ffmpeg/libavformat/tls_schannel.c

/*
 * Copyright (c) 2015 Hendrik Leppkes
 *
 * 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
 */

/** Based on the CURL SChannel module */

#include "libavutil/mem.h"
#include "avformat.h"
#include "internal.h"
#include "network.h"
#include "os_support.h"
#include "url.h"
#include "tls.h"

#define SECURITY_WIN32
#include <windows.h>
#include <security.h>
#include <schnlsp.h>
#include <sddl.h>

#define SCHANNEL_INITIAL_BUFFER_SIZE   4096
#define SCHANNEL_FREE_BUFFER_SIZE      1024

/* mingw does not define this symbol */
#ifndef SECBUFFER_ALERT
#define SECBUFFER_ALERT                17
#endif

/* This is the name used for the private key in the MS Keystore.
 * There is as of time of writing no way to use schannel without
 * persisting the private key. Which usually means the default MS
 * keystore will write it to disk unencrypted, user-read/writable.
 * To combat this as much as possible, the code makes sure to
 * delete the private key ASAP once SChannel has gotten ahold of
 * it.
 * Apparently this is because SChannel neglects marshaling the
 * private key alongside the certificate for the out-of-process
 * tls handler.
 * See this GitHub issue for the most detailed explanation out there:
 * https://github.com/dotnet/runtime/issues/23749#issuecomment-485947319
 */
#define FF_NCRYPT_TEMP_KEY_NAME L"FFMPEG_TEMP_TLS_KEY"

static int der_to_pem(const char *data, size_t len, const char *header, char *buf, size_t bufsize)
{
    const int line_length = 64;
    AVBPrint pem;
    DWORD base64len = 0;
    char *base64 = NULL;
    int ret = 0;

    if (!CryptBinaryToStringA(data, len, CRYPT_STRING_BASE64 | CRYPT_STRING_NOCRLF, NULL, &base64len)) {
        av_log(NULL, AV_LOG_ERROR, "CryptBinaryToString failed\n");
        ret = AVERROR_EXTERNAL;
        goto end;
    }

    base64 = av_malloc(base64len);

    if (!CryptBinaryToStringA(data, len, CRYPT_STRING_BASE64 | CRYPT_STRING_NOCRLF, base64, &base64len)) {
        av_log(NULL, AV_LOG_ERROR, "CryptBinaryToString failed\n");
        ret = AVERROR_EXTERNAL;
        goto end;
    }

    av_bprint_init_for_buffer(&pem, buf, bufsize);
    av_bprintf(&pem, "-----BEGIN %s-----\n", header);

    for (DWORD i = 0; i < base64len; i += line_length) {
        av_bprintf(&pem, "%.*s\n", line_length, base64 + i);
    }

    av_bprintf(&pem, "-----END %s-----\n", header);

    if (!av_bprint_is_complete(&pem)) {
        ret = AVERROR(ENOSPC);
        goto end;
    }

end:
    av_free(base64);
    return ret;
}

static int pem_to_der(const char *pem, char **buf, int *out_len)
{
    DWORD derlen = 0;

    if (!CryptStringToBinaryA(pem, 0, CRYPT_STRING_BASE64HEADER, NULL, &derlen, NULL, NULL)) {
        av_log(NULL, AV_LOG_ERROR, "CryptStringToBinaryA failed\n");
        return AVERROR(EINVAL);
    }

    *buf = av_malloc(derlen);
    if (!*buf)
        return AVERROR(ENOMEM);

    if (!CryptStringToBinaryA(pem, 0, CRYPT_STRING_BASE64HEADER, *buf, &derlen, NULL, NULL)) {
        av_log(NULL, AV_LOG_ERROR, "CryptStringToBinaryA failed\n");
        return AVERROR(EINVAL);
    }

    *out_len = derlen;

    return 0;
}

static int der_to_fingerprint(const char *data, size_t len, char **fingerprint)
{
    AVBPrint buf;
    unsigned char hash[32];
    DWORD hashsize = sizeof(hash);

    if (!CryptHashCertificate2(BCRYPT_SHA256_ALGORITHM, 0, NULL, data, len, hash, &hashsize))
    {
        av_log(NULL, AV_LOG_ERROR, "CryptHashCertificate2 failed\n");
        return AVERROR_EXTERNAL;
    }

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

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

    return av_bprint_finalize(&buf, fingerprint);
}

static int tls_gen_self_signed(NCRYPT_KEY_HANDLE *key, PCCERT_CONTEXT *crtctx)
{
    NCRYPT_PROV_HANDLE provider = 0;
    CERT_NAME_BLOB subject = { 0 };

    DWORD export_props = NCRYPT_ALLOW_EXPORT_FLAG | NCRYPT_ALLOW_PLAINTEXT_EXPORT_FLAG;
    DWORD usage_props = NCRYPT_ALLOW_ALL_USAGES;
    LPCSTR ext_usages[] = { szOID_PKIX_KP_SERVER_AUTH };
    BYTE key_usage = CERT_KEY_ENCIPHERMENT_KEY_USAGE | CERT_DIGITAL_SIGNATURE_KEY_USAGE;
    CRYPT_BIT_BLOB key_usage_blob = { 0 };
    CERT_ENHKEY_USAGE eku = { 0 };
    CERT_BASIC_CONSTRAINTS2_INFO basic_constraints = { 0 };
    CERT_ALT_NAME_ENTRY san_entry = { 0 };
    CERT_ALT_NAME_INFO san_info = { 0 };
    CERT_EXTENSION ext[4] = { 0 };
    CERT_EXTENSIONS exts = { 0 };
    CRYPT_ALGORITHM_IDENTIFIER sig_alg = { (LPSTR)szOID_ECDSA_SHA256 };
    CRYPT_KEY_PROV_INFO prov_info = { 0 };
    const char *subj_str = "CN=lavf";

    SECURITY_STATUS sspi_ret;
    int ret = 0;

    *crtctx = NULL;

    sspi_ret = NCryptOpenStorageProvider(&provider, MS_KEY_STORAGE_PROVIDER, 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptOpenStorageProvider failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    sspi_ret = NCryptCreatePersistedKey(provider, key, BCRYPT_ECDSA_P256_ALGORITHM, FF_NCRYPT_TEMP_KEY_NAME, 0, NCRYPT_OVERWRITE_KEY_FLAG);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptCreatePersistedKey failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    sspi_ret = NCryptSetProperty(*key, NCRYPT_EXPORT_POLICY_PROPERTY, (PBYTE)&export_props, sizeof(export_props), 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptSetProperty(NCRYPT_EXPORT_POLICY_PROPERTY) failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    sspi_ret = NCryptSetProperty(*key, NCRYPT_KEY_USAGE_PROPERTY, (PBYTE)&usage_props, sizeof(usage_props), 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptSetProperty(NCRYPT_KEY_USAGE_PROPERTY) failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    sspi_ret = NCryptFinalizeKey(*key, 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptFinalizeKey failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    if (!CertStrToNameA(X509_ASN_ENCODING, subj_str, 0, NULL, NULL, &subject.cbData, NULL))
    {
        av_log(NULL, AV_LOG_ERROR, "Initial subj init failed\n");
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    subject.pbData = av_malloc(subject.cbData);
    if (!subject.pbData) {
        ret = AVERROR(ENOMEM);
        goto fail;
    }

    if (!CertStrToNameA(X509_ASN_ENCODING, subj_str, 0, NULL, subject.pbData, &subject.cbData, NULL))
    {
        av_log(NULL, AV_LOG_ERROR, "Subj init failed\n");
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    // Extended Key Usage extension
    eku.cUsageIdentifier = 1;
    eku.rgpszUsageIdentifier = (LPSTR*)ext_usages;

    if (!CryptEncodeObjectEx(X509_ASN_ENCODING, X509_ENHANCED_KEY_USAGE, &eku,
                             CRYPT_ENCODE_ALLOC_FLAG, NULL, &ext[0].Value.pbData, &ext[0].Value.cbData)) {
        av_log(NULL, AV_LOG_ERROR, "CryptEncodeObjectEx for EKU failed\n");
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    ext[0].pszObjId = (LPSTR)szOID_ENHANCED_KEY_USAGE;
    ext[0].fCritical = TRUE;

    // Key usage extension
    key_usage_blob.cbData = sizeof(key_usage);
    key_usage_blob.pbData = &key_usage;

    if (!CryptEncodeObjectEx(X509_ASN_ENCODING, X509_BITS, &key_usage_blob,
                             CRYPT_ENCODE_ALLOC_FLAG, NULL, &ext[1].Value.pbData, &ext[1].Value.cbData)) {
        av_log(NULL, AV_LOG_ERROR, "CryptEncodeObjectEx for KU failed\n");
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    ext[1].pszObjId = (LPSTR)szOID_KEY_USAGE;
    ext[1].fCritical = TRUE;

    // Cert Basic Constraints
    basic_constraints.fCA = FALSE;

    if (!CryptEncodeObjectEx(X509_ASN_ENCODING, X509_BASIC_CONSTRAINTS2, &basic_constraints,
                             CRYPT_ENCODE_ALLOC_FLAG, NULL, &ext[2].Value.pbData, &ext[2].Value.cbData)) {
        av_log(NULL, AV_LOG_ERROR, "CryptEncodeObjectEx for KU failed\n");
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    ext[2].pszObjId = (LPSTR)szOID_BASIC_CONSTRAINTS2;
    ext[2].fCritical = TRUE;

    // Subject Alt Names
    san_entry.dwAltNameChoice = CERT_ALT_NAME_DNS_NAME;
    san_entry.pwszDNSName = (LPWSTR)L"localhost";

    san_info.cAltEntry = 1;
    san_info.rgAltEntry = &san_entry;

    if (!CryptEncodeObjectEx(X509_ASN_ENCODING, X509_ALTERNATE_NAME, &san_info,
                             CRYPT_ENCODE_ALLOC_FLAG, NULL, &ext[3].Value.pbData, &ext[3].Value.cbData)) {
        av_log(NULL, AV_LOG_ERROR, "CryptEncodeObjectEx for KU failed\n");
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    ext[3].pszObjId = (LPSTR)szOID_SUBJECT_ALT_NAME2;
    ext[3].fCritical = TRUE;

    exts.cExtension = 4;
    exts.rgExtension = ext;

    prov_info.pwszProvName = (LPWSTR)MS_KEY_STORAGE_PROVIDER;
    prov_info.pwszContainerName = (LPWSTR)FF_NCRYPT_TEMP_KEY_NAME;
    prov_info.dwFlags = CERT_SET_KEY_CONTEXT_PROP_ID;

    *crtctx = CertCreateSelfSignCertificate(*key, &subject, 0, &prov_info, &sig_alg, NULL, NULL, &exts);
    if (!*crtctx) {
        av_log(NULL, AV_LOG_ERROR, "CertCreateSelfSignCertificate failed: %lu\n", GetLastError());
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    NCryptFreeObject(provider);
    av_free(subject.pbData);
    for (int i = 0; i < FF_ARRAY_ELEMS(ext); i++)
        LocalFree(ext[i].Value.pbData);

    return 0;

fail:
    if (*crtctx)
        CertFreeCertificateContext(*crtctx);
    if (*key)
        if (NCryptDeleteKey(*key, NCRYPT_SILENT_FLAG) != ERROR_SUCCESS)
            NCryptFreeObject(*key);
    if (provider)
        NCryptFreeObject(provider);
    if (subject.pbData)
        av_free(subject.pbData);
    for (int i = 0; i < FF_ARRAY_ELEMS(ext); i++)
        if (ext[i].Value.pbData)
            LocalFree(ext[i].Value.pbData);

    *key = 0;
    *crtctx = NULL;

    return ret;
}

static int tls_export_key_cert(NCRYPT_KEY_HANDLE key, PCCERT_CONTEXT crtctx,
                               char *key_buf, size_t key_sz, char *cert_buf, size_t cert_sz, char **fingerprint)
{
    DWORD keysize = 0;
    char *keybuf = NULL;

    SECURITY_STATUS sspi_ret;
    int ret = 0;

    sspi_ret = NCryptExportKey(key, 0, NCRYPT_PKCS8_PRIVATE_KEY_BLOB, NULL, NULL, 0, &keysize, 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "Initial NCryptExportKey failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto end;
    }

    keybuf = av_malloc(keysize);
    if (!keybuf) {
        ret = AVERROR(ENOMEM);
        goto end;
    }

    sspi_ret = NCryptExportKey(key, 0, NCRYPT_PKCS8_PRIVATE_KEY_BLOB, NULL, keybuf, keysize, &keysize, 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "Initial NCryptExportKey failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto end;
    }

    ret = der_to_pem(keybuf, keysize, "PRIVATE KEY", key_buf, key_sz);
    if (ret < 0)
        goto end;

    ret = der_to_pem(crtctx->pbCertEncoded, crtctx->cbCertEncoded, "CERTIFICATE", cert_buf, cert_sz);
    if (ret < 0)
        goto end;

    ret = der_to_fingerprint(crtctx->pbCertEncoded, crtctx->cbCertEncoded, fingerprint);
    if (ret < 0)
        goto end;

end:
    av_free(keybuf);
    return ret;
}

int ff_ssl_gen_key_cert(char *key_buf, size_t key_sz, char *cert_buf, size_t cert_sz, char **fingerprint)
{
    NCRYPT_KEY_HANDLE key = 0;
    PCCERT_CONTEXT crtctx = NULL;

    int ret = tls_gen_self_signed(&key, &crtctx);
    if (ret < 0)
        goto end;

    ret = tls_export_key_cert(key, crtctx, key_buf, key_sz, cert_buf, cert_sz, fingerprint);
    if (ret < 0)
        goto end;

end:
    if (key)
        if (NCryptDeleteKey(key, NCRYPT_SILENT_FLAG) != ERROR_SUCCESS)
            NCryptFreeObject(key);
    if (crtctx)
        CertFreeCertificateContext(crtctx);

    return ret;
}

static int tls_import_key_cert(char *key_buf, char *cert_buf, NCRYPT_KEY_HANDLE *key, PCCERT_CONTEXT *crtctx)
{
    NCRYPT_PROV_HANDLE provider = 0;

    DWORD export_props = NCRYPT_ALLOW_EXPORT_FLAG | NCRYPT_ALLOW_PLAINTEXT_EXPORT_FLAG;
    DWORD usage_props = NCRYPT_ALLOW_ALL_USAGES;
    NCryptBufferDesc buffer_desc = { 0 };
    NCryptBuffer buffer = { 0 };
    CRYPT_KEY_PROV_INFO prov_info = { 0 };

    int key_der_len = 0, cert_der_len = 0;
    char *key_der = NULL, *cert_der = NULL;

    SECURITY_STATUS sspi_ret;
    int ret = 0;

    ret = pem_to_der(key_buf, &key_der, &key_der_len);
    if (ret < 0)
        goto fail;

    ret = pem_to_der(cert_buf, &cert_der, &cert_der_len);
    if (ret < 0)
        goto fail;

    sspi_ret = NCryptOpenStorageProvider(&provider, MS_KEY_STORAGE_PROVIDER, 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptOpenStorageProvider failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    buffer_desc.ulVersion = NCRYPTBUFFER_VERSION;
    buffer_desc.cBuffers = 1;
    buffer_desc.pBuffers = &buffer;

    buffer.BufferType = NCRYPTBUFFER_PKCS_KEY_NAME;
    buffer.pvBuffer = (LPWSTR)FF_NCRYPT_TEMP_KEY_NAME;
    buffer.cbBuffer = sizeof(FF_NCRYPT_TEMP_KEY_NAME);

    sspi_ret = NCryptImportKey(provider, 0, NCRYPT_PKCS8_PRIVATE_KEY_BLOB, &buffer_desc, key, key_der, key_der_len, NCRYPT_DO_NOT_FINALIZE_FLAG | NCRYPT_OVERWRITE_KEY_FLAG);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptImportKey failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    sspi_ret = NCryptSetProperty(*key, NCRYPT_EXPORT_POLICY_PROPERTY, (PBYTE)&export_props, sizeof(export_props), 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptSetProperty(NCRYPT_EXPORT_POLICY_PROPERTY) failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    sspi_ret = NCryptSetProperty(*key, NCRYPT_KEY_USAGE_PROPERTY, (PBYTE)&usage_props, sizeof(usage_props), 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptSetProperty(NCRYPT_KEY_USAGE_PROPERTY) failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    sspi_ret = NCryptFinalizeKey(*key, 0);
    if (sspi_ret != ERROR_SUCCESS) {
        av_log(NULL, AV_LOG_ERROR, "NCryptFinalizeKey failed(0x%lx)\n", sspi_ret);
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    *crtctx = CertCreateCertificateContext(X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, cert_der, cert_der_len);
    if (!*crtctx) {
        av_log(NULL, AV_LOG_ERROR, "CertCreateCertificateContext failed: %lu\n", GetLastError());
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    if (!CertSetCertificateContextProperty(*crtctx, CERT_NCRYPT_KEY_HANDLE_PROP_ID, 0, key)) {
        av_log(NULL, AV_LOG_ERROR, "CertSetCertificateContextProperty(CERT_NCRYPT_KEY_HANDLE_PROP_ID) failed: %lu\n", GetLastError());
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    prov_info.pwszProvName = (LPWSTR)MS_KEY_STORAGE_PROVIDER;
    prov_info.pwszContainerName = (LPWSTR)FF_NCRYPT_TEMP_KEY_NAME;
    prov_info.dwFlags = CERT_SET_KEY_CONTEXT_PROP_ID;

    if (!CertSetCertificateContextProperty(*crtctx, CERT_KEY_PROV_INFO_PROP_ID, 0, &prov_info)) {
        av_log(NULL, AV_LOG_ERROR, "CertSetCertificateContextProperty(CERT_KEY_PROV_INFO_PROP_ID) failed: %lu\n", GetLastError());
        ret = AVERROR_EXTERNAL;
        goto fail;
    }

    goto end;

fail:
    if (*key)
        if (NCryptDeleteKey(*key, NCRYPT_SILENT_FLAG) != ERROR_SUCCESS)
            NCryptFreeObject(*key);
    if (*crtctx)
        CertFreeCertificateContext(*crtctx);

    *key = 0;
    *crtctx = NULL;

end:
    if (key_der)
        av_free(key_der);
    if (cert_der)
        av_free(cert_der);
    if (provider)
        NCryptFreeObject(provider);
    return ret;
}

static int tls_load_key_cert(char *key_url, char *cert_url, NCRYPT_KEY_HANDLE *key, PCCERT_CONTEXT *crtctx)
{
    AVBPrint key_bp, cert_bp;
    int ret = 0;

    av_bprint_init(&key_bp, 1, MAX_CERTIFICATE_SIZE);
    av_bprint_init(&cert_bp, 1, MAX_CERTIFICATE_SIZE);

    /* Read key file. */
    ret = ff_url_read_all(key_url, &key_bp);
    if (ret < 0) {
        av_log(NULL, AV_LOG_ERROR, "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, "Failed to open cert file %s\n", cert_url);
        goto end;
    }

    ret = tls_import_key_cert(key_bp.str, cert_bp.str, key, crtctx);
    if (ret < 0)
        goto end;

end:
    av_bprint_finalize(&key_bp, NULL);
    av_bprint_finalize(&cert_bp, NULL);

    return ret;
}

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)
{
    NCRYPT_KEY_HANDLE key = 0;
    PCCERT_CONTEXT crtctx = NULL;

    int ret = tls_load_key_cert(key_url, cert_url, &key, &crtctx);
    if (ret < 0)
        goto end;

    ret = tls_export_key_cert(key, crtctx, key_buf, key_sz, cert_buf, cert_sz, fingerprint);
    if (ret < 0)
        goto end;

end:
    if (key)
        if (NCryptDeleteKey(key, NCRYPT_SILENT_FLAG) != ERROR_SUCCESS)
            NCryptFreeObject(key);
    if (crtctx)
        CertFreeCertificateContext(crtctx);

    return ret;
}

typedef struct TLSContext {
    const AVClass *class;
    TLSShared tls_shared;

    CredHandle cred_handle;
    TimeStamp cred_timestamp;

    CtxtHandle ctxt_handle;
    int have_context;
    TimeStamp ctxt_timestamp;

    ULONG request_flags;
    ULONG context_flags;

    uint8_t *enc_buf;
    int enc_buf_size;
    int enc_buf_offset;

    uint8_t *dec_buf;
    int dec_buf_size;
    int dec_buf_offset;

    SecPkgContext_StreamSizes sizes;

    int connected;
    int connection_closed;
    int sspi_close_notify;
} TLSContext;

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

    if (s->is_dtls)
        c->tls_shared.udp = sock;
    else
        c->tls_shared.tcp = sock;

    return 0;
}

int ff_dtls_export_materials(URLContext *h, char *dtls_srtp_materials, size_t materials_sz)
{
    TLSContext *c = h->priv_data;

    SecPkgContext_KeyingMaterialInfo keying_info = { 0 };
    SecPkgContext_KeyingMaterial keying_material = { 0 };

    const char* dst = "EXTRACTOR-dtls_srtp";
    SECURITY_STATUS sspi_ret;

    if (!c->have_context)
        return AVERROR(EINVAL);

    keying_info.cbLabel = strlen(dst) + 1;
    keying_info.pszLabel = (LPSTR)dst;
    keying_info.cbContextValue = 0;
    keying_info.pbContextValue = NULL;
    keying_info.cbKeyingMaterial = materials_sz;

    sspi_ret = SetContextAttributes(&c->ctxt_handle, SECPKG_ATTR_KEYING_MATERIAL_INFO, &keying_info, sizeof(keying_info));
    if (sspi_ret != SEC_E_OK) {
        av_log(h, AV_LOG_ERROR, "Setting keying material info failed: %lx\n", sspi_ret);
        return AVERROR_EXTERNAL;
    }

    sspi_ret = QueryContextAttributes(&c->ctxt_handle, SECPKG_ATTR_KEYING_MATERIAL, &keying_material);
    if (sspi_ret != SEC_E_OK) {
        av_log(h, AV_LOG_ERROR, "Querying keying material failed: %lx\n", sspi_ret);
        return AVERROR_EXTERNAL;
    }

    memcpy(dtls_srtp_materials, keying_material.pbKeyingMaterial, FFMIN(materials_sz, keying_material.cbKeyingMaterial));
    FreeContextBuffer(keying_material.pbKeyingMaterial);

    if (keying_material.cbKeyingMaterial > materials_sz) {
        av_log(h, AV_LOG_WARNING, "Keying material size mismatch: %ld > %zu\n", keying_material.cbKeyingMaterial, materials_sz);
        return AVERROR(ENOSPC);
    }

    return 0;
}

int ff_dtls_state(URLContext *h)
{
    TLSContext *c = h->priv_data;
    return c->tls_shared.state;
}

static void init_sec_buffer(SecBuffer *buffer, unsigned long type,
                            void *data, unsigned long size)
{
    buffer->cbBuffer   = size;
    buffer->BufferType = type;
    buffer->pvBuffer   = data;
}

static void init_sec_buffer_desc(SecBufferDesc *desc, SecBuffer *buffers,
                                 unsigned long buffer_count)
{
    desc->ulVersion = SECBUFFER_VERSION;
    desc->pBuffers = buffers;
    desc->cBuffers = buffer_count;
}

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

    if (c->connected) {
        SecBufferDesc BuffDesc;
        SecBuffer Buffer;
        SECURITY_STATUS sspi_ret;
        SecBuffer outbuf;
        SecBufferDesc outbuf_desc;

        DWORD dwshut = SCHANNEL_SHUTDOWN;
        init_sec_buffer(&Buffer, SECBUFFER_TOKEN, &dwshut, sizeof(dwshut));
        init_sec_buffer_desc(&BuffDesc, &Buffer, 1);

        sspi_ret = ApplyControlToken(&c->ctxt_handle, &BuffDesc);
        if (sspi_ret != SEC_E_OK)
            av_log(h, AV_LOG_ERROR, "ApplyControlToken failed\n");

        init_sec_buffer(&outbuf, SECBUFFER_TOKEN, NULL, 0);
        init_sec_buffer_desc(&outbuf_desc, &outbuf, 1);

        do {
            if (s->listen)
                sspi_ret = AcceptSecurityContext(&c->cred_handle, &c->ctxt_handle, NULL, c->request_flags, 0,
                                                 &c->ctxt_handle, &outbuf_desc, &c->context_flags,
                                                 &c->ctxt_timestamp);
            else
                sspi_ret = InitializeSecurityContext(&c->cred_handle, &c->ctxt_handle, s->host,
                                                     c->request_flags, 0, 0, NULL, 0, &c->ctxt_handle,
                                                     &outbuf_desc, &c->context_flags, &c->ctxt_timestamp);

            if (outbuf.pvBuffer) {
                if (outbuf.cbBuffer > 0) {
                    uc->flags &= ~AVIO_FLAG_NONBLOCK;
                    ret = ffurl_write(uc, outbuf.pvBuffer, outbuf.cbBuffer);
                    if (ret < 0 || ret != outbuf.cbBuffer)
                        av_log(h, AV_LOG_ERROR, "Failed to send close message\n");
                }
                FreeContextBuffer(outbuf.pvBuffer);
            }
        } while(sspi_ret == SEC_I_MESSAGE_FRAGMENT || sspi_ret == SEC_I_CONTINUE_NEEDED);

        av_log(h, AV_LOG_DEBUG, "Close session result: 0x%lx\n", sspi_ret);

        c->connected = 0;
    }
    return 0;
}

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

    tls_shutdown_client(h);

    DeleteSecurityContext(&c->ctxt_handle);
    FreeCredentialsHandle(&c->cred_handle);

    av_freep(&c->enc_buf);
    c->enc_buf_size = c->enc_buf_offset = 0;

    av_freep(&c->dec_buf);
    c->dec_buf_size = c->dec_buf_offset = 0;

    if (s->is_dtls) {
        if (!s->external_sock)
            ffurl_closep(&c->tls_shared.udp);
    } else {
        ffurl_closep(&c->tls_shared.tcp);
    }

    return 0;
}

static int tls_handshake_loop(URLContext *h, int initial)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;
    URLContext *uc = s->is_dtls ? s->udp : s->tcp;
    SECURITY_STATUS sspi_ret;
    SecBuffer outbuf[3] = { 0 };
    SecBufferDesc outbuf_desc;
    SecBuffer inbuf[3];
    SecBufferDesc inbuf_desc;
    struct sockaddr_storage recv_addr = { 0 };
    socklen_t recv_addr_len = 0;
    int i, ret = 0, read_data = initial;

    if (c->enc_buf == NULL) {
        c->enc_buf_offset = 0;
        ret = av_reallocp(&c->enc_buf, SCHANNEL_INITIAL_BUFFER_SIZE);
        if (ret < 0)
            goto fail;
        c->enc_buf_size = SCHANNEL_INITIAL_BUFFER_SIZE;
    }

    if (c->dec_buf == NULL) {
        c->dec_buf_offset = 0;
        ret = av_reallocp(&c->dec_buf, SCHANNEL_INITIAL_BUFFER_SIZE);
        if (ret < 0)
            goto fail;
        c->dec_buf_size = SCHANNEL_INITIAL_BUFFER_SIZE;
    }

    uc->flags &= ~AVIO_FLAG_NONBLOCK;

    while (1) {
        if (c->enc_buf_size - c->enc_buf_offset < SCHANNEL_FREE_BUFFER_SIZE) {
            c->enc_buf_size = c->enc_buf_offset + SCHANNEL_FREE_BUFFER_SIZE;
            ret = av_reallocp(&c->enc_buf, c->enc_buf_size);
            if (ret < 0) {
                c->enc_buf_size = c->enc_buf_offset = 0;
                goto fail;
            }
        }

        if (read_data) {
            ret = ffurl_read(uc, c->enc_buf + c->enc_buf_offset, c->enc_buf_size - c->enc_buf_offset);
            if (ret < 0) {
                av_log(h, AV_LOG_ERROR, "Failed to read handshake response\n");
                goto fail;
            }
            c->enc_buf_offset += ret;
            if (s->is_dtls && !recv_addr_len) {
                ff_udp_get_last_recv_addr(uc, &recv_addr, &recv_addr_len);

                if (s->listen) {
                    ret = ff_udp_set_remote_addr(uc, (struct sockaddr *)&recv_addr, recv_addr_len, 1);
                    if (ret < 0) {
                        av_log(h, AV_LOG_ERROR, "Failed connecting udp context\n");
                        goto fail;
                    }
                    av_log(h, AV_LOG_TRACE, "Set UDP remote addr on UDP socket, now 'connected'\n");
                }
            }
        }

        /* input buffers */
        init_sec_buffer(&inbuf[0], SECBUFFER_TOKEN, av_malloc(c->enc_buf_offset), c->enc_buf_offset);
        init_sec_buffer(&inbuf[1], SECBUFFER_EMPTY, NULL, 0);
        if (s->listen && s->is_dtls) {
            init_sec_buffer(&inbuf[2], SECBUFFER_EXTRA, &recv_addr, recv_addr_len);
            init_sec_buffer_desc(&inbuf_desc, inbuf, 3);
        } else {
            init_sec_buffer_desc(&inbuf_desc, inbuf, 2);
        }

        if (inbuf[0].pvBuffer == NULL) {
            av_log(h, AV_LOG_ERROR, "Failed to allocate input buffer\n");
            ret = AVERROR(ENOMEM);
            goto fail;
        }

        memcpy(inbuf[0].pvBuffer, c->enc_buf, c->enc_buf_offset);

        /* output buffers */
        init_sec_buffer(&outbuf[0], SECBUFFER_TOKEN, NULL, 0);
        init_sec_buffer(&outbuf[1], SECBUFFER_ALERT, NULL, 0);
        init_sec_buffer(&outbuf[2], SECBUFFER_EMPTY, NULL, 0);
        init_sec_buffer_desc(&outbuf_desc, outbuf, 3);

        if (s->listen)
            sspi_ret = AcceptSecurityContext(&c->cred_handle, c->have_context ? &c->ctxt_handle : NULL, &inbuf_desc,
                                             c->request_flags, 0, &c->ctxt_handle, &outbuf_desc,
                                             &c->context_flags, &c->ctxt_timestamp);
        else
            sspi_ret = InitializeSecurityContext(&c->cred_handle, c->have_context ? &c->ctxt_handle : NULL,
                                                 s->host, c->request_flags, 0, 0, &inbuf_desc, 0, &c->ctxt_handle,
                                                 &outbuf_desc, &c->context_flags, &c->ctxt_timestamp);
        av_freep(&inbuf[0].pvBuffer);

        av_log(h, AV_LOG_TRACE, "Handshake res with %d bytes of data: 0x%lx\n", c->enc_buf_offset, sspi_ret);

        if (sspi_ret == SEC_E_INCOMPLETE_MESSAGE) {
            av_log(h, AV_LOG_TRACE, "Received incomplete handshake, need more data\n");
            read_data = 1;
            continue;
        }

        c->have_context = 1;

        /* remote requests a client certificate - attempt to continue without one anyway */
        if (sspi_ret == SEC_I_INCOMPLETE_CREDENTIALS &&
            !(c->request_flags & ISC_REQ_USE_SUPPLIED_CREDS)) {
            av_log(h, AV_LOG_VERBOSE, "Client certificate has been requested, ignoring\n");
            c->request_flags |= ISC_REQ_USE_SUPPLIED_CREDS;
            read_data = 0;
            continue;
        }

        /* continue handshake */
        if (sspi_ret == SEC_I_CONTINUE_NEEDED || sspi_ret == SEC_I_MESSAGE_FRAGMENT || sspi_ret == SEC_E_OK) {
            for (i = 0; i < 3; i++) {
                if (outbuf[i].BufferType == SECBUFFER_TOKEN && outbuf[i].cbBuffer > 0) {
                    ret = ffurl_write(uc, outbuf[i].pvBuffer, outbuf[i].cbBuffer);
                    if (ret < 0 || ret != outbuf[i].cbBuffer) {
                        av_log(h, AV_LOG_VERBOSE, "Failed to send handshake data\n");
                        ret = AVERROR(EIO);
                        goto fail;
                    }
                }

                if (outbuf[i].pvBuffer != NULL) {
                    FreeContextBuffer(outbuf[i].pvBuffer);
                    outbuf[i].pvBuffer = NULL;
                }
            }
        } else {
            if (sspi_ret == SEC_E_WRONG_PRINCIPAL)
                av_log(h, AV_LOG_ERROR, "SNI or certificate check failed\n");
            else
                av_log(h, AV_LOG_ERROR, "Creating security context failed (0x%lx)\n", sspi_ret);
            ret = AVERROR_UNKNOWN;
            goto fail;
        }

        if (sspi_ret == SEC_I_MESSAGE_FRAGMENT) {
            av_log(h, AV_LOG_TRACE, "Writing fragmented output message part\n");
            read_data = 0;
            continue;
        }

        if (inbuf[1].BufferType == SECBUFFER_EXTRA && inbuf[1].cbBuffer > 0) {
            if (c->enc_buf_offset > inbuf[1].cbBuffer) {
                memmove(c->enc_buf, (c->enc_buf + c->enc_buf_offset) - inbuf[1].cbBuffer,
                        inbuf[1].cbBuffer);
                c->enc_buf_offset = inbuf[1].cbBuffer;
                if (sspi_ret == SEC_I_CONTINUE_NEEDED) {
                    av_log(h, AV_LOG_TRACE, "Sent reply, handshake continues. %d extra bytes\n", (int)inbuf[1].cbBuffer);
                    read_data = 0;
                    continue;
                }
            }
        } else {
            c->enc_buf_offset  = 0;
        }

        if (sspi_ret == SEC_I_CONTINUE_NEEDED) {
            av_log(h, AV_LOG_TRACE, "Handshake continues\n");
            read_data = 1;
            continue;
        }

        break;
    }

    av_log(h, AV_LOG_TRACE, "Handshake completed\n");

    return 0;

fail:
    /* free any remaining output data */
    for (i = 0; i < 3; i++) {
        if (outbuf[i].pvBuffer != NULL) {
            FreeContextBuffer(outbuf[i].pvBuffer);
            outbuf[i].pvBuffer = NULL;
        }
    }

    av_log(h, AV_LOG_TRACE, "Handshake failed\n");

    return ret;
}

static int tls_client_handshake(URLContext *h)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;
    URLContext *uc = s->is_dtls ? s->udp : s->tcp;
    SecBuffer outbuf;
    SecBufferDesc outbuf_desc;
    SECURITY_STATUS sspi_ret;
    int ret;

    init_sec_buffer(&outbuf, SECBUFFER_EMPTY, NULL, 0);
    init_sec_buffer_desc(&outbuf_desc, &outbuf, 1);

    c->request_flags = ISC_REQ_SEQUENCE_DETECT | ISC_REQ_REPLAY_DETECT |
                       ISC_REQ_CONFIDENTIALITY | ISC_REQ_ALLOCATE_MEMORY;
    if (s->is_dtls)
        c->request_flags |= ISC_REQ_DATAGRAM;
    else
        c->request_flags |= ISC_REQ_STREAM;

    sspi_ret = InitializeSecurityContext(&c->cred_handle, NULL, s->host, c->request_flags, 0, 0,
                                         NULL, 0, &c->ctxt_handle, &outbuf_desc, &c->context_flags,
                                         &c->ctxt_timestamp);
    if (sspi_ret != SEC_I_CONTINUE_NEEDED) {
        av_log(h, AV_LOG_ERROR, "Unable to create initial security context (0x%lx)\n", sspi_ret);
        ret = AVERROR_UNKNOWN;
        goto fail;
    }

    c->have_context = 1;

    uc->flags &= ~AVIO_FLAG_NONBLOCK;
    ret = ffurl_write(uc, outbuf.pvBuffer, outbuf.cbBuffer);
    FreeContextBuffer(outbuf.pvBuffer);
    if (ret < 0 || ret != outbuf.cbBuffer) {
        av_log(h, AV_LOG_ERROR, "Failed to send initial handshake data\n");
        ret = AVERROR(EIO);
        goto fail;
    }

    return tls_handshake_loop(h, 1);

fail:
    DeleteSecurityContext(&c->ctxt_handle);
    return ret;
}

static int tls_server_handshake(URLContext *h)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;

    c->request_flags = ASC_REQ_SEQUENCE_DETECT | ASC_REQ_REPLAY_DETECT |
                       ASC_REQ_CONFIDENTIALITY | ASC_REQ_ALLOCATE_MEMORY;
    if (s->is_dtls)
        c->request_flags |= ASC_REQ_DATAGRAM;
    else
        c->request_flags |= ASC_REQ_STREAM;

    c->have_context = 0;

    return tls_handshake_loop(h, 1);
}

static int tls_handshake(URLContext *h)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;
    SECURITY_STATUS sspi_ret;
    int ret = 0;

    if (s->listen)
        ret = tls_server_handshake(h);
    else
        ret = tls_client_handshake(h);

    if (ret < 0)
        goto fail;

    if (s->is_dtls && s->mtu > 0) {
        ULONG mtu = s->mtu;
        sspi_ret = SetContextAttributes(&c->ctxt_handle, SECPKG_ATTR_DTLS_MTU, &mtu, sizeof(mtu));
        if (sspi_ret != SEC_E_OK) {
            av_log(h, AV_LOG_ERROR, "Failed setting DTLS MTU to %d.\n", s->mtu);
            ret = AVERROR(EINVAL);
            goto fail;
        }
        av_log(h, AV_LOG_VERBOSE, "Set DTLS MTU to %d\n", s->mtu);
    }

    c->connected = 1;
    s->state = DTLS_STATE_FINISHED;

fail:
    return ret;
}

static int tls_open(URLContext *h, const char *uri, int flags, AVDictionary **options)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;
    SECURITY_STATUS sspi_ret;
    SCHANNEL_CRED schannel_cred = { 0 };
    PCCERT_CONTEXT crtctx = NULL;
    NCRYPT_KEY_HANDLE key = 0;
    int ret = 0;

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

    /* SChannel Options */
    schannel_cred.dwVersion = SCHANNEL_CRED_VERSION;

    if (s->listen) {
        if (s->key_buf && s->cert_buf) {
            ret = tls_import_key_cert(s->key_buf, s->cert_buf, &key, &crtctx);
            if (ret < 0)
                goto fail;
        } else if (s->key_file && s->cert_file) {
            ret = tls_load_key_cert(s->key_file, s->cert_file, &key, &crtctx);
            if (ret < 0)
                goto fail;
        } else {
            av_log(h, AV_LOG_VERBOSE, "No server certificate provided, using self-signed\n");
            ret = tls_gen_self_signed(&key, &crtctx);
            if (ret < 0)
                goto fail;
        }

        schannel_cred.cCreds = 1;
        schannel_cred.paCred = &crtctx;

        schannel_cred.dwFlags = SCH_CRED_NO_SYSTEM_MAPPER | SCH_CRED_MANUAL_CRED_VALIDATION;

        if (s->is_dtls)
            schannel_cred.grbitEnabledProtocols = SP_PROT_DTLS1_X_SERVER;
    } else {
        if (s->verify)
            schannel_cred.dwFlags = SCH_CRED_AUTO_CRED_VALIDATION |
                                    SCH_CRED_REVOCATION_CHECK_CHAIN;
        else
            schannel_cred.dwFlags = SCH_CRED_MANUAL_CRED_VALIDATION |
                                    SCH_CRED_IGNORE_NO_REVOCATION_CHECK |
                                    SCH_CRED_IGNORE_REVOCATION_OFFLINE;

        if (s->is_dtls)
            schannel_cred.grbitEnabledProtocols = SP_PROT_DTLS1_X_CLIENT;
    }

    /* Get credential handle */
    sspi_ret = AcquireCredentialsHandle(NULL, (TCHAR *)UNISP_NAME,
                                        s->listen ? SECPKG_CRED_INBOUND : SECPKG_CRED_OUTBOUND,
                                        NULL, &schannel_cred, NULL, NULL, &c->cred_handle,
                                        &c->cred_timestamp);
    if (sspi_ret != SEC_E_OK) {
        av_log(h, AV_LOG_ERROR, "Unable to acquire security credentials (0x%lx)\n", sspi_ret);
        ret = AVERROR_UNKNOWN;
        goto fail;
    }

    if (!s->external_sock) {
        ret = tls_handshake(h);
        if (ret < 0)
            goto fail;
    }

    goto end;

fail:
    tls_close(h);

end:
    if (crtctx)
        CertFreeCertificateContext(crtctx);
    if (key)
        if (NCryptDeleteKey(key, NCRYPT_SILENT_FLAG) != ERROR_SUCCESS)
            NCryptFreeObject(key);

    return ret;
}

static int dtls_open(URLContext *h, const char *uri, int flags, AVDictionary **options)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;

    s->is_dtls = 1;

    return tls_open(h, uri, flags, options);
}

static int tls_read(URLContext *h, uint8_t *buf, int len)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;
    URLContext *uc = s->is_dtls ? s->udp : s->tcp;
    SECURITY_STATUS sspi_ret = SEC_E_OK;
    SecBuffer inbuf[4];
    SecBufferDesc inbuf_desc;
    int size, ret = 0;
    int min_enc_buf_size = len + SCHANNEL_FREE_BUFFER_SIZE;

    /* If we have some left-over data from previous network activity,
     * return it first in case it is enough. It may contain
     * data that is required to know whether this connection
     * is still required or not, esp. in case of HTTP keep-alive
     * connections. */
    if (c->dec_buf_offset > 0)
        goto cleanup;

    if (c->sspi_close_notify)
        goto cleanup;

    if (!c->connection_closed) {
        size = c->enc_buf_size - c->enc_buf_offset;
        if (size < SCHANNEL_FREE_BUFFER_SIZE || c->enc_buf_size < min_enc_buf_size) {
            c->enc_buf_size = c->enc_buf_offset + SCHANNEL_FREE_BUFFER_SIZE;
            if (c->enc_buf_size < min_enc_buf_size)
                c->enc_buf_size = min_enc_buf_size;
            ret = av_reallocp(&c->enc_buf, c->enc_buf_size);
            if (ret < 0) {
                c->enc_buf_size = c->enc_buf_offset = 0;
                return ret;
            }
        }

        uc->flags &= ~AVIO_FLAG_NONBLOCK;
        uc->flags |= h->flags & AVIO_FLAG_NONBLOCK;

        ret = ffurl_read(uc, c->enc_buf + c->enc_buf_offset,
                         c->enc_buf_size - c->enc_buf_offset);
        if (ret == AVERROR_EOF) {
            c->connection_closed = 1;
            ret = 0;
        } else if (ret == AVERROR(EAGAIN)) {
            ret = 0;
        } else if (ret < 0) {
            av_log(h, AV_LOG_ERROR, "Unable to read from socket\n");
            return ret;
        }

        c->enc_buf_offset += ret;
    }

    while (c->enc_buf_offset > 0 && sspi_ret == SEC_E_OK) {
        /*  input buffer */
        init_sec_buffer(&inbuf[0], SECBUFFER_DATA, c->enc_buf, c->enc_buf_offset);

        /* additional buffers for possible output */
        init_sec_buffer(&inbuf[1], SECBUFFER_EMPTY, NULL, 0);
        init_sec_buffer(&inbuf[2], SECBUFFER_EMPTY, NULL, 0);
        init_sec_buffer(&inbuf[3], SECBUFFER_EMPTY, NULL, 0);
        init_sec_buffer_desc(&inbuf_desc, inbuf, 4);

        sspi_ret = DecryptMessage(&c->ctxt_handle, &inbuf_desc, 0, NULL);
        if (sspi_ret == SEC_E_OK || sspi_ret == SEC_I_RENEGOTIATE ||
            sspi_ret == SEC_I_CONTEXT_EXPIRED) {
            /* handle decrypted data */
            if (inbuf[1].BufferType == SECBUFFER_DATA) {
                /* grow buffer if needed */
                size = inbuf[1].cbBuffer > SCHANNEL_FREE_BUFFER_SIZE ?
                       inbuf[1].cbBuffer : SCHANNEL_FREE_BUFFER_SIZE;
                if (c->dec_buf_size - c->dec_buf_offset < size || c->dec_buf_size < len)  {
                    c->dec_buf_size = c->dec_buf_offset + size;
                    if (c->dec_buf_size < len)
                        c->dec_buf_size = len;
                    ret = av_reallocp(&c->dec_buf, c->dec_buf_size);
                    if (ret < 0) {
                        c->dec_buf_size = c->dec_buf_offset = 0;
                        return ret;
                    }
                }

                /* copy decrypted data to buffer */
                size = inbuf[1].cbBuffer;
                if (size) {
                    memcpy(c->dec_buf + c->dec_buf_offset, inbuf[1].pvBuffer, size);
                    c->dec_buf_offset += size;
                }
            }
            if (inbuf[3].BufferType == SECBUFFER_EXTRA && inbuf[3].cbBuffer > 0) {
                if (c->enc_buf_offset > inbuf[3].cbBuffer) {
                    memmove(c->enc_buf, (c->enc_buf + c->enc_buf_offset) - inbuf[3].cbBuffer,
                    inbuf[3].cbBuffer);
                    c->enc_buf_offset = inbuf[3].cbBuffer;
                }
            } else
                c->enc_buf_offset = 0;

            if (sspi_ret == SEC_I_RENEGOTIATE) {
                if (c->enc_buf_offset) {
                    av_log(h, AV_LOG_ERROR, "Cannot renegotiate, encrypted data buffer not empty\n");
                    ret = AVERROR_UNKNOWN;
                    goto cleanup;
                }

                av_log(h, AV_LOG_VERBOSE, "Re-negotiating security context\n");
                ret = tls_handshake_loop(h, 0);
                if (ret < 0) {
                    goto cleanup;
                }
                sspi_ret = SEC_E_OK;
                continue;
            } else if (sspi_ret == SEC_I_CONTEXT_EXPIRED) {
                c->sspi_close_notify = 1;
                if (!c->connection_closed) {
                    c->connection_closed = 1;
                    av_log(h, AV_LOG_VERBOSE, "Server closed the connection\n");
                }
                ret = 0;
                goto cleanup;
            }
        } else if (sspi_ret == SEC_E_INCOMPLETE_MESSAGE) {
            ret = AVERROR(EAGAIN);
            goto cleanup;
        } else {
            av_log(h, AV_LOG_ERROR, "Unable to decrypt message (error 0x%x)\n", (unsigned)sspi_ret);
            ret = AVERROR(EIO);
            goto cleanup;
        }
    }

    ret = 0;

cleanup:
    size = FFMIN(len, c->dec_buf_offset);
    if (size) {
        memcpy(buf, c->dec_buf, size);
        memmove(c->dec_buf, c->dec_buf + size, c->dec_buf_offset - size);
        c->dec_buf_offset -= size;

        return size;
    }

    if (ret == 0 && !c->connection_closed)
        ret = AVERROR(EAGAIN);

    return ret < 0 ? ret : AVERROR_EOF;
}

static int tls_write(URLContext *h, const uint8_t *buf, int len)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;
    URLContext *uc = s->is_dtls ? s->udp : s->tcp;
    SECURITY_STATUS sspi_ret;
    int ret = 0, data_size;
    uint8_t *data = NULL;
    SecBuffer outbuf[4];
    SecBufferDesc outbuf_desc;

    if (c->sizes.cbMaximumMessage == 0) {
        sspi_ret = QueryContextAttributes(&c->ctxt_handle, SECPKG_ATTR_STREAM_SIZES, &c->sizes);
        if (sspi_ret != SEC_E_OK)
            return AVERROR_UNKNOWN;
    }

    /* limit how much data we can consume */
    len = FFMIN(len, c->sizes.cbMaximumMessage - c->sizes.cbHeader - c->sizes.cbTrailer);

    data_size = c->sizes.cbHeader + len + c->sizes.cbTrailer;
    data = av_malloc(data_size);
    if (data == NULL)
        return AVERROR(ENOMEM);

    init_sec_buffer(&outbuf[0], SECBUFFER_STREAM_HEADER,
                  data, c->sizes.cbHeader);
    init_sec_buffer(&outbuf[1], SECBUFFER_DATA,
                  data + c->sizes.cbHeader, len);
    init_sec_buffer(&outbuf[2], SECBUFFER_STREAM_TRAILER,
                  data + c->sizes.cbHeader + len,
                  c->sizes.cbTrailer);
    init_sec_buffer(&outbuf[3], SECBUFFER_EMPTY, NULL, 0);
    init_sec_buffer_desc(&outbuf_desc, outbuf, 4);

    memcpy(outbuf[1].pvBuffer, buf, len);

    sspi_ret = EncryptMessage(&c->ctxt_handle, 0, &outbuf_desc, 0);
    if (sspi_ret == SEC_E_OK)  {
        len = outbuf[0].cbBuffer + outbuf[1].cbBuffer + outbuf[2].cbBuffer;

        uc->flags &= ~AVIO_FLAG_NONBLOCK;
        uc->flags |= h->flags & AVIO_FLAG_NONBLOCK;

        ret = ffurl_write(uc, data, len);
        if (ret == AVERROR(EAGAIN)) {
            goto done;
        } else if (ret < 0 || ret != len) {
            ret = AVERROR(EIO);
            av_log(h, AV_LOG_ERROR, "Writing encrypted data to socket failed\n");
            goto done;
        }
    } else {
        av_log(h, AV_LOG_ERROR, "Encrypting data failed\n");
        if (sspi_ret == SEC_E_INSUFFICIENT_MEMORY)
            ret = AVERROR(ENOMEM);
        else
            ret = AVERROR(EIO);
        goto done;
    }

done:
    av_freep(&data);
    return ret < 0 ? ret : outbuf[1].cbBuffer;
}

static int tls_get_file_handle(URLContext *h)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;
    return ffurl_get_file_handle(s->is_dtls ? s->udp : s->tcp);
}

static int tls_get_short_seek(URLContext *h)
{
    TLSContext *c = h->priv_data;
    TLSShared *s = &c->tls_shared;
    return ffurl_get_short_seek(s->is_dtls ? s->udp : s->tcp);
}

static const AVOption options[] = {
    TLS_COMMON_OPTIONS(TLSContext, tls_shared),
    { 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_close      = tls_close,
    .url_read       = tls_read,
    .url_write      = tls_write,
    .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,
};