hypersig

% SPDX-FileCopyrightText: 2025 Emerald <emerald@emeraldgreen.dev>
%
% SPDX-License-Identifier: GPL-3.0-or-later

-module(public_key_ffi).

-export([generate_key_pair/0, decode_public_key/1, decode_private_key/1, encode_public_key/1, encode_private_key/1, do_sign/2, do_verify/3 ]).

-include_lib("public_key/include/public_key.hrl").

encode_public_key(Ent) ->
    Entry = public_key:pem_entry_encode('RSAPublicKey', Ent),
    public_key:pem_encode([Entry]).

encode_private_key(Ent) ->
    Entry = public_key:pem_entry_encode('RSAPrivateKey', Ent),
    public_key:pem_encode([Entry]).

decode_public_key(Pem) ->
    case do_decode_pem(Pem) of
        {ok, Key} -> case Key of
            Key = #'RSAPublicKey'{ } -> {ok, Key};
            _Other -> {error, expected_public_key}
        end;
        Other -> Other
    end.

decode_private_key(Pem) ->
    case do_decode_pem(Pem) of
        {ok, Key} -> case Key of
            Key = #'RSAPrivateKey'{ } -> {ok, Key};
            _Other -> {error, expected_private_key}
        end;
        Other -> Other
    end.

do_decode_pem(Pem) ->
    [PemEntry] = public_key:pem_decode(Pem),
    case public_key:pem_entry_decode(PemEntry) of
        Key = #'RSAPublicKey'{ } -> {ok, Key};
        Key = #'RSAPrivateKey'{ } -> {ok, Key};
        _ -> {error, unexpected_key_format}
    end.

    
do_sign(Message, Key) ->
    try
        {ok, public_key:sign(Message, sha256, Key)}
    catch
        _:Reason:_ -> {error, {runtime_error, Reason }}
    end.

do_verify(Message, Signature, Key) ->
    try
        {ok, public_key:verify(Message, sha256, Signature, Key)}
    catch
        _:Reason:_ -> {error, {runtime_error, Reason}}
    end.

generate_key_pair() ->
    case public_key:generate_key({rsa, 2048, 65537}) of 
        PrivateKey = #'RSAPrivateKey'{ } -> 
            PublicKey = #'RSAPublicKey'{
                modulus = PrivateKey#'RSAPrivateKey'.modulus,
                publicExponent = PrivateKey#'RSAPrivateKey'.publicExponent
            },
            {ok, {PublicKey, PrivateKey}};

        _ -> {error, unexpected_key_format}

    end.