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After reading this question/answer I thought I'd try and implement the SHA-256 for my own education. My initial thought for converting the input into a number was to use a line of code like sum([ord(character) for character in input_string]), I quickly realized this is a terrible idea because I'm greatly reducing the entropy of the input by mapping a lot of highly varied strings to a relatively small number of integers. My second though was to get a hex representation of the string then get the base 16 integer representation of that hex string

import binascii
input_integer = int(binascii.hexlify('hello world'), 16)

However since I'm not an expert in hashing algorithms there may be something wrong with my second implementation that I'm not aware of.

How do you convert a string to a number to be used in a hash algorithm?

My code is written in python, for reference

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closed as unclear what you're asking by yyyyyyy, Maarten Bodewes, otus, SEJPM, e-sushi Apr 12 '17 at 14:11

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ You could use Python's built in int() function. Pass your string and its base: int('0100',2)=4. Default is big endian. $\endgroup$ – Q-Club Apr 11 '17 at 20:03
  • $\begingroup$ I'm asking if my second example is secure. I don't need help with the implementation ... yet. $\endgroup$ – John Apr 11 '17 at 20:06
  • $\begingroup$ I have absolutely no idea what you are trying to do. You say you are trying to "implement the (sic) SHA-256", but your algorithm obviously has nothing to do with SHA-256. $\endgroup$ – fkraiem Apr 11 '17 at 20:12
  • $\begingroup$ @fkraiem SHA-256 operates on number not strings. How do you safely convert a number to a string so that you can perform the hashing operations on the number? $\endgroup$ – John Apr 11 '17 at 20:16
  • $\begingroup$ I meant string to number. $\endgroup$ – John Apr 11 '17 at 20:42
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The input format of the data doesn't affect the security of the algorithm.

Any format that can be represented by a sequence of bits will be fine. You can use raw ASCII byte values, 6-bit Base64 values, anything which is in binary form.

If you convert your string into ASCII bytes, for example, you'll end up with a set of 8 bit numbers. Join them together and there's your input.

Since SHA256 uses 32-bit words, it's common to use a byte format for the data (4 bytes = 32 bits). After converting your input to a set of bits, your first task will be to append a 1 bit, pad with zeroes to 448 bits and then append a 64-bit length (the original bit length of the input data) to give you a 512 bit buffer.

I'm sure you can handle the rest.

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  • $\begingroup$ I'm not asking about the input format. If you convert your string into ASCII bytes, for example, you'll end up with a set of 8 bit numbers. Join them together and there's your input. this is the answer I was looking for. Your explanation of how sha256 works doesn't account for cases where the input exceeds 448 bits. I already know that you pad to the (nearest multiple of 512) - 64. Thanks for answering. $\endgroup$ – John Apr 11 '17 at 20:35

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