41 questions linked to/from How reassuring is 64-bit (in)security?
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### Does "Shattered" actually show SHA-1-signed certificates are "unsafe"?

Note: I am not advocating anyone continues using SHA1-signed certificates: they are dead as far as security is concerned and should no longer be used. I'm just trying to clarify my understanding of ...
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### After Google's collision attack, is RSA-SHA1 signature still safe?

Google succeeded to get a collision in SHA-1 last year in an attack called shattered. Does this fact make certificates based RSA-SHA1 Signature risky for creating fraud certificates? If RSA-SHA1 ...
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### In 2020, SHA-1 practically broken in chosen-prefix collision (CP-collision). Can double SHA-1 hashing prevent CP-collision?

In a recent study SHA-1 is a Shambles - First Chosen-Prefix Collision on SHA-1 and Application to the PGP Web of Trust by Gaëtan Leurent and Thomas Peyrin. 2020, they showed the first practical chosen-...
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### Has AES-128 been fully broken?

Has AES-128 been broken over the full 10 rounds? If so, by what means? By a commercial entity? By a supercomputer? If not, why is AES-256 used to replace AES-128 so frequently?
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### Is it possible to find the key for AES ECB if I have a list of plaintext and corresponding ciphertext?

Assume I have a list of plaintext text and its corresponding ciphertext which was created using a specific key with AES in ECB mode. Can I recover that key? If, how big does the list of plaintext ...
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### 80-bit vs 128-bit security in today's world

In today's world of applications, I see a lot of the time a 256-bit encryption key is used, but what about an 80 or 128? What makes 256 the one to use. Is a 80 or 128 easily decrypted? Are comp ...
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### Recovery Passphrase Collission for BIP-39 and BIP-44

Referring to the standards of [BIP-39] and [BIP-44]: a 'master password' consisting of 12 words uniformly selected from a 2048-word dictionary corresponds to 128 bits of entropy, that is then used as ...
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### Is it theoretically possible to create an unbreakable cipher?

I know this question might sound strange, but is it theoretically possible to create an unbreakable cipher if we don't consider bruteforce? Some of us believe that it is possible to create ciphers and ...
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### 80-bit security and attack time

Many designer claimed that their cryptography scheme has 80-bit security. So how to calculate the time of attcking this 80-bit security cryptography scheme, such as 80-bit security RSA using a kind of ...
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### Given partial key exposure and encryption oracle, can we recover full AES key?

Suppose I have an encryption oracle for AES with some key $k$ (16 bytes) and that I know $n$ bytes of it. Is it possible to recover the rest ($16 - n$) in complexity less than $256^{16-n}$?
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### How to make my hash more robust to the brute force?

I'm using PBKDF2 SHA 256 with 100 000 iterations to generate a secret. I want to increase the cost of brute forcing the passphrase I use to generate the secret. I'm thinking of using scrypt after ...
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### How long would it take all of the supercomputers or cloud computing on Earth to bruteforce a significantly long password?

I was arguing with a colleague who thinks that SHA256 (password + 64 character static salt) is "insecure." My argument is that nothing in cryptography is "secure," it's all a ...
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### MD5 hash: retrieve an element of a source string

Suppose you have a string, precisely an MD5 hash string, which basically it is computed in the following way: "element1:element2:element3" So, in order to get ...
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### Good pre-image resistance value for hash visualization

I want to do "hash visualization", i.e. derive a human-meaningful information from a hash, like a phrase or an avatar. But the current techniques usually don't use many bits, for example tripphrases ...
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### Hash collisions in sha512 hash of secp256k1 public keys

For a sha512 hash of a secp256k1 public key, how many other public keys could generate that hash? I would assume zero since the key size is equal to the hash length (secp256k1 public keys are 64 bytes,...
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### DES - encrypt 3 times - DES(DES(DES, k), k'), k) - stronger than 2DES with 2 different keys?

What if were to use DES in the following way: For a given plaintext x and key k we will perform: ...
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### Which passphrase length is good so it's hard to break bitcoin's PBKDF2 key?

According to https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#From_mnemonic_to_seed To create a binary seed from the mnemonic, we use the PBKDF2 function with a mnemonic sentence (in ...
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### Supercomputer to crash hash

For NVIDIA TESLA V100 I know a hashcat performance for SHA1: it is about 17000 MH/s. Performance index for V100 is FP32 5120, FP64 2560. But what about supercomputers? For example Summit ...
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### Algorithm/encryption technique which outputs a set number of numerical digits e.g. 20 digits from a given input

What the name of the algorithm/encryption technique which outputs a set number of numerical digits e.g. 20 digits based on some input. You can input some data e.g. text or numbers but the output is ...
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### AES-128 with doubled 8Byte key

Assuming I encrypt data with AES-128 and a random 8-byte key x in the following way: ...
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### How to calculate time needed for decryption of 64-bit key

I am having trouble figuring out how long it takes to decrypt a 64-bit key, given that a computer can do 1 billion trials per second. I know that there are $2^{64} = 1.844 \times 10^{19}$ possible ...
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### Can Trivium ciphertext be decrypted by an adversary if the key is known, but the IV is not?

Suppose that the adversary is able to recover the key of Trivium cipher. But the associated IV is unknown to him. Will he be able to decrypt the ciphertexts without any complexity?
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### What is meant by encrypting/decrypting a known plaintext/ciphertext with every possible key in meet-in-the-middle?

I am working on the Meet-in-the-middle attack on 2DES and I have got some questions I am not sure about. I read several websites/articles about it so I have got an idea of what it is and how it works. ...
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### Brute force strategy

I am a beginner in this field, and I was thinking about brute force strategies to break symmetric key encryption. Let's say we have a block cipher in CTR mode and the key is 56 bits in size. What ...
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### Show that if a fixed key MAC is not collision resistant then the MAC function is not computation resistant for every key K

I'm really having some trouble with this one. Let $H$ be a MAC function. For every key $K$ we can create an unkeyed hash function (i.e.an MDC) by using $H$ to hash messages with the fixed key $K$. ...
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### Calculating DES key knowing message before and after encryption [duplicate]

I've 8 bytes before encryption (for example: 01 02 03 04 05 06 07 08) and 8 bytes after DES encryption: ...
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### Finding and matching SHA512 Unsalted Hash

We are given a list of possible strings, there are $32^{16}$ ($=2^{80}$) to be exact. We also have the unsalted SHA512 of the original target string. How long would it take to go through those ...