What you will prove

The bytes you have either match a recorded digest or they do not.

SHA-256 reads bytes. A changed word, line ending, encoding, or final newline changes the result. This exercise fixes all of those inputs with two downloadable UTF-8 files.

Step 1

Download all three files into one directory.

original.txt — the expected bytes
changed.txt — one phrase changed
check_sha256.py — the standard-library checker

Both text fixtures use UTF-8, LF line endings, and one final newline. The checker calls read_bytes(), so it does not translate text or line endings before hashing.

Read the lesson-file license

Step 2

Confirm the original file.

python check_sha256.py e079f56bca7a9447e85e311560f561c44184164e55cc6555f365ee4aa2a06faf original.txt

file: original.txt
expected: e079f56bca7a9447e85e311560f561c44184164e55cc6555f365ee4aa2a06faf
actual:   e079f56bca7a9447e85e311560f561c44184164e55cc6555f365ee4aa2a06faf
result:   MATCH

The checker exits with status 0 when the two digests are equal.

Step 3

Use the same expected digest against the changed file.

python check_sha256.py e079f56bca7a9447e85e311560f561c44184164e55cc6555f365ee4aa2a06faf changed.txt

file: changed.txt
expected: e079f56bca7a9447e85e311560f561c44184164e55cc6555f365ee4aa2a06faf
actual:   70e1c149e4359d34bc23e7c182d63a21f0accbb340832898b1c9ca205e24158d
result:   MISMATCH

The checker exits with status 1. That failure is the useful result: it catches that changed.txt is not byte-for-byte identical to the recorded input.

Boundary

Equality is a narrow claim.

A matching digest is strong evidence that the checked bytes equal the bytes behind the expected digest. It does not show who created the file, whether the expected digest came from a trusted source, whether the content is true, or whether the code is safe or correct. Record the digest and its source together.

Troubleshooting

When your result differs

Confirm the filename and the 64-character expected digest.
Download the fixture rather than copying it through an editor that may change line endings.
On Windows, try py check_sha256.py ... if python is not available.
A mismatch should stay a failure until you can explain the changed bytes.

Next step

See how Magogi classifies evidence

Move from one digest check to the wider evidence model: what is runnable, build-recorded, attested, or still absent.