/*

 * Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.

 * Copyright 2017 Ribose Inc. All Rights Reserved.

 * Ported from Ribose contributions from Botan.

 *

 * Licensed under the OpenSSL license (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

#include "crypto/sm2.h"

#include "crypto/sm2err.h"

#include "crypto/ec.h" /* ecdh_KDF_X9_63() */

#include <openssl/err.h>

#include <openssl/evp.h>

#include <openssl/bn.h>

#include <openssl/asn1.h>

#include <openssl/asn1t.h>

#include <string.h>

typedef struct SM2_Ciphertext_st SM2_Ciphertext;

DECLARE_ASN1_FUNCTIONS(SM2_Ciphertext)

struct SM2_Ciphertext_st {

    BIGNUM *C1x;

    BIGNUM *C1y;

    ASN1_OCTET_STRING *C3;

    ASN1_OCTET_STRING *C2;

};

ASN1_SEQUENCE(SM2_Ciphertext) = {

    ASN1_SIMPLE(SM2_Ciphertext, C1x, BIGNUM),

    ASN1_SIMPLE(SM2_Ciphertext, C1y, BIGNUM),

    ASN1_SIMPLE(SM2_Ciphertext, C3, ASN1_OCTET_STRING),

    ASN1_SIMPLE(SM2_Ciphertext, C2, ASN1_OCTET_STRING),

} ASN1_SEQUENCE_END(SM2_Ciphertext)

IMPLEMENT_ASN1_FUNCTIONS(SM2_Ciphertext)

static size_t ec_field_size(const EC_GROUP *group)

{

    /* Is there some simpler way to do this? */

    BIGNUM *p = BN_new();

    BIGNUM *a = BN_new();

    BIGNUM *b = BN_new();

    size_t field_size = 0;

    if (p == NULL || a == NULL || b == NULL)

       goto done;

    if (!EC_GROUP_get_curve(group, p, a, b, NULL))

        goto done;

    field_size = (BN_num_bits(p) + 7) / 8;

 done:

    BN_free(p);

    BN_free(a);

    BN_free(b);

    return field_size;

}

int sm2_plaintext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,

                       size_t *pt_size)

{

    const size_t field_size = ec_field_size(EC_KEY_get0_group(key));

    const int md_size = EVP_MD_size(digest);

    size_t overhead;

    if (md_size < 0) {

        SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_DIGEST);

        return 0;

    }

    if (field_size == 0) {

        SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_FIELD);

        return 0;

    }

    overhead = 10 + 2 * field_size + (size_t)md_size;

    if (msg_len <= overhead) {

        SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_ENCODING);

        return 0;

    }

    *pt_size = msg_len - overhead;

    return 1;

}

int sm2_ciphertext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,

                        size_t *ct_size)

{

    const size_t field_size = ec_field_size(EC_KEY_get0_group(key));

    const int md_size = EVP_MD_size(digest);

    size_t sz;

    if (field_size == 0 || md_size < 0)

        return 0;

    /* Integer and string are simple type; set constructed = 0, means primitive and definite length encoding. */

    sz = 2 * ASN1_object_size(0, field_size + 1, V_ASN1_INTEGER)

         + ASN1_object_size(0, md_size, V_ASN1_OCTET_STRING)

         + ASN1_object_size(0, msg_len, V_ASN1_OCTET_STRING);

    /* Sequence is structured type; set constructed = 1, means constructed and definite length encoding. */

    *ct_size = ASN1_object_size(1, sz, V_ASN1_SEQUENCE);

    return 1;

}

int sm2_encrypt(const EC_KEY *key,

                const EVP_MD *digest,

                const uint8_t *msg,

                size_t msg_len, uint8_t *ciphertext_buf, size_t *ciphertext_len)

{

    int rc = 0, ciphertext_leni;

    size_t i;

    BN_CTX *ctx = NULL;

    BIGNUM *k = NULL;

    BIGNUM *x1 = NULL;

    BIGNUM *y1 = NULL;

    BIGNUM *x2 = NULL;

    BIGNUM *y2 = NULL;

    EVP_MD_CTX *hash = EVP_MD_CTX_new();

    struct SM2_Ciphertext_st ctext_struct;

    const EC_GROUP *group = EC_KEY_get0_group(key);

    const BIGNUM *order = EC_GROUP_get0_order(group);

    const EC_POINT *P = EC_KEY_get0_public_key(key);

    EC_POINT *kG = NULL;

    EC_POINT *kP = NULL;

    uint8_t *msg_mask = NULL;

    uint8_t *x2y2 = NULL;

    uint8_t *C3 = NULL;

    size_t field_size;

    const int C3_size = EVP_MD_size(digest);

    /* NULL these before any "goto done" */

    ctext_struct.C2 = NULL;

    ctext_struct.C3 = NULL;

    if (hash == NULL || C3_size <= 0) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);

        goto done;

    }

    field_size = ec_field_size(group);

    if (field_size == 0) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);

        goto done;

    }

    kG = EC_POINT_new(group);

    kP = EC_POINT_new(group);

    ctx = BN_CTX_new();

    if (kG == NULL || kP == NULL || ctx == NULL) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);

        goto done;

    }

    BN_CTX_start(ctx);

    k = BN_CTX_get(ctx);

    x1 = BN_CTX_get(ctx);

    x2 = BN_CTX_get(ctx);

    y1 = BN_CTX_get(ctx);

    y2 = BN_CTX_get(ctx);

    if (y2 == NULL) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_BN_LIB);

        goto done;

    }

    x2y2 = OPENSSL_zalloc(2 * field_size);

    C3 = OPENSSL_zalloc(C3_size);

    if (x2y2 == NULL || C3 == NULL) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);

        goto done;

    }

    memset(ciphertext_buf, 0, *ciphertext_len);

    if (!BN_priv_rand_range(k, order)) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);

        goto done;

    }

    if (!EC_POINT_mul(group, kG, k, NULL, NULL, ctx)

            || !EC_POINT_get_affine_coordinates(group, kG, x1, y1, ctx)

            || !EC_POINT_mul(group, kP, NULL, P, k, ctx)

            || !EC_POINT_get_affine_coordinates(group, kP, x2, y2, ctx)) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EC_LIB);

        goto done;

    }

    if (BN_bn2binpad(x2, x2y2, field_size) < 0

            || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);

        goto done;

    }

    msg_mask = OPENSSL_zalloc(msg_len);

    if (msg_mask == NULL) {

       SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);

       goto done;

   }

    /* X9.63 with no salt happens to match the KDF used in SM2 */

    if (!ecdh_KDF_X9_63(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,

                        digest)) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EVP_LIB);

        goto done;

    }

    for (i = 0; i != msg_len; ++i)

        msg_mask[i] ^= msg[i];

    if (EVP_DigestInit(hash, digest) == 0

            || EVP_DigestUpdate(hash, x2y2, field_size) == 0

            || EVP_DigestUpdate(hash, msg, msg_len) == 0

            || EVP_DigestUpdate(hash, x2y2 + field_size, field_size) == 0

            || EVP_DigestFinal(hash, C3, NULL) == 0) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EVP_LIB);

        goto done;

    }

    ctext_struct.C1x = x1;

    ctext_struct.C1y = y1;

    ctext_struct.C3 = ASN1_OCTET_STRING_new();

    ctext_struct.C2 = ASN1_OCTET_STRING_new();

    if (ctext_struct.C3 == NULL || ctext_struct.C2 == NULL) {

       SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);

       goto done;

    }

    if (!ASN1_OCTET_STRING_set(ctext_struct.C3, C3, C3_size)

            || !ASN1_OCTET_STRING_set(ctext_struct.C2, msg_mask, msg_len)) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);

        goto done;

    }

    ciphertext_leni = i2d_SM2_Ciphertext(&ctext_struct, &ciphertext_buf);

    /* Ensure cast to size_t is safe */

    if (ciphertext_leni < 0) {

        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);

        goto done;

    }

    *ciphertext_len = (size_t)ciphertext_leni;

    rc = 1;

 done:

    ASN1_OCTET_STRING_free(ctext_struct.C2);

    ASN1_OCTET_STRING_free(ctext_struct.C3);

    OPENSSL_free(msg_mask);

    OPENSSL_free(x2y2);

    OPENSSL_free(C3);

    EVP_MD_CTX_free(hash);

    BN_CTX_free(ctx);

    EC_POINT_free(kG);

    EC_POINT_free(kP);

    return rc;

}

int sm2_decrypt(const EC_KEY *key,

                const EVP_MD *digest,

                const uint8_t *ciphertext,

                size_t ciphertext_len, uint8_t *ptext_buf, size_t *ptext_len)

{

    int rc = 0;

    int i;

    BN_CTX *ctx = NULL;

    const EC_GROUP *group = EC_KEY_get0_group(key);

    EC_POINT *C1 = NULL;

    struct SM2_Ciphertext_st *sm2_ctext = NULL;

    BIGNUM *x2 = NULL;

    BIGNUM *y2 = NULL;

    uint8_t *x2y2 = NULL;

    uint8_t *computed_C3 = NULL;

    const size_t field_size = ec_field_size(group);

    const int hash_size = EVP_MD_size(digest);

    uint8_t *msg_mask = NULL;

    const uint8_t *C2 = NULL;

    const uint8_t *C3 = NULL;

    int msg_len = 0;

    EVP_MD_CTX *hash = NULL;

    if (field_size == 0 || hash_size <= 0)

       goto done;

    memset(ptext_buf, 0xFF, *ptext_len);

    sm2_ctext = d2i_SM2_Ciphertext(NULL, &ciphertext, ciphertext_len);

    if (sm2_ctext == NULL) {

        SM2err(SM2_F_SM2_DECRYPT, SM2_R_ASN1_ERROR);

        goto done;

    }

    if (sm2_ctext->C3->length != hash_size) {

        SM2err(SM2_F_SM2_DECRYPT, SM2_R_INVALID_ENCODING);

        goto done;

    }

    C2 = sm2_ctext->C2->data;

    C3 = sm2_ctext->C3->data;

    msg_len = sm2_ctext->C2->length;

    ctx = BN_CTX_new();

    if (ctx == NULL) {

        SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);

        goto done;

    }

    BN_CTX_start(ctx);

    x2 = BN_CTX_get(ctx);

    y2 = BN_CTX_get(ctx);

    if (y2 == NULL) {

        SM2err(SM2_F_SM2_DECRYPT, ERR_R_BN_LIB);

        goto done;

    }

    msg_mask = OPENSSL_zalloc(msg_len);

    x2y2 = OPENSSL_zalloc(2 * field_size);

    computed_C3 = OPENSSL_zalloc(hash_size);

    if (msg_mask == NULL || x2y2 == NULL || computed_C3 == NULL) {

        SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);

        goto done;

    }

    C1 = EC_POINT_new(group);

    if (C1 == NULL) {

        SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);

        goto done;

    }

    if (!EC_POINT_set_affine_coordinates(group, C1, sm2_ctext->C1x,

                                         sm2_ctext->C1y, ctx)

            || !EC_POINT_mul(group, C1, NULL, C1, EC_KEY_get0_private_key(key),

                             ctx)

            || !EC_POINT_get_affine_coordinates(group, C1, x2, y2, ctx)) {

        SM2err(SM2_F_SM2_DECRYPT, ERR_R_EC_LIB);

        goto done;

    }

    if (BN_bn2binpad(x2, x2y2, field_size) < 0

            || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0

            || !ecdh_KDF_X9_63(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,

                               digest)) {

        SM2err(SM2_F_SM2_DECRYPT, ERR_R_INTERNAL_ERROR);

        goto done;

    }

    for (i = 0; i != msg_len; ++i)

        ptext_buf[i] = C2[i] ^ msg_mask[i];

    hash = EVP_MD_CTX_new();

    if (hash == NULL) {

        SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);

        goto done;

    }

    if (!EVP_DigestInit(hash, digest)

            || !EVP_DigestUpdate(hash, x2y2, field_size)

            || !EVP_DigestUpdate(hash, ptext_buf, msg_len)

            || !EVP_DigestUpdate(hash, x2y2 + field_size, field_size)

            || !EVP_DigestFinal(hash, computed_C3, NULL)) {

        SM2err(SM2_F_SM2_DECRYPT, ERR_R_EVP_LIB);

        goto done;

    }

    if (CRYPTO_memcmp(computed_C3, C3, hash_size) != 0) {

        SM2err(SM2_F_SM2_DECRYPT, SM2_R_INVALID_DIGEST);

        goto done;

    }

    rc = 1;

    *ptext_len = msg_len;

 done:

    if (rc == 0)

        memset(ptext_buf, 0, *ptext_len);

    OPENSSL_free(msg_mask);

    OPENSSL_free(x2y2);

    OPENSSL_free(computed_C3);

    EC_POINT_free(C1);

    BN_CTX_free(ctx);

    SM2_Ciphertext_free(sm2_ctext);

    EVP_MD_CTX_free(hash);

    return rc;

}