从OpenSSL和BouncyCastle派生的ECDH共享秘密并不总是相同的，尽管两者的常数和域参数相同

Question

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但是解密的消息并不总是与客户端发送的消息相同。

由于我也开发了一个Android应用程序，它使用相同的过程，但使用BouncyCastle进行加密，因此我怀疑使用OpenSSL实现代码的正确性，因此在这里展示代码，以帮助其他人解决这个问题。我为计算共享秘密而实现的内容如下

- (void)calculateSharedSecret
{
    BN_CTX* bn_ctx;

    EC_KEY*     client_key_curve = NULL;
    EC_KEY*     server_key_curve = NULL;
    EC_GROUP*   client_key_group = NULL;
    EC_GROUP*   server_key_group = NULL;
    EC_POINT*   client_publicKey = NULL;
    EC_POINT*   server_publicKey = NULL;
    BIGNUM*     client_privatKey = NULL;

    BIGNUM* client_publicK_x = NULL;
    BIGNUM* client_publicK_y = NULL;
    BIGNUM* server_publicK_x = NULL;
    BIGNUM* server_publicK_y = NULL;

    NSException *p = [NSException exceptionWithName:@"" reason:@"" userInfo:nil];

    bn_ctx = BN_CTX_new();
    BN_CTX_start(bn_ctx);

    client_publicK_x = BN_CTX_get(bn_ctx);
    client_publicK_y = BN_CTX_get(bn_ctx);
    client_privatKey = BN_CTX_get(bn_ctx);
    server_publicK_x = BN_CTX_get(bn_ctx);
    server_publicK_y = BN_CTX_get(bn_ctx);

    // client

    if ((client_key_curve = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1)) == NULL)
        @throw p;

    if ((client_key_group = (EC_GROUP *)EC_KEY_get0_group(client_key_curve)) == NULL)
        @throw p;

    if (EC_KEY_generate_key(client_key_curve) != 1)
        @throw p;

    if ((client_publicKey = (EC_POINT *)EC_KEY_get0_public_key(client_key_curve)) == NULL)
        @throw p;

    if (EC_KEY_check_key(client_key_curve) != 1)
        @throw p;

    client_privatKey = (BIGNUM *)EC_KEY_get0_private_key(client_key_curve);

    char *client_public_key = EC_POINT_point2hex(client_key_group, client_publicKey, POINT_CONVERSION_COMPRESSED, bn_ctx);
    char *client_privat_key = BN_bn2hex(client_privatKey);

    _clientPublicKey = [NSString stringWithCString:client_public_key encoding:NSUTF8StringEncoding];

    // server

    NSArray* lines = [self loadServerPublicKeyXY];

    NSString *public_str_x = [lines objectAtIndex:0];
    NSString *public_str_y = [lines objectAtIndex:1];

    BN_dec2bn(&server_publicK_x, [public_str_x UTF8String]);
    BN_dec2bn(&server_publicK_y, [public_str_y UTF8String]);

    if ((server_key_curve = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1)) == NULL)
        @throw p;

    if ((server_key_group = (EC_GROUP *)EC_KEY_get0_group(server_key_curve)) == NULL)
        @throw p;

    if (EC_KEY_generate_key(server_key_curve) != 1)
        @throw p;

    if ((server_publicKey = EC_POINT_new(server_key_group)) == NULL)
        @throw p;

    if (EC_POINT_set_affine_coordinates_GFp(server_key_group, server_publicKey, server_publicK_x, server_publicK_y, bn_ctx) != 1)
        @throw p;

    if (EC_KEY_check_key(server_key_curve) != 1)
        @throw p;

    unsigned char *key_agreement = NULL;
    key_agreement = (unsigned char *)OPENSSL_malloc(SHA_DIGEST_LENGTH);
    if (ECDH_compute_key(key_agreement, SHA_DIGEST_LENGTH, server_publicKey, client_key_curve, KDF1_SHA1) == 0)
        @throw p;
    _symmetricKey = [NSData dataWithBytes:key_agreement length:16];
}

和

void *KDF1_SHA1(const void *input, size_t inlen, void *output, size_t *outlen)
{
    if (*outlen < SHA_DIGEST_LENGTH)
        return NULL;
    else
        *outlen = SHA_DIGEST_LENGTH;
    return SHA1(input, inlen, output);
}

public byte[] generateAESSymmetricKey(byte[] client_public_key_hex) throws InvalidRequest{
    try {
        // ECDH Private Key as well as other prime256v1 params was generated by Java "keytool" and stored in a JKS file
        KeyStore keyStore = ...;
        PrivateKey privateKey = (PrivateKey) keyStore.getKey("keyAlias", "keyStorePassword".toCharArray());
        ECPrivateKeyParameters ecdhPrivateKeyParameters = (ECPrivateKeyParameters) (PrivateKeyFactory.createKey(privateKey.getEncoded()));

        ECCurve ecCurve = ecdhPrivateKeyParameters.getParameters().getCurve();
        ECDomainParameters ecDomainParameters = ecdhPrivateKeyParameters.getParameters();
        ECPublicKeyParameters client_public_key = new ECPublicKeyParameters(ecCurve.decodePoint(client_public_key_hex), ecDomainParameters);

        BasicAgreement agree = new ECDHBasicAgreement();
        agree.init(ecdhPrivateKeyParameters);
        byte[] keyAgreement = agree.calculateAgreement(client_public_key).toByteArray();

        SHA1Digest sha1Digest = new SHA1Digest();
        sha1Digest.update(keyAgreement, 0, keyAgreement.length);
        byte hashKeyAgreement[] = new byte[sha1Digest.getDigestSize()];
        sha1Digest.doFinal(hashKeyAgreement, 0);

        byte[] server_calculatd_symmetric_key = new byte[16];
        System.arraycopy(hashKeyAgreement, 0, server_calculatd_symmetric_key, 0, server_calculatd_symmetric_key.length);
        return server_calculatd_symmetric_key;
    } catch (Throwable ignored) {
        return null;
    }
}

编辑2：作为对@PeterDettman回答的反馈，我做了一些修改来反映他的建议，尽管不平等率降低了，但双方生成的密钥协议（共享秘密）并不是在所有情况下都是平等的。

有可能用以下数据再现一个不等式情况

• 公钥:02e05c058c3df6e8d63791660d9c5ea98b5a0822ab93339b0b8815322131119c4c
• privat密钥:062e8ac930bd6009cf929e51b37432498075d21c335bd00086bf68ce09933aca
• 由OpenSSL生成共享秘密:51d027264f8540e5d0fde7000000000000
• 由BouncyCastle生成共享机密:51d027264f8540e5d0fde700e5db0fab

Answer 1

服务器代码中ECDH协议值转换为字节的方式存在问题：

byte[] keyAgreement = agree.calculateAgreement(client_public_key).toByteArray();

请尝试以下操作：

BigInteger agreementValue = agree.calculateAgreement(client_public_key);
byte[] keyAgreement = BigIntegers.asUnsignedByteArray(agree.getFieldSize(), agreementValue);

这将确保一个固定大小的字节数组作为输出，这是将EC字段元素转换为八位元组字符串的必要条件（搜索“字段元素到八位元组字符串转换原语”以获得更多详细信息）。