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You may want to consider using the Web Cryptography API for client-side cryptography in the web browser. Then, you can create a keypair using the webcrypto api, and store the CryptoKey object, containing the user's private key, with the .extractable property set to false, using Indexed DB storage. This way the private key can only be used for decrypting ...

9

GPG's AES-256 symmetric encryption is believed to be as secure as it is difficult to guess the passphrase or compromise the machine used to perform encryption and decryption. Guessing the passphrase should be harder if one uses gpg --s2k-mode 3 --s2k-count 65011712 --s2k-digest-algo SHA512 --s2k-cipher-algo AES256 or equivalently puts in the gpg.conf ...

8

It could enable a key exchange based off of symmetric primitives alone. For example, suppose I can provide to you a program that will allow you to perform AES-256 encryption of a single plaintext block. I could send you this program, you could perform your encryption and send me the result, and due to the whitebox nature of the algorithm, only I can decrypt ...

8

The cloud trend brought its problems. In the classical system, your servers were near to you, so the side-channel capability was limited. They were mostly on the smart-card systems where the card reader was malicious. There are side-channel attacks on the cloud if the attacker can co-locate with you. For this, you need to use a shared machine to reduce your ...

7

Not sure if hash trees miss some of your requirements, but many of requirements you have could be satisfied with hash trees. Note: The scheme described below is essentially "Merkle Hash Tree-based Storage Enforcing Scheme (MHT-SE)[Golle et al. 2002]". So my question is, if we relax the requirement of being able to perform an unbounded number of ...

7

I do not know of any approaches in context of proofs or retrievability (PoRs)/provable data possession (PDP) that use homomorphic encryption. However, many of those schemes employ homomorphic (linear) authenticators/tags for the metadata such that the proofs delivered by the server can be of constant size, i.e., by aggregating single tags. Now to some ...

7

Specifically, why should hash functions not be used for data clearing? I take it you mean that we would overwrite the storage with output produced by feeding its sensitive contents to a hash function. The problem then is that this output, being a function of the data you're overwriting, therefore provides information about that input. In particular, it ...

7

All the parameters you've mentioned can be public. Furthermore, only the salt, IV and ciphertext cannot simply be guessed. The IV is generally easy to retrieve once the key is known, so the making the IV secret doesn't make sense. In CBC mode and many other modes you may just not get the first plaintext block if the IV is completely absent, but the rest of ...

6

Given a vector $[S_0 S_1 x_1, S_0 S_1 x_2, ...]$, it is quite easy to recover $S_0 S_1$ (by computing the GCD of the various elements). With that information, the attacker can then recover the values $x_1, x_2, ...$, and so yes, a semihonest adversary could easily recover the $X_{reg}$ values.

6

It's common for encryption algorithm specs to specify a hard limit of how much data you should encrypt with the same key. For example, consider the AES-XTS encryption algorithm, which was designed specifically for full-disk encryption: The IEEE specification recommends that the length of a "data unit" (e.g., disk sector or block) encrypted with a single ...

6

In practice, “secrets do not leave the token” is not beneficial. Ouch, I think I would rather like to know where my keys are. This is about the same as saying that you don't care if your house keys got copied or not. For example, a banking application. This program is not able to execute on a token since tokens have insufficient UI. Hence this program will ...

5

Loading and using encrypted firmware usually requires one of the following conditions to be met: You have a security (co-)processor and the processor is trusted to follow the instructions given by that (co-)processor You have a trusted processor and some tamper-resistant storage Scenario 1 You have a security (co-)processor and the processor is trusted to ...

5

Storing passwords in such a way as to allow comparison against portions of the hashed password is by definition less secure than traditional cryptographic hashing. As a rule, this is simply never done. On the other hand, you could safely make comparisons of portions of your new password (for which you necessarily have the plain text) against the entirety of ...

5

At least one benefit of tokens is that even if the token is temporarily abused because "the UI device is breached", the key itself does not leak. Therefore, in some applications like server authentication, it's enough to restore the integrity of the breached machine to be back and running without changing the key. That capability is necessary in ...

5

Suppose you have a set of key-value pairs $(k_1, v_1), (k_2,v_2), \ldots$. You can store the coefficients of a polynomial $P$ that satisfies $P(k_i)=v_i$. The polynomial can be evaluated at any point to give a plausible output. The degree of the polynomial leaks the number of key-value pairs, but if the $v_i$'s are uniform then the polynomial leaks nothing ...

4

With your constraints, there is no way to safely store keys, and this is from a hardware perspective. If they exist in memory, there is pretty much a way to get them out. If you have a way to update the firmware, I can get something in there to get the keys out. It would have cost less than a penny to add a hardware core if you had a custom IC. (I go over ...

4

The requirements for storing public keys and private keys are quite different. Public keys need to be in a trust store in order to be able to trust them. Care should be taken that an attacker cannot replace them or trick the system into using a different trust store. Public keys - as the name implies - do not have to be confidential. The requirements for ...

4

We can divide the applications into several categories according to the security notions related to white-box cryptography. Unbreakability: means protecting against key extraction in the worst case attacking model where an adversary fully controls the running environment. The mobile payment(e.g. HCE), digital contents distribution and soft-keyboard-typed ...

4

Specifically, why should hash functions not be used for data clearing? Several reasons, the main being that there is no need to use one. If you were thinking about reading the data from the device in chunks, running it through a hash function of equal size, Luis' answer points out why that is a bad idea from a security perspective. It is also slow, as it ...

4

Reffering to the question provided by me: "Where and how to store private keys in web applications for private messaging with web browsers?" which means that I want to find a bullet proof mechanism to permanently store and protect public keys in web-browser for end-to-end encrypted messaging without needing more than: web-browser HTTPS support javascript ...

4

Elaborate their claims / point me to some source where I can get an overview of the concepts to eradicate my suspicion This answer will focus on this part of the question: elaborating on the listed claims. All data is encrypted, including Entry names, Category definitions and the data itself. As long as that doesn't impede functionality such as ...

4

I read that something like this might be insecure as hashes become less secure the more often you hash them again. While this is technically true, you shouldn't worry about it. This paper has precise bounds on how bad it is to iterate a random function and with the iteration count $r<10$ as you are worrying right now this is a non-issue for security. ...

4

The key is stored physically anyway in the hardware, so access is still possible The assumption is that it is practically impossible to read the keys that reside (permanently or temporarily) inside the HSM. They will be present in usable form, and used, only inside the HSM, and it is the HSM's job to protect these keys (including enforcing restrictions ...

4

if there's an inner-layer error correcting code, will it be able to work without an encryption algorithm based on a stream cipher? Depends on how the inner error correcting code works; what you want is an encryption method that does not radically increase the 'size' of any ciphertext errors (where 'size' is what's relevant to the error correcting code), ...

4

Kelalaka gave a great answer detailing many side channel attacks relvant to the cloud. But it is important to note that none of these are relevant if your secret key isn't in the cloud. If you store encrypted data in the cloud but only do encryption/decryption locally, the cloud specific vectors are irrelevant. Anyone who wants to do a side channel attack ...

4

While you did not mention the source, here one. Actually, XSalsa family is described in Bernstein's paper; 2011, Extending the Salsa20 nonce, D.J.B. Does the "X" in XSalsa20Poly1305 just mean a 192 bit nonce? Yes, it means the nonce sizes of XSalsa is 192-bit while Salsa has 64-bit. This is so huge that even for random nonces one has to generate ...

3

To answer the question we first need to take a quick look at how XTS encrypts data: $$C=E_{k_1}(P\oplus(E_{k_2}(n)\otimes\alpha^i))\oplus(E_{k_2}(n)\otimes\alpha^i)$$ With $\oplus$ denoting bitwise XOR, $n$ denoting the sector index, $i$ denoting the block index within the sector. $\alpha$ is a polynomial in the $GF(2^{128})$ and is exponentiated ...

3

See Theorem 6, page 38-39.. Also, this lower bound ignores any ability of the "RAM" to perform computation. Typically, there are two application scenarios for ORAM: 1) A literal processor communicating along a literal CPU bus to a literal stick of RAM 2) A client communicating over the internet to a cloud server In the latter case, it makes sense for the ...

3

It is related to Cloud storage in the sense that you don't have to trust the server you put your data on. Usually, the access control is done via authentication. This requires the server to be trusted. However in the case of Cloud storage, you don't know anything about the server hosting the data, so being able to do access control with the encryption ...

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