Hidden Strings

LNHiddenStrings.hh

/**
 The MIT License (MIT)
 
 Copyright (c) 2024 Léo Natan
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
 to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in all
 copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 */

//
//  LNHiddenStrings.hh
//

#import <Foundation/Foundation.h>
#include <array>

CF_EXTERN_C_BEGIN

namespace hidden_strings {

extern "C++"
template <size_t N>
struct base64_string : std::array<char, N> {
    consteval base64_string(const char (&input)[N]) : base64_string(input, std::make_index_sequence<N>{}) {}
    template <size_t... Is>
    consteval base64_string(const char (&input)[N], std::index_sequence<Is...>) : std::array<char, N>{ input[Is]... } {}
};

extern "C++"
template <size_t N>
consteval const base64_string<4 * (((N - 1) + 2) / 3) + 1> base64Encode(const char(&input)[N]) {
    constexpr char kEncodingTable[] = {
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
        'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
        'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
    };
    
    size_t in_len = N - 1;
    char output[4 * (((N - 1) + 2) / 3) + 1] {0};
    size_t i = 0;
    char *p = const_cast<char *>(output);
    
    for (i = 0; in_len > 2 && i < in_len - 2; i += 3) {
        *p++ = kEncodingTable[(input[i] >> 2) & 0x3F];
        *p++ = kEncodingTable[((input[i] & 0x3) << 4) |
                              ((int)(input[i + 1] & 0xF0) >> 4)];
        *p++ = kEncodingTable[((input[i + 1] & 0xF) << 2) |
                              ((int)(input[i + 2] & 0xC0) >> 6)];
        *p++ = kEncodingTable[input[i + 2] & 0x3F];
    }
    if (i < in_len) {
        *p++ = kEncodingTable[(input[i] >> 2) & 0x3F];
        if (i == (in_len - 1)) {
            *p++ = kEncodingTable[((input[i] & 0x3) << 4)];
            *p++ = '=';
        } else {
            *p++ = kEncodingTable[((input[i] & 0x3) << 4) |
                                  ((int)(input[i + 1] & 0xF0) >> 4)];
            *p++ = kEncodingTable[((input[i + 1] & 0xF) << 2)];
        }
        *p++ = '=';
    }
    
    return base64_string<4 * (((N - 1) + 2) / 3) + 1>(output);
}

extern "C++"
template <typename T>
CF_INLINE
NSString* decodeHiddenString(T encoded)
{
    return [[NSString alloc] initWithData:[[NSData alloc] initWithBase64EncodedString:@(encoded.data()) options:0] encoding:NSUTF8StringEncoding];
}

} //namespace hidden_strings

#define HiddenString(input) hidden_strings::decodeHiddenString(hidden_strings::base64Encode("" input ""))

CF_EXTERN_C_END

//
//  test.mm
//

#import "LNHiddenStrings.hh"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSLog(@"%@", HiddenString("Hello, Secret World!"));
    }
    return 0;
}

/**
 strings output:
 
     ➜ strings -a test
     SGVsbG8sIFNlY3JldCBXb3JsZCE=
     initWithBase64EncodedString:options:
     initWithData:encoding:
     stringWithUTF8String:
 
 strings output without using HiddenString:
 
     ➜ strings -a test
     Hello, Secret World!
 */