CODEWITHSUNDEEP
pythonhashcryptographysha256
StartingHash
StartingHash

Reputation: 21

How to correctly do a double SHA256 hashing?

This might be basic stuff, but am pretty new to coding in general.

How do you properly do a double sha256 code?

For example, for the string "abc" the correct output of the double hash should be: 4f8b42c22dd3729b519ba6f68d2da7cc5b2d606d05daed5ad5128cc03e6c6358

However, in the script I provide below, I get another output, altough I do not know where I went wrong. What am I missing in the code?

abc = 'abc'.encode("utf-8")

hashed_abc = hashlib.sha256(abc)

hashed_abc = hashlib.sha256(hashed_abc.hexdigest().encode('utf-8'))
print((hashed_abc.hexdigest()))

Thank you.

Upvotes: 2

Views: 2406

Answers (2)

kelalaka
kelalaka

Reputation: 5636

Cryptographic hash functions are working on bytes and output bytes, too. The double SHA256 or written as SHA256D should work in this way, too.

import hashlib
import binascii
 
   
def SHA256D(data): 

   hash = hashlib.sha256(data).digest()

   #Uncomment me for testing
   #print(hashlib.sha256(data.encode('utf-8')).hexdigest() )
      
   return hashlib.sha256(hash).digest()
   
   
toHashB = "hello".encode('utf-8')

print(SHA256D(toHashB))

doublehashed = SHA256D(toHashB)

print( binascii.hexlify(doublehashed).decode('utf8'))

The double SHA256 hash of the string "hello" is given as an example on Bitcoin pages. This outputs

9595c9df90075148eb06860365df33584b75bff782a510c6cd4883a419833d50

Note that the other answer had two problems;

  1. There is an error on the string "hello" binascii.Error: Odd-length string
  2. The SHA256D executes the hex decoding and encoding. This should be outside of the SHA256D

Upvotes: 0

Thornily
Thornily

Reputation: 582

import hashlib
import binascii
 
def doubleSha256(hex): 
   bin = binascii.unhexlify(hex)
   hash = hashlib.sha256(bin).digest()
   hash2 = hashlib.sha256(hash).digest()
   print("Input Hex: "+str(hex,"ascii"))
   print("SHA256:\n   "+str(binascii.hexlify(hash),"ascii"))
   print("Double-SHA256:\n   "+str(binascii.hexlify(hash2),"ascii"))

You could use something like this and it works for me.

To add:

If you are having trouble passing in “abc” use this.

ascii = "abc"
hex = binascii.hexlify(bytes(ascii,"ascii"))
doubleSha256(hex)

Upvotes: 2

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