# libft_ssl

A C library implementing cryptographic hash functions from scratch.

Each algorithm exposes a uniform streaming API — `init` / `update` / `final`

## Algorithms

| Algorithm  | Digest | Block | Notes |
|------------|--------|-------|-------|
| MD5        | 128-bit | 512-bit | RFC 1321 - broken, non-security use only |
| SHA-256    | 256-bit | 512-bit | SHA-2 family, NSA/NIST - widely used in TLS, Bitcoin |
| Whirlpool  | 512-bit | 512-bit | ISO/IEC 10118-3 - Miyaguchi-Preneel construction |

## API

The public interface lives in `<libft_ssl/libft_ssl.h>`.

```c
struct digest_algo {
    const char  *name;
    size_t       digest_size;   /* bytes */
    size_t       block_size;    /* bytes */
    void (*init)  (void *ctx);
    void (*update)(void *ctx, const uint8_t *data, size_t len);
    void (*final) (void *ctx, uint8_t *out);
};

union digest_ctx { /* one allocation covers all algorithm contexts */
    struct md5_ctx       md5;
    struct sha256_ctx    sha256;
    struct whirlpool_ctx whirlpool;
};
```

One global instance is provided per algorithm: `g_md5`, `g_sha256`,
`g_whirlpool`.

### Example

```c
#include <libft_ssl/libft_ssl.h>
#include <stdio.h>

int main(void)
{
    const struct digest_algo *algo = &g_sha256;
    union digest_ctx          ctx;
    uint8_t                   digest[32];

    algo->init(&ctx);
    algo->update(&ctx, (const uint8_t *)"hello", 5);
    algo->final(&ctx, digest);

    for (size_t i = 0; i < algo->digest_size; i++)
        printf("%02x", digest[i]);
    puts("");
}
```

Compile with:

```sh
cc example.c -lft_ssl -o example
# or with pkg-config:
cc example.c $(pkg-config --cflags --libs libft_ssl) -o example
```

## Building

### Dependencies

- C99 compiler
- autoconf
- automake
- libtool
- `pdflatex` — only if building documentation (`--enable-doc`)

### Steps

```sh
./autogen.sh          # generate the build system (first checkout only)
./configure
make
make install          # installs to /usr/local by default
```

Common `configure` options:

| Flag | Default | Description |
|------|---------|-------------|
| `--prefix=PATH` | `/usr/local` | Installation prefix |
| `--enable-debug` | no | Build with `-g -O0` instead of `-O2` |
| `--enable-doc` | no | Build PDF documentation (requires `pdflatex`) |

### pkg-config

After installation the library registers itself with pkg-config:

```sh
pkg-config --cflags --libs libft_ssl
```

## Project structure

```
include/          public and internal headers
src/
  md5/            MD5 init / update / compress / final
  sha256/         SHA-256 init / update / compress / final
  whirlpool/      Whirlpool init / update / compress / final
  libft_ssl.c     algorithm descriptor table (X-macro generated)
doc/              LaTeX source for the technical documentation
```

## Documentation

The full technical write-up is available at <https://lohic.dev/libft_ssl.html> ([PDF](https://lohic.dev/libft_ssl.pdf)).

## License

GPLv3 — see [LICENSE](LICENSE).