modcryptolib.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2017-2018 Paul Sokolovsky
 * Copyright (c) 2018 Yonatan Goldschmidt
 *
 * 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.
 */

#include "py/mpconfig.h"

#if MICROPY_PY_CRYPTOLIB

#include <assert.h>
#include <string.h>

#include "py/runtime.h"

// This module implements crypto ciphers API, roughly following
// https://www.python.org/dev/peps/pep-0272/ . Exact implementation
// of PEP 272 can be made with a simple wrapper which adds all the
// needed boilerplate.

// values follow PEP 272
enum {
    UCRYPTOLIB_MODE_ECB = 1,
    UCRYPTOLIB_MODE_CBC = 2,
    UCRYPTOLIB_MODE_CTR = 6,
};

struct ctr_params {
    // counter is the IV of the AES context.

    size_t offset; // in encrypted_counter
    // encrypted counter
    uint8_t encrypted_counter[16];
};

#if MICROPY_SSL_AXTLS
#include "lib/axtls/crypto/crypto.h"

#define AES_CTX_IMPL AES_CTX
#endif

#if MICROPY_SSL_MBEDTLS
#include <mbedtls/aes.h>

// we can't run mbedtls AES key schedule until we know whether we're used for encrypt or decrypt.
// therefore, we store the key & keysize and on the first call to encrypt/decrypt we override them
// with the mbedtls_aes_context, as they are not longer required. (this is done to save space)
struct mbedtls_aes_ctx_with_key {
    union {
        mbedtls_aes_context mbedtls_ctx;
        struct {
            uint8_t key[32];
            uint8_t keysize;
        } init_data;
    } u;
    unsigned char iv[16];
};
#define AES_CTX_IMPL struct mbedtls_aes_ctx_with_key
#endif

typedef struct _mp_obj_aes_t {
    mp_obj_base_t base;
    AES_CTX_IMPL ctx;
    uint8_t block_mode : 6;
#define AES_KEYTYPE_NONE 0
#define AES_KEYTYPE_ENC  1
#define AES_KEYTYPE_DEC  2
    uint8_t key_type : 2;
    struct ctr_params ctr_params[]; // optional
} mp_obj_aes_t;

static inline bool is_ctr_mode(int block_mode) {
    #if MICROPY_PY_CRYPTOLIB_CTR
    return block_mode == UCRYPTOLIB_MODE_CTR;
    #else
    return false;
    #endif
}

static inline struct ctr_params *ctr_params_from_aes(mp_obj_aes_t *o) {
    return &o->ctr_params[0];
}

#if MICROPY_SSL_AXTLS
static void aes_initial_set_key_impl(AES_CTX_IMPL *ctx, const uint8_t *key, size_t keysize, const uint8_t iv[16]) {
    assert(16 == keysize || 32 == keysize);
    AES_set_key(ctx, key, iv, (16 == keysize) ? AES_MODE_128 : AES_MODE_256);
}

static void aes_final_set_key_impl(AES_CTX_IMPL *ctx, bool encrypt) {
    if (!encrypt) {
        AES_convert_key(ctx);
    }
}

static void aes_process_ecb_impl(AES_CTX_IMPL *ctx, const uint8_t in[16], uint8_t out[16], bool encrypt) {
    memcpy(out, in, 16);
    // We assume that out (vstr.buf or given output buffer) is uint32_t aligned
    uint32_t *p = (uint32_t *)out;
    // axTLS likes it weird and complicated with byteswaps
    for (int i = 0; i < 4; i++) {
        p[i] = MP_HTOBE32(p[i]);
    }
    if (encrypt) {
        AES_encrypt(ctx, p);
    } else {
        AES_decrypt(ctx, p);
    }
    for (int i = 0; i < 4; i++) {
        p[i] = MP_BE32TOH(p[i]);
    }
}

static void aes_process_cbc_impl(AES_CTX_IMPL *ctx, const uint8_t *in, uint8_t *out, size_t in_len, bool encrypt) {
    if (encrypt) {
        AES_cbc_encrypt(ctx, in, out, in_len);
    } else {
        AES_cbc_decrypt(ctx, in, out, in_len);
    }
}

#if MICROPY_PY_CRYPTOLIB_CTR
// axTLS doesn't have CTR support out of the box. This implements the counter part using the ECB primitive.
static void aes_process_ctr_impl(AES_CTX_IMPL *ctx, const uint8_t *in, uint8_t *out, size_t in_len, struct ctr_params *ctr_params) {
    size_t n = ctr_params->offset;
    uint8_t *const counter = ctx->iv;

    while (in_len--) {
        if (n == 0) {
            aes_process_ecb_impl(ctx, counter, ctr_params->encrypted_counter, true);

            // increment the 128-bit counter
            for (int i = 15; i >= 0; --i) {
                if (++counter[i] != 0) {
                    break;
                }
            }
        }

        *out++ = *in++ ^ ctr_params->encrypted_counter[n];
        n = (n + 1) & 0xf;
    }

    ctr_params->offset = n;
}
#endif

#endif

#if MICROPY_SSL_MBEDTLS
static void aes_initial_set_key_impl(AES_CTX_IMPL *ctx, const uint8_t *key, size_t keysize, const uint8_t iv[16]) {
    ctx->u.init_data.keysize = keysize;
    memcpy(ctx->u.init_data.key, key, keysize);

    if (NULL != iv) {
        memcpy(ctx->iv, iv, sizeof(ctx->iv));
    }
}

static void aes_final_set_key_impl(AES_CTX_IMPL *ctx, bool encrypt) {
    // first, copy key aside
    uint8_t key[32];
    uint8_t keysize = ctx->u.init_data.keysize;
    memcpy(key, ctx->u.init_data.key, keysize);
    // now, override key with the mbedtls context object
    mbedtls_aes_init(&ctx->u.mbedtls_ctx);

    // setkey call will succeed, we've already checked the keysize earlier.
    assert(16 == keysize || 32 == keysize);
    if (encrypt) {
        mbedtls_aes_setkey_enc(&ctx->u.mbedtls_ctx, key, keysize * 8);
    } else {
        mbedtls_aes_setkey_dec(&ctx->u.mbedtls_ctx, key, keysize * 8);
    }
}

static void aes_process_ecb_impl(AES_CTX_IMPL *ctx, const uint8_t in[16], uint8_t out[16], bool encrypt) {
    mbedtls_aes_crypt_ecb(&ctx->u.mbedtls_ctx, encrypt ? MBEDTLS_AES_ENCRYPT : MBEDTLS_AES_DECRYPT, in, out);
}

static void aes_process_cbc_impl(AES_CTX_IMPL *ctx, const uint8_t *in, uint8_t *out, size_t in_len, bool encrypt) {
    mbedtls_aes_crypt_cbc(&ctx->u.mbedtls_ctx, encrypt ? MBEDTLS_AES_ENCRYPT : MBEDTLS_AES_DECRYPT, in_len, ctx->iv, in, out);
}

#if MICROPY_PY_CRYPTOLIB_CTR
static void aes_process_ctr_impl(AES_CTX_IMPL *ctx, const uint8_t *in, uint8_t *out, size_t in_len, struct ctr_params *ctr_params) {
    mbedtls_aes_crypt_ctr(&ctx->u.mbedtls_ctx, in_len, &ctr_params->offset, ctx->iv, ctr_params->encrypted_counter, in, out);
}
#endif

#endif

static mp_obj_t cryptolib_aes_make_new(const mp_obj_type_t *type, size_t n_args, size_t n_kw, const mp_obj_t *args) {
    mp_arg_check_num(n_args, n_kw, 2, 3, false);

    const mp_int_t block_mode = mp_obj_get_int(args[1]);

    switch (block_mode) {
        case UCRYPTOLIB_MODE_ECB:
        case UCRYPTOLIB_MODE_CBC:
        #if MICROPY_PY_CRYPTOLIB_CTR
        case UCRYPTOLIB_MODE_CTR:
        #endif
            break;

        default:
            mp_raise_ValueError(MP_ERROR_TEXT("mode"));
    }

    mp_obj_aes_t *o = mp_obj_malloc_var(mp_obj_aes_t, ctr_params, struct ctr_params, !!is_ctr_mode(block_mode), type);

    o->block_mode = block_mode;
    o->key_type = AES_KEYTYPE_NONE;

    mp_buffer_info_t keyinfo;
    mp_get_buffer_raise(args[0], &keyinfo, MP_BUFFER_READ);
    if (32 != keyinfo.len && 16 != keyinfo.len) {
        mp_raise_ValueError(MP_ERROR_TEXT("key"));
    }

    mp_buffer_info_t ivinfo;
    ivinfo.buf = NULL;
    if (n_args > 2 && args[2] != mp_const_none) {
        mp_get_buffer_raise(args[2], &ivinfo, MP_BUFFER_READ);

        if (16 != ivinfo.len) {
            mp_raise_ValueError(MP_ERROR_TEXT("IV"));
        }
    } else if (o->block_mode == UCRYPTOLIB_MODE_CBC || is_ctr_mode(o->block_mode)) {
        mp_raise_ValueError(MP_ERROR_TEXT("IV"));
    }

    if (is_ctr_mode(block_mode)) {
        ctr_params_from_aes(o)->offset = 0;
    }

    aes_initial_set_key_impl(&o->ctx, keyinfo.buf, keyinfo.len, ivinfo.buf);

    return MP_OBJ_FROM_PTR(o);
}

static mp_obj_t aes_process(size_t n_args, const mp_obj_t *args, bool encrypt) {
    mp_obj_aes_t *self = MP_OBJ_TO_PTR(args[0]);

    mp_obj_t in_buf = args[1];
    mp_obj_t out_buf = MP_OBJ_NULL;
    if (n_args > 2) {
        out_buf = args[2];
    }

    mp_buffer_info_t in_bufinfo;
    mp_get_buffer_raise(in_buf, &in_bufinfo, MP_BUFFER_READ);

    if (!is_ctr_mode(self->block_mode) && in_bufinfo.len % 16 != 0) {
        mp_raise_ValueError(MP_ERROR_TEXT("blksize % 16"));
    }

    vstr_t vstr;
    mp_buffer_info_t out_bufinfo;
    uint8_t *out_buf_ptr;

    if (out_buf != MP_OBJ_NULL) {
        mp_get_buffer_raise(out_buf, &out_bufinfo, MP_BUFFER_WRITE);
        if (out_bufinfo.len < in_bufinfo.len) {
            mp_raise_ValueError(MP_ERROR_TEXT("output too small"));
        }
        out_buf_ptr = out_bufinfo.buf;
    } else {
        vstr_init_len(&vstr, in_bufinfo.len);
        out_buf_ptr = (uint8_t *)vstr.buf;
    }

    if (AES_KEYTYPE_NONE == self->key_type) {
        // always set key for encryption if CTR mode.
        const bool encrypt_mode = encrypt || is_ctr_mode(self->block_mode);
        aes_final_set_key_impl(&self->ctx, encrypt_mode);
        self->key_type = encrypt ? AES_KEYTYPE_ENC : AES_KEYTYPE_DEC;
    } else {
        if ((encrypt && self->key_type == AES_KEYTYPE_DEC) ||
            (!encrypt && self->key_type == AES_KEYTYPE_ENC)) {

            mp_raise_ValueError(MP_ERROR_TEXT("can't encrypt & decrypt"));
        }
    }

    switch (self->block_mode) {
        case UCRYPTOLIB_MODE_ECB: {
            uint8_t *in = in_bufinfo.buf, *out = out_buf_ptr;
            uint8_t *top = in + in_bufinfo.len;
            for (; in < top; in += 16, out += 16) {
                aes_process_ecb_impl(&self->ctx, in, out, encrypt);
            }
            break;
        }

        case UCRYPTOLIB_MODE_CBC:
            aes_process_cbc_impl(&self->ctx, in_bufinfo.buf, out_buf_ptr, in_bufinfo.len, encrypt);
            break;

        #if MICROPY_PY_CRYPTOLIB_CTR
        case UCRYPTOLIB_MODE_CTR:
            aes_process_ctr_impl(&self->ctx, in_bufinfo.buf, out_buf_ptr, in_bufinfo.len,
                ctr_params_from_aes(self));
            break;
        #endif
    }

    if (out_buf != MP_OBJ_NULL) {
        return out_buf;
    }
    return mp_obj_new_bytes_from_vstr(&vstr);
}

static mp_obj_t cryptolib_aes_encrypt(size_t n_args, const mp_obj_t *args) {
    return aes_process(n_args, args, true);
}
static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(cryptolib_aes_encrypt_obj, 2, 3, cryptolib_aes_encrypt);

static mp_obj_t cryptolib_aes_decrypt(size_t n_args, const mp_obj_t *args) {
    return aes_process(n_args, args, false);
}
static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(cryptolib_aes_decrypt_obj, 2, 3, cryptolib_aes_decrypt);

static const mp_rom_map_elem_t cryptolib_aes_locals_dict_table[] = {
    { MP_ROM_QSTR(MP_QSTR_encrypt), MP_ROM_PTR(&cryptolib_aes_encrypt_obj) },
    { MP_ROM_QSTR(MP_QSTR_decrypt), MP_ROM_PTR(&cryptolib_aes_decrypt_obj) },
};
static MP_DEFINE_CONST_DICT(cryptolib_aes_locals_dict, cryptolib_aes_locals_dict_table);

static MP_DEFINE_CONST_OBJ_TYPE(
    cryptolib_aes_type,
    MP_QSTR_aes,
    MP_TYPE_FLAG_NONE,
    make_new, cryptolib_aes_make_new,
    locals_dict, &cryptolib_aes_locals_dict
    );

static const mp_rom_map_elem_t mp_module_cryptolib_globals_table[] = {
    { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_cryptolib) },
    { MP_ROM_QSTR(MP_QSTR_aes), MP_ROM_PTR(&cryptolib_aes_type) },
    #if MICROPY_PY_CRYPTOLIB_CONSTS
    { MP_ROM_QSTR(MP_QSTR_MODE_ECB), MP_ROM_INT(UCRYPTOLIB_MODE_ECB) },
    { MP_ROM_QSTR(MP_QSTR_MODE_CBC), MP_ROM_INT(UCRYPTOLIB_MODE_CBC) },
    #if MICROPY_PY_CRYPTOLIB_CTR
    { MP_ROM_QSTR(MP_QSTR_MODE_CTR), MP_ROM_INT(UCRYPTOLIB_MODE_CTR) },
    #endif
    #endif
};

static MP_DEFINE_CONST_DICT(mp_module_cryptolib_globals, mp_module_cryptolib_globals_table);

const mp_obj_module_t mp_module_cryptolib = {
    .base = { &mp_type_module },
    .globals = (mp_obj_dict_t *)&mp_module_cryptolib_globals,
};

// This module should not be extensible (as it is not a CPython standard
// library nor is it necessary to override from the filesystem), however it
// has previously been known as `ucryptolib`, so by making it extensible the
// `ucryptolib` alias will continue to work.
MP_REGISTER_EXTENSIBLE_MODULE(MP_QSTR_cryptolib, mp_module_cryptolib);

#endif // MICROPY_PY_CRYPTOLIB