FFmpeg/libavformat/tls_mbedtls.c

/*
 * TLS/SSL Protocol
 * Copyright (c) 2018 Thomas Volkert
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <mbedtls/version.h>
#include <mbedtls/ctr_drbg.h>
#include <mbedtls/entropy.h>
#include <mbedtls/net_sockets.h>
#include <mbedtls/platform.h>
#include <mbedtls/ssl.h>
#include <mbedtls/x509_crt.h>
#include <mbedtls/debug.h>
#include <mbedtls/timing.h>
#ifdef MBEDTLS_PSA_CRYPTO_C
#include <psa/crypto.h>
#endif

#include "avformat.h"
#include "internal.h"
#include "network.h"
#include "url.h"
#include "tls.h"
#include "libavutil/mem.h"
#include "libavutil/parseutils.h"
#include "libavutil/avstring.h"
#include "libavutil/random_seed.h"

static int mbedtls_x509_fingerprint(char *cert_buf, size_t cert_sz, char **fingerprint)
{
    unsigned char md[32];
    size_t n = sizeof(md);
    AVBPrint buf;
    int ret;
    mbedtls_x509_crt crt;

    mbedtls_x509_crt_init(&crt);

    if ((ret = mbedtls_x509_crt_parse(&crt, cert_buf, cert_sz)) != 0) {
        mbedtls_x509_crt_free(&crt);
        return AVERROR(EINVAL);
    }

    if ((ret = mbedtls_sha256(crt.raw.p, crt.raw.len, md, 0)) != 0) {
        mbedtls_x509_crt_free(&crt);
        return AVERROR(EINVAL);
    }

    av_bprint_init(&buf, n*3, n*3);

    for (int i = 0; i < n - 1; i++)
        av_bprintf(&buf, "%02X:", md[i]);
    av_bprintf(&buf, "%02X", md[n - 1]);

    return av_bprint_finalize(&buf, fingerprint);
}

int ff_ssl_read_key_cert(char *key_url, char *cert_url, char *key_buf, size_t key_sz, char *cert_buf, size_t cert_sz, char **fingerprint)
{
    int ret = 0;
    AVBPrint key_bp, cert_bp;
    av_bprint_init(&key_bp, 1, MAX_CERTIFICATE_SIZE);
    av_bprint_init(&cert_bp, 1, MAX_CERTIFICATE_SIZE);

    ret = ff_url_read_all(key_url, &key_bp);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "TLS: Failed to open key file %s\n", key_url);
        goto end;
    }

    ret = ff_url_read_all(cert_url, &cert_bp);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "TLS: Failed to open cert file %s\n", cert_url);
        goto end;
    }

    if (key_sz < key_bp.size || cert_sz < cert_bp.size) {
        av_log(NULL, AV_LOG_ERROR, "TLS: Key or Cert buffer is too samall\n");
        ret = AVERROR_BUFFER_TOO_SMALL;
        goto end;
    }

    key_buf = key_bp.str;
    cert_buf = cert_bp.str;

    ret = mbedtls_x509_fingerprint(cert_buf, cert_sz, fingerprint);
    if (ret < 0)
        av_log(NULL, AV_LOG_ERROR, "TLS: Failed to generate fingerprint\n");
end:
    av_bprint_finalize(&key_bp, NULL);
    av_bprint_finalize(&cert_bp, NULL);
    return ret;
}

static int mbedtls_gen_pkey(mbedtls_pk_context *key)
{
    int ret = 0;
    mbedtls_entropy_context entropy;
    mbedtls_ctr_drbg_context ctr_drbg;

    mbedtls_entropy_init(&entropy);
    mbedtls_ctr_drbg_init(&ctr_drbg);

    if ((ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func,
                                     &entropy, NULL, 0)) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_ctr_drbg_seed returned %d\n", ret);
        goto end;
    }

    if ((ret = mbedtls_pk_setup(key,
                            mbedtls_pk_info_from_type(MBEDTLS_PK_ECKEY))) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_pk_setup returned %d\n", ret);
        goto end;
    }
    /**
     * See RFC 8827 section 6.5,
     * All implementations MUST support DTLS 1.2 with the
     * TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 cipher suite
     * and the P-256 curve.
     */
    if ((ret = mbedtls_ecp_gen_key(MBEDTLS_ECP_DP_SECP256R1,
                                mbedtls_pk_ec(*key),
                                mbedtls_ctr_drbg_random, &ctr_drbg)) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_ecp_gen_key returned %d\n", ret);
        goto end;
    }
end:
    mbedtls_entropy_free(&entropy);
    mbedtls_ctr_drbg_free(&ctr_drbg);
    return ret;
}

static int mbedtls_gen_x509_cert(mbedtls_pk_context *key, char *cert_buf, size_t cert_sz)
{
    int ret = 0;
    const char *name = "CN=lavf";
    time_t now;
    struct tm tm;
    char not_before[16], not_after[16];
    unsigned char serial[20];
    mbedtls_entropy_context entropy;
    mbedtls_ctr_drbg_context ctr_drbg;
    mbedtls_x509write_cert crt;

    mbedtls_entropy_init(&entropy);
    mbedtls_ctr_drbg_init(&ctr_drbg);
    mbedtls_x509write_crt_init(&crt);

    if ((ret = mbedtls_ctr_drbg_seed(&ctr_drbg, mbedtls_entropy_func, &entropy, NULL, 0)) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_ctr_drbg_seed returned %d\n", ret);
        goto end;
    }

    mbedtls_x509write_crt_set_subject_key(&crt, key);
    mbedtls_x509write_crt_set_issuer_key(&crt, key);
    if ((ret = mbedtls_x509write_crt_set_subject_name(&crt, name)) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_x509write_crt_set_subject_name returned %d\n", ret);
        goto end;
    }

    if ((ret = mbedtls_x509write_crt_set_issuer_name(&crt, name)) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_x509write_crt_set_issuer_name returned %d\n", ret);
        goto end;
    }
    mbedtls_x509write_crt_set_version(&crt, MBEDTLS_X509_CRT_VERSION_3);
    mbedtls_x509write_crt_set_md_alg(&crt, MBEDTLS_MD_SHA256);

    ret = av_random_bytes((uint8_t *)serial, sizeof(serial));
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "Failed to generate random serial number!\n");
        return ret;
    }

    if ((ret = mbedtls_x509write_crt_set_serial_raw(&crt, serial, sizeof(serial))) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_x509write_crt_set_serial_raw returned %d\n", ret);
        goto end;
    }

    time(&now);
    gmtime_r(&now, &tm);
    strftime(not_before, sizeof(not_before), "%Y%m%d%H%M%S", &tm);
    tm.tm_year += 1;
    strftime(not_after, sizeof(not_after), "%Y%m%d%H%M%S", &tm);

    if ((ret = mbedtls_x509write_crt_set_validity(&crt, not_before, not_after)) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_x509write_crt_set_validity returned %d\n", ret);
        goto end;
    }

    if ((ret = mbedtls_x509write_crt_pem(&crt, cert_buf, cert_sz,
                                        mbedtls_ctr_drbg_random, &ctr_drbg)) != 0) {
        av_log(NULL, AV_LOG_ERROR, "mbedtls_x509write_crt_pem returned %d\n", ret);
        return ret;
    }

end:
    mbedtls_entropy_free(&entropy);
    mbedtls_ctr_drbg_free(&ctr_drbg);
    mbedtls_x509write_crt_free(&crt);
    return ret;
}

int ff_ssl_gen_key_cert(char *key_buf, size_t key_sz, char *cert_buf, size_t cert_sz, char **fingerprint)
{
    int ret = 0;
    mbedtls_pk_context key;

    mbedtls_pk_init(&key);

    if ((ret = mbedtls_gen_pkey(&key)) != 0)
        goto end;

    if ((ret = mbedtls_pk_write_key_pem(&key, key_buf, key_sz)) != 0)
        goto end;

    if ((ret = mbedtls_gen_x509_cert(&key, cert_buf, cert_sz)) != 0)
        goto end;

    ret = mbedtls_x509_fingerprint(cert_buf, cert_sz, fingerprint);
    if (ret < 0)
        av_log(NULL, AV_LOG_ERROR, "TLS: Failed to generate fingerprint\n");

end:
    mbedtls_pk_free(&key);
    return ret;
}

typedef struct dtls_srtp_keys {
    unsigned char master_secret[48];
    unsigned char randbytes[64];
    mbedtls_tls_prf_types tls_prf_type;
} dtls_srtp_keys;

typedef struct TLSContext {
    TLSShared tls_shared;
    mbedtls_ssl_context ssl_context;
    mbedtls_ssl_config ssl_config;
    mbedtls_entropy_context entropy_context;
    mbedtls_ctr_drbg_context ctr_drbg_context;
    mbedtls_timing_delay_context timer;
    mbedtls_x509_crt ca_cert;
    mbedtls_x509_crt own_cert;
    mbedtls_pk_context priv_key;
    char *priv_key_pw;
    dtls_srtp_keys srtp_key;
    struct sockaddr_storage dest_addr;
    socklen_t dest_addr_len;
} TLSContext;

int ff_tls_set_external_socket(URLContext *h, URLContext *sock)
{
    TLSContext *tls_ctx = h->priv_data;
    TLSShared *shr = &tls_ctx->tls_shared;

    if (shr->is_dtls)
        shr->udp = sock;
    else
        shr->tcp = sock;

    return 0;
}

#if defined(MBEDTLS_SSL_DTLS_SRTP)
static void dtls_srtp_key_derivation(void *p_expkey,
                                     mbedtls_ssl_key_export_type secret_type,
                                     const unsigned char *secret,
                                     size_t secret_len,
                                     const unsigned char client_random[32],
                                     const unsigned char server_random[32],
                                     mbedtls_tls_prf_types tls_prf_type)
{
    dtls_srtp_keys *keys = (dtls_srtp_keys *) p_expkey;

    if (secret_len != sizeof(keys->master_secret))
        return;

    memcpy(keys->master_secret, secret, secret_len);
    memcpy(keys->randbytes, client_random, 32);
    memcpy(keys->randbytes + 32, server_random, 32);
    keys->tls_prf_type = tls_prf_type;
}
#endif

int ff_dtls_export_materials(URLContext *h, char *dtls_srtp_materials, size_t materials_sz)
{
    int ret = 0;
    TLSContext *tls_ctx = h->priv_data;
#if defined(MBEDTLS_SSL_DTLS_SRTP)
    const char* dst = "EXTRACTOR-dtls_srtp";
    mbedtls_dtls_srtp_info dtls_srtp_negotiation_result;
    mbedtls_ssl_get_dtls_srtp_negotiation_result(&tls_ctx->ssl_context, &dtls_srtp_negotiation_result);

    if ((ret = mbedtls_ssl_tls_prf(tls_ctx->srtp_key.tls_prf_type,
                                    tls_ctx->srtp_key.master_secret,
                                    sizeof(tls_ctx->srtp_key.master_secret),
                                    dst,
                                    tls_ctx->srtp_key.randbytes,
                                    sizeof(tls_ctx->srtp_key.randbytes),
                                    dtls_srtp_materials,
                                    materials_sz)) != 0) {
        av_log(h, AV_LOG_ERROR,"mbedtls_ssl_tls_prf returned %d\n", ret);
        ret = AVERROR(EINVAL);
    }
#else
    av_log(h, AV_LOG_ERROR, "DTLS-SRTP is not supported in this mbedtls build\n");
    ret = AVERROR(ENOSYS);
#endif
    return ret;
}

#define OFFSET(x) offsetof(TLSContext, x)

static int tls_close(URLContext *h)
{
    TLSContext *tls_ctx = h->priv_data;
    TLSShared *shr = &tls_ctx->tls_shared;

    mbedtls_ssl_close_notify(&tls_ctx->ssl_context);
    mbedtls_pk_free(&tls_ctx->priv_key);
    mbedtls_x509_crt_free(&tls_ctx->ca_cert);
    mbedtls_x509_crt_free(&tls_ctx->own_cert);
    mbedtls_ssl_free(&tls_ctx->ssl_context);
    mbedtls_ssl_config_free(&tls_ctx->ssl_config);
    mbedtls_ctr_drbg_free(&tls_ctx->ctr_drbg_context);
    mbedtls_entropy_free(&tls_ctx->entropy_context);
    if (!shr->external_sock)
        ffurl_closep(shr->is_dtls ? &shr->udp : &shr->tcp);
    return 0;
}

static int handle_transport_error(URLContext *h, const char* func_name, int react_on_eagain, int ret)
{
    switch (ret) {
    case AVERROR(EAGAIN):
        return react_on_eagain;
    case AVERROR_EXIT:
        return 0;
    case AVERROR(EPIPE):
    case AVERROR(ECONNRESET):
        return MBEDTLS_ERR_NET_CONN_RESET;
    default:
        av_log(h, AV_LOG_ERROR, "%s returned 0x%x\n", func_name, ret);
        errno = EIO;
        return MBEDTLS_ERR_NET_SEND_FAILED;
    }
}

static int mbedtls_send(void *ctx, const unsigned char *buf, size_t len)
{
    TLSContext *tls_ctx = (TLSContext*) ctx;
    TLSShared *shr = &tls_ctx->tls_shared;
    URLContext *h = shr->is_dtls ? shr->udp : shr->tcp;
    int ret = ffurl_write(h, buf, len);
    if (ret >= 0)
        return ret;

    if (h->max_packet_size && len > h->max_packet_size)
        return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;

    return handle_transport_error(h, "ffurl_write", MBEDTLS_ERR_SSL_WANT_WRITE, ret);
}

static int mbedtls_recv(void *ctx, unsigned char *buf, size_t len)
{
    TLSContext *tls_ctx = (TLSContext*) ctx;
    TLSShared *shr = &tls_ctx->tls_shared;
    URLContext *h = shr->is_dtls ? shr->udp : shr->tcp;
    int ret = ffurl_read(h, buf, len);
    if (ret >= 0) {
        if (shr->is_dtls && shr->listen && !tls_ctx->dest_addr_len) {
            int err_ret;

            ff_udp_get_last_recv_addr(shr->udp, &tls_ctx->dest_addr, &tls_ctx->dest_addr_len);
            err_ret = ff_udp_set_remote_addr(shr->udp, (struct sockaddr *)&tls_ctx->dest_addr, tls_ctx->dest_addr_len, 1);
            if (err_ret < 0) {
                av_log(tls_ctx, AV_LOG_ERROR, "Failed connecting udp context\n");
                return err_ret;
            }
            av_log(tls_ctx, AV_LOG_TRACE, "Set UDP remote addr on UDP socket, now 'connected'\n");
        }
        return ret;
    }
    if (h->max_packet_size && len > h->max_packet_size)
        return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;

    return handle_transport_error(h, "ffurl_read", MBEDTLS_ERR_SSL_WANT_READ, ret);
}

static void mbedtls_debug(void *ctx, int lvl, const char *file, int line, const char *msg)
{
    URLContext *h = (URLContext*) ctx;
    int av_lvl = lvl >= 4 ? AV_LOG_TRACE : AV_LOG_DEBUG;
    av_log(h, av_lvl, "%s:%d: %s", av_basename(file), line, msg);
}

static void handle_pk_parse_error(URLContext *h, int ret)
{
    switch (ret) {
    case MBEDTLS_ERR_PK_FILE_IO_ERROR:
        av_log(h, AV_LOG_ERROR, "Read of key file failed. Is it actually there, are the access permissions correct?\n");
        break;
    case MBEDTLS_ERR_PK_PASSWORD_REQUIRED:
        av_log(h, AV_LOG_ERROR, "A password for the private key is missing.\n");
        break;
    case MBEDTLS_ERR_PK_PASSWORD_MISMATCH:
        av_log(h, AV_LOG_ERROR, "The given password for the private key is wrong.\n");
        break;
    default:
        av_log(h, AV_LOG_ERROR, "mbedtls_pk_parse_key returned -0x%x\n", -ret);
        break;
    }
}

static void handle_handshake_error(URLContext *h, int ret)
{
    switch (ret) {
#if MBEDTLS_VERSION_MAJOR < 3
    case MBEDTLS_ERR_SSL_NO_USABLE_CIPHERSUITE:
        av_log(h, AV_LOG_ERROR, "None of the common ciphersuites is usable. Was the local certificate correctly set?\n");
        break;
#else
    case MBEDTLS_ERR_SSL_HANDSHAKE_FAILURE:
        av_log(h, AV_LOG_ERROR, "TLS handshake failed.\n");
        break;
    case MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION:
        av_log(h, AV_LOG_ERROR, "TLS protocol version mismatch.\n");
        break;
#endif
    case MBEDTLS_ERR_SSL_FATAL_ALERT_MESSAGE:
        av_log(h, AV_LOG_ERROR, "A fatal alert message was received from the peer, has the peer a correct certificate?\n");
        break;
    case MBEDTLS_ERR_SSL_CA_CHAIN_REQUIRED:
        av_log(h, AV_LOG_ERROR, "No CA chain is set, but required to operate. Was the CA correctly set?\n");
        break;
    case MBEDTLS_ERR_SSL_INTERNAL_ERROR:
        av_log(h, AV_LOG_ERROR, "Internal error encountered.\n");
        break;
    case MBEDTLS_ERR_NET_CONN_RESET:
        av_log(h, AV_LOG_ERROR, "TLS handshake was aborted by peer.\n");
        break;
    case MBEDTLS_ERR_X509_CERT_VERIFY_FAILED:
        av_log(h, AV_LOG_ERROR, "Certificate verification failed.\n");
        break;
    default:
        av_log(h, AV_LOG_ERROR, "mbedtls_ssl_handshake returned -0x%x\n", -ret);
        break;
    }
}

static int tls_handshake(URLContext *h)
{
    TLSContext *tls_ctx = h->priv_data;
    TLSShared *shr = &tls_ctx->tls_shared;
    URLContext *uc = shr->is_dtls ? shr->udp : shr->tcp;
    int ret;

    uc->flags &= ~AVIO_FLAG_NONBLOCK;

    while (1) {
        ret = mbedtls_ssl_handshake(&tls_ctx->ssl_context);

        if (!ret)
            break;
        if (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE) {
            handle_handshake_error(h, ret);
            return ret;
        }
    }

    return ret;
}

static int tls_open(URLContext *h, const char *uri, int flags, AVDictionary **options)
{
    TLSContext *tls_ctx = h->priv_data;
    TLSShared *shr = &tls_ctx->tls_shared;
    uint32_t verify_res_flags;
    int ret;
#if defined(MBEDTLS_SSL_DTLS_SRTP)
    const mbedtls_ssl_srtp_profile profiles[] = {
        MBEDTLS_TLS_SRTP_AES128_CM_HMAC_SHA1_80,
        MBEDTLS_TLS_SRTP_UNSET
    };
#endif

    if (!shr->external_sock) {
        if ((ret = ff_tls_open_underlying(shr, h, uri, options)) < 0)
            goto fail;
    }

#ifdef MBEDTLS_PSA_CRYPTO_C
    if ((ret = psa_crypto_init()) != PSA_SUCCESS) {
        av_log(h, AV_LOG_ERROR, "psa_crypto_init returned %d\n", ret);
        goto fail;
    }
#endif

    mbedtls_ssl_init(&tls_ctx->ssl_context);
    mbedtls_ssl_config_init(&tls_ctx->ssl_config);
    mbedtls_entropy_init(&tls_ctx->entropy_context);
    mbedtls_ctr_drbg_init(&tls_ctx->ctr_drbg_context);
    mbedtls_x509_crt_init(&tls_ctx->ca_cert);
    mbedtls_pk_init(&tls_ctx->priv_key);

    if (av_log_get_level() >= AV_LOG_DEBUG) {
        mbedtls_ssl_conf_dbg(&tls_ctx->ssl_config, mbedtls_debug, shr->is_dtls ? shr->udp : shr->tcp);
        /*
         * Note: we can't call mbedtls_debug_set_threshold() here because
         * it's global state. The user is thus expected to manage this.
         */
    }

    // load trusted CA
    if (shr->ca_file) {
        if ((ret = mbedtls_x509_crt_parse_file(&tls_ctx->ca_cert, shr->ca_file)) != 0) {
            av_log(h, AV_LOG_ERROR, "mbedtls_x509_crt_parse_file for CA cert returned %d\n", ret);
            goto fail;
        }
    }

    // load own certificate
    if (shr->cert_file) {
        if ((ret = mbedtls_x509_crt_parse_file(&tls_ctx->own_cert, shr->cert_file)) != 0) {
            av_log(h, AV_LOG_ERROR, "mbedtls_x509_crt_parse_file for own cert returned %d\n", ret);
            goto fail;
        }
    } else if (shr->cert_buf) {
        if ((ret = mbedtls_x509_crt_parse(&tls_ctx->own_cert, shr->cert_buf, strlen(shr->cert_buf) + 1)) != 0) {
            av_log(h, AV_LOG_ERROR, "mbedtls_x509_crt_parse for own cert returned %d\n", ret);
            goto fail;
        }
    }

    // seed the random number generator
    if ((ret = mbedtls_ctr_drbg_seed(&tls_ctx->ctr_drbg_context,
                                     mbedtls_entropy_func,
                                     &tls_ctx->entropy_context,
                                     NULL, 0)) != 0) {
        av_log(h, AV_LOG_ERROR, "mbedtls_ctr_drbg_seed returned %d\n", ret);
        goto fail;
    }

    // load key file
    if (shr->key_file) {
        if ((ret = mbedtls_pk_parse_keyfile(&tls_ctx->priv_key,
                                            shr->key_file,
                                            tls_ctx->priv_key_pw
#if MBEDTLS_VERSION_MAJOR >= 3
                                            , mbedtls_ctr_drbg_random,
                                            &tls_ctx->ctr_drbg_context
#endif
                                            )) != 0) {
            handle_pk_parse_error(h, ret);
            goto fail;
        }
    } else if (shr->key_buf) {
        if ((ret = mbedtls_pk_parse_key(&tls_ctx->priv_key,
                                        shr->key_buf,
                                        strlen(shr->key_buf) + 1,
                                        NULL,
                                        0
#if MBEDTLS_VERSION_MAJOR >= 3
                                        , mbedtls_ctr_drbg_random,
                                        &tls_ctx->ctr_drbg_context
#endif
                                        )) != 0) {
            handle_pk_parse_error(h, ret);
            goto fail;
        }
    }

    if (shr->listen && !shr->cert_file && !shr->cert_buf && !shr->key_file && !shr->key_buf) {
        char buf[4096];
        if ((ret = mbedtls_gen_pkey(&tls_ctx->priv_key)) != 0) {
            av_log(h, AV_LOG_ERROR, "failed to generate priv_key, returned %d\n", ret);
            goto fail;
        }
        if ((ret = mbedtls_gen_x509_cert(&tls_ctx->priv_key, buf, sizeof(buf))) != 0) {
            av_log(h, AV_LOG_ERROR, "failed to generate cert, returned %d\n", ret);
            goto fail;
        }
        if ((ret = mbedtls_x509_crt_parse(&tls_ctx->own_cert, buf, sizeof(buf))) != 0) {
            av_log(h, AV_LOG_ERROR, "failed to parse generated cert, returned %d\n", ret);
            goto fail;
        }
    }

    if ((ret = mbedtls_ssl_config_defaults(&tls_ctx->ssl_config,
                                           shr->listen ? MBEDTLS_SSL_IS_SERVER : MBEDTLS_SSL_IS_CLIENT,
                                           shr->is_dtls ? MBEDTLS_SSL_TRANSPORT_DATAGRAM : MBEDTLS_SSL_TRANSPORT_STREAM,
                                           MBEDTLS_SSL_PRESET_DEFAULT)) != 0) {
        av_log(h, AV_LOG_ERROR, "mbedtls_ssl_config_defaults returned %d\n", ret);
        goto fail;
    }

#ifdef MBEDTLS_SSL_PROTO_TLS1_3
    // this version does not allow disabling certificate verification with TLSv1.3 (yes, really).
    if (mbedtls_version_get_number() == 0x03060000 && !shr->verify) {
        av_log(h, AV_LOG_INFO, "Forcing TLSv1.2 because certificate verification is disabled\n");
        mbedtls_ssl_conf_max_tls_version(&tls_ctx->ssl_config, MBEDTLS_SSL_VERSION_TLS1_2);
    }
#endif

    // not VERIFY_REQUIRED because we manually check after handshake
    mbedtls_ssl_conf_authmode(&tls_ctx->ssl_config,
                              shr->verify ? MBEDTLS_SSL_VERIFY_OPTIONAL : MBEDTLS_SSL_VERIFY_NONE);
    mbedtls_ssl_conf_rng(&tls_ctx->ssl_config, mbedtls_ctr_drbg_random, &tls_ctx->ctr_drbg_context);
    mbedtls_ssl_conf_ca_chain(&tls_ctx->ssl_config, &tls_ctx->ca_cert, NULL);

    // set own certificate and private key
    if ((ret = mbedtls_ssl_conf_own_cert(&tls_ctx->ssl_config, &tls_ctx->own_cert, &tls_ctx->priv_key)) != 0) {
        av_log(h, AV_LOG_ERROR, "mbedtls_ssl_conf_own_cert returned %d\n", ret);
        goto fail;
    }
    if (shr->is_dtls) {
        mbedtls_ssl_conf_dtls_cookies(&tls_ctx->ssl_config, NULL, NULL, NULL);
        if (shr->use_srtp) {
#if defined(MBEDTLS_SSL_DTLS_SRTP)
            if ((ret = mbedtls_ssl_conf_dtls_srtp_protection_profiles(&tls_ctx->ssl_config, profiles)) != 0) {
                av_log(h, AV_LOG_ERROR, "mbedtls_ssl_conf_dtls_srtp_protection_profiles returned %d\n", ret);
                goto fail;
            }
            mbedtls_ssl_set_export_keys_cb(&tls_ctx->ssl_context, dtls_srtp_key_derivation, &tls_ctx->srtp_key);
#else
            av_log(h, AV_LOG_ERROR, "DTLS-SRTP is not supported in this mbedtls build\n");
            ret = AVERROR(ENOSYS);
            goto fail;
#endif
        }

    }
    if ((ret = mbedtls_ssl_setup(&tls_ctx->ssl_context, &tls_ctx->ssl_config)) != 0) {
        av_log(h, AV_LOG_ERROR, "mbedtls_ssl_setup returned %d\n", ret);
        goto fail;
    }

    if (!shr->listen && !shr->numerichost) {
        if ((ret = mbedtls_ssl_set_hostname(&tls_ctx->ssl_context, shr->host)) != 0) {
            av_log(h, AV_LOG_ERROR, "mbedtls_ssl_set_hostname returned %d\n", ret);
            goto fail;
        }
    }

    // set I/O functions to use FFmpeg internal code for transport layer
    mbedtls_ssl_set_bio(&tls_ctx->ssl_context, tls_ctx, mbedtls_send, mbedtls_recv, NULL);

    if (shr->is_dtls) {
        mbedtls_ssl_set_timer_cb(&tls_ctx->ssl_context, &tls_ctx->timer, mbedtls_timing_set_delay, mbedtls_timing_get_delay);
        if (shr->mtu)
            mbedtls_ssl_set_mtu(&tls_ctx->ssl_context, shr->mtu);
    }
    if (!shr->external_sock) {
        ret = tls_handshake(h);
        if (ret < 0)
            goto fail;
    }

    if (shr->verify) {
        // check the result of the certificate verification
        if ((verify_res_flags = mbedtls_ssl_get_verify_result(&tls_ctx->ssl_context)) != 0) {
            av_log(h, AV_LOG_ERROR, "mbedtls_ssl_get_verify_result reported problems "\
                                    "with the certificate verification, returned flags: %"PRIu32"\n",
                                    verify_res_flags);
            if (verify_res_flags & MBEDTLS_X509_BADCERT_NOT_TRUSTED)
                av_log(h, AV_LOG_ERROR, "The certificate is not correctly signed by the trusted CA.\n");
            goto fail;
        }
    }

    return 0;

fail:
    tls_close(h);
    return AVERROR(EIO);
}

static int dtls_open(URLContext *h, const char *uri, int flags, AVDictionary **options)
{
    TLSContext *tls_ctx = h->priv_data;
    TLSShared *shr = &tls_ctx->tls_shared;
    shr->is_dtls = 1;
    return tls_open(h, uri, flags, options);
}

static int handle_tls_error(URLContext *h, const char* func_name, int ret)
{
    switch (ret) {
    case MBEDTLS_ERR_SSL_WANT_READ:
    case MBEDTLS_ERR_SSL_WANT_WRITE:
#ifdef MBEDTLS_ERR_SSL_RECEIVED_NEW_SESSION_TICKET
    case MBEDTLS_ERR_SSL_RECEIVED_NEW_SESSION_TICKET:
#endif
        return AVERROR(EAGAIN);
    case MBEDTLS_ERR_NET_SEND_FAILED:
    case MBEDTLS_ERR_NET_RECV_FAILED:
        return AVERROR(EIO);
    case MBEDTLS_ERR_NET_CONN_RESET:
    case MBEDTLS_ERR_SSL_PEER_CLOSE_NOTIFY:
        av_log(h, AV_LOG_WARNING, "%s reported connection reset by peer\n", func_name);
        return AVERROR_EOF;
    default:
        av_log(h, AV_LOG_ERROR, "%s returned -0x%x\n", func_name, -ret);
        return AVERROR(EIO);
    }
}

static int tls_read(URLContext *h, uint8_t *buf, int size)
{
    TLSContext *tls_ctx = h->priv_data;
    TLSShared *shr = &tls_ctx->tls_shared;
    URLContext *uc = shr->is_dtls ? shr->udp : shr->tcp;
    int ret;

    uc->flags &= ~AVIO_FLAG_NONBLOCK;
    uc->flags |= h->flags & AVIO_FLAG_NONBLOCK;
    if ((ret = mbedtls_ssl_read(&tls_ctx->ssl_context, buf, size)) > 0) {
        // return read length
        return ret;
    }

    return handle_tls_error(h, "mbedtls_ssl_read", ret);
}

static int tls_write(URLContext *h, const uint8_t *buf, int size)
{
    TLSContext *tls_ctx = h->priv_data;
    TLSShared *shr = &tls_ctx->tls_shared;
    URLContext *uc = shr->is_dtls ? shr->udp : shr->tcp;
    int ret;

    uc->flags &= ~AVIO_FLAG_NONBLOCK;
    uc->flags |= h->flags & AVIO_FLAG_NONBLOCK;
    if ((ret = mbedtls_ssl_write(&tls_ctx->ssl_context, buf, size)) > 0) {
        // return written length
        return ret;
    }

    return handle_tls_error(h, "mbedtls_ssl_write", ret);
}

static int tls_get_file_handle(URLContext *h)
{
    TLSContext *c = h->priv_data;
    return ffurl_get_file_handle(c->tls_shared.tcp);
}

static int tls_get_short_seek(URLContext *h)
{
    TLSContext *s = h->priv_data;
    return ffurl_get_short_seek(s->tls_shared.tcp);
}

static const AVOption options[] = {
    TLS_COMMON_OPTIONS(TLSContext, tls_shared), \
    {"key_password", "Password for the private key file", OFFSET(priv_key_pw),  AV_OPT_TYPE_STRING, .flags = TLS_OPTFL }, \
    { NULL }
};

static const AVClass tls_class = {
    .class_name = "tls",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
};

const URLProtocol ff_tls_protocol = {
    .name           = "tls",
    .url_open2      = tls_open,
    .url_read       = tls_read,
    .url_write      = tls_write,
    .url_close      = tls_close,
    .url_get_file_handle = tls_get_file_handle,
    .url_get_short_seek  = tls_get_short_seek,
    .priv_data_size = sizeof(TLSContext),
    .flags          = URL_PROTOCOL_FLAG_NETWORK,
    .priv_data_class = &tls_class,
};

static const AVClass dtls_class = {
    .class_name = "dtls",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
};

const URLProtocol ff_dtls_protocol = {
    .name           = "dtls",
    .url_open2      = dtls_open,
    .url_handshake  = tls_handshake,
    .url_read       = tls_read,
    .url_write      = tls_write,
    .url_close      = tls_close,
    .url_get_file_handle = tls_get_file_handle,
    .url_get_short_seek  = tls_get_short_seek,
    .priv_data_size = sizeof(TLSContext),
    .flags          = URL_PROTOCOL_FLAG_NETWORK,
    .priv_data_class = &dtls_class,
};