# Tag Info

Accepted

### Is using the same IV in AES similar to not using an IV in the first place?

Lets see if I can clarify things for you. For one, the IV is not specifically related to AES at all. AES is a keyed invertible transform from a 128 bit value to a 128 bit value; that's all it can do....
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### Rubik's Cube as Encryption

Can this be considered as Encryption If the sequence of necessary moves is treated as the key, yes. how secure can this encryption scheme be? First some details about the cube: 6 faces, ...
• 1,187
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### Is 128-bit security still considered strong in 2020, within the context of both ECC Asym & Sym ciphers

I strongly disagree with saying that AES-128 is broken, in any way, shape or form, and likewise ECC with 256-bit keys. Note that even in this answer by @kelaka regarding AES-128, you would need over ...
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### Isn't AES-NI useless because now the key length need to be longer?

No, AES-NI provides a hardware implementation of AES. Before AES-NI, anyone could have purchased a specialized hardware encryption device that ran AES in hardware. So having AES-NI doesn't really ...
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• 85k
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### Isn't AES-NI useless because now the key length need to be longer?

You might gain some perspective from reading up on specialized AES search hardware, like these two systems: COPACOBANA Its successor RIVYERA If you go to the second link and expand the "...
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### What exactly does s2k do in gpg

The "s2k" options correspond to the String-to-Key specifiers. An s2k transform turns a human-compatible symmetric secret (a password or passphrase) into a symmetric key suitable for a ...
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### Authentication using AES

TL;DR No, the approach is not secure. Use a standard like CMAC instead. Or even better, check your AES accelerator module to see if it supports any AEAD modes of encryption like GCM, CCM, EAX. Long ...
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### Is 128-bit security still considered strong in 2020, within the context of both ECC Asym & Sym ciphers

As you specifically asked for comparisons of the 128-bit security with concrete things, here is some food for thoughts (to complement the other answers): $2^{61} ≈$ SHA-1 chosen-prefix collision (i.e....
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### Is Caesar cipher perfectly secret?

What you described it not a Caesar cipher. A Caesar cipher is a cipher where all letters are shifted by the same number of positions. In the question text you are describing a shift cipher. This is ...
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### Difference between “ECDH with cofactor key” and “ECDH without cofactor key”?

First, a bit of background. If we refer to the size of an elliptic curve group as $n$, we select an elliptic curve with $n = hq$, where $q$ is a large prime, and $h$ is a small integer called the ...
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### Found a way to crack AES-128, what now?

In complete honesty: if you have to ask this question, it's overwhelmingly unlikely that you have actually succeeded in breaking the security of AES. At best, you may have discovered a well-known ...
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### What is the difference between PBE and symmetric key encryption?

As typically implemented, PBE takes a low-entropy, user-supplied password, adds some entropy to it, and thus strengthens it before turning it into a key. This key can then be used for symmetric ...
• 316
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### Is CAST5 still a secure algorithm to use?

CAST5 seems to be a solid 64-bit block cipher with 128-bit key. As far as I can tell after a short literature search, it's definition is sound and unbroken, despite nearly two decades of exposure (...
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### Do key collisions for symmetric ciphers exist?

Apparently there's at least one real-life example of a block cipher with equivalent keys: TEA has a few weaknesses. Most notably, it suffers from equivalent keys—each key is equivalent to three ...
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### How to generate the exact AES key in both client and server side?

There are two main ways to have the same symmetric key on both parties: key exchange using asymmetric crypto generate the key from a known secret (eg: a password), such as using a password-based key-...
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### Why does applying 56-bit DES twice only give 57 bits of security?

Decrypt the ciphertext with every possible key and store the result: $2^{56}$ decryptions. Now encrypt the (known) plaintext of the ciphertext with every possible key: $2^{56}$ encryptions. Now you ...
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### For a typical n-bit symmetric key, how many keys would be considered too weak to use?

I understand that all zeros or all ones would be weak for any cipher. This isn't actually true. For good cipher there are no weak keys. And certain ciphers, e.g. DES, have a list of weak keys. But ...
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### What should the nonce value be for client-side encryption?

The library uses XChaCha20Poly1305 and that requires a nonce of 192-bit (24-byte). It is an extension of ChaCha20Poly1305 to increase the nonce size, ChaCha20 had ...
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### Post Quantum Symmetric Cryptography

AES-256 is still considered the strongest (and is considered secure) as related key attacks are not particular to analysis with quantum computers. Related key attacks could happen when AES is used ...
• 85k
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### Symmetric cipher key size vs number of rounds. Longer key = more secure cipher?

With enough plaintext/ciphertext available (sizably more plaintext than keysize), any cipher can be attacked by trying all the keys; that's brute force. Therefore, for any cipher, too short key ⟹ ...
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### Found a way to crack AES-128, what now?

Assuming you really had broken AES or another frequently used algorithm that is thought to be secure, the first step would be to prove it. Write the code for the attack. Verify that it works on ...
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