Path: ...!eternal-september.org!feeder3.eternal-september.org!i2pn.org!i2pn2.org!.POSTED!not-for-mail
From: Stefan Claas <fgrsna.pynnf@vagrearg.eh>
Newsgroups: sci.crypt
Subject: Putting encrypted data in an X-Face Header :-)
Date: Sat, 22 Mar 2025 12:53:51 +0100
Organization: i2pn2 (i2pn.org)
Message-ID: <640286bde8850f22227e92c0156e382704f6e916@i2pn2.org>
MIME-Version: 1.0
Injection-Date: Sat, 22 Mar 2025 11:53:51 -0000 (UTC)
Injection-Info: i2pn2.org;
	logging-data="1265485"; mail-complaints-to="usenet@i2pn2.org";
	posting-account="ieSrCjSDShpZNyqIW52mlwIkg76Hsp+TOOO6KTdfCN8";
User-Agent: flnews/1.3.0pre29 (for GNU/Linux)
Cancel-Lock: sha1:rQ/6hLTGFpAi3+hXRuoDW+cW+SE=
X-Date: It's Sat Sep 11526 12:53:51 PM CET 1993, the September that never ends.
X-Spam-Checker-Version: SpamAssassin 4.0.0
X-Ed25519-Sig: 42eb9641913c28a5c063925bd9dbf0b8d24c34701d01489fb8ed5d9b8f0a60e7
 f68d0b93e306a720b0d66263ffc6374c4b0950b8d7d77357272ef5844f0adf0a
X-Ed25519-Pub: c0ffee5a36e581eb10f60b2831b3cdb955d2e7ef680dd282a8d43ad8b84b357a
Bytes: 7449
Lines: 185

Hi all,

just for fun. You can put up to 288 bytes in an X-Face header. If the
message is shorter than 288 bytes it will be padded with a checkerboard
pattern.

https://www.dairiki.org/xface/

$ echo "Hello sci.crypt community. :-)" | d2x
#define image_width 48
#define image_height 48
static unsigned char image_bits[] = {
 0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x73, 0x63, 0x69, 0x2e, 0x63, 0x72,
 0x79, 0x70, 0x74, 0x20, 0x63, 0x6f, 0x6d, 0x6d, 0x75, 0x6e, 0x69, 0x74,
 0x79, 0x2e, 0x20, 0x3a, 0x2d, 0x29, 0x0a, 0x00, 0xff, 0x00, 0xff, 0x00,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff
};

Here is the C source code:

// d2x - data to xbm

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>

#define IMAGE_WIDTH 48
#define IMAGE_HEIGHT 48
#define IMAGE_SIZE (IMAGE_WIDTH * IMAGE_HEIGHT / 8) // 288 Bytes
#define INPUT_SIZE IMAGE_SIZE                      // 288 Bytes

// Function to embed data into an image with checkerboard padding
void encode(uint8_t *image, const uint8_t *data, size_t bytesRead) {
    for (size_t i = 0; i < bytesRead; i++) {
        image[i] = data[i];
    }

    // Checkerboard padding
    for (size_t i = bytesRead; i < IMAGE_SIZE; i++) {
        // Alternate between 0xFF and 0x00 based on row and column
        if ((i / IMAGE_WIDTH) % 2 == (i % IMAGE_WIDTH) % 2) {
            image[i] = 0xFF; // White
        } else {
            image[i] = 0x00; // Black
        }
    }
}

// Function to extract data from an image
void decode(const uint8_t *image, uint8_t *data) {
    for (int i = 0; i < INPUT_SIZE; i++) {
        data[i] = image[i];
    }
}

// Function to write the XBM format
void write_xbm(const uint8_t *image, FILE *out) {
    fprintf(out, "#define image_width %d\n", IMAGE_WIDTH);
    fprintf(out, "#define image_height %d\n", IMAGE_HEIGHT);
    fprintf(out, "static unsigned char image_bits[] = {\n");

    for (int i = 0; i < IMAGE_SIZE; i++) {
        // Single space before the first hex value on each line
        if (i % 12 == 0) {
            fprintf(out, " ");
        }

        // Write the hex value
        fprintf(out, "0x%02x", image[i]);

        // Add a comma unless it's the last value
        if (i < IMAGE_SIZE - 1) {
            fprintf(out, ",");
        }

        // Add a space after each value
        fprintf(out, " ");

        // Add a newline after every 12 values
        if ((i + 1) % 12 == 0 || i == IMAGE_SIZE - 1) {
            fprintf(out, "\n");
        }
    }

    fprintf(out, "};\n");
}

// Function to read the XBM format
int read_xbm(FILE *input, uint8_t *image) {
    char line[256];
    int index = 0;

    while (fgets(line, sizeof(line), input)) {
        // Skip lines that do not contain hex values
        if (!strstr(line, "0x")) {
            continue;
        }

        // Parse hex values
        char *token = strtok(line, ",");
        while (token != NULL) {
            if (sscanf(token, " 0x%02hhx", &image[index]) == 1) {
                index++;
            }
            token = strtok(NULL, ",");
        }
    }

    return index;
}

// Main function
int main(int argc, char *argv[]) {
    int mode = 0; // 0 = Encode, 1 = Decode

    // Argument check
    if (argc > 1) {
        if (strcmp(argv[1], "-d") == 0) {
            mode = 1; // Decode mode
        } else {
            fprintf(stderr, "Usage:\n");
            fprintf(stderr, "  sx     Put data (max. 288 bytes) from stdin into XBM format and write to stdout\n");
            fprintf(stderr, "  sx -d  Decode XBM image from stdin and write data to stdout\n");
            return 1;
        }
    }

    if (mode == 1) {
        // Decode mode
        uint8_t image[IMAGE_SIZE] = {0};
        int bytesRead = read_xbm(stdin, image);

        if (bytesRead != IMAGE_SIZE) {
            fprintf(stderr, "Error: Invalid image size (expected %d bytes, got %d)\n", IMAGE_SIZE, bytesRead);
            return 1;
        }

        uint8_t data[INPUT_SIZE] = {0};
        decode(image, data);
        fwrite(data, 1, INPUT_SIZE, stdout);
    } else {
        // Encode mode
        uint8_t data[INPUT_SIZE] = {0};
        size_t bytesRead = fread(data, 1, INPUT_SIZE, stdin);

        if (bytesRead > INPUT_SIZE) {
            fprintf(stderr, "Error: Input data too large\n");
            return 1;
        }

        uint8_t image[IMAGE_SIZE] = {0};
        encode(image, data, bytesRead);
        write_xbm(image, stdout);
    }

    return 0;
}
========== REMAINDER OF ARTICLE TRUNCATED ==========