Trying to recreate SHA256 hashing from the pseudocode on the wiki and it says to convert an integer to a 64 bit big endian integer.
I can't find how to do this anywhere online and when I look up the step by step process of how SHA256 works it doesn't make sense to me when it gets to that part as it seems they are just using a 7 bit unsigned binary integer in their example: https://qvault.io/cryptography/how-sha-2-works-step-by-step-sha-256/
can anyone help?
Ints in Python 3 have a method called to_bytes() with arguments for length in bytes and endianness which returns a bytes object.
>>> num = 5
>>> print(num.to_bytes(8, 'big')) # 8 bytes aka 64 bits long, big endian
b'\x00\x00\x00\x00\x00\x00\x00\x05'
You certain can do this with struct:
>>> import struct
>>> val = 1234
>>> struct.pack('>Q',val)
b'\x00\x00\x00\x00\x00\x00\x04\xd2'
Whether that's the best thing to use for SHA256 is a question for the philosophers.
it seems they are just using a 7 bit unsigned binary integer in their example: https://qvault.io/cryptography/how-sha-2-works-step-by-step-sha-256/
In that example the integer 88 has a bit length of 7 (1011000) however if you look closely at the pre-processing steps you'll see it is appended to the data as 64 bits:
00000000 00000000 00000000 00000000 00000000 00000000 00000000 01011000
One way to get the 64-bit integer for length is format(L,"064b"), where L is the bit length of the original message. For a bit length of 88 this would return 0000000000000000000000000000000000000000000000000000000001011000.
