SHA-256 is part of the SHA-2 family of hash functions with a 256-bit output and a 128-bit security level.

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Key size for HMAC-SHA256 [duplicate]

After reading a bunch of past stack exchange posts like this one and RFCs 5869, 2104, and 4868 I felt comfortable that a 32-byte key was sufficient for HMAC-SHA256. However, I am implementing my code ...
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Find SHA256(secret||data) using SHA256(secret) and data

I need to find the SHA256 hash of s string like this: "part1-part2". I know the SHA256(part1), length of part1 and I know part2, but I don't know what is the contents of part1. Is there any chance I ...
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65 views

SHA256(RsaPrivateKey) == AES key?

I have an RSA private key (more specifically, an SSH key in Putty format, 4096bit) and want to use its SHA256 hash as an AES256 key, instead of using an independent newly generated AES key. Are ...
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368 views

Does the SHA-256 sum of a 256-bit key help you crack it?

If I have the SHA-256 sum of a 256-bit AES key, can I determine the key any faster than if I merely had a ciphertext and the corresponding plaintext?
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49 views

Is this SHA256 hash implementation secure from rainbow table, brute forcing attacks?

So I have an implementation where by we have an $8$-byte random input (entirely random, not user defined) which we hash with $\text{SHA256}$. The hash is shared with many parties to the point that we ...
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51 views

How succeptible to accidental collision is the construct sha256(uuid4 + now) in Python?

I need 32 byte pseudorandom sequences that denote unique filenames and am currently using this Python code: ...
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64 views

Can two files/strings have the same SHA-256 value?

I was wondering whether, theoretically, 2 files can have the same SHA-256 value. Since there are only $16^{256}$ or $2^{1024}$ SHA256 sums, all 1024-bit files (with $2^{1024}$ different combinations) ...
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24 views

A simple keyed message authentication code using XOR

Suppose I have a key that is at least 32 characters in length and provides at least 128-bits of entropy. If I picked from the character set of [a-hjkmnp-z2-9-], ...
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Randomness and reversibility of a sequence generated by taking sha256 hashes of an predictably-changing input?

Let's say we generate a sentence in a way like for example this: Fix an initial seed. Attach '1' at the end of the seed and compute sha256 of such a string. This hash is our first number. Now attach 2 ...
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Can the SHA256 hashes of consecutive integers be attacked?

Suppose that the attacker knows the SHA256 values of integers $n, n+1, n+2 ... n+k$. $n$ is sufficiently big, so we do not expect to be able to brute force $n$ just by $\operatorname{SHA256}(n)$ ...
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How to deal with collisions in Bitcoin addresses?

When creating a Bitcoin account, you need to issue a couple of private/public ECDSA-keys. Then, you derive your account address by taking a 160-bit hash (through sha-256 and ripemd) of the public key ...
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Decrypting SHA-256 with SHA-256 as input?

Is there a way to somewhat decrypt a SHA-256 hash, provided that the initial string was also a SHA-256 hash? If not, could anyone link me to a rainbow table containing some of the $16^{64}$ possible ...
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Can a list of hashes with property $X_{n+1} = \operatorname{SHA-256}(X_n)$ loop?

This is the situation: I have a list of hashes where each hash is always the SHA-256 of the one above it. If I keep going down the list it must at some point loop since there can only be $16^{64}$ ...
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52 views

Is it safer to use timestamp in REST authentication?

I am working on a personal project to build a REST authentication system which authenticate clients via three parameters: ...
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42 views

Merkle tree (dm-verity) with SHA-256 vs. SHA-1

Is there any knowledge or research on the use of different hash functions within a Merkle tree? My use case is file integrity protection. I am thinking about using different hash functions due to ...
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78 views

SHA256 for large files

I have a hardware engine for SHA256 which can process 64K of data, but the input data size I am getting is around 1MB. What should I do to process 1MB size. What should be my input after 1st 64KB ...
3
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72 views

Security of this scheme

I am developing a software and I am not sure if it is completely secure. I have 22 Mb of data to encrypt used multiple times, random IV (generated using RAND_bytes from OpenSSL lib) and password ...
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40 views

Keys and key-stretching when authenticating requests?

I'm making a REST application and still a bit confused about this issue. basically, to authenticate incoming requests, I give out userId, issued timestamp, expiry timestamp (normally 3 months after ...
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676 views

Which bitwise operations are used in SHA-256?

From the wikipedia entry on SHA-256 I'm a bit confused about which operations actually go into the algorithm. From the pseudo code it appears the operations are $\texttt{xor}$, $\texttt{and}$, rotate, ...
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46 views

SHA256 message bytes

I have been reviewing the documentation for SHA256 and I believe the last two words (64 bits) for each chunk are not used in creating the message schedule. From Wikipedia... Extend the first 16 ...
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237 views

What size should the HMAC key be with SHA-256?

I'm trying to generate a secret key to be used for HMAC SHA-256 signature processing. I've seen many sample of keys with variable length from 32 characters to 96 characters. What is the ironclad rule ...
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383 views

What do numbers in a crypto algorithm stand for? Is there a convention?

What do the numbers stand for in the names of cryptographic functions, for example AES-256, RSA-1024 or ...
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234 views

Authenticated Encryption of UDP packets

I am working on a UDP based file transfer protocol. Congestion Control, Resending of packages and other UDP challenges are dealt with - speedtests shows that the protocol is up to 10 times faster than ...
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237 views

Keyless integrity checking with SHA-256

Currently a program is loading some files from an untrustworthy source (e.g. a CDN) which could have been tampered with. It has a known SHA-256 hash of the file stored locally, then it downloads the ...
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Is this ECC based messaging method secure?

I developing an encrypted messaging for ZeroNet (aP2P file-based network, website: zeronet.io) and would like to have some guidelines if any of this could work. My first idea: In ZeroNet every user ...
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69 views

Is a nonce considered 'secret' enough for HMAC?

We're implementing a mobile application which communicates with a web service, and on first install the user sends its deviceid to the web service (over TLS, unauthenticated at this point) - which ...
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Is this a correct way of use symmetric encryption?

If I want to encrypt some block of text in AES, but at the time of decryption I don't have a way to check if the symmetric key is the correct one. So I: Generate a randomKey, and use that to encrypt ...
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125 views

SHA-256 Hash over multiple SHA-256 Hashes

I am trying to implement a checksum over multiple files. We can assume, that i have a package containing N files. I want to identify such a package uniquely by following calculation: SHA256-Hash ...
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Designing an AES-based protocol for controlling and acessing ioT boards via RF

I'm designing an open ioT protocol to be used on ioT boards based on Texas Instruments RF-based MCUs. These MCUs have an AES module to easily encrypt and decrypt AES content, so that's why I choose a ...
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170 views

HMAC-SHA256 on large data files

I currently need to encrypt large files (video, over 6 Gbytes) for our customers. To ensure authenticity and integrity, we chose HMAC-256 as we already use it in our internal messaging system. But ...
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118 views

AES-256 mode with per-block-key being a SHA-256 of SHA-256 of secret key, random public salt and block number. What's amiss?

Please criticize the (homebrew?) mode described below; to point out a single major defect/uncertainty or the link to (the analysis of) an equivalent construction is quite enough. Assume the ...
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258 views

SHA256: Padding a 512 bits length message

I am currently implementing the SHA256 hash-algorithm for a "custom-built" embeded-device. Obviously I have a problem with message padding. The routine I wrote does not work with message whose size ...
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176 views

SHA-256 “almost unique”?

I have seen numerous references on the internet of people describing SHA-256 as generating an "almost unique" hash. Exhibit A. there are more. Is there some mathematical basis to the almost ...
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76 views

Is this scheme to derive multiple keys secure?

I need a cryptographic scheme to generate a deterministic chain of private keys that look random to outside observer but can always be reconstructed from a single root key, also: Neither private ...
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SHA-256 Reversing A String of Equal Length

I've done a lot of reading on how SHA-256, I've found that SHA-256 is irreversible because more data is fed into the hashed string than the hash string contains. But, what if the data that was ...
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Hashing entropy with only 128 bits of internal state

I am looking to implement the Fortuna algorithm (https://www.schneier.com/fortuna.pdf) on a system with very restrictive memory constraints, using AES-128 as the underlying cipher. As the key size is ...
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Is a 256 bit HMAC-SHA256 key compromised if the tail is used for identification?

Using a truncated hash of a key seems to be a safe way to identify the key (i.e. key fingerprint), but what about truncating a key itself in the case of HMAC-SHA256? Example: ...
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How does the HOTP dynamic truncation function generalize to longer hashes?

HOTP, the HMAC-based One-Time Password algorithm from RFC 4226, uses a "dynamic truncation" function to turn the 20 byte HMAC-SHA-1 value into a 31 bit string. The dynamic truncation (from Section ...
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Chopping off SHA256 entropy?

I have a NoSQL key-value database. I want to insert couple million of records to it. For the key generation, I'm, using a prefix (something like data-one-) and ...
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349 views

How to crack SHA256 only letters

I recently created a program that hashes a password using SHA256 and potentially using salt. How can I crack that if I know that the password only contains lowercase letters?
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AES + CBC encryption for a stream of UDP packets

I am developing an application that is based on UDP, and I need to send a stream of packets. As you can imagine, packets can get lost or corrupted. I need to make sure that the content of those ...
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533 views

SHA-256 exhaustive search

How do I calculate the number of computations needed to break SHA256 in case we are using it for safely storing passwords (together with a salt)? Are there any formulas that can be employed? For ...
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140 views

Can I use HKDF to improve security of HMAC used with weak hash function?

I am writing a framework which encrypts/decrypts files (or streams, in general) with symmetric key using block cipher (for example, AES). To authenticate encrypted file, I use HMAC, which is ...
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SHA512 faster than SHA256?

I'm getting this strange result that SHA512 is around 50% faster than SHA256. I'm using .net's SHA512Managed and SHA256Managed ...
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SHA256_HMAC for deriving session keys using a counter

I need to generate some session keys from a master key that was generated from an ECDH key exchange. The master key is 256 bits and I need 256 bit sessions keys. Is it safe to use SHA256_HMAC with ...
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322 views

SHA-256 hash of null input?

What is the SHA-256 hash if the input is null, i.e. an empty bitstring? (Not the hash of 0 or "0".)
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114 views

DPA Attack on HMAC SHA-256

I have read the paper Differential Power Analysis of HMAC SHA-2 in the Hamming Weight Model and I want to understand the DPA Attack. In section 3.2.1 Path 1 (page 4) there is written: The last ...
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Hash length extension attack - SHA256 to 512 - impossible, correct?

Just want to be sure about something before I sign off on a method we're about to put into place. We have a secret, to which a user-defined key is appended. The user can see the SHA256 hash of the ...
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573 views

The difference in size between ECDSA output and hash size

So if I use secp256k1 for example, I've got my key size of 256 bit, and say I sign a SHA256 hash of a message, with size 256 bit, I get an output of size 512bit. Why is there a difference between the ...
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DH with AES - is that an acceptable security scheme over UPnP?

I'm trying to devise a good security scheme to protect comms over Wi-Fi. Right now, I have 2 devices that already communicate via UPnP but I need to secure this communication. I've come up with this: ...