJS AES-GCM module. Or alternatively, you can use the OpenSSL library to write your own GCM decryption code, here's a quick tutorial. The OpenSSL utility has historically not supported GCM encryption/decryption via command line parameters, likely due to the auth tag issue. I don't think that anything has changed since then, so you may want to ...


2

Unless you are absolutely sure that you don't need to and that the cost is going to be significant then I would absolutely say you should use authenticated encryption. One reason is bit-flipping attacks - flipping a few bits at the 'right' point in your encrypted message might lead well to a message that is legal (the classic example is if someone learns ...


2

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 ...


1

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 ...


1

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 ...


1

There exists a case where developers implemented a new version of the GHASH algorithm that used the new PCLMULQDQ instruction found in Intel processors, and a bug in the implementation allowed message forgery. The code change appeared to improve the performance of AES-GCM on newer processors as well as processors with additional cores that do not support ...



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