e-sushi
  • Member for 8 years, 8 months
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Desirable S-box properties
10 votes

Desirable Properties For simplicity, I’m skipping some of the details here… but the main criteria of a good s-box are: miul It should have balanced component functions, The non-linearity of its ...

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Can someone give me an example of a Merkle–Damgård transformation?
4 votes

You get it wrong when saying Since input-output = # of blocks, the 6-bit input should be divided into two blocks, each with the 3-bits because you have a …compression function that takes ...

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What changed in PKCS#1 v2.2, and why?
Accepted answer
11 votes

It's merely an update to align the hashing algorithms. There are in fact no real "consequences" which might have any negative impact as the v2.1 schemes are still supported. The positive ...

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Frequency analysis of transposition ciphers
5 votes

I did it for substitution ciphers but am unable to do it for transposition ciphers. When it comes to transposition ciphers, it’s not really surprising frequency analysis doesn’t turn out to be as ...

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How does one verify a GPG/PGP key revocation?
8 votes

How does one verify a key revocation? As Jon Callas already stated: you simply don’t. In case a different wording helps, here’s a quote related to the exact same question… https://lists.gnupg.org/...

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If you wrote a reversible SHA-256 algorithm, how many "metadata" bits would be required for reversability?
Accepted answer
3 votes

If you wrote a reversible SHA-256 algorithm, how many "metadata" bits would be required for reversability? If you would write such an algo, it would not be SHA-256 anymore. Also, it would lose its ...

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Size of A Hashed String Using SHA-512
0 votes

When hashing a messages of size of n, does the SHA2 algorithm always produce the same sized hashed value? SHA-2 output is always fixed. SHA-512 will always produce a message digest of 512 bits – ...

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Decrypting SHA-512
Accepted answer
3 votes

A cryptographic hash function like SHA-512 is a “one-way compression function” – so it can not simply be “decrypted” with some tool. Instead, when you are trying to “break“ a hash output like the hex ...

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Is there a consensus on what text encoding to use when hashing a string?
3 votes

The consensus is: a hash generally expects binary bits as input (practically, most implementations therefore handle it using binary bytes, aka 8-bit unsigned chars in the range 0x00-0xFF) and it will ...

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How can I create a stream cipher from a block cipher?
1 votes

Assuming k is the key (128 bit) and m is the message (128 bit), how can I use the block cipher blockenc(k,m) to make a stream cipher… Probably the easiest way to achieve that would be to use Counter ...

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Is it possible for a cryptographic algorithm to limit the number of times a package/ciphertext can be decrypted?
4 votes

At first, I tended to agree with @fgrieu that this is not really a "cryptography" question. If, it would belong more into the general information security corner, because – generally – the problem ...

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How to interpret the article claiming NIST P-256 curve to be unsafe?
4 votes

Quoting CodesInChaos: P256 is secure, it just lacks some nice-to-have features that make writing a fast and secure implementation easier.

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Multiple Encryption - One-Time Pad
2 votes

Even though you’re encrypting it in some way, you are reusing the key (aka "pad") and thereby violating the OTP definition. Per definition, OTP requires the “key“ to be… a truly random one-time pad ...

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Is it possible to crack a LFSR encrypted file without using bruteforce?
4 votes

First up: a 5 bit LFSR is horribly small, so getting the initial seed which was used is a piece of cake. But indeed, it’ll basically boil down to a (rather quick) brute-force job where – unless that ...

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Writing your own Encryption algorithm?
3 votes

If you really expect it to be … 100% uncrackable… you’ll have to start by abandoning your “keep certain parts private” idea and assume that “the enemy knows the system”. See Kerckhoffs’ ...

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FIPS 140-2, Level 1 validation vs. compilation
3 votes

You can convert/cross-compile the code, but that won’t port over any validation or even certification. In the end, a cross-compiled product is a new product – requiring revalidation. Unless such (re)...

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How to attack RSA with 13 primes
4 votes

Could give me method to attack RSA when N decomposes into multiple primes First, factor N, e.g. using trial division or Pollard's rho. Next, compute the decryption exponent, or use the method ...

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Do any non-US ciphers exist?
16 votes

Plenty of ciphers come out of the USA from government research or selection competitions. AES and DES are examples. Indeed, the US is known from some crypto-related competitions that were/are open to ...

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Why is SHA3 prefixed with SHA despite the fact that it is structurally different from SHA2 and SHA1?
9 votes

SHA… This naming was introduced by NIST (see https://csrc.nist.gov/Projects/Hash-Functions) way back in 1993 during SHA-0 standardization efforts (which ended in SHA-1). SHA stands for Secure Hash ...

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Why is SHA-3 a Sponge function?
20 votes

… SHA3 (Bouncycastle) constrains me … Bouncycastle offers the NIST approved, fixed, and standardized output lengths of the keccak sponge function. See, when talking about SHA-3, you're talking about ...

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What is an example of asymmetric cryptography?
4 votes

Actually, your favorite search engine should bring up a truckload of examples and our site here also contains ample pointers. But just to have a canonical Q&A related to this… First up, note that ...

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Anti-spamming hash-based proof-of-work?
1 votes

I have to contradict the other answer by DannyNiu which wrongly states POW (proof of work) does not work here. It does. As a matter a fact, you are about to reinvent the wheel. See HashCash which ...

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secretKey ⊕ (secretKey ≪ 1), is randomness lost?
0 votes

Converting my comments into an answer: If your secret key is cryptographically secure, you don't really gain anything by applying such a shift-XOR — but indeed, there is no entropy loss. What's a ...

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Best way to encrypt lots of private keys with the same passphrase
4 votes

From a cryptographical perspective, a HSM comes to mind. The main reason for using a HSM-based solution here is that you gain assurance against attacks. After all, HSMs are robustly designed for ...

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Is it generally considered acceptable for app owners to be able to retrieve private keys from users when their apps offer end-to-end encryption?
Accepted answer
3 votes

Is it generally considered acceptable for app owners to be able to retrieve private keys from users when their apps offer end-to-end encryption? No, it's not acceptable if the app providing service ...

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How does Naver Line PC client obtain private key for end-to-end encryption (letter-sealing)?
Accepted answer
1 votes

Converting a lengthy comment exchange to an answer: How does Naver Line send my private key stored on my phone to the PC client? LINE has provided a technical whitepaper which described how ...

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Zero knowledge proof protocol example?
29 votes

This is a classical example. Here is the proof system… Bob gives two gloves to Alice so that she is holding one in each hand. Bob can see the gloves at this point, but Bob doesn't tell Alice which ...

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Did non-military cryptography appear in the 50's and 60's only due to NSA leaks?
15 votes

I won't answer your question up to every detail, as I would have to write a book to answer the pretty broad question to full length. But I'll give you some hints as it would be wrong to let you think ...

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What happens if a SHA-256 input is too long (longer than 512 bits)?
9 votes

If the input message is longer than 512 bits, the input is chopped in “chunks” (read: pieces) with fitting length (512 bits) and those are successively fed to the hash compression function. See, in ...

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What is the difference between these two TLS suites?
4 votes

There is no difference. It’s just the way the devs described it; which actually makes sense because X25519 implies ECDH is used. Also, X25519 is not the curve… it’s the function (to be used with ...

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