Working with bytes in Python using SHA-256

Question

So I want to use SHA-256 for a specific problem: Calculate digest from a bytearray, then concatenate the resulting digest to another block of bytes ( a 1024 byte block for this problem ) and calculate the digest for the concatenated values.

For example:

Here are my two byte blocks:

from hashlib import sha256
rawhex4 = b'\x44'*773
rawhex3 = b'\x33'*1024

h = sha256()
h.update(rawhex4)
aux = h.digest()

This hexdigest is: d8f8a9eadd284c4dbd94af448fefb24940251e75ca2943df31f7cfbb6a4f97ed

then I want to concatenate this 32 byte digest to my next block and hash it but I am not getting the correct answer. I do the following:

h.update(rawhex3 + aux)

I know for fact that hashing rawhex3 + hash(rawhex4) will give me this digest:

26949e3320c315f179e2dfc95a4158dcf9a9f6ebf3dfc69252cd83ad274eeafa

What could I be missing? I am pretty new to Python

Robᵩ · Accepted Answer · 2016-04-08 02:26:47Z

4

Try this:

from hashlib import sha256
rawhex4 = b'\x44'*773
rawhex3 = b'\x33'*1024

h1 = sha256()
h1.update(rawhex4)
aux = h1.digest()

h2 = sha256()
h2.update(rawhex3 + aux)
print h2.hexdigest()

answered Apr 8, 2016 at 2:26

Robᵩ

170k20 gold badges251 silver badges323 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

robyschek · Accepted Answer · 2016-04-08 02:25:53Z

3

You are reusing the hash object which already contains bits from rawhex4. If you create a new one, you'll get your 26..fa result.

answered Apr 8, 2016 at 2:25

robyschek

2,04515 silver badges19 bronze badges

2 Comments

Robᵩ Over a year ago

Good explanation. Steal my code for an example if you feel the need; I'll delete my answer in a little while.

Jesus Fernandez Over a year ago

Wow I thought with h.update() the hash function was cleared so I thought my problem was in concatenating bytes... couldn't see the simple solution... Thanks!!

Collectives™ on Stack Overflow

Working with bytes in Python using SHA-256

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related