diff --git a/library/ssl_misc.h b/library/ssl_misc.h
new file mode 100644
index 0000000..85f7fc4
--- /dev/null
+++ b/library/ssl_misc.h
@@ -0,0 +1,1309 @@
+/**
+ * \file ssl_misc.h
+ *
+ * \brief Internal functions shared by the SSL modules
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+#ifndef MBEDTLS_SSL_MISC_H
+#define MBEDTLS_SSL_MISC_H
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "mbedtls/config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#include "mbedtls/ssl.h"
+#include "mbedtls/cipher.h"
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#include "psa/crypto.h"
+#endif
+
+#if defined(MBEDTLS_MD5_C)
+#include "mbedtls/md5.h"
+#endif
+
+#if defined(MBEDTLS_SHA1_C)
+#include "mbedtls/sha1.h"
+#endif
+
+#if defined(MBEDTLS_SHA256_C)
+#include "mbedtls/sha256.h"
+#endif
+
+#if defined(MBEDTLS_SHA512_C)
+#include "mbedtls/sha512.h"
+#endif
+
+#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+#include "mbedtls/ecjpake.h"
+#endif
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#include "psa/crypto.h"
+#include "mbedtls/psa_util.h"
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+#if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
+    !defined(inline) && !defined(__cplusplus)
+#define inline __inline
+#endif
+
+/* Determine minimum supported version */
+#define MBEDTLS_SSL_MIN_MAJOR_VERSION           MBEDTLS_SSL_MAJOR_VERSION_3
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+#define MBEDTLS_SSL_MIN_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_0
+#else
+#if defined(MBEDTLS_SSL_PROTO_TLS1)
+#define MBEDTLS_SSL_MIN_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_1
+#else
+#if defined(MBEDTLS_SSL_PROTO_TLS1_1)
+#define MBEDTLS_SSL_MIN_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_2
+#else
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+#define MBEDTLS_SSL_MIN_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_3
+#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
+#endif /* MBEDTLS_SSL_PROTO_TLS1_1 */
+#endif /* MBEDTLS_SSL_PROTO_TLS1   */
+#endif /* MBEDTLS_SSL_PROTO_SSL3   */
+
+#define MBEDTLS_SSL_MIN_VALID_MINOR_VERSION MBEDTLS_SSL_MINOR_VERSION_1
+#define MBEDTLS_SSL_MIN_VALID_MAJOR_VERSION MBEDTLS_SSL_MAJOR_VERSION_3
+
+/* Determine maximum supported version */
+#define MBEDTLS_SSL_MAX_MAJOR_VERSION           MBEDTLS_SSL_MAJOR_VERSION_3
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+#define MBEDTLS_SSL_MAX_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_3
+#else
+#if defined(MBEDTLS_SSL_PROTO_TLS1_1)
+#define MBEDTLS_SSL_MAX_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_2
+#else
+#if defined(MBEDTLS_SSL_PROTO_TLS1)
+#define MBEDTLS_SSL_MAX_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_1
+#else
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+#define MBEDTLS_SSL_MAX_MINOR_VERSION           MBEDTLS_SSL_MINOR_VERSION_0
+#endif /* MBEDTLS_SSL_PROTO_SSL3   */
+#endif /* MBEDTLS_SSL_PROTO_TLS1   */
+#endif /* MBEDTLS_SSL_PROTO_TLS1_1 */
+#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
+
+/* Shorthand for restartable ECC */
+#if defined(MBEDTLS_ECP_RESTARTABLE) && \
+    defined(MBEDTLS_SSL_CLI_C) && \
+    defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
+    defined(MBEDTLS_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
+#define MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED
+#endif
+
+#define MBEDTLS_SSL_INITIAL_HANDSHAKE           0
+#define MBEDTLS_SSL_RENEGOTIATION_IN_PROGRESS   1   /* In progress */
+#define MBEDTLS_SSL_RENEGOTIATION_DONE          2   /* Done or aborted */
+#define MBEDTLS_SSL_RENEGOTIATION_PENDING       3   /* Requested (server only) */
+
+/*
+ * DTLS retransmission states, see RFC 6347 4.2.4
+ *
+ * The SENDING state is merged in PREPARING for initial sends,
+ * but is distinct for resends.
+ *
+ * Note: initial state is wrong for server, but is not used anyway.
+ */
+#define MBEDTLS_SSL_RETRANS_PREPARING       0
+#define MBEDTLS_SSL_RETRANS_SENDING         1
+#define MBEDTLS_SSL_RETRANS_WAITING         2
+#define MBEDTLS_SSL_RETRANS_FINISHED        3
+
+/*
+ * Allow extra bytes for record, authentication and encryption overhead:
+ * counter (8) + header (5) + IV(16) + MAC (16-48) + padding (0-256)
+ * and allow for a maximum of 1024 of compression expansion if
+ * enabled.
+ */
+#if defined(MBEDTLS_ZLIB_SUPPORT)
+#define MBEDTLS_SSL_COMPRESSION_ADD          1024
+#else
+#define MBEDTLS_SSL_COMPRESSION_ADD             0
+#endif
+
+/* This macro determines whether CBC is supported. */
+#if defined(MBEDTLS_CIPHER_MODE_CBC) &&                               \
+    ( defined(MBEDTLS_AES_C)      ||                                  \
+      defined(MBEDTLS_CAMELLIA_C) ||                                  \
+      defined(MBEDTLS_ARIA_C)     ||                                  \
+      defined(MBEDTLS_DES_C) )
+#define MBEDTLS_SSL_SOME_SUITES_USE_CBC
+#endif
+
+/* This macro determines whether the CBC construct used in TLS 1.0-1.2 (as
+ * opposed to the very different CBC construct used in SSLv3) is supported. */
+#if defined(MBEDTLS_SSL_SOME_SUITES_USE_CBC) && \
+    ( defined(MBEDTLS_SSL_PROTO_TLS1) ||        \
+      defined(MBEDTLS_SSL_PROTO_TLS1_1) ||      \
+      defined(MBEDTLS_SSL_PROTO_TLS1_2) )
+#define MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC
+#endif
+
+#if defined(MBEDTLS_ARC4_C) || defined(MBEDTLS_CIPHER_NULL_CIPHER) ||   \
+    defined(MBEDTLS_SSL_SOME_SUITES_USE_CBC)
+#define MBEDTLS_SSL_SOME_MODES_USE_MAC
+#endif
+
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
+/* Ciphersuites using HMAC */
+#if defined(MBEDTLS_SHA512_C)
+#define MBEDTLS_SSL_MAC_ADD                 48  /* SHA-384 used for HMAC */
+#elif defined(MBEDTLS_SHA256_C)
+#define MBEDTLS_SSL_MAC_ADD                 32  /* SHA-256 used for HMAC */
+#else
+#define MBEDTLS_SSL_MAC_ADD                 20  /* SHA-1   used for HMAC */
+#endif
+#else /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
+/* AEAD ciphersuites: GCM and CCM use a 128 bits tag */
+#define MBEDTLS_SSL_MAC_ADD                 16
+#endif
+
+#if defined(MBEDTLS_CIPHER_MODE_CBC)
+#define MBEDTLS_SSL_PADDING_ADD            256
+#else
+#define MBEDTLS_SSL_PADDING_ADD              0
+#endif
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+#define MBEDTLS_SSL_MAX_CID_EXPANSION      MBEDTLS_SSL_CID_PADDING_GRANULARITY
+#else
+#define MBEDTLS_SSL_MAX_CID_EXPANSION        0
+#endif
+
+#define MBEDTLS_SSL_PAYLOAD_OVERHEAD ( MBEDTLS_SSL_COMPRESSION_ADD +    \
+                                       MBEDTLS_MAX_IV_LENGTH +          \
+                                       MBEDTLS_SSL_MAC_ADD +            \
+                                       MBEDTLS_SSL_PADDING_ADD +        \
+                                       MBEDTLS_SSL_MAX_CID_EXPANSION    \
+                                       )
+
+#define MBEDTLS_SSL_IN_PAYLOAD_LEN ( MBEDTLS_SSL_PAYLOAD_OVERHEAD + \
+                                     ( MBEDTLS_SSL_IN_CONTENT_LEN ) )
+
+#define MBEDTLS_SSL_OUT_PAYLOAD_LEN ( MBEDTLS_SSL_PAYLOAD_OVERHEAD + \
+                                      ( MBEDTLS_SSL_OUT_CONTENT_LEN ) )
+
+/* The maximum number of buffered handshake messages. */
+#define MBEDTLS_SSL_MAX_BUFFERED_HS 4
+
+/* Maximum length we can advertise as our max content length for
+   RFC 6066 max_fragment_length extension negotiation purposes
+   (the lesser of both sizes, if they are unequal.)
+ */
+#define MBEDTLS_TLS_EXT_ADV_CONTENT_LEN (                            \
+        (MBEDTLS_SSL_IN_CONTENT_LEN > MBEDTLS_SSL_OUT_CONTENT_LEN)   \
+        ? ( MBEDTLS_SSL_OUT_CONTENT_LEN )                            \
+        : ( MBEDTLS_SSL_IN_CONTENT_LEN )                             \
+        )
+
+/* Maximum size in bytes of list in sig-hash algorithm ext., RFC 5246 */
+#define MBEDTLS_SSL_MAX_SIG_HASH_ALG_LIST_LEN  65534
+
+/* Maximum size in bytes of list in supported elliptic curve ext., RFC 4492 */
+#define MBEDTLS_SSL_MAX_CURVE_LIST_LEN         65535
+
+/*
+ * Check that we obey the standard's message size bounds
+ */
+
+#if MBEDTLS_SSL_MAX_CONTENT_LEN > 16384
+#error "Bad configuration - record content too large."
+#endif
+
+#if MBEDTLS_SSL_IN_CONTENT_LEN > MBEDTLS_SSL_MAX_CONTENT_LEN
+#error "Bad configuration - incoming record content should not be larger than MBEDTLS_SSL_MAX_CONTENT_LEN."
+#endif
+
+#if MBEDTLS_SSL_OUT_CONTENT_LEN > MBEDTLS_SSL_MAX_CONTENT_LEN
+#error "Bad configuration - outgoing record content should not be larger than MBEDTLS_SSL_MAX_CONTENT_LEN."
+#endif
+
+#if MBEDTLS_SSL_IN_PAYLOAD_LEN > MBEDTLS_SSL_MAX_CONTENT_LEN + 2048
+#error "Bad configuration - incoming protected record payload too large."
+#endif
+
+#if MBEDTLS_SSL_OUT_PAYLOAD_LEN > MBEDTLS_SSL_MAX_CONTENT_LEN + 2048
+#error "Bad configuration - outgoing protected record payload too large."
+#endif
+
+/* Calculate buffer sizes */
+
+/* Note: Even though the TLS record header is only 5 bytes
+   long, we're internally using 8 bytes to store the
+   implicit sequence number. */
+#define MBEDTLS_SSL_HEADER_LEN 13
+
+#if !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+#define MBEDTLS_SSL_IN_BUFFER_LEN  \
+    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_IN_PAYLOAD_LEN ) )
+#else
+#define MBEDTLS_SSL_IN_BUFFER_LEN  \
+    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_IN_PAYLOAD_LEN ) \
+      + ( MBEDTLS_SSL_CID_IN_LEN_MAX ) )
+#endif
+
+#if !defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+#define MBEDTLS_SSL_OUT_BUFFER_LEN  \
+    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_OUT_PAYLOAD_LEN ) )
+#else
+#define MBEDTLS_SSL_OUT_BUFFER_LEN                               \
+    ( ( MBEDTLS_SSL_HEADER_LEN ) + ( MBEDTLS_SSL_OUT_PAYLOAD_LEN )    \
+      + ( MBEDTLS_SSL_CID_OUT_LEN_MAX ) )
+#endif
+
+#if defined(MBEDTLS_SSL_VARIABLE_BUFFER_LENGTH)
+static inline size_t mbedtls_ssl_get_output_buflen( const mbedtls_ssl_context *ctx )
+{
+#if defined (MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    return mbedtls_ssl_get_output_max_frag_len( ctx )
+               + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD
+               + MBEDTLS_SSL_CID_OUT_LEN_MAX;
+#else
+    return mbedtls_ssl_get_output_max_frag_len( ctx )
+               + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD;
+#endif
+}
+
+static inline size_t mbedtls_ssl_get_input_buflen( const mbedtls_ssl_context *ctx )
+{
+#if defined (MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    return mbedtls_ssl_get_input_max_frag_len( ctx )
+               + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD
+               + MBEDTLS_SSL_CID_IN_LEN_MAX;
+#else
+    return mbedtls_ssl_get_input_max_frag_len( ctx )
+               + MBEDTLS_SSL_HEADER_LEN + MBEDTLS_SSL_PAYLOAD_OVERHEAD;
+#endif
+}
+#endif
+
+#ifdef MBEDTLS_ZLIB_SUPPORT
+/* Compression buffer holds both IN and OUT buffers, so should be size of the larger */
+#define MBEDTLS_SSL_COMPRESS_BUFFER_LEN (                               \
+        ( MBEDTLS_SSL_IN_BUFFER_LEN > MBEDTLS_SSL_OUT_BUFFER_LEN )      \
+        ? MBEDTLS_SSL_IN_BUFFER_LEN                                     \
+        : MBEDTLS_SSL_OUT_BUFFER_LEN                                    \
+        )
+#endif
+
+/*
+ * TLS extension flags (for extensions with outgoing ServerHello content
+ * that need it (e.g. for RENEGOTIATION_INFO the server already knows because
+ * of state of the renegotiation flag, so no indicator is required)
+ */
+#define MBEDTLS_TLS_EXT_SUPPORTED_POINT_FORMATS_PRESENT (1 << 0)
+#define MBEDTLS_TLS_EXT_ECJPAKE_KKPP_OK                 (1 << 1)
+
+/**
+ * \brief        This function checks if the remaining size in a buffer is
+ *               greater or equal than a needed space.
+ *
+ * \param cur    Pointer to the current position in the buffer.
+ * \param end    Pointer to one past the end of the buffer.
+ * \param need   Needed space in bytes.
+ *
+ * \return       Zero if the needed space is available in the buffer, non-zero
+ *               otherwise.
+ */
+static inline int mbedtls_ssl_chk_buf_ptr( const uint8_t *cur,
+                                           const uint8_t *end, size_t need )
+{
+    return( ( cur > end ) || ( need > (size_t)( end - cur ) ) );
+}
+
+/**
+ * \brief        This macro checks if the remaining size in a buffer is
+ *               greater or equal than a needed space. If it is not the case,
+ *               it returns an SSL_BUFFER_TOO_SMALL error.
+ *
+ * \param cur    Pointer to the current position in the buffer.
+ * \param end    Pointer to one past the end of the buffer.
+ * \param need   Needed space in bytes.
+ *
+ */
+#define MBEDTLS_SSL_CHK_BUF_PTR( cur, end, need )                        \
+    do {                                                                 \
+        if( mbedtls_ssl_chk_buf_ptr( ( cur ), ( end ), ( need ) ) != 0 ) \
+        {                                                                \
+            return( MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL );                  \
+        }                                                                \
+    } while( 0 )
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
+    defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+/*
+ * Abstraction for a grid of allowed signature-hash-algorithm pairs.
+ */
+struct mbedtls_ssl_sig_hash_set_t
+{
+    /* At the moment, we only need to remember a single suitable
+     * hash algorithm per signature algorithm. As long as that's
+     * the case - and we don't need a general lookup function -
+     * we can implement the sig-hash-set as a map from signatures
+     * to hash algorithms. */
+    mbedtls_md_type_t rsa;
+    mbedtls_md_type_t ecdsa;
+};
+#endif /* MBEDTLS_SSL_PROTO_TLS1_2 &&
+          MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
+
+typedef int  mbedtls_ssl_tls_prf_cb( const unsigned char *secret, size_t slen,
+                                     const char *label,
+                                     const unsigned char *random, size_t rlen,
+                                     unsigned char *dstbuf, size_t dlen );
+
+/* cipher.h exports the maximum IV, key and block length from
+ * all ciphers enabled in the config, regardless of whether those
+ * ciphers are actually usable in SSL/TLS. Notably, XTS is enabled
+ * in the default configuration and uses 64 Byte keys, but it is
+ * not used for record protection in SSL/TLS.
+ *
+ * In order to prevent unnecessary inflation of key structures,
+ * we introduce SSL-specific variants of the max-{key,block,IV}
+ * macros here which are meant to only take those ciphers into
+ * account which can be negotiated in SSL/TLS.
+ *
+ * Since the current definitions of MBEDTLS_MAX_{KEY|BLOCK|IV}_LENGTH
+ * in cipher.h are rough overapproximations of the real maxima, here
+ * we content ourselves with replicating those overapproximations
+ * for the maximum block and IV length, and excluding XTS from the
+ * computation of the maximum key length. */
+#define MBEDTLS_SSL_MAX_BLOCK_LENGTH 16
+#define MBEDTLS_SSL_MAX_IV_LENGTH    16
+#define MBEDTLS_SSL_MAX_KEY_LENGTH   32
+
+/**
+ * \brief   The data structure holding the cryptographic material (key and IV)
+ *          used for record protection in TLS 1.3.
+ */
+struct mbedtls_ssl_key_set
+{
+    /*! The key for client->server records. */
+    unsigned char client_write_key[ MBEDTLS_SSL_MAX_KEY_LENGTH ];
+    /*! The key for server->client records. */
+    unsigned char server_write_key[ MBEDTLS_SSL_MAX_KEY_LENGTH ];
+    /*! The IV  for client->server records. */
+    unsigned char client_write_iv[ MBEDTLS_SSL_MAX_IV_LENGTH ];
+    /*! The IV  for server->client records. */
+    unsigned char server_write_iv[ MBEDTLS_SSL_MAX_IV_LENGTH ];
+
+    size_t key_len; /*!< The length of client_write_key and
+                     *   server_write_key, in Bytes. */
+    size_t iv_len;  /*!< The length of client_write_iv and
+                     *   server_write_iv, in Bytes. */
+};
+typedef struct mbedtls_ssl_key_set mbedtls_ssl_key_set;
+
+/*
+ * This structure contains the parameters only needed during handshake.
+ */
+struct mbedtls_ssl_handshake_params
+{
+    /*
+     * Handshake specific crypto variables
+     */
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
+    defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+    mbedtls_ssl_sig_hash_set_t hash_algs;             /*!<  Set of suitable sig-hash pairs */
+#endif
+#if defined(MBEDTLS_DHM_C)
+    mbedtls_dhm_context dhm_ctx;                /*!<  DHM key exchange        */
+#endif
+/* Adding guard for MBEDTLS_ECDSA_C to ensure no compile errors due
+ * to guards also being in ssl_srv.c and ssl_cli.c. There is a gap
+ * in functionality that access to ecdh_ctx structure is needed for
+ * MBEDTLS_ECDSA_C which does not seem correct.
+ */
+#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C)
+    mbedtls_ecdh_context ecdh_ctx;              /*!<  ECDH key exchange       */
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    psa_key_type_t ecdh_psa_type;
+    uint16_t ecdh_bits;
+    psa_key_id_t ecdh_psa_privkey;
+    unsigned char ecdh_psa_peerkey[MBEDTLS_PSA_MAX_EC_PUBKEY_LENGTH];
+    size_t ecdh_psa_peerkey_len;
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+#endif /* MBEDTLS_ECDH_C || MBEDTLS_ECDSA_C */
+
+#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+    mbedtls_ecjpake_context ecjpake_ctx;        /*!< EC J-PAKE key exchange */
+#if defined(MBEDTLS_SSL_CLI_C)
+    unsigned char *ecjpake_cache;               /*!< Cache for ClientHello ext */
+    size_t ecjpake_cache_len;                   /*!< Length of cached data */
+#endif
+#endif /* MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED */
+#if defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
+    defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
+    const mbedtls_ecp_curve_info **curves;      /*!<  Supported elliptic curves */
+#endif
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    psa_key_id_t psk_opaque;            /*!< Opaque PSK from the callback   */
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+    unsigned char *psk;                 /*!<  PSK from the callback         */
+    size_t psk_len;                     /*!<  Length of PSK from callback   */
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
+#if defined(MBEDTLS_X509_CRT_PARSE_C)
+    mbedtls_ssl_key_cert *key_cert;     /*!< chosen key/cert pair (server)  */
+#if defined(MBEDTLS_SSL_SERVER_NAME_INDICATION)
+    int sni_authmode;                   /*!< authmode from SNI callback     */
+    mbedtls_ssl_key_cert *sni_key_cert; /*!< key/cert list from SNI         */
+    mbedtls_x509_crt *sni_ca_chain;     /*!< trusted CAs from SNI callback  */
+    mbedtls_x509_crl *sni_ca_crl;       /*!< trusted CAs CRLs from SNI      */
+#endif /* MBEDTLS_SSL_SERVER_NAME_INDICATION */
+#endif /* MBEDTLS_X509_CRT_PARSE_C */
+#if defined(MBEDTLS_SSL_ECP_RESTARTABLE_ENABLED)
+    int ecrs_enabled;                   /*!< Handshake supports EC restart? */
+    mbedtls_x509_crt_restart_ctx ecrs_ctx;  /*!< restart context            */
+    enum { /* this complements ssl->state with info on intra-state operations */
+        ssl_ecrs_none = 0,              /*!< nothing going on (yet)         */
+        ssl_ecrs_crt_verify,            /*!< Certificate: crt_verify()      */
+        ssl_ecrs_ske_start_processing,  /*!< ServerKeyExchange: pk_verify() */
+        ssl_ecrs_cke_ecdh_calc_secret,  /*!< ClientKeyExchange: ECDH step 2 */
+        ssl_ecrs_crt_vrfy_sign,         /*!< CertificateVerify: pk_sign()   */
+    } ecrs_state;                       /*!< current (or last) operation    */
+    mbedtls_x509_crt *ecrs_peer_cert;   /*!< The peer's CRT chain.          */
+    size_t ecrs_n;                      /*!< place for saving a length      */
+#endif
+#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
+    !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
+    mbedtls_pk_context peer_pubkey;     /*!< The public key from the peer.  */
+#endif /* MBEDTLS_X509_CRT_PARSE_C && !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    unsigned int out_msg_seq;           /*!<  Outgoing handshake sequence number */
+    unsigned int in_msg_seq;            /*!<  Incoming handshake sequence number */
+
+    unsigned char *verify_cookie;       /*!<  Cli: HelloVerifyRequest cookie
+                                              Srv: unused                    */
+    unsigned char verify_cookie_len;    /*!<  Cli: cookie length
+                                              Srv: flag for sending a cookie */
+
+    uint32_t retransmit_timeout;        /*!<  Current value of timeout       */
+    unsigned char retransmit_state;     /*!<  Retransmission state           */
+    mbedtls_ssl_flight_item *flight;    /*!<  Current outgoing flight        */
+    mbedtls_ssl_flight_item *cur_msg;   /*!<  Current message in flight      */
+    unsigned char *cur_msg_p;           /*!<  Position in current message    */
+    unsigned int in_flight_start_seq;   /*!<  Minimum message sequence in the
+                                              flight being received          */
+    mbedtls_ssl_transform *alt_transform_out;   /*!<  Alternative transform for
+                                              resending messages             */
+    unsigned char alt_out_ctr[8];       /*!<  Alternative record epoch/counter
+                                              for resending messages         */
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    /* The state of CID configuration in this handshake. */
+
+    uint8_t cid_in_use; /*!< This indicates whether the use of the CID extension
+                         *   has been negotiated. Possible values are
+                         *   #MBEDTLS_SSL_CID_ENABLED and
+                         *   #MBEDTLS_SSL_CID_DISABLED. */
+    unsigned char peer_cid[ MBEDTLS_SSL_CID_OUT_LEN_MAX ]; /*! The peer's CID */
+    uint8_t peer_cid_len;                                  /*!< The length of
+                                                            *   \c peer_cid.  */
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+    struct
+    {
+        size_t total_bytes_buffered; /*!< Cumulative size of heap allocated
+                                      *   buffers used for message buffering. */
+
+        uint8_t seen_ccs;               /*!< Indicates if a CCS message has
+                                         *   been seen in the current flight. */
+
+        struct mbedtls_ssl_hs_buffer
+        {
+            unsigned is_valid      : 1;
+            unsigned is_fragmented : 1;
+            unsigned is_complete   : 1;
+            unsigned char *data;
+            size_t data_len;
+        } hs[MBEDTLS_SSL_MAX_BUFFERED_HS];
+
+        struct
+        {
+            unsigned char *data;
+            size_t len;
+            unsigned epoch;
+        } future_record;
+
+    } buffering;
+
+    uint16_t mtu;                       /*!<  Handshake mtu, used to fragment outgoing messages */
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+    /*
+     * Checksum contexts
+     */
+#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
+    defined(MBEDTLS_SSL_PROTO_TLS1_1)
+       mbedtls_md5_context fin_md5;
+      mbedtls_sha1_context fin_sha1;
+#endif
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+#if defined(MBEDTLS_SHA256_C)
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    psa_hash_operation_t fin_sha256_psa;
+#else
+    mbedtls_sha256_context fin_sha256;
+#endif
+#endif
+#if defined(MBEDTLS_SHA512_C)
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+    psa_hash_operation_t fin_sha384_psa;
+#else
+    mbedtls_sha512_context fin_sha512;
+#endif
+#endif
+#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
+
+    void (*update_checksum)(mbedtls_ssl_context *, const unsigned char *, size_t);
+    void (*calc_verify)(const mbedtls_ssl_context *, unsigned char *, size_t *);
+    void (*calc_finished)(mbedtls_ssl_context *, unsigned char *, int);
+    mbedtls_ssl_tls_prf_cb *tls_prf;
+
+    mbedtls_ssl_ciphersuite_t const *ciphersuite_info;
+
+    size_t pmslen;                      /*!<  premaster length        */
+
+    unsigned char randbytes[64];        /*!<  random bytes            */
+    unsigned char premaster[MBEDTLS_PREMASTER_SIZE];
+                                        /*!<  premaster secret        */
+
+    int resume;                         /*!<  session resume indicator*/
+    int max_major_ver;                  /*!< max. major version client*/
+    int max_minor_ver;                  /*!< max. minor version client*/
+    int cli_exts;                       /*!< client extension presence*/
+
+#if defined(MBEDTLS_SSL_SESSION_TICKETS)
+    int new_session_ticket;             /*!< use NewSessionTicket?    */
+#endif /* MBEDTLS_SSL_SESSION_TICKETS */
+#if defined(MBEDTLS_SSL_EXTENDED_MASTER_SECRET)
+    int extended_ms;                    /*!< use Extended Master Secret? */
+#endif
+
+#if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
+    unsigned int async_in_progress : 1; /*!< an asynchronous operation is in progress */
+#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
+
+#if defined(MBEDTLS_SSL_ASYNC_PRIVATE)
+    /** Asynchronous operation context. This field is meant for use by the
+     * asynchronous operation callbacks (mbedtls_ssl_config::f_async_sign_start,
+     * mbedtls_ssl_config::f_async_decrypt_start,
+     * mbedtls_ssl_config::f_async_resume, mbedtls_ssl_config::f_async_cancel).
+     * The library does not use it internally. */
+    void *user_async_ctx;
+#endif /* MBEDTLS_SSL_ASYNC_PRIVATE */
+};
+
+typedef struct mbedtls_ssl_hs_buffer mbedtls_ssl_hs_buffer;
+
+/*
+ * Representation of decryption/encryption transformations on records
+ *
+ * There are the following general types of record transformations:
+ * - Stream transformations (TLS versions <= 1.2 only)
+ *   Transformation adding a MAC and applying a stream-cipher
+ *   to the authenticated message.
+ * - CBC block cipher transformations ([D]TLS versions <= 1.2 only)
+ *   In addition to the distinction of the order of encryption and
+ *   authentication, there's a fundamental difference between the
+ *   handling in SSL3 & TLS 1.0 and TLS 1.1 and TLS 1.2: For SSL3
+ *   and TLS 1.0, the final IV after processing a record is used
+ *   as the IV for the next record. No explicit IV is contained
+ *   in an encrypted record. The IV for the first record is extracted
+ *   at key extraction time. In contrast, for TLS 1.1 and 1.2, no
+ *   IV is generated at key extraction time, but every encrypted
+ *   record is explicitly prefixed by the IV with which it was encrypted.
+ * - AEAD transformations ([D]TLS versions >= 1.2 only)
+ *   These come in two fundamentally different versions, the first one
+ *   used in TLS 1.2, excluding ChaChaPoly ciphersuites, and the second
+ *   one used for ChaChaPoly ciphersuites in TLS 1.2 as well as for TLS 1.3.
+ *   In the first transformation, the IV to be used for a record is obtained
+ *   as the concatenation of an explicit, static 4-byte IV and the 8-byte
+ *   record sequence number, and explicitly prepending this sequence number
+ *   to the encrypted record. In contrast, in the second transformation
+ *   the IV is obtained by XOR'ing a static IV obtained at key extraction
+ *   time with the 8-byte record sequence number, without prepending the
+ *   latter to the encrypted record.
+ *
+ * Additionally, DTLS 1.2 + CID as well as TLS 1.3 use an inner plaintext
+ * which allows to add flexible length padding and to hide a record's true
+ * content type.
+ *
+ * In addition to type and version, the following parameters are relevant:
+ * - The symmetric cipher algorithm to be used.
+ * - The (static) encryption/decryption keys for the cipher.
+ * - For stream/CBC, the type of message digest to be used.
+ * - For stream/CBC, (static) encryption/decryption keys for the digest.
+ * - For AEAD transformations, the size (potentially 0) of an explicit,
+ *   random initialization vector placed in encrypted records.
+ * - For some transformations (currently AEAD and CBC in SSL3 and TLS 1.0)
+ *   an implicit IV. It may be static (e.g. AEAD) or dynamic (e.g. CBC)
+ *   and (if present) is combined with the explicit IV in a transformation-
+ *   dependent way (e.g. appending in TLS 1.2 and XOR'ing in TLS 1.3).
+ * - For stream/CBC, a flag determining the order of encryption and MAC.
+ * - The details of the transformation depend on the SSL/TLS version.
+ * - The length of the authentication tag.
+ *
+ * Note: Except for CBC in SSL3 and TLS 1.0, these parameters are
+ *       constant across multiple encryption/decryption operations.
+ *       For CBC, the implicit IV needs to be updated after each
+ *       operation.
+ *
+ * The struct below refines this abstract view as follows:
+ * - The cipher underlying the transformation is managed in
+ *   cipher contexts cipher_ctx_{enc/dec}, which must have the
+ *   same cipher type. The mode of these cipher contexts determines
+ *   the type of the transformation in the sense above: e.g., if
+ *   the type is MBEDTLS_CIPHER_AES_256_CBC resp. MBEDTLS_CIPHER_AES_192_GCM
+ *   then the transformation has type CBC resp. AEAD.
+ * - The cipher keys are never stored explicitly but
+ *   are maintained within cipher_ctx_{enc/dec}.
+ * - For stream/CBC transformations, the message digest contexts
+ *   used for the MAC's are stored in md_ctx_{enc/dec}. These contexts
+ *   are unused for AEAD transformations.
+ * - For stream/CBC transformations and versions > SSL3, the
+ *   MAC keys are not stored explicitly but maintained within
+ *   md_ctx_{enc/dec}.
+ * - For stream/CBC transformations and version SSL3, the MAC
+ *   keys are stored explicitly in mac_enc, mac_dec and have
+ *   a fixed size of 20 bytes. These fields are unused for
+ *   AEAD transformations or transformations >= TLS 1.0.
+ * - For transformations using an implicit IV maintained within
+ *   the transformation context, its contents are stored within
+ *   iv_{enc/dec}.
+ * - The value of ivlen indicates the length of the IV.
+ *   This is redundant in case of stream/CBC transformations
+ *   which always use 0 resp. the cipher's block length as the
+ *   IV length, but is needed for AEAD ciphers and may be
+ *   different from the underlying cipher's block length
+ *   in this case.
+ * - The field fixed_ivlen is nonzero for AEAD transformations only
+ *   and indicates the length of the static part of the IV which is
+ *   constant throughout the communication, and which is stored in
+ *   the first fixed_ivlen bytes of the iv_{enc/dec} arrays.
+ *   Note: For CBC in SSL3 and TLS 1.0, the fields iv_{enc/dec}
+ *   still store IV's for continued use across multiple transformations,
+ *   so it is not true that fixed_ivlen == 0 means that iv_{enc/dec} are
+ *   not being used!
+ * - minor_ver denotes the SSL/TLS version
+ * - For stream/CBC transformations, maclen denotes the length of the
+ *   authentication tag, while taglen is unused and 0.
+ * - For AEAD transformations, taglen denotes the length of the
+ *   authentication tag, while maclen is unused and 0.
+ * - For CBC transformations, encrypt_then_mac determines the
+ *   order of encryption and authentication. This field is unused
+ *   in other transformations.
+ *
+ */
+struct mbedtls_ssl_transform
+{
+    /*
+     * Session specific crypto layer
+     */
+    size_t minlen;                      /*!<  min. ciphertext length  */
+    size_t ivlen;                       /*!<  IV length               */
+    size_t fixed_ivlen;                 /*!<  Fixed part of IV (AEAD) */
+    size_t maclen;                      /*!<  MAC(CBC) len            */
+    size_t taglen;                      /*!<  TAG(AEAD) len           */
+
+    unsigned char iv_enc[16];           /*!<  IV (encryption)         */
+    unsigned char iv_dec[16];           /*!<  IV (decryption)         */
+
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3)
+    /* Needed only for SSL v3.0 secret */
+    unsigned char mac_enc[20];          /*!<  SSL v3.0 secret (enc)   */
+    unsigned char mac_dec[20];          /*!<  SSL v3.0 secret (dec)   */
+#endif /* MBEDTLS_SSL_PROTO_SSL3 */
+
+    mbedtls_md_context_t md_ctx_enc;            /*!<  MAC (encryption)        */
+    mbedtls_md_context_t md_ctx_dec;            /*!<  MAC (decryption)        */
+
+#if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
+    int encrypt_then_mac;       /*!< flag for EtM activation                */
+#endif
+
+#endif /* MBEDTLS_SSL_SOME_MODES_USE_MAC */
+
+    mbedtls_cipher_context_t cipher_ctx_enc;    /*!<  encryption context      */
+    mbedtls_cipher_context_t cipher_ctx_dec;    /*!<  decryption context      */
+    int minor_ver;
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    uint8_t in_cid_len;
+    uint8_t out_cid_len;
+    unsigned char in_cid [ MBEDTLS_SSL_CID_OUT_LEN_MAX ];
+    unsigned char out_cid[ MBEDTLS_SSL_CID_OUT_LEN_MAX ];
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+    /*
+     * Session specific compression layer
+     */
+#if defined(MBEDTLS_ZLIB_SUPPORT)
+    z_stream ctx_deflate;               /*!<  compression context     */
+    z_stream ctx_inflate;               /*!<  decompression context   */
+#endif
+
+#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)
+    /* We need the Hello random bytes in order to re-derive keys from the
+     * Master Secret and other session info, see ssl_populate_transform() */
+    unsigned char randbytes[64]; /*!< ServerHello.random+ClientHello.random */
+#endif /* MBEDTLS_SSL_CONTEXT_SERIALIZATION */
+};
+
+/*
+ * Return 1 if the transform uses an AEAD cipher, 0 otherwise.
+ * Equivalently, return 0 if a separate MAC is used, 1 otherwise.
+ */
+static inline int mbedtls_ssl_transform_uses_aead(
+        const mbedtls_ssl_transform *transform )
+{
+#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC)
+    return( transform->maclen == 0 && transform->taglen != 0 );
+#else
+    (void) transform;
+    return( 1 );
+#endif
+}
+
+/*
+ * Internal representation of record frames
+ *
+ * Instances come in two flavors:
+ * (1) Encrypted
+ *     These always have data_offset = 0
+ * (2) Unencrypted
+ *     These have data_offset set to the amount of
+ *     pre-expansion during record protection. Concretely,
+ *     this is the length of the fixed part of the explicit IV
+ *     used for encryption, or 0 if no explicit IV is used
+ *     (e.g. for CBC in TLS 1.0, or stream ciphers).
+ *
+ * The reason for the data_offset in the unencrypted case
+ * is to allow for in-place conversion of an unencrypted to
+ * an encrypted record. If the offset wasn't included, the
+ * encrypted content would need to be shifted afterwards to
+ * make space for the fixed IV.
+ *
+ */
+#if MBEDTLS_SSL_CID_OUT_LEN_MAX > MBEDTLS_SSL_CID_IN_LEN_MAX
+#define MBEDTLS_SSL_CID_LEN_MAX MBEDTLS_SSL_CID_OUT_LEN_MAX
+#else
+#define MBEDTLS_SSL_CID_LEN_MAX MBEDTLS_SSL_CID_IN_LEN_MAX
+#endif
+
+typedef struct
+{
+    uint8_t ctr[8];         /* In TLS:  The implicit record sequence number.
+                             * In DTLS: The 2-byte epoch followed by
+                             *          the 6-byte sequence number.
+                             * This is stored as a raw big endian byte array
+                             * as opposed to a uint64_t because we rarely
+                             * need to perform arithmetic on this, but do
+                             * need it as a Byte array for the purpose of
+                             * MAC computations.                             */
+    uint8_t type;           /* The record content type.                      */
+    uint8_t ver[2];         /* SSL/TLS version as present on the wire.
+                             * Convert to internal presentation of versions
+                             * using mbedtls_ssl_read_version() and
+                             * mbedtls_ssl_write_version().
+                             * Keep wire-format for MAC computations.        */
+
+    unsigned char *buf;     /* Memory buffer enclosing the record content    */
+    size_t buf_len;         /* Buffer length                                 */
+    size_t data_offset;     /* Offset of record content                      */
+    size_t data_len;        /* Length of record content                      */
+
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+    uint8_t cid_len;        /* Length of the CID (0 if not present)          */
+    unsigned char cid[ MBEDTLS_SSL_CID_LEN_MAX ]; /* The CID                 */
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+} mbedtls_record;
+
+#if defined(MBEDTLS_X509_CRT_PARSE_C)
+/*
+ * List of certificate + private key pairs
+ */
+struct mbedtls_ssl_key_cert
+{
+    mbedtls_x509_crt *cert;                 /*!< cert                       */
+    mbedtls_pk_context *key;                /*!< private key                */
+    mbedtls_ssl_key_cert *next;             /*!< next key/cert pair         */
+};
+#endif /* MBEDTLS_X509_CRT_PARSE_C */
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+/*
+ * List of handshake messages kept around for resending
+ */
+struct mbedtls_ssl_flight_item
+{
+    unsigned char *p;       /*!< message, including handshake headers   */
+    size_t len;             /*!< length of p                            */
+    unsigned char type;     /*!< type of the message: handshake or CCS  */
+    mbedtls_ssl_flight_item *next;  /*!< next handshake message(s)              */
+};
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
+    defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+
+/* Find an entry in a signature-hash set matching a given hash algorithm. */
+mbedtls_md_type_t mbedtls_ssl_sig_hash_set_find( mbedtls_ssl_sig_hash_set_t *set,
+                                                 mbedtls_pk_type_t sig_alg );
+/* Add a signature-hash-pair to a signature-hash set */
+void mbedtls_ssl_sig_hash_set_add( mbedtls_ssl_sig_hash_set_t *set,
+                                   mbedtls_pk_type_t sig_alg,
+                                   mbedtls_md_type_t md_alg );
+/* Allow exactly one hash algorithm for each signature. */
+void mbedtls_ssl_sig_hash_set_const_hash( mbedtls_ssl_sig_hash_set_t *set,
+                                          mbedtls_md_type_t md_alg );
+
+/* Setup an empty signature-hash set */
+static inline void mbedtls_ssl_sig_hash_set_init( mbedtls_ssl_sig_hash_set_t *set )
+{
+    mbedtls_ssl_sig_hash_set_const_hash( set, MBEDTLS_MD_NONE );
+}
+
+#endif /* MBEDTLS_SSL_PROTO_TLS1_2) &&
+          MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED */
+
+/**
+ * \brief           Free referenced items in an SSL transform context and clear
+ *                  memory
+ *
+ * \param transform SSL transform context
+ */
+void mbedtls_ssl_transform_free( mbedtls_ssl_transform *transform );
+
+/**
+ * \brief           Free referenced items in an SSL handshake context and clear
+ *                  memory
+ *
+ * \param ssl       SSL context
+ */
+void mbedtls_ssl_handshake_free( mbedtls_ssl_context *ssl );
+
+int mbedtls_ssl_handshake_client_step( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_handshake_server_step( mbedtls_ssl_context *ssl );
+void mbedtls_ssl_handshake_wrapup( mbedtls_ssl_context *ssl );
+
+int mbedtls_ssl_send_fatal_handshake_failure( mbedtls_ssl_context *ssl );
+
+void mbedtls_ssl_reset_checksum( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_derive_keys( mbedtls_ssl_context *ssl );
+
+int mbedtls_ssl_handle_message_type( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_prepare_handshake_record( mbedtls_ssl_context *ssl );
+void mbedtls_ssl_update_handshake_status( mbedtls_ssl_context *ssl );
+
+/**
+ * \brief       Update record layer
+ *
+ *              This function roughly separates the implementation
+ *              of the logic of (D)TLS from the implementation
+ *              of the secure transport.
+ *
+ * \param  ssl              The SSL context to use.
+ * \param  update_hs_digest This indicates if the handshake digest
+ *                          should be automatically updated in case
+ *                          a handshake message is found.
+ *
+ * \return      0 or non-zero error code.
+ *
+ * \note        A clarification on what is called 'record layer' here
+ *              is in order, as many sensible definitions are possible:
+ *
+ *              The record layer takes as input an untrusted underlying
+ *              transport (stream or datagram) and transforms it into
+ *              a serially multiplexed, secure transport, which
+ *              conceptually provides the following:
+ *
+ *              (1) Three datagram based, content-agnostic transports
+ *                  for handshake, alert and CCS messages.
+ *              (2) One stream- or datagram-based transport
+ *                  for application data.
+ *              (3) Functionality for changing the underlying transform
+ *                  securing the contents.
+ *
+ *              The interface to this functionality is given as follows:
+ *
+ *              a Updating
+ *                [Currently implemented by mbedtls_ssl_read_record]
+ *
+ *                Check if and on which of the four 'ports' data is pending:
+ *                Nothing, a controlling datagram of type (1), or application
+ *                data (2). In any case data is present, internal buffers
+ *                provide access to the data for the user to process it.
+ *                Consumption of type (1) datagrams is done automatically
+ *                on the next update, invalidating that the internal buffers
+ *                for previous datagrams, while consumption of application
+ *                data (2) is user-controlled.
+ *
+ *              b Reading of application data
+ *                [Currently manual adaption of ssl->in_offt pointer]
+ *
+ *                As mentioned in the last paragraph, consumption of data
+ *                is different from the automatic consumption of control
+ *                datagrams (1) because application data is treated as a stream.
+ *
+ *              c Tracking availability of application data
+ *                [Currently manually through decreasing ssl->in_msglen]
+ *
+ *                For efficiency and to retain datagram semantics for
+ *                application data in case of DTLS, the record layer
+ *                provides functionality for checking how much application
+ *                data is still available in the internal buffer.
+ *
+ *              d Changing the transformation securing the communication.
+ *
+ *              Given an opaque implementation of the record layer in the
+ *              above sense, it should be possible to implement the logic
+ *              of (D)TLS on top of it without the need to know anything
+ *              about the record layer's internals. This is done e.g.
+ *              in all the handshake handling functions, and in the
+ *              application data reading function mbedtls_ssl_read.
+ *
+ * \note        The above tries to give a conceptual picture of the
+ *              record layer, but the current implementation deviates
+ *              from it in some places. For example, our implementation of
+ *              the update functionality through mbedtls_ssl_read_record
+ *              discards datagrams depending on the current state, which
+ *              wouldn't fall under the record layer's responsibility
+ *              following the above definition.
+ *
+ */
+int mbedtls_ssl_read_record( mbedtls_ssl_context *ssl,
+                             unsigned update_hs_digest );
+int mbedtls_ssl_fetch_input( mbedtls_ssl_context *ssl, size_t nb_want );
+
+int mbedtls_ssl_write_handshake_msg( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_write_record( mbedtls_ssl_context *ssl, uint8_t force_flush );
+int mbedtls_ssl_flush_output( mbedtls_ssl_context *ssl );
+
+int mbedtls_ssl_parse_certificate( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_write_certificate( mbedtls_ssl_context *ssl );
+
+int mbedtls_ssl_parse_change_cipher_spec( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_write_change_cipher_spec( mbedtls_ssl_context *ssl );
+
+int mbedtls_ssl_parse_finished( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_write_finished( mbedtls_ssl_context *ssl );
+
+void mbedtls_ssl_optimize_checksum( mbedtls_ssl_context *ssl,
+                            const mbedtls_ssl_ciphersuite_t *ciphersuite_info );
+
+#if defined(MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED)
+int mbedtls_ssl_psk_derive_premaster( mbedtls_ssl_context *ssl, mbedtls_key_exchange_type_t key_ex );
+
+/**
+ * Get the first defined PSK by order of precedence:
+ * 1. handshake PSK set by \c mbedtls_ssl_set_hs_psk() in the PSK callback
+ * 2. static PSK configured by \c mbedtls_ssl_conf_psk()
+ * Return a code and update the pair (PSK, PSK length) passed to this function
+ */
+static inline int mbedtls_ssl_get_psk( const mbedtls_ssl_context *ssl,
+    const unsigned char **psk, size_t *psk_len )
+{
+    if( ssl->handshake->psk != NULL && ssl->handshake->psk_len > 0 )
+    {
+        *psk = ssl->handshake->psk;
+        *psk_len = ssl->handshake->psk_len;
+    }
+
+    else if( ssl->conf->psk != NULL && ssl->conf->psk_len > 0 )
+    {
+        *psk = ssl->conf->psk;
+        *psk_len = ssl->conf->psk_len;
+    }
+
+    else
+    {
+        *psk = NULL;
+        *psk_len = 0;
+        return( MBEDTLS_ERR_SSL_PRIVATE_KEY_REQUIRED );
+    }
+
+    return( 0 );
+}
+
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+/**
+ * Get the first defined opaque PSK by order of precedence:
+ * 1. handshake PSK set by \c mbedtls_ssl_set_hs_psk_opaque() in the PSK
+ *    callback
+ * 2. static PSK configured by \c mbedtls_ssl_conf_psk_opaque()
+ * Return an opaque PSK
+ */
+static inline psa_key_id_t mbedtls_ssl_get_opaque_psk(
+    const mbedtls_ssl_context *ssl )
+{
+    if( ! mbedtls_svc_key_id_is_null( ssl->handshake->psk_opaque ) )
+        return( ssl->handshake->psk_opaque );
+
+    if( ! mbedtls_svc_key_id_is_null( ssl->conf->psk_opaque ) )
+        return( ssl->conf->psk_opaque );
+
+    return( MBEDTLS_SVC_KEY_ID_INIT );
+}
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
+
+#endif /* MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
+
+#if defined(MBEDTLS_PK_C)
+unsigned char mbedtls_ssl_sig_from_pk( mbedtls_pk_context *pk );
+unsigned char mbedtls_ssl_sig_from_pk_alg( mbedtls_pk_type_t type );
+mbedtls_pk_type_t mbedtls_ssl_pk_alg_from_sig( unsigned char sig );
+#endif
+
+mbedtls_md_type_t mbedtls_ssl_md_alg_from_hash( unsigned char hash );
+unsigned char mbedtls_ssl_hash_from_md_alg( int md );
+int mbedtls_ssl_set_calc_verify_md( mbedtls_ssl_context *ssl, int md );
+
+#if defined(MBEDTLS_ECP_C)
+int mbedtls_ssl_check_curve( const mbedtls_ssl_context *ssl, mbedtls_ecp_group_id grp_id );
+#endif
+
+#if defined(MBEDTLS_KEY_EXCHANGE_WITH_CERT_ENABLED)
+int mbedtls_ssl_check_sig_hash( const mbedtls_ssl_context *ssl,
+                                mbedtls_md_type_t md );
+#endif
+
+#if defined(MBEDTLS_SSL_DTLS_SRTP)
+static inline mbedtls_ssl_srtp_profile mbedtls_ssl_check_srtp_profile_value
+                                                    ( const uint16_t srtp_profile_value )
+{
+    switch( srtp_profile_value )
+    {
+        case MBEDTLS_TLS_SRTP_AES128_CM_HMAC_SHA1_80:
+        case MBEDTLS_TLS_SRTP_AES128_CM_HMAC_SHA1_32:
+        case MBEDTLS_TLS_SRTP_NULL_HMAC_SHA1_80:
+        case MBEDTLS_TLS_SRTP_NULL_HMAC_SHA1_32:
+            return srtp_profile_value;
+        default: break;
+    }
+    return( MBEDTLS_TLS_SRTP_UNSET );
+}
+#endif
+
+#if defined(MBEDTLS_X509_CRT_PARSE_C)
+static inline mbedtls_pk_context *mbedtls_ssl_own_key( mbedtls_ssl_context *ssl )
+{
+    mbedtls_ssl_key_cert *key_cert;
+
+    if( ssl->handshake != NULL && ssl->handshake->key_cert != NULL )
+        key_cert = ssl->handshake->key_cert;
+    else
+        key_cert = ssl->conf->key_cert;
+
+    return( key_cert == NULL ? NULL : key_cert->key );
+}
+
+static inline mbedtls_x509_crt *mbedtls_ssl_own_cert( mbedtls_ssl_context *ssl )
+{
+    mbedtls_ssl_key_cert *key_cert;
+
+    if( ssl->handshake != NULL && ssl->handshake->key_cert != NULL )
+        key_cert = ssl->handshake->key_cert;
+    else
+        key_cert = ssl->conf->key_cert;
+
+    return( key_cert == NULL ? NULL : key_cert->cert );
+}
+
+/*
+ * Check usage of a certificate wrt extensions:
+ * keyUsage, extendedKeyUsage (later), and nSCertType (later).
+ *
+ * Warning: cert_endpoint is the endpoint of the cert (ie, of our peer when we
+ * check a cert we received from them)!
+ *
+ * Return 0 if everything is OK, -1 if not.
+ */
+int mbedtls_ssl_check_cert_usage( const mbedtls_x509_crt *cert,
+                          const mbedtls_ssl_ciphersuite_t *ciphersuite,
+                          int cert_endpoint,
+                          uint32_t *flags );
+#endif /* MBEDTLS_X509_CRT_PARSE_C */
+
+void mbedtls_ssl_write_version( int major, int minor, int transport,
+                        unsigned char ver[2] );
+void mbedtls_ssl_read_version( int *major, int *minor, int transport,
+                       const unsigned char ver[2] );
+
+static inline size_t mbedtls_ssl_in_hdr_len( const mbedtls_ssl_context *ssl )
+{
+#if !defined(MBEDTLS_SSL_PROTO_DTLS)
+    ((void) ssl);
+#endif
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+    {
+        return( 13 );
+    }
+    else
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+    {
+        return( 5 );
+    }
+}
+
+static inline size_t mbedtls_ssl_out_hdr_len( const mbedtls_ssl_context *ssl )
+{
+    return( (size_t) ( ssl->out_iv - ssl->out_hdr ) );
+}
+
+static inline size_t mbedtls_ssl_hs_hdr_len( const mbedtls_ssl_context *ssl )
+{
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        return( 12 );
+#else
+    ((void) ssl);
+#endif
+    return( 4 );
+}
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+void mbedtls_ssl_send_flight_completed( mbedtls_ssl_context *ssl );
+void mbedtls_ssl_recv_flight_completed( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_resend( mbedtls_ssl_context *ssl );
+int mbedtls_ssl_flight_transmit( mbedtls_ssl_context *ssl );
+#endif
+
+/* Visible for testing purposes only */
+#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
+int mbedtls_ssl_dtls_replay_check( mbedtls_ssl_context const *ssl );
+void mbedtls_ssl_dtls_replay_update( mbedtls_ssl_context *ssl );
+#endif
+
+int mbedtls_ssl_session_copy( mbedtls_ssl_session *dst,
+                              const mbedtls_ssl_session *src );
+
+/* constant-time buffer comparison */
+static inline int mbedtls_ssl_safer_memcmp( const void *a, const void *b, size_t n )
+{
+    size_t i;
+    volatile const unsigned char *A = (volatile const unsigned char *) a;
+    volatile const unsigned char *B = (volatile const unsigned char *) b;
+    volatile unsigned char diff = 0;
+
+    for( i = 0; i < n; i++ )
+    {
+        /* Read volatile data in order before computing diff.
+         * This avoids IAR compiler warning:
+         * 'the order of volatile accesses is undefined ..' */
+        unsigned char x = A[i], y = B[i];
+        diff |= x ^ y;
+    }
+
+    return( diff );
+}
+
+#if defined(MBEDTLS_SSL_PROTO_SSL3) || defined(MBEDTLS_SSL_PROTO_TLS1) || \
+    defined(MBEDTLS_SSL_PROTO_TLS1_1)
+int mbedtls_ssl_get_key_exchange_md_ssl_tls( mbedtls_ssl_context *ssl,
+                                        unsigned char *output,
+                                        unsigned char *data, size_t data_len );
+#endif /* MBEDTLS_SSL_PROTO_SSL3 || MBEDTLS_SSL_PROTO_TLS1 || \
+          MBEDTLS_SSL_PROTO_TLS1_1 */
+
+#if defined(MBEDTLS_SSL_PROTO_TLS1) || defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
+    defined(MBEDTLS_SSL_PROTO_TLS1_2)
+/* The hash buffer must have at least MBEDTLS_MD_MAX_SIZE bytes of length. */
+int mbedtls_ssl_get_key_exchange_md_tls1_2( mbedtls_ssl_context *ssl,
+                                            unsigned char *hash, size_t *hashlen,
+                                            unsigned char *data, size_t data_len,
+                                            mbedtls_md_type_t md_alg );
+#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \
+          MBEDTLS_SSL_PROTO_TLS1_2 */
+
+#ifdef __cplusplus
+}
+#endif
+
+void mbedtls_ssl_transform_init( mbedtls_ssl_transform *transform );
+int mbedtls_ssl_encrypt_buf( mbedtls_ssl_context *ssl,
+                             mbedtls_ssl_transform *transform,
+                             mbedtls_record *rec,
+                             int (*f_rng)(void *, unsigned char *, size_t),
+                             void *p_rng );
+int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
+                             mbedtls_ssl_transform *transform,
+                             mbedtls_record *rec );
+
+/* Length of the "epoch" field in the record header */
+static inline size_t mbedtls_ssl_ep_len( const mbedtls_ssl_context *ssl )
+{
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+    if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM )
+        return( 2 );
+#else
+    ((void) ssl);
+#endif
+    return( 0 );
+}
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+int mbedtls_ssl_resend_hello_request( mbedtls_ssl_context *ssl );
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+void mbedtls_ssl_set_timer( mbedtls_ssl_context *ssl, uint32_t millisecs );
+int mbedtls_ssl_check_timer( mbedtls_ssl_context *ssl );
+
+void mbedtls_ssl_reset_in_out_pointers( mbedtls_ssl_context *ssl );
+void mbedtls_ssl_update_out_pointers( mbedtls_ssl_context *ssl,
+                              mbedtls_ssl_transform *transform );
+void mbedtls_ssl_update_in_pointers( mbedtls_ssl_context *ssl );
+
+int mbedtls_ssl_session_reset_int( mbedtls_ssl_context *ssl, int partial );
+
+#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
+void mbedtls_ssl_dtls_replay_reset( mbedtls_ssl_context *ssl );
+#endif
+
+void mbedtls_ssl_handshake_wrapup_free_hs_transform( mbedtls_ssl_context *ssl );
+
+#if defined(MBEDTLS_SSL_RENEGOTIATION)
+int mbedtls_ssl_start_renegotiation( mbedtls_ssl_context *ssl );
+#endif /* MBEDTLS_SSL_RENEGOTIATION */
+
+#if defined(MBEDTLS_SSL_PROTO_DTLS)
+size_t mbedtls_ssl_get_current_mtu( const mbedtls_ssl_context *ssl );
+void mbedtls_ssl_buffering_free( mbedtls_ssl_context *ssl );
+void mbedtls_ssl_flight_free( mbedtls_ssl_flight_item *flight );
+#endif /* MBEDTLS_SSL_PROTO_DTLS */
+
+#endif /* ssl_misc.h */