text: /* Written by Nils Larsch for the OpenSSL project. */
  /* ====================================================================
   * Copyright (c) 2000-2003 The OpenSSL Project.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer. 
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. All advertising materials mentioning features or use of this
   *    software must display the following acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
   *
   * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
   *    endorse or promote products derived from this software without
   *    prior written permission. For written permission, please contact
   *    licensing@OpenSSL.org.
   *
   * 5. Products derived from this software may not be called "OpenSSL"
   *    nor may "OpenSSL" appear in their names without prior written
   *    permission of the OpenSSL Project.
   *
   * 6. Redistributions of any form whatsoever must retain the following
   *    acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
   *
   * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
   * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE.
   * ====================================================================
   *
   * This product includes cryptographic software written by Eric Young
   * (eay@cryptsoft.com).  This product includes software written by Tim
   * Hudson (tjh@cryptsoft.com). */
  
  #include <openssl/ec.h>
  
  #include <limits.h>
  #include <string.h>
  
  #include <openssl/bytestring.h>
  #include <openssl/bn.h>
  #include <openssl/err.h>
  #include <openssl/mem.h>
  #include <openssl/nid.h>
  
  #include "internal.h"
  #include "../bytestring/internal.h"
  #include "../internal.h"
  
  
  static const uint8_t kParametersTag =
      CBS_ASN1_CONSTRUCTED | CBS_ASN1_CONTEXT_SPECIFIC | 0;
  static const uint8_t kPublicKeyTag =
      CBS_ASN1_CONSTRUCTED | CBS_ASN1_CONTEXT_SPECIFIC | 1;
  
  EC_KEY *EC_KEY_parse_private_key(CBS *cbs, const EC_GROUP *group) {
    CBS ec_private_key, private_key;
    uint64_t version;
    if (!CBS_get_asn1(cbs, &ec_private_key, CBS_ASN1_SEQUENCE) ||
        !CBS_get_asn1_uint64(&ec_private_key, &version) ||
        version != 1 ||
        !CBS_get_asn1(&ec_private_key, &private_key, CBS_ASN1_OCTETSTRING)) {
      OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
      return NULL;
    }
  
    /* Parse the optional parameters field. */
    EC_GROUP *inner_group = NULL;
    EC_KEY *ret = NULL;
    if (CBS_peek_asn1_tag(&ec_private_key, kParametersTag)) {
      /* Per SEC 1, as an alternative to omitting it, one is allowed to specify
       * this field and put in a NULL to mean inheriting this value. This was
       * omitted in a previous version of this logic without problems, so leave it
       * unimplemented. */
      CBS child;
      if (!CBS_get_asn1(&ec_private_key, &child, kParametersTag)) {
        OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
        goto err;
      }
      inner_group = EC_KEY_parse_parameters(&child);
      if (inner_group == NULL) {
        goto err;
      }
      if (group == NULL) {
        group = inner_group;
      } else if (EC_GROUP_cmp(group, inner_group, NULL) != 0) {
        /* If a group was supplied externally, it must match. */
        OPENSSL_PUT_ERROR(EC, EC_R_GROUP_MISMATCH);
        goto err;
      }
      if (CBS_len(&child) != 0) {
        OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
        goto err;
      }
    }
  
    if (group == NULL) {
      OPENSSL_PUT_ERROR(EC, EC_R_MISSING_PARAMETERS);
      goto err;
    }
  
    ret = EC_KEY_new();
    if (ret == NULL || !EC_KEY_set_group(ret, group)) {
      goto err;
    }
  
    /* Although RFC 5915 specifies the length of the key, OpenSSL historically
     * got this wrong, so accept any length. See upstream's
     * 30cd4ff294252c4b6a4b69cbef6a5b4117705d22. */
    ret->priv_key =
        BN_bin2bn(CBS_data(&private_key), CBS_len(&private_key), NULL);
    ret->pub_key = EC_POINT_new(group);
    if (ret->priv_key == NULL || ret->pub_key == NULL) {
      goto err;
    }
  
    if (BN_cmp(ret->priv_key, EC_GROUP_get0_order(group)) >= 0) {
      OPENSSL_PUT_ERROR(EC, EC_R_WRONG_ORDER);
      goto err;
    }
  
    if (CBS_peek_asn1_tag(&ec_private_key, kPublicKeyTag)) {
      CBS child, public_key;
      uint8_t padding;
      if (!CBS_get_asn1(&ec_private_key, &child, kPublicKeyTag) ||
          !CBS_get_asn1(&child, &public_key, CBS_ASN1_BITSTRING) ||
          /* As in a SubjectPublicKeyInfo, the byte-encoded public key is then
           * encoded as a BIT STRING with bits ordered as in the DER encoding. */
          !CBS_get_u8(&public_key, &padding) ||
          padding != 0 ||
          /* Explicitly check |public_key| is non-empty to save the conversion
           * form later. */
          CBS_len(&public_key) == 0 ||
          !EC_POINT_oct2point(group, ret->pub_key, CBS_data(&public_key),
                              CBS_len(&public_key), NULL) ||
          CBS_len(&child) != 0) {
        OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
        goto err;
      }
  
      /* Save the point conversion form.
       * TODO(davidben): Consider removing this. */
      ret->conv_form = (point_conversion_form_t)(CBS_data(&public_key)[0] & ~0x01);
    } else {
      /* Compute the public key instead. */
      if (!EC_POINT_mul(group, ret->pub_key, ret->priv_key, NULL, NULL, NULL)) {
        goto err;
      }
      /* Remember the original private-key-only encoding.
       * TODO(davidben): Consider removing this. */
      ret->enc_flag |= EC_PKEY_NO_PUBKEY;
    }
  
    if (CBS_len(&ec_private_key) != 0) {
      OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
      goto err;
    }
  
    /* Ensure the resulting key is valid. */
    if (!EC_KEY_check_key(ret)) {
      goto err;
    }
  
    EC_GROUP_free(inner_group);
    return ret;
  
  err:
    EC_KEY_free(ret);
    EC_GROUP_free(inner_group);
    return NULL;
  }
  
  int EC_KEY_marshal_private_key(CBB *cbb, const EC_KEY *key,
                                 unsigned enc_flags) {
    if (key == NULL || key->group == NULL || key->priv_key == NULL) {
      OPENSSL_PUT_ERROR(EC, ERR_R_PASSED_NULL_PARAMETER);
      return 0;
    }
  
    CBB ec_private_key, private_key;
    if (!CBB_add_asn1(cbb, &ec_private_key, CBS_ASN1_SEQUENCE) ||
        !CBB_add_asn1_uint64(&ec_private_key, 1 /* version */) ||
        !CBB_add_asn1(&ec_private_key, &private_key, CBS_ASN1_OCTETSTRING) ||
        !BN_bn2cbb_padded(&private_key,
                          BN_num_bytes(EC_GROUP_get0_order(key->group)),
                          key->priv_key)) {
      OPENSSL_PUT_ERROR(EC, EC_R_ENCODE_ERROR);
      return 0;
    }
  
    if (!(enc_flags & EC_PKEY_NO_PARAMETERS)) {
      CBB child;
      if (!CBB_add_asn1(&ec_private_key, &child, kParametersTag) ||
          !EC_KEY_marshal_curve_name(&child, key->group) ||
          !CBB_flush(&ec_private_key)) {
        OPENSSL_PUT_ERROR(EC, EC_R_ENCODE_ERROR);
        return 0;
      }
    }
  
    /* TODO(fork): replace this flexibility with sensible default? */
    if (!(enc_flags & EC_PKEY_NO_PUBKEY) && key->pub_key != NULL) {
      CBB child, public_key;
      if (!CBB_add_asn1(&ec_private_key, &child, kPublicKeyTag) ||
          !CBB_add_asn1(&child, &public_key, CBS_ASN1_BITSTRING) ||
          /* As in a SubjectPublicKeyInfo, the byte-encoded public key is then
           * encoded as a BIT STRING with bits ordered as in the DER encoding. */
          !CBB_add_u8(&public_key, 0 /* padding */) ||
          !EC_POINT_point2cbb(&public_key, key->group, key->pub_key,
                              key->conv_form, NULL) ||
          !CBB_flush(&ec_private_key)) {
        OPENSSL_PUT_ERROR(EC, EC_R_ENCODE_ERROR);
        return 0;
      }
    }
  
    if (!CBB_flush(cbb)) {
      OPENSSL_PUT_ERROR(EC, EC_R_ENCODE_ERROR);
      return 0;
    }
  
    return 1;
  }
  
  /* is_unsigned_integer returns one if |cbs| is a valid unsigned DER INTEGER and
   * zero otherwise. */
  static int is_unsigned_integer(const CBS *cbs) {
    if (CBS_len(cbs) == 0) {
      return 0;
    }
    uint8_t byte = CBS_data(cbs)[0];
    if ((byte & 0x80) ||
        (byte == 0 && CBS_len(cbs) > 1 && (CBS_data(cbs)[1] & 0x80) == 0)) {
      /* Negative or not minimally-encoded. */
      return 0;
    }
    return 1;
  }
  
  /* kPrimeFieldOID is the encoding of 1.2.840.10045.1.1. */
  static const uint8_t kPrimeField[] = {0x2a, 0x86, 0x48, 0xce, 0x3d, 0x01, 0x01};
  
  static int parse_explicit_prime_curve(CBS *in, CBS *out_prime, CBS *out_a,
                                        CBS *out_b, CBS *out_base_x,
                                        CBS *out_base_y, CBS *out_order) {
    /* See RFC 3279, section 2.3.5. Note that RFC 3279 calls this structure an
     * ECParameters while RFC 5480 calls it a SpecifiedECDomain. */
    CBS params, field_id, field_type, curve, base;
    uint64_t version;
    if (!CBS_get_asn1(in, &params, CBS_ASN1_SEQUENCE) ||
        !CBS_get_asn1_uint64(&params, &version) ||
        version != 1 ||
        !CBS_get_asn1(&params, &field_id, CBS_ASN1_SEQUENCE) ||
        !CBS_get_asn1(&field_id, &field_type, CBS_ASN1_OBJECT) ||
        CBS_len(&field_type) != sizeof(kPrimeField) ||
        OPENSSL_memcmp(CBS_data(&field_type), kPrimeField, sizeof(kPrimeField)) != 0 ||
        !CBS_get_asn1(&field_id, out_prime, CBS_ASN1_INTEGER) ||
        !is_unsigned_integer(out_prime) ||
        CBS_len(&field_id) != 0 ||
        !CBS_get_asn1(&params, &curve, CBS_ASN1_SEQUENCE) ||
        !CBS_get_asn1(&curve, out_a, CBS_ASN1_OCTETSTRING) ||
        !CBS_get_asn1(&curve, out_b, CBS_ASN1_OCTETSTRING) ||
        /* |curve| has an optional BIT STRING seed which we ignore. */
        !CBS_get_asn1(&params, &base, CBS_ASN1_OCTETSTRING) ||
        !CBS_get_asn1(&params, out_order, CBS_ASN1_INTEGER) ||
        !is_unsigned_integer(out_order)) {
      OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
      return 0;
    }
  
    /* |params| has an optional cofactor which we ignore. With the optional seed
     * in |curve|, a group already has arbitrarily many encodings. Parse enough to
     * uniquely determine the curve. */
  
    /* Require that the base point use uncompressed form. */
    uint8_t form;
    if (!CBS_get_u8(&base, &form) || form != POINT_CONVERSION_UNCOMPRESSED) {
      OPENSSL_PUT_ERROR(EC, EC_R_INVALID_FORM);
      return 0;
    }
  
    if (CBS_len(&base) % 2 != 0) {
      OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
      return 0;
    }
    size_t field_len = CBS_len(&base) / 2;
    CBS_init(out_base_x, CBS_data(&base), field_len);
    CBS_init(out_base_y, CBS_data(&base) + field_len, field_len);
  
    return 1;
  }
  
  /* integers_equal returns one if |a| and |b| are equal, up to leading zeros, and
   * zero otherwise. */
  static int integers_equal(const CBS *a, const uint8_t *b, size_t b_len) {
    /* Remove leading zeros from |a| and |b|. */
    CBS a_copy = *a;
    while (CBS_len(&a_copy) > 0 && CBS_data(&a_copy)[0] == 0) {
      CBS_skip(&a_copy, 1);
    }
    while (b_len > 0 && b[0] == 0) {
      b++;
      b_len--;
    }
    return CBS_mem_equal(&a_copy, b, b_len);
  }
  
  EC_GROUP *EC_KEY_parse_curve_name(CBS *cbs) {
    CBS named_curve;
    if (!CBS_get_asn1(cbs, &named_curve, CBS_ASN1_OBJECT)) {
      OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
      return NULL;
    }
  
    /* Look for a matching curve. */
    unsigned i;
    for (i = 0; OPENSSL_built_in_curves[i].nid != NID_undef; i++) {
      const struct built_in_curve *curve = &OPENSSL_built_in_curves[i];
      if (CBS_len(&named_curve) == curve->oid_len &&
          OPENSSL_memcmp(CBS_data(&named_curve), curve->oid, curve->oid_len) == 0) {
        return EC_GROUP_new_by_curve_name(curve->nid);
      }
    }
  
    OPENSSL_PUT_ERROR(EC, EC_R_UNKNOWN_GROUP);
    return NULL;
  }
  
  int EC_KEY_marshal_curve_name(CBB *cbb, const EC_GROUP *group) {
    int nid = EC_GROUP_get_curve_name(group);
    if (nid == NID_undef) {
      OPENSSL_PUT_ERROR(EC, EC_R_UNKNOWN_GROUP);
      return 0;
    }
  
    unsigned i;
    for (i = 0; OPENSSL_built_in_curves[i].nid != NID_undef; i++) {
      const struct built_in_curve *curve = &OPENSSL_built_in_curves[i];
      if (curve->nid == nid) {
        CBB child;
        return CBB_add_asn1(cbb, &child, CBS_ASN1_OBJECT) &&
               CBB_add_bytes(&child, curve->oid, curve->oid_len) &&
               CBB_flush(cbb);
      }
    }
  
    OPENSSL_PUT_ERROR(EC, EC_R_UNKNOWN_GROUP);
    return 0;
  }
  
  EC_GROUP *EC_KEY_parse_parameters(CBS *cbs) {
    if (!CBS_peek_asn1_tag(cbs, CBS_ASN1_SEQUENCE)) {
      return EC_KEY_parse_curve_name(cbs);
    }
  
    /* OpenSSL sometimes produces ECPrivateKeys with explicitly-encoded versions
     * of named curves.
     *
     * TODO(davidben): Remove support for this. */
    CBS prime, a, b, base_x, base_y, order;
    if (!parse_explicit_prime_curve(cbs, &prime, &a, &b, &base_x, &base_y,
                                    &order)) {
      return NULL;
    }
  
    /* Look for a matching prime curve. */
    unsigned i;
    for (i = 0; OPENSSL_built_in_curves[i].nid != NID_undef; i++) {
      const struct built_in_curve *curve = &OPENSSL_built_in_curves[i];
      const unsigned param_len = curve->data->param_len;
      /* |curve->data->data| is ordered p, a, b, x, y, order, each component
       * zero-padded up to the field length. Although SEC 1 states that the
       * Field-Element-to-Octet-String conversion also pads, OpenSSL mis-encodes
       * |a| and |b|, so this comparison must allow omitting leading zeros. (This
       * is relevant for P-521 whose |b| has a leading 0.) */
      if (integers_equal(&prime, curve->data->data, param_len) &&
          integers_equal(&a, curve->data->data + param_len, param_len) &&
          integers_equal(&b, curve->data->data + param_len * 2, param_len) &&
          integers_equal(&base_x, curve->data->data + param_len * 3, param_len) &&
          integers_equal(&base_y, curve->data->data + param_len * 4, param_len) &&
          integers_equal(&order, curve->data->data + param_len * 5, param_len)) {
        return EC_GROUP_new_by_curve_name(curve->nid);
      }
    }
  
    OPENSSL_PUT_ERROR(EC, EC_R_UNKNOWN_GROUP);
    return NULL;
  }
  
  EC_KEY *d2i_ECPrivateKey(EC_KEY **out, const uint8_t **inp, long len) {
    /* This function treats its |out| parameter differently from other |d2i|
     * functions. If supplied, take the group from |*out|. */
    const EC_GROUP *group = NULL;
    if (out != NULL && *out != NULL) {
      group = EC_KEY_get0_group(*out);
    }
  
    if (len < 0) {
      OPENSSL_PUT_ERROR(EC, EC_R_DECODE_ERROR);
      return NULL;
    }
    CBS cbs;
    CBS_init(&cbs, *inp, (size_t)len);
    EC_KEY *ret = EC_KEY_parse_private_key(&cbs, group);
    if (ret == NULL) {
      return NULL;
    }
    if (out != NULL) {
      EC_KEY_free(*out);
      *out = ret;
    }
    *inp = CBS_data(&cbs);
    return ret;
  }
  
  int i2d_ECPrivateKey(const EC_KEY *key, uint8_t **outp) {
    CBB cbb;
    if (!CBB_init(&cbb, 0) ||
        !EC_KEY_marshal_private_key(&cbb, key, EC_KEY_get_enc_flags(key))) {
      CBB_cleanup(&cbb);
      return -1;
    }
    return CBB_finish_i2d(&cbb, outp);
  }
  
  EC_KEY *d2i_ECParameters(EC_KEY **out_key, const uint8_t **inp, long len) {
    if (len < 0) {
      return NULL;
    }
  
    CBS cbs;
    CBS_init(&cbs, *inp, (size_t)len);
    EC_GROUP *group = EC_KEY_parse_parameters(&cbs);
    if (group == NULL) {
      return NULL;
    }
  
    EC_KEY *ret = EC_KEY_new();
    if (ret == NULL || !EC_KEY_set_group(ret, group)) {
      EC_GROUP_free(group);
      EC_KEY_free(ret);
      return NULL;
    }
    EC_GROUP_free(group);
  
    if (out_key != NULL) {
      EC_KEY_free(*out_key);
      *out_key = ret;
    }
    *inp = CBS_data(&cbs);
    return ret;
  }
  
  int i2d_ECParameters(const EC_KEY *key, uint8_t **outp) {
    if (key == NULL || key->group == NULL) {
      OPENSSL_PUT_ERROR(EC, ERR_R_PASSED_NULL_PARAMETER);
      return -1;
    }
  
    CBB cbb;
    if (!CBB_init(&cbb, 0) ||
        !EC_KEY_marshal_curve_name(&cbb, key->group)) {
      CBB_cleanup(&cbb);
      return -1;
    }
    return CBB_finish_i2d(&cbb, outp);
  }
  
  EC_KEY *o2i_ECPublicKey(EC_KEY **keyp, const uint8_t **inp, long len) {
    EC_KEY *ret = NULL;
  
    if (keyp == NULL || *keyp == NULL || (*keyp)->group == NULL) {
      OPENSSL_PUT_ERROR(EC, ERR_R_PASSED_NULL_PARAMETER);
      return NULL;
    }
    ret = *keyp;
    if (ret->pub_key == NULL &&
        (ret->pub_key = EC_POINT_new(ret->group)) == NULL) {
      OPENSSL_PUT_ERROR(EC, ERR_R_MALLOC_FAILURE);
      return NULL;
    }
    if (!EC_POINT_oct2point(ret->group, ret->pub_key, *inp, len, NULL)) {
      OPENSSL_PUT_ERROR(EC, ERR_R_EC_LIB);
      return NULL;
    }
    /* save the point conversion form */
    ret->conv_form = (point_conversion_form_t)(*inp[0] & ~0x01);
    *inp += len;
    return ret;
  }
  
  int i2o_ECPublicKey(const EC_KEY *key, uint8_t **outp) {
    size_t buf_len = 0;
    int new_buffer = 0;
  
    if (key == NULL) {
      OPENSSL_PUT_ERROR(EC, ERR_R_PASSED_NULL_PARAMETER);
      return 0;
    }
  
    buf_len = EC_POINT_point2oct(key->group, key->pub_key, key->conv_form, NULL,
                                 0, NULL);
  
    if (outp == NULL || buf_len == 0) {
      /* out == NULL => just return the length of the octet string */
      return buf_len;
    }
  
    if (*outp == NULL) {
      *outp = OPENSSL_malloc(buf_len);
      if (*outp == NULL) {
        OPENSSL_PUT_ERROR(EC, ERR_R_MALLOC_FAILURE);
        return 0;
      }
      new_buffer = 1;
    }
    if (!EC_POINT_point2oct(key->group, key->pub_key, key->conv_form, *outp,
                            buf_len, NULL)) {
      OPENSSL_PUT_ERROR(EC, ERR_R_EC_LIB);
      if (new_buffer) {
        OPENSSL_free(*outp);
        *outp = NULL;
      }
      return 0;
    }
  
    if (!new_buffer) {
      *outp += buf_len;
    }
    return buf_len;
  }
  