Sha256 Hashes in Prolog

Here’s the translation of the SHA256 Hashes example from Go to Prolog, formatted in Markdown suitable for Hugo:

In Prolog, we don’t have built-in cryptographic functions like SHA256. However, we can use external libraries or implement the algorithm ourselves. For this example, we’ll use the crypto_hash predicate from the crypto library, which is available in some Prolog implementations like SWI-Prolog.

:- use_module(library(crypto)).

sha256_hash(String, Hash) :-
    crypto_data_hash(String, Hash, [algorithm(sha256), encoding(hex)]).

main :-
    String = "sha256 this string",
    sha256_hash(String, Hash),
    format('~w~n', [String]),
    format('~s~n', [Hash]).

In this Prolog implementation:

1. We import the crypto library, which provides cryptographic functions.

2. We define a predicate sha256_hash/2 that takes a String and unifies the result with Hash. It uses the crypto_data_hash/3 predicate from the crypto library, specifying SHA256 as the algorithm and hex as the encoding.

3. In the main/0 predicate:

   • We define the input string.
   • We call sha256_hash/2 to compute the hash.
   • We print the original string and the computed hash.

To run the program, save it in a file (e.g., sha256_hashes.pl) and use your Prolog interpreter. For example, with SWI-Prolog:

$ swipl -s sha256_hashes.pl -g main -t halt
sha256 this string
1af1dfa857bf1d8814fe1af8983c18080019922e557f15a8a...

Note that the exact output may vary depending on the Prolog implementation and the available cryptographic libraries.

If you need to compute other hashes, you can modify the algorithm option in the crypto_data_hash/3 predicate. For example, to compute SHA512 hashes, you could use algorithm(sha512).

It’s important to note that if you need cryptographically secure hashes, you should carefully research hash strength and ensure that your Prolog implementation and its cryptographic libraries are up-to-date and secure.