Is the file just read bit by bit to calculate the hash with those values or is there more to it?
Are there any resources to read a bit more about file hashing?
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Hash functions operate on blocks like SHA-256 has 512-bit input block. In SHA-256, your data $m$ is divided into 512-bits blocks $m_1,\ldots,m_n$ where each entered into the hash function. The final block, $m_n$ is padded as
$$k=(447−l) \bmod 512$$ where data size is $l$ and $k$ is the number of zeros following the 1 after $m$ and finally the message size in 64 bits. The message size can also 128 which allows larger files to be hashed. So the input to SHA-256 is
Each other hash function defined in a similar way, an example from FRC4634
The hash functions specified herein are used to compute a message digest for a message or data file that is provided as input. The message or data file should be considered to be a bit string. The length of the message is the number of bits in the message (the empty message has length 0). If the number of bits in a message is a multiple of 8, for compactness we can represent the message in hex. The purpose of message padding is to make the total length of a padded message a multiple of 512 for SHA-224 and SHA-256 or a multiple of 1024 for SHA-384 and SHA-512.
Note: The 64-bit (or 128-bit) message size also determines the maximum input size for a SHA-256 hash.
Not quite. File hashing is a way of creating a
unique identifier for a specific input with incredibly low chance of collision. A collision happens when two inputs map to the same output. So far we have not seen any cases of collision for SHA256 or SHA3; two of the most prominent hashing algorithms. In terms of what goes on inside a hashing algorithm, its not just mapping one bit to another bit. There can be different methods including (but not limited to) bit substitution, logical operations, and many other bitwise operations. A good hashing algorithm should be complex enough that two very similar inputs map to very different outputs, again making it a
SHA256(0000000) = ABD4562B6AEE9F
SHA256(0000001) = 255FBA9C5C33ED